Guide to the Code for Assessment, Repair, and
Rehabilitation of Existing Concrete Structures
University of Toronto User.
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MNL-3(20)
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An ACI / ICRI Manual
A Companion to ACI 562-19
Guide to the Code Requirements
for Assessment, Repair, and
Rehabilitation of Existing Concrete
Structures
ACI MNL-3(20)
Third Edition
Updated by Khaled Nahlawi, ACI Distinguished Engineer, under the review and
approval of an ACI/ICRI review group consisting of Chair Keith E. Kesner and
members Tarek Alkhrdaji, Eric L. Edelson, and Fred R. Goodwin
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1
University of Toronto User.
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Guide to the Code Requirements for Assessment, Repair, and
Rehabilitation of Existing Concrete Structures
ACI MNL-3(20)
Third Edition
First Printing: November 2020
ISBN: 978-1-64195-121-0
Copyright © 2020 by the American Concrete Institute and the
International Concrete Repair Institute.
All rights reserved.
Managing Editor: Khaled Nahlawi, PhD, PE
Art Program: Claire Hiltz
Photo Editor: Ken Lozen, FICRI, FACI
Director, Events and Publishing Services: Lauren E. Mentz
Production Editors: Kaitlyn J. Dobberteen, Tiesha Elam, Hannah Genig,
Kelli R. Slayden
Page Design & Composition: Ryan Jay
Front cover photos: copyright 2010 Mark Johnson Photography
Manufacturing: Marie Fuller
Printed in Eau Claire, WI
American Concrete Institute
38800 Country Club Drive
Farmington Hills, MI 48331
USA
www.concrete.org
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International Concrete Repair Institute
1000 Westgate Drive, Suite #252
St Paul, MN 55114
USA
www.icri.org
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On the Cover
Inspection and Evaluation
Together with the Houston Fire
Department, the Engineer performed
an initial visual review. The extent of
the fire damage was confined within
the two bays adjacent to the garage
expansion joint on the east side.
Shoring and cleaning requirements for
the damaged members were provided
on-site on April 26, 2018, the same
day that the fire occurred.
Available background information and plans were reviewed, and a
follow-up visual assessment of the
damage was conducted on May 2,
2018. Prior to the second visual evaluation, the structural members within
the fire-damaged area were cleaned
using dry ice blasting that allowed a
closer look at the extent of the damage.
Fig. 1—University of Houston East Garage
Fig. 2—Fire damage on Level 3 of parking garage
Fig. 3—Fire damage at exterior of garage
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Fig. 4—Shoring
installed in affected areas
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University of Houston East
Garage Fire Emergency
Response
2019 ICRI Award of Excellence –
Parking Structures Category
The following summary is taken
from the November/December 2019
issue of the ICRI Concrete Repair
Bulletin.
The University of Houston’s 2006
Campus Framework Plan included
the addition of parking spaces to
accommodate the growing population of students. The East Garage was
designed to meet the needs of students,
faculty, visitors, and residents of the
nearby campus lofts (Fig. 1). Utilizing
a “double zero” ramp configuration,
the garage was designed to have
“nested” visitor parking with the capability to use the upper levels for overflow parking.
In April 2018, a multiple-vehicle
fire occurred on the third level of the
four-level University of Houston East
Garage (Fig. 2). Significant structural
damage occurred to two columns, the
framing of the level above, and the exterior signage (Fig. 3). Before a survey
of the damage could be completed,
shoring was installed as a precaution
to prevent the possible collapse of
damaged members (Fig. 4).
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3
Fig. 7—Spandrel beam replacement
Site Preparation, Demolition, and Repairs
Repairs included replacement of members that experienced severe distress,
along with localized repairs of members with moderate or minor distress. Repair
drawings were issued on June 1, 2018.
Once mobilization took place, the perimeter of the precast double tees was
saw-cut, creating separation of each member to be replaced prior to removal.
In preparation of hoisting the existing damaged precast double tees, cores were
drilled at each of the four pick points, allowing a sling to be wrapped around the
stem for each double tee. A 350 ton (317,500 kg) crane was used to bring down
each damaged precast double tee, with a total of six removed and four new double
tees reinstalled. Two of the damaged double tees were found to be salvageable after
removal. These
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members were temporarily placed on the ground, repaired, and
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In addition to visual observations, a
limited floor delamination survey was
performed utilizing a chain dragging
device to detect unsound concrete.
An acoustical monitoring wheel and
hammer sounding was used to detect
delaminated concrete on the vertical
and overhead elements.
Concrete testing was performed
(compressive strength and petrographic
examination) and nondestructive evaluation (NDE) methods were used to
determine the severity of damage and
repair approach. NDE methods included
ground-penetrating radar (GPR) survey,
ultrasonic pulse velocity (UPV) testing,
and pulse-echo scanning (Fig. 5).
The visual reviews and delamination survey indicated that fire-related
Fig. 5—Nondestructive testing performed at damaged column
distress had occurred in the form
of concrete cracking and spalling,
including delaminations identified
in several crucial structural beams
and columns (Fig. 6). The concrete
distress was more severe at members
near the expansion joint. Core
compressive strength testing did not
show degradation of compressive
strength as a result of the fire event.
However, the petrographic examination of the concrete cores indicated
the extent of surficial concrete damage
as a result of exposure to fire-elevated
temperatures was up to a depth of
0.4 in. (10 mm).
Significant
carbonation
and
cracking were also observed in several
core samples and correlated with the
Fig. 6—Concrete cracking and spalling due to fire
NDE (UPV and pulse echo) results at
multiple locations at each structural member. GPR scanning of cracked doubletee beams with significant longitudinal cracking showed that these cracks were
located along the prestressing strands, thus indicating possible debonding between
the strand and concrete with subsequent reduction in structural capacity. The petrographic examinations also indicated that the concrete members were exposed to
elevated temperatures up to 1400°F (800°C).
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4
reinstalled in their original position.
Two spandrel beams were hoisted
down, removed from the site, and
replaced with new members (Fig. 7).
New replacement double tees were
hoisted into place for final repairs
(Fig. 8).
Other repair works included the
repair of concrete columns supporting
Level 4 (Fig. 9), spandrel beams on
Levels 3 and 4, double-tee members
on Level 4, topping slab replacement
on Level 3, and waterproofing installation on Levels 3 and 4. The damaged
expansion joint system on Level 3 was
replaced and a new expansion joint
system was installed on Level 4. Joints
were tooled in the topping slab and
sealed above the double-tee flange-toflange joints, and construction joints
were routed and sealed. Cove sealant
was installed at the perimeter bumper
wall and columns.
Fig. 8—New replacement double-tee beams at completion
Logistics
The public garage proved to be
a limited-space jobsite, leaving
little room for repair materials and
contractor
use/laydown.
While
complexities were abundant, the
project team worked efficiently to
have the garage fully operational by
the start of the fall semester. Ultimately, the team was able to come in
under budget and ahead of schedule
on repairs.
Fig. 9—Column during repair (left) and after repair (right)
University of Houston East Garage Fire Emergency Response
OWNER
University of Houston
Houston, TX
PROJECT ENGINEER/DESIGNER
Walter P Moore & Associates, Inc.
Houston, TX
REPAIR CONTRACTOR
United Restoration and Preservation
Houston, TX
MATERIALS SUPPLIER/MANUFACTURER
BASF
Houston, TX
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Safety
Emergency shoring addressed the
initial safety concerns for assessing
the damage and reduce the threat of a
possible collapse. With student finals
around the corner at the University of
Houston, it was understood that the
East Garage would need to remain
in use on all undamaged levels. This
presented another challenge to the
construction team: safely making
localized repairs to damaged elements
with limited intrusion to occupants
while considering the safety.
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5
Acknowledgments
edition of the repair code, “Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete
Structures (ACI 562-19) and Commentary,” and this guide
corresponding to the new repair code, have been updated to
address comments received from users. The major revisions
in ACI 562-19 are as follows:
(a) Text was added to simplify use of new materials that
have the equivalent of an ICC-ES evaluation report in
Chapter 1.
(b) The requirements for the basis of design report were
simplified in Chapter 1.
(c) Clarified requirements related to detailing of existing
reinforcing steel in Chapter 7.
(d) The commentary in Chapter 8 was updated to include a
listing of exposure categories that may affect durability.
This edition contains updated chapters to reflect the
changes in ACI 562-19, updated Examples 1 through 5, three
new examples (Examples 6 through 8), and a new Appendix
B, which provides an overview of the new “Specifications
for Repair of Concrete in Buildings (ACI 563-18).”
“Vision 2020: A Vision for the Concrete Repair, Protection
and Strengthening Industry” was published in 2006 with the
facilitation of the Strategic Development Council (SDC) (a
council of the ACI Foundation). One goal in Vision 2020
was the development of a concrete repair code. SDC also
called for the development of documents in a more expedient
manner than typically achieved in the volunteer committee
development process. Their support of these goals continues
with this document. ACI and ICRI would like to thank SDC
for their vision in calling for the development of a concrete
repair code and for providing financial support toward the
development of the first two editions of this guide.
Finally, ACI and ICRI would like to thank the review
group for this guide consisting of Chair Keith E. Kesner
and members Tarek Alkhrdaji, Eric L. Edelson, and Fred R.
Goodwin. Their careful review and dedication to the project
on top of all their other volunteer time for both Institutes made
it possible to develop and revise this guide in a timely manner
while maintaining the quality expected by the industry.
Khaled Nahlawi
Managing Editor
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The development of “Code Requirements for Evaluation, Repair, and Rehabilitation of Concrete Buildings
(ACI 562-13) and Commentary” and the first edition of
the “Guide to the Code for Evaluation, Repair, and Rehabilitation of Concrete Buildings” were major milestones
in the concrete repair industry. Prior to the publication of
these documents in 2013, the industry lacked code requirements specific to the repair of concrete buildings, leading
to inconsistent repair practices. To provide guidance to the
repair community, yet maintain the flexibility necessary to
address widely varying conditions, many of the repair code
requirements took the form of performance requirements
rather than the prescriptive requirements seen in many other
concrete industry codes. Because of the performance nature
of the requirements, however, there was significant room
for interpretation when deciding whether a particular code
requirement had been met.
Early in the development of ACI 562-13, the need was
recognized for a document that would provide guidance and
examples to assist engineers in understanding how to satisfy
the Repair Code requirements. This was particularly important
considering that ACI 562 was a new code that engineers
would be using for the first time and with which they would
have no prior experience.
The second edition of the repair code, “Code Requirements
for Assessment, Repair, and Rehabilitation of Existing Concrete
Structures (ACI 562-16) and Commentary,” and corresponding
guide to the repair code, were updated to address comments
received from these first-time users. Chapters 1 and 4 were
reorganized and properly defined the difference between evaluation and assessment. A new section in Chapter 7 addressed
bond interface between an existing concrete substrate and a new
concrete overlay. Appendix A was added to provide requirements in cases where a jurisdiction has not adopted a repair
code, allowing ACI 562-16 to be used as a stand-alone code.
If a jurisdiction had adopted a repair code, then the licensed
design professional must use Chapter 4.
For the third edition of the repair guide, examples were
updated to reflect the changes in ACI 562-19. The current
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6
Preface
University of Toronto User.
Introduction to the ACI 562-19 Code
ingly, while ACI 562 currently defines the standard for the
Advancements in the practice of assessment, repair, rehabiliconcrete assessment, repair, and rehabilitation industry, the
tation, and strengthening of concrete structures have developed
code provisions of ACI 562 will likely then become mandathrough a collaboration of design professionals, contractors,
tory requirements as part of the governing building codes
suppliers, manufacturers, researchers, educators, and lawyers.
that regulate work in existing buildings.
The annual cost to owners for repair, protection, and strengthening of existing concrete structures is estimated between $18
Overview of the guide to ACI 562 Code content
and $21 billion (Vision 2020). Simply put, even sound concrete
The primary purpose of this guide is to help licensed design
may require repair, rehabilitation, maintenance, or strengthprofessionals (LDPs) gain more knowledge, skill, and judgening throughout the service life of a structure. Accordingly,
ment to interpret and properly use the ACI 562 Code. Although
from 2004 to 2006, the Strategic Development Council (SDC),
specifically developed for LDPs, this guide also provides
an interindustry development group dedicated to supporting the
insight into the use and benefits of ACI 562 for contractors,
concrete industry’s strategic needs, facilitated the development
material manufacturers, and building owners and building
of “Vision 2020: A Vision for the Concrete Repair, Protection,
officials. To achieve this goal, the guide is separated into three
and Strengthening Industry” to establish a set of goals that
main components: Chapter Guides including Appendix A,
would improve the efficiency, safety, and quality of concrete
Project Examples, and Appendix B, providing an overall view
repair and protection activities. One of the goals established by
of the new standard, ACI 563, “Specifications for Repair of
Vision 2020 was to create a concrete repair and rehabilitation
Concrete in Buildings.”
code by 2015. The ACI 562-13 standard, “Code Requirements
The Chapter Guides and Project Examples are provided in
for Evaluation, Repair, and Rehabilitation of Concrete Buildtandem for clarity and understanding of the relative portions
ings and Commentary,” is the end result of that initiative. ACI
of ACI 562 Code. The Project Examples illustrate the process
562-19 is the third edition of the Code with revisions, additions,
of carrying out a concrete building assessment, repair, rehaand reorganized information to enhance the Code, providing
bilitation, or strengthening project from inception through
more clarity and additional, updated information to assist the
completion. This guide, including the Project Examples, is
design professional.
intended as a supplement to the ACI 562 Code and not as a
The purpose of the ACI 562 Code is to provide minimum
“how-to” manual for performing concrete assessment, repair,
material and design requirements for the assessment, repair,
rehabilitation, or strengthening. Several additional documents
and rehabilitation of structural concrete members. Like other
are referenced in ACI 562 Commentary and this guide to assist
ACI codes, ACI 562 is organized in a dual-column format,
in evaluating the various options and approaches to performing
with mandatory code provisions to the left of each page,
successful concrete assessment, repair, rehabilitation, or
and nonmandatory commentary to the right to provide addistrengthening projects. The intent of each Project Example is
tional guidance and information on the content presented in
not to be a prescriptive formula for each of the project scenarios
the Code provisions. Unlike other ACI standards, ACI 562
presented, but to illustrate how various sections of ACI 562
includes both prescriptive and performance requirements.
are applied together to execute the project. For convenience,
The performance requirements provide great latitude and
related provision numbers from ACI 562 are given at the top
flexibility to the licensed design professional in satisfying
of each corresponding paragraph of the project example text.
the requirements of ACI 562. Accordingly, ACI 562 serves to
Eight Project Examples are included within the guide:
unify and strengthen concrete assessment, repair, and rehabili1. Typical parking structure repairs
tation projects while accommodating the diverse and unique
2. Typical façade repairs
strategies and materials used in the industry.
3. Repair of historic structure for adaptive reuse
In general, the overall use and function of ACI 562, with
4. Strengthening of two-way flat slab
respect to existing concrete structures, can be compared to that
5. Strengthening of double-tee stems for shear
of ACI 318-19, “Building Code Requirements for Structural
6. Concrete beam repair by section enlargement
Concrete and Commentary,” with new concrete construction.
7. Concrete repair by steel jacket
As with ACI 318 and the 2018 International Building Code
8. Beam repair with fire protection analysis:
(2018 IBC), plans are underway for ACI 562 an ANSI stana. Beam strengthening due to live load increase
dard, to be adopted into the International Existing Building
b. Beam with inadequate existing concrete cover
Code (IEBC) to address matters pertaining to assessment,
In the third edition of this repair guide, a new chapter,
repair, rehabilitation, and strengthening of concrete members
Appendix B, was added to address specifications. This is
within existing buildings. Local jurisdictions and building
another goal by Vision 2020 to create a concrete repair specauthorities can also adopt ACI 562 directly. Cities and states
ification standard. The ACI 563-18 standard, “Specification
have both adopted ACI 562 and adopted use of ACI 562 on
for Repair of Concrete in Buildings,” is a reference stanspecific projects. Other jurisdictions are in the process of
dard that the LDP can apply to any construction repair and
reviewing the Code for consideration and adoption.
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7
repair and rehabilitation for varying levels of damage, deterioration, or faulty construction. Load combinations in Chapter 5,
which define the minimum strength of a structure with unprotected external reinforcement, were revised. Chapter 6 directs
the LDP to provide an assessment before rehabilitation of an
existing structure. This chapter includes historical material
property data to help the design professional in the assessment if existing documents related to the existing structure
are not available or physical samples cannot be extracted,
because of the historical value of the structure. The interface bond provisions in Chapter 7 were revised to provide
specific requirements based on shear test, as well as when to
provide interface reinforcement, and commentary in Chapter
8 was clarified.
The third edition of ACI 562, published in 2019, has:
(a) Added text to simplify use of new materials that have the
equivalent of an ICC-ES evaluation report in Chapter 1;
(b) Simplified the requirements for the basis of design
reported in Chapter 1;
(c) Clarified requirements related to detailing of existing
reinforcing steel in Chapter 7; and
(d) Updated commentary in Chapter 8 to include a listing of
exposure categories that may affect durability.
In addition, three new repair examples are added to
demonstrate the flexibility of the Code and its applicability
to different repair and strengthening methods. Example 6
is related to concrete beam repair by section enlargement,
Example 7 addresses concrete frame strengthening by steel
jacketing, and Example 8 focuses on the effect of fire on
concrete members and possible protection based on two
scenarios: scenario one—concrete structure subjected to
increase in live load; and scenario two—reinforcement with
low concrete cover.
Lastly, a summary of the various provisions of ACI 562,
as well as the corresponding location where each provision
is covered within the guide, is provided in the Provision
Coverage Matrix at the end of this guide. This serves as a
useful tool when searching for additional information to a
specific provision of ACI 562.
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it in the Project Specifications. It provides direction to the
contractor and clearly defines the responsibilities and scope
of the repair, rehabilitation, or strengthening. The specifications detail the work, material, and installation required to
complete a project the way the client wants.
The Chapter Guides follow the general organization of
ACI 562, broken down by the corresponding sections of ACI
562. Section numbers in Chapters 1 to 10 and Appendix A
of this guide correspond to the provision numbers in ACI
562. The Chapter Guides include background information
and an explanation of the various ACI 562 provisions, with
particular insight into how the particular chapter and section
of the Code fit within the project. Where applicable, flowcharts are provided to illustrate how to navigate the various
provisions of ACI 562. References to Project Examples are
provided where applicable to illustrate how specific provisions within each chapter of ACI 562 are incorporated into
the design process. In some instances, additional limitedscope examples are included to better illustrate a point that
is not covered by the Project Examples.
The first edition of ACI 562 was published in 2013, and
was not available when the work for the projects discussed
in the Project Examples was actually performed. All Project
Examples assume that ACI 562 was available and accepted
by local jurisdiction when the example projects were
performed.
The second edition of ACI 562, published in 2016, includes
additional definitions used in the Code for consistency with
2018 IEBC and other similar standards for existing structures. The title of ACI 562-16 was changed by replacing
the word “Evaluation” with “Assessment.” The two terms,
which are used interchangeably by other standards and the
first version of this Code, have received distinct definitions in
the second edition of ACI 562 (Stevens et al. 2016). Specific
criteria requirements for assessment and design of repair and
rehabilitation for varying levels of damage, deterioration, or
faulty construction was added in Chapter 4 when using the
Code with IEBC, and in Appendix A when using the Code as
a stand-alone code. Chapters 1 and 4 were revised to include
specific criteria requirements for assessment and design of
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8
Contents
Acknowledgments
6
Preface
7
About This Book
12
Chapter 1—General Requirements
1.1—General
1.2—Criteria for the assessment and design of
repair and rehabilitation of existing concrete
structures
1.3—Applicability of the Code
1.4—Administration
1.5—Responsibilities of licensed design
professional
1.6—Construction documents
1.7—Preliminary assessment
13
13
Chapter 2—Notation and Definitions
2.1—Notation
2.2—Definitions
19
19
19
Chapter 3—Referenced Standards
21
14
15
16
16
16
16
Chapter 5—Loads, Factored Load Combinations,
and Strength Reduction Factors
31
5.1—General
32
5.2—Load factors and load combinations
33
5.3—Strength reduction factors for repair design 33
5.4—Strength reduction factors for assessment 33
5.5—Additional load combinations for structures
rehabilitated with external reinforcing systems 34
37
37
38
40
Chapter 7—Design of Structural Repairs
7.1—General
7.2—Strength and serviceability
7.3—Behavior of repaired systems
7.4—Interface bond
7.5—Materials
7.6—Design and detailing considerations
7.7—Repair using supplemental post-tensioning
7.8—Repair using fiber-reinforced polymer (FRP)
composites
7.9—Performance under fire and elevated
temperatures
47
47
47
48
49
57
57
58
44
45
45
45
46
46
59
60
Chapter 8—Durability
8.1—General
8.2—Cover
8.3—Cracks and deterioration of reinforcement
and metallic embedments
8.4—Corrosion
8.5—Surface treatments and coatings
61
61
62
Chapter 9—Construction
9.1—General
9.2—Stability and temporary shoring requirements
9.3—Temporary conditions
9.4—Environmental issues
65
65
65
66
68
Chapter 10—Quality Assurance
10.1—General
10.2—Inspection
10.3—Testing of repair materials
10.4—Construction observations
69
69
70
70
70
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62
63
64
University of Toronto User.
Chapter 4—Basis for Compliance
23
4.1—General
23
4.2—Compliance method
24
4.3—Potentially dangerous structural conditions 25
4.4—Substantial structural damage
26
4.5—Conditions of deterioration, faulty construction,
or damage less than substantial structural
damage
26
4.6—Conditions of deterioration, faulty construction,
or damage less than substantial structural
damage without strengthening
30
4.7—Additions, 4.8—Alterations, 4.9—Changes in
occupancy
30
Chapter 6—Assessment, Evaluation, and Analysis
6.1—Structural assessment
6.2—Investigation and structural evaluation
6.3—Material properties
6.4—Test methods to determine or confirm
material properties
6.5—Structural analysis of existing structures
6.6—Structural serviceability
6.7—Structural analysis for repair design
6.8—Strength evaluation by load testing
6.9—Recommendations
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9
Chapter 11: Commentary References
71
Appendix A—Criteria When Using ACI 562 as a
Stand-Alone Code
73
A.1—General
73
A.2—Design-basis code criteria
73
A.3—Potentially dangerous structural conditions 75
A.4—Substantial structural damage
76
A.5—Conditions of deterioration, faulty construction,
or damage less than substantial structural
damage
76
A.6—Conditions of deterioration, faulty construction,
or damage less than substantial structural
damage without strengthening
78
A.7—Additions
79
A.8—Alterations
80
A.9—Changes in occupancy
82
Project Examples
104
Chapter 13: Project Example 2—Typical Façade
Repair
121
Description of structure
121
Project initiation and objectives
122
Governing building codes
122
Preliminary observations and assessment
123
Observed concrete conditions
124
Laboratory findings
125
Findings
125
Structural assessment and repair design
126
Shear wall reveal strip repairs
126
North and south walls away from reveal strips
and east and west slab and column edges 128
Balcony repairs
128
Performance under fire and elevated temperatures 130
Contract specifications
130
Construction
131
Quality assurance
131
Project close-out
132
Periodic maintenance
132
Record documents
132
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Appendix B—Repair Guide
83
General
83
Section 1—General requirements
83
General procedures
84
Preinstallation conference
84
Quality assurance, quality control, testing, and
inspection
85
Quality assurance (QA)
85
Advantages of quality assurance
87
Disadvantages of quality assurance
87
Quality control (QC)
87
Advantages of quality control
87
Disadvantages of quality control
87
Testing and inspection
88
Section 2—Shoring and bracing
90
Section 3—Concrete removal and preparation for
repair
91
Section 4—Formwork
94
Section 5—Reinforcement and reinforcement
supports
97
Section 6—Conventional concrete mixtures
99
Section 7—Handling and placing of conventional
concrete
101
Section 8—Proprietary cementitious and polymer
repair materials
102
Sections 9 and 10
102
Notes to Specifier (nonmandatory)
102
Checklists
102
Chapter 12: Project Example 1—Typical Parking
Structure Repair
105
Description of structure
105
Project initiation and objectives
105
Governing building codes
106
Preliminary assessment
107
Investigation of existing site conditions
107
Capacity and demand of existing structure
108
Findings of preliminary assessment
108
Area 1
109
Area 2
111
Report to owner
113
Structural Assessment
113
Existing conditions
113
Structural analysis for repair design
114
Area 1
115
Area 2
115
Design of structural repairs and durability
116
Slab Area 1
116
Slab Area 2 and columns
117
Slab soffit repairs
118
Construction specifications
118
Construction
119
Quality assurance
119
Project close-out
120
Periodic maintenance
120
Record documents
120
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10
Chapter 14: Project Example 3—Adaptive Reuse of
Historic Depot
133
Description of structure
133
Project initiation and objectives
134
Governing building codes
134
Preliminary observations and evaluation
135
Concrete conditions
135
Material evaluation findings
137
Summary
137
Structural assessment
138
Requirement for structural assessment
138
Existing properties
138
Structural analysis
138
Structural analysis findings
139
Recommended repair program
140
Train deck rehabilitation
140
Column rehabilitation
142
Concrete repair details
144
Contract specifications
146
Construction
148
Quality assurance
148
Project close-out
148
Periodic maintenance
148
Record documents
148
149
149
149
149
150
150
150
150
153
154
154
154
155
155
155
155
156
157
159
160
163
163
163
163
167
168
168
168
169
169
169
170
171
171
171
171
173
173
173
174
176
176
176
177
177
178
179
179
179
180
181
181
182
182
182
182
183
183
186
186
186
Chapter 17: Project Example 6—Concrete Beam
Repair by Section Enlargement
187
Description of structure
187
Project initiation and objectives
187
Governing building code
188
Structural assessment
189
Structural analysis
189
Repair options
190
Design of repairs
191
Durability of repairs
192
Contract documents
193
Construction specifications
193
Construction
193
Quality assurance/construction observations
193
Project Close-out
194
Periodic maintenance
194
Record documents
194
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University of Toronto User.
Chapter 15: Project Example 4—Parking/Plaza
Slab Strengthening
Description of structure
Project initiation and objectives
Governing building codes
Preliminary evaluation
Document review
Existing site conditions
Strength of as-built structure
Compliance method and design-basis code
Structural assessment
Requirement for structural assessment
Structural assessment
Structural analysis
Strengthening concepts
Strengthening Concept 1
Strengthening Concept 2
Assessment of strengthening concepts
Structural analysis for repair design
Design of structural repairs and durability
Contract specifications
Construction
Quality assurance
Load test
Test procedure
Test results
Project close-out
Periodic maintenance
Record documents
Chapter 16: Project Example 5—Precast/
Prestressed Double-Tee Repair
Description of structure
Project initiation and objectives
Governing building codes
Preliminary assessment
Existing site conditions
Design strength of existing structure
Findings of preliminary assessment
Design-basis code
Structural evaluation
Existing site conditions
Structural analysis for evaluation
Structural safety
Repair/replacement options
Repair/replacement Option 1
Repair/replacement Option 2
Repair/replacement Option 3
Repair/replacement Option 4
Evaluation of repair/replacement options
Design of strengthening repairs
Structural analysis for repair design
Design of strengthening repairs
Design of structural repairs and durability
Development and bond of CFRP strips
Acceptance of CFRP repairs by the authorities
having jurisdiction
Durability of repairs
Aesthetics of repairs
Contract specifications
Construction
Quality assurance
Project close-out
Periodic maintenance
Record documents
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11
Chapter 18: Project Example 7—Concrete Frame
Strengthening by Steel Jacket
195
Description of structure
195
Project initiation and objectives
195
Governing building codes
196
Preliminary evaluation
196
Strengthening concepts
199
Structural analysis and repair design
199
Durability
200
Contract documents
200
Construction specifications
200
Construction
203
Quality assurance
203
Project close-out
204
Periodic maintenance
204
Record documents
204
Chapter 19: Project Example 8—Building
Subjected to Fire
Description of structure
Project initiation, objectives, and remediation
summary
Governing codes
Fire resistance rating calculations
Contract specifications
Construction
Quality assurance
Load test
Test procedure
Project close-out
Periodic maintenance
Record documents
References
Referenced Standards and Reports
Authored documents
205
205
206
208
208
217
218
218
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About This Book
mance provisions of ACI 562. It does not, however, purport
to represent the only suitable way to satisfy the requirements
for every project. Engineering judgment must be applied to
the unique requirements of individual projects.
This edition added Appendix B, which provides an overall
view of ACI 563-18, “Specifications for Repair of Concrete
in Buildings.”
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@Seismicisolation
University of Toronto User.
The Chapter Guides in Chapters 1 to 11 and Appendix A of
this guide correspond to the identically numbered sections of
ACI 562-19, “Code Requirements for Assessment, Repair, and
Rehabilitation of Existing Concrete Structures.” Related ACI 562
provision numbers are included at the top of each corresponding
paragraph of the Project Example text in Examples 1 to 8.
This Guide is intended to provide examples and guidance
for how licensed design professionals may satisfy the perfor-
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12
Structural strengthening of girders with carbon fiber-reinforced polymer (CFRP) at a bridge in Canada
(Photo courtesy of KMo Foto on www.flickr.com)
1.1—General
ACI 562 Code is written to the licensed design professional (LDP) and provides
guidance and consistency when assessing, designing, repairing, and rehabilitating
concrete structures. It is intended to supplement the International Existing Building
Code (IEBC), as part of a locally adopted code governing existing buildings or
structures, or as a stand-alone code for existing concrete structures. The intent of
the Code is to address minimum safety requirements and provide some uniformity and
standardization to the industry for assessing existing concrete structures. The requirements based on performance, which encompass the majority of the requirements in
ACI 562 Code, direct the design professional to satisfy specific requirements, while
providing some leeway, flexibility, and direction with the repair and rehabilitation
of concrete structures. Concrete structures constructed before 1971 that require
@Seismicisolation
repair, rehabilitation, or strengthening were probably
designed based on the
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13
University of Toronto User.
Overview
Chapter 1 of ACI 562 specifies the applicability of ACI 562, including review of
the various building codes that might affect the repair design, as well as selecting
the building code for the repair design; applicability of the code; responsibilities of
the licensed design professional including submittals to building officials and the
owner; and development of maintenance recommendations. Chapter 1 also specifies
the requirements for performing a preliminary assessment by examining the available
information and determining if the proposed changes, imposed changes, or both,
are safe, followed by how the structure will be affected by these changes.
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Chapter 1—General Requirements
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
allowable stress approach, whereas the demand and capacity
requirements of ACI 562 are based on strength design. The
LDP is encouraged to consider strength design provisions of
this Code as a check when assessing existing structures originally designed with allowable stress methods.
An existing structure, as defined in Chapter 2, is one
for which a legal certificate of occupancy has been issued,
or one that is finished and permitted for use. If no certificate of occupancy has been issued, or the building has not
been permitted for use, the building is still considered new
construction, and existing design provisions of ACI 318
will govern.
Licensed design professional—The LDP, as defined in the
Code and consistent with ACI Concrete Terminology (CT),
refers to an individual for a project who is licensed to provide
design services as defined by the statutory requirements of
professional licensing laws of the state or jurisdiction in which
the project is to be executed, and who is in responsible charge
of the structural assessment, rehabilitation design, or both. The
LDP should exercise sound engineering knowledge, experience, and judgment when interpreting and applying ACI 562.
University of Toronto User.
building may undergo several alterations, additions, rehabilitations, repairs, or strengthening during its service life,
spanning several code cycles, and more than one code type
may have been applied. Therefore, the LDP should determine the original building code for each of the alterations,
additions, rehabilitations, repair, or strengthening, during the
preliminary assessment and apply the specific original code
for the area where work will be done.
There are cases of existing concrete structures where
alterations, additions, rehabilitations, repair, or strengthening were completed prior to the adoption of a building
code by the jurisdiction where the structure is located. The
LDP should, in this case, research available standards and
practices in effect at the time of construction. The Historic
American Engineering Record, a program of the United
States Park Service, has information on construction and
preservation of historic structures (https://www.nps.gov/
hdp/haer/index.htm).
In the U.S., the existing building code is most often based
on an edition of the IEBC, which was first published in 2003.
As of January 2016, the IEBC has been adopted in approximately 80 percent of the United States, Guam, and Puerto
1.2—Criteria for the assessment and design of
Rico (International Code Council 2014). Chapter 34 of the
repair and rehabilitation of existing concrete
IBC, before the 2015 edition, also covers existing structures
structures
and has similar provisions as IEBC that permit the use of
Determination of applicable building codes—Before
the original code for rehabilitations, and when it is required
performing an assessment, repair, rehabilitation, or strengthto upgrade an existing structure to the current code. Chapter
ening of an existing concrete building or concrete structural
34 has since been deleted from the 2015 IBC. The intent of
element, the LDP of the project should first determine the
ACI 562 is that existing building code refers to the IEBC
building codes applicable to the project, understand their releand not sections of other current building codes that contain
vance to assessment and repair, rehabilitation, and strengthprovisions pertinent to existing construction. For jurisdicening design decisions, and the relationship between the
tions that have not adopted an edition of the IEBC or the
different standards. Per ACI 562, the LDP should identify the
IBC with Chapter 34 version before 2015, that jurisdiction
following codes per the specific section numbers of ACI 562:
is considered to have no existing building code. In this case,
a. Current building code (1.2.2)
the provisions of Appendix A of ACI 562 and any chapters
b. Original building code (1.2.3)
in the current building code that address existing buildings
c. Existing building code (1.2.1)
must be met.
d. Design-basis code (1.2.4)
Once the original building code and current building
In the United States, the current building code is usually
code have been identified, the LDP can use the flowchart
based on an edition of the International Building Code (IBC),
presented in Fig. 1.2 as a guide to determine the design-basis
which was first published in 2000; a few large cities have
code for repair, rehabilitation, or strengthening design. The
their own customized building codes. The current building
design-basis code is dependent on the adoption of an existing
code establishes the design and construction regulations
building code within the jurisdiction of the project. If a jurisfor new construction and provides limits that need not be
diction has not adopted an existing building code, Appendix
exceeded if designing new construction or assessing and
A of ACI 562 is used to determine the design-basis code. In
designing repairs and rehabilitation of existing structures.
jurisdictions that have adopted an existing building code, the
For the design and construction of new concrete structures,
design-basis code is determined in accordance with Chapter 4
IBC references ACI 318. The code used to initially design
of ACI 562. The Project Examples included within this guide
the building is referred to as the original building code and is
illustrate how Fig. 1.2 is used to determine the design-basis
typically identified in the construction documents, or may be
code. Chapter 4 and Appendix A provide the design-basis
obtained by contacting the local jurisdiction and requesting
criteria for the repair and rehabilitation work. Designing new
information regarding the building code in effect at the time
members and their connections to existing structures must be
of original construction. The most common original codes
based on ACI 318.
prior to the IBC in the U.S. include the Building Officials
The LDP may forego the determination of the design-basis
Code Administrators National Building Code (BOCA/
code based on Chapter 4 or Appendix A and select the current
NBC), the Uniform Building Code (UBC), and the Stanbuilding code for assessment criteria. This is a conservative
dard Building Code (SBC) that typically reference previous
approach and may result in expensive repair or strengthening
versions of ACI 318 with modification. An existing concrete
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options. The LDP should, therefore, review this option with
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the owner before proceeding with the assessment.
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14
1.3—Applicability of the Code
tion work, or installing remedial work of existing structures.
Owners are required to maintain existing structures to
The Code applies to nonstructural concrete or for aesthetic
prevent unsafe conditions from occurring, or repair potentially
improvements, if there is a potential for these materials to fail
dangerous conditions that are present. ACI 562 is applicable
resulting in a potentially dangerous condition.
to existing concrete structures including the concrete elements
Provisions for seismic resistance—ACI 562 refers to
of buildings; nonbuilding structures; building foundation
the existing building code for the evaluation of seismic
members, both plain and reinforced concrete; soil-supported
resistance and seismic rehabilitation design. If an existing
structural slabs; concrete portions of composite members; and
building code has not been adopted, ACI 562 requires that
prestressed and precast concrete structures including cladthe LDP use ASCE/SEI 41 for voluntary seismic retrofits
ding, which transmits lateral loads to diaphragms or bracing
supplemented by ACI 369.1. These references provide guidmembers. ACI 562 includes provisions specific to performing
ance for the LDP regarding forces, analysis and modeling
assessment, repair, rehabilitation, and strengthening of existing
procedures, and seismic rehabilitation design. The effect
concrete elements of buildings or nonbuilding concrete strucof repairs or rehabilitations to existing concrete buildings
tures. These provisions provide minimum level of repair for
should be considered in the assessment of the structure’s
an existing building and typically address these unsafe and
seismic response per ACI 562, 6.7.4.
potentially dangerous conditions. The LDP can exceed the
ACI 562 permits voluntary retrofit for seismic resistance if
minimum requirements of ACI 562, such as those for progresthe existing building code or ACI 562 do not require rehabilsive collapse resistance, redundancy, or integrity provisions.
itation for existing buildings. If IEBC is adopted, then IEBC
Regulations of the current building code, however, need not
and ACI 562 are used for voluntary retrofit of seismic resisbe exceeded when assessing, designing repair and @Seismicisolation
rehabilitatance. If, however, an existing building code has not been
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University of Toronto User.
Fig. 1.2—Flowchart for determination of design basis code in ACI 562-19.
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Chapter 1—General Requirements15
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Which ACI Code Governs?
The assessment, repair, and rehabilitation of existing
concrete structures present several unique considerations as compared to the design and construction
of new concrete structures. Accordingly, ACI 562
provides directions for how existing structures are
treated with respect to various building codes. For
example, repairs, additions, or alterations to structures may result in the redistribution of moments in
continuous flexural members. ACI 562 provisions
address these effects and allow the analysis of existing
structures to consider the actual state of redistributed
moments, even if they exceed the moment distribution
permitted in ACI 318 (ACI 562, R6.5.4).
Some of the provisions, calculations, and methods
presented in ACI 318 are also applicable to the design of
repair and rehabilitation measures for existing concrete
structures. In these instances, ACI 562 provides direcadopted, then ACI 562 directs the LDP to use the current
building code supplemented by ASCE/SEI 41 and ASCE/
SEI 7 to design seismic retrofits.
be presented to the owner and jurisdictional authorities in
form of a basis of design report. The items to be included in a
basis of design report are summarized in the following titled
text box “Basis of design report example.”
The Project Examples presented in this guide provide
specific examples of the responsibilities of the LDP, including
the responsibility for notifying and communicating information
to the owner through the duration of the assessment, repair,
and rehabilitation. Specifically, Project Example 4 presents
the reporting of potentially dangerous structural conditions.
1.6—Construction documents
Construction documents need to clearly communicate
the information necessary to perform the repair, rehabilitation, or strengthening work, and the material specified must
satisfy ACI 562 and the local jurisdictional authority. The
LDP may perform calculations necessary to evaluate the
structure and design the repairs. Computer analyses and
model analysis may be used. Pertinent calculations are
required to be submitted to the building official if required.
The LDP will furnish the owner with copies of the project
documents, including reports, repair documents, construction submittals, field reports, and locations of completed
repairs to the extent of the LDP’s contractual obligations.
The Project Examples presented in this guide provide specific
examples of the types of information that are to be specified in the
construction documents, as well as any additional information
that should be delivered to the owner, the building official, or
both throughout the duration of the assessment, repair, and
rehabilitation. Essential information that should be included
in the construction documents is listed in the following titled
text box “Construction document example.”
1.5—Responsibilities of licensed design
professional
The LDP for the project is responsible for the repair
process, from assessing a structure to designing and specifying repair materials, developing details to producing
quality assurance programs covering the repairs, and
advising the owner on future maintenance requirements to
maintain a durable structure.
ACI 562, 1.5.2, requires the LDP to report observations of
exposed structural defects within the work area representing
obvious conditions requiring immediate attention to the
owner and should alert the contractor of potentially dangerous
conditions that require urgent action that may be discovered
during construction to protect the public. Some jurisdictions
may require the LDP to report potentially dangerous conditions directly to them. The LDP should be aware of thoese
requirements when working in such a jurisdiction.
The LDP should document these findings in a report
that includes a summary of the assessment of the existing
1.7—Preliminary assessment
structure, and a summary of or reference to the construcA preliminary assessment is the first step in the repair
tion documents used for rehabilitation. These findings may
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process in which the LDP reviews plans, construction data,
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University of Toronto User.
1.4—Administration
This Code, unless in conflict with the IEBC or jurisdiction authority regulations, will govern in the assessment and
repair or rehabilitation of existing concrete structures. If ACI
562, however, is in conflict with requirements in referenced
standards in thie ACI 562, then this Code will govern. ACI
562 permits the use of repair design or construction systems
that do not conform to ACI 562, provided such systems are
approved by the building official based on successful use,
analysis, or testing in accordance with ACI 562, 1.4.2.
tion regarding the scope and applicability of ACI
318 provisions for use with existing structures. For
example, horizontal shear and shear-friction provisions
presented in ACI 318 are applicable for force transfer
at the interface between existing members and repair
materials, and designing supplementary reinforcement
for repairs (ACI 562, 7.3.2 and 7.4.1). Similarly, postinstalled anchors and dowels are often used in repairs of
existing concrete members. Accordingly, the provisions
provided in ACI 318 Chapter 17 are applicable for the
design of post-installed anchors in existing structures
(ACI 562, 7.6.5).
Chapter 1 of ACI 562 describes how ACI 562, ACI
318, and other codes adopted by the local jurisdiction are used by the licensed design professional in
the assessment, repair, and rehabilitation of existing
concrete structures.
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16
Basis of design report example*
1. Building description including:
a. Address
b. Date of construction
c. Structural systems
d. Original building code
e. Past and current uses
2. Documenting of potentially dangerous structural
conditions in the work area, as determined in the
assessment
3. Documenting of substantial structural damage in
the work area
4. History of concrete repairs and rehabilitations
5. Members and systems of the work area requiring
increase in capacity beyond the demand of the
original building code
6. Modifications such as additions, alterations, or
changes in occupancy
7. Conditions and details of the proposed rehabilitation work
8. Assessment criteria and findings
9. Design-basis code criteria and basis of rehabilitation design
10. Material selection parameters
11. Shoring needs
12. Quality assurance and quality control (QA/QC)
requirements
13. Types and frequency of future inspection
14. Types and frequency of future maintenance
*
A basis design report should include, but is not
limited to, this information.
Construction document example*
5. Magnitude and location of prestressing forces†
6. Anchor details for prestressing reinforcement†
7. Development length of reinforcement and length
of lap splices
8. Type and location of mechanical or welded splices
of reinforcement†
9. Shoring or bracing criteria necessary before,
during, and at completion of the assessment,
repair, or rehabilitation projects†
10. Quality assurance program including specific
inspections and testing requirements
*
A construction document should include, but is not
limited to, this information.
†
Items not required on every project.
reports, local jurisdictional codes, and other available docubuilding code, Appendix A of ACI 562 is applicable and
ments of the existing structure to assess the damage, capacity,
provides criteria for selecting the design-basis code.
or load thresholds that will determine the design-basis code.
The level and extent of the preliminary assessment is
The preliminary assessment is done to determine if visibly
subject to the professional judgment of the LDP. In some
dangerous structural conditions are present. If present, the
cases, where the repair project addresses structural damage,
LDP must report these conditions to the owner, contractor,
the extent of deterioration or deficiency and cause of damage
or both (ACI 562, Section 1.7.2). For additions and alteraare clearly defined and known. If the structure’s historical
tions, the preliminary assessment will generally include the
performance and visual observation of the structural condidetermination of the effect of the work on live and dead
tion of members and systems are acceptable, the level of
loads and the capacity of members. The level of damage to
damage or deterioration is low and modifications for addian existing structure is also an important determining factor
tions, alterations, and changes in occupancy are not planned,
in selecting the design-basis code and, therefore, a prelimithen, per ACI 562, 4.6 or A.6, the structure is acceptable and
nary assessment is carried out to assess the level of structural
repairs addressing durability and serviceability issues could
damage, to determine that the structure is in compliance with
be performed without performing analysis.
the original design code, and that the structure is safe.
A preliminary assessment is also important to determine
Chapter 4 applies if a jurisdiction has adopted the IEBC
if an existing member, portions of a structure, or the entire
and defines the design-basis code criteria references. In
structure exhibits signs of deterioration, structural deficiency,
the case of a jurisdiction that has not adopted an
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existing
or behavior that are inconsistent with available design and
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University of Toronto User.
1. Name and date of issue of building code and
supplements to which the assessment, repairs, or
rehabilitation conforms
2. Design-basis code criteria used for conditions
addressed by the documents
3. Design assumptions and construction requirements, including specified properties of existing
and remedial materials used for the project and
the strength requirements at stated ages or stages
of construction
4. Details, locations, and notes indicating the size,
configuration, reinforcement, anchors, repair
materials, preparation requirements, and other
pertinent information to implement the repairs,
strengthening, or rehabilitation of the structure
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Chapter 1—General Requirements17
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Useful references for evaluating existing concrete structures
The following documents are listed in the commentary of ACI 562 and may provide guidance for evaluating existing concrete structures.
ACI 201.2R––Guide to Durable Concrete
ACI 214.4R––Guide to Obtaining Cores and Interpreting Compressive Strength Results
ACI 228.1R––In-Place Methods to Estimate
Concrete Strength
ACI 364.1R––Guide for Evaluation of Concrete
Structures before Rehabilitation
AC1 437.1R––Load Tests of Concrete Structures:
Methods, Magnitude, Protocols, and Acceptance
Criteria
ASCE/SEI 11––Guideline for Structural Condition
Assessment of Existing Buildings
ASCE/SEI 31––Seismic Evaluation of Existing
Buildings
ASCE/SEI 41––Seismic Rehabilitation of Existing
Buildings
FEMA P-58—Seismic Performance Assessment of
Buildings
FEMA P-154—Rapid Visual Screening of Buildings for Potential Seismic Hazards
FEMA 306 and 307—Evaluation of Earthquake
Damaged Concrete and Masonry Wall Buildings
The Concrete Society TR 68––Assessment, Design
and Repair of Fire-damaged Concrete Structures
International Organization for Standardization
(ISO)
Maintenance and Repair of Concrete Structures
16311-3:2014 (ISO/TC 71/SC 71)
documents are available, then listed material properties
can be used in a preliminary assessment. If construction
documents, however, are not available, ACI 562 Chapter
6 provides historical properties based on typical values
used at the time of construction.
The LDP should document all deficiencies including
cracking, spalls, member deflection, cross section dimensions
different than specified on the original construction drawings,
and construction tolerances exceeding those permitted under
the original building code. Deficiencies or unusual behavior
identified in the preliminary assessment are evaluated in more
detail through a structural assessment, structural analysis, or
both, as discussed in Chapter 6 of ACI 562.
The existing conditions, as well as any observed deficiencies or deterioration, should be considered in the course of a
preliminary assessment. In other cases, a preliminary assessment may suggest the need for a more detailed assessment,
when a member or structure exhibits damage, displacements, deterioration, or structural deficiencies, or behavior
that is unexpected or inconsistent with available design and
construction documents or code requirements in effect at the
time of construction of the structure (Section 1.7.5).
As described in the ACI 562 commentary, numerous
published references are available for guidance on
performing assessments of existing concrete structures.
Several of these are listed in “Useful references for evaluating existing concrete structure.” Each of the Project Examples provides a specific example of performing a preliminary
assessment, including some of the assumptions and professional judgments that may be considered by the LDP.
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University of Toronto User.
construction documents or code requirements in effect at the
time of construction (ACI 562, 6.2.1). The LDP of the project
may limit the access to the structure, take specific measures to
mitigate these conditions, or require the installation of shoring
to support the structure or member, if potentially dangerous
conditions are present.
As deemed necessary by the LDP, the preliminary assessment may include a review of design and construction documents and verification of existing site conditions by visual
inspection and other means. Per ACI 562, 1.7.4, the preliminary assessment should also include a determination of the
design strength of the existing structure, including the impact
of deficiencies, and a determination if substantial structural
damage has occurred. The concept of substantial structural
damage is not addressed by ACI 562 if a jurisdiction has
adopted the IEBC as an existing code; thus the LDP should
use IEBC to determine if substantial structural damage has
occurred. The LDP, however, should use ACI 562 Appendix
A, A.4, that defines substantial structural damage if a jurisdiction has not adopted an existing building code.
The preliminary assessment should be based on
in-place conditions and should use actual material
properties and member sizes to calculate the impact of
damage on the members and the overall performance of
the existing structure. Fire damage or other deterioration mechanisms could affect the material properties of
reinforced concrete members; for example, compressive
strength and modulus of elasticity of concrete and loss
of steel reinforcement area due to corrosion. If a member
does not show significant deterioration and construction
ATC 20––Post Earthquake Evaluation of Buildings
ATC 45––Field Manual: Safety Evaluation of
Buildings after Wind Storms and Floods
ATC 78—Identification and Mitigation of Nonductile Concrete Buildings
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18
Concrete spalling and corrosion of reinforcing steel at floor slab underside (left).
Severe concrete and reinforcing steel deterioration in a wastewater treatment basin (right)
Overview
Chapter 2 of ACI 562 provides a summary of the notation and terminology used
in the ACI 562 Code.
2.2—Definitions
Section 2.2 of ACI 562 defines unique and specific terminology used in the code
and commentary of ACI 562. In some cases, multiple, slightly different definitions
are provided for the same term where it is uncertain which definition might be most
appropriate for a given scenario or use. For example, “repair process” may have
several possible definitions.
The list of definitions provided in Section 2.2 of ACI 562 is not intended to be
comprehensive of all terminology used within ACI 562. ACI and the International
Concrete Repair Institute (ICRI) provide online resources for terminology:
a. ACI––“ACI CT-16 Concrete Terminology,”
https://www.concrete.org/store/productdetail.aspx?ItemID=CT18&For
mat=DOWNLOAD&Language=English&Units=US_Units
b. ICRI––“ICRI Concrete Repair Terminology,”
https://www.icri.org/page/terminology_H?&hhsearchterms=%22termin
ology%22
Where indicated in the commentary, some definitions in ACI 562 are repeated
verbatim from the 2018 International Existing Building Code (IEBC). Other terms
used can differ from the definitions provided within other building codes, specifically the 2018 IEBC. In such cases, the definitions@Seismicisolation
provided in Section 2.2 of ACI
@Seismicisolation
19
University of Toronto User.
2.1—Notation
Section 2.1 of ACI 562 defines the various symbols and letters used in the
formulas and text in the ACI 562 code and commentary. Most often the notation
used in a given formula is also defined within the text of the code after the formula
is presented. Section 2.1 of ACI 562 is intended to provide the user with an easy
single-source reference location.
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Chapter 2—Notation and Definitions
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
562 or the definitions provided in ACI CT should be used
when interpreting the language of ACI 562. Similarly, the
definitions presented in 2018 IEBC should be used when
interpreting the language of 2018 IEBC.
To further assist the user, specific terminology that is
defined in unique ways to ACI 562 and 2018 IEBC are
presented as follows:
Existing structure —
a. ACI definition: structure for which a legal certificate of occupancy has been issued. For structures
that are not covered by a certificate of occupancy,
existing structures are those that are complete and
permitted for use or otherwise legally defined as an
existing structure or building.
b. IEBC definition: a structure erected prior to the
date of adoption of the appropriate code, or one for
which a legal building permit has been issued.
Rehabilitation—
a. ACI definition: repairing or modifying an existing
structure to a desired useful condition.
b. IEBC definition: any work, as described by the
categories of work defined herein, undertaken in
an existing building (2018 IEBC).
Repair—
a. ACI definition: the reconstruction or renewal of
concrete parts of an existing structure for the
purpose of its maintenance or to correct deterioration, damage, or faulty construction of members or
systems of a structure.
b. IEBC definition: the reconstruction, replacement,
or renewal of any part of an existing building for
the purpose of its maintenance or to correct damage
(2018 IEBC).
Repair section—
the combination of the installed repair material(s) and
the substrate material(s).
Restoration—
a. ACI definition: the process of reestablishing
the materials, form, and appearance of a structure to those of a particular era of the structure
(ACI CT-16).
b. IEBC definition: no specific definition provided in
2018 IEBC.
Structural repair—
a. ACI definition: restoring a damaged or deteriorated
structure or increasing the capacity of a structure.
b. IEBC definition: no specific definition provided in
2018 IEBC.
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20
University of Toronto User.
@Seismicisolation
@Seismicisolation
Application of an epoxy-based, quartz-reinforced composite overlay on effluent trough of a clarifier basin
21
University of Toronto User.
Overview
Chapter 3 of ACI 562 provides the full document titles for referenced standards
presented in the code portion of ACI 562. These standards include building codes,
specifications, and test methods, and are referenced to specify, clarify, or expand
upon the code requirements presented within ACI 562. Each of these standards are
written with mandatory language and considered part of the code requirements of
ACI 562 for the purposes indicated within ACI 562.
The context of the reference within the code language of ACI 562 governs the
use and applicability of each of the referenced standards. In some cases, the code
requirements of ACI 562 limit the applicability of the referenced standard. The
entire standard is not necessarily considered part of the code requirements of ACI
562. For example, Section 5.1.6 of ACI 562 limits the use of ASCE/SEI 7, “Minimum
Design Loads for Buildings and Other Structures,” by excluding seismic load
requirements, but references ASCE/SEI 41, “Seismic Rehabilitation of Existing
Buildings,” for the treatment of seismic loads.
Current, past, and withdrawn standards are referenced as indicated in Chapter 3 of ACI
562. The dates provided refer to the applicable version of the reference. Those references
indicated as being withdrawn refer to the standard at the time it was withdrawn, and
not the superseding standard. For example, ASTM A160, “Specifications for Axle-Steel
Bars for Concrete Reinforcement (withdrawn 1969),” refers to the version in effect in
1969, and not ASTM A617/A617M, “Standard Specification for Axle-Steel Deformed
and Plain Bars for Concrete Reinforcement,” which superseded this standard.
Additional resources that are referenced within the commentary text of ACI 562
are listed in Chapter 11 of ACI 562.
The following ACI codes are referenced in Chapter 3 of ACI 562. A brief description of each document is included.
@Seismicisolation
@Seismicisolation
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Chapter 3—Referenced Standards
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
ACI 216.1-14—Code
Requirements for
Determining Fire
Resistance of Concrete
and Masonry Construction
Assemblies
Fire resistance of building
elements is an important consideration in building design. While
structural design considerations
for concrete and masonry at
ambient temperature conditions
are addressed by ACI 318 and TMS 402/ACI 530/ASCE 5,
respectively, these codes do not consider the impact of fire
on concrete and masonry construction. This standard contains
design and analytical procedures for determining the fire resistance of concrete and masonry members and building assemblies. Where differences occur in specific design requirements
between this standard and the aforementioned codes, as in the
case of cover protection of steel reinforcement, the more stringent of the requirements shall apply.
Much of the research data referenced in preparing the Code
arecited for the user desiring to study individual questions
in greater detail. Other documents that provide suggestions
for carrying out the requirements of the Code are also cited.
ACI 437.2-13—Code
Requirements for Load
Testing of Existing
Concrete Structures and
Commentary
This code provides requirements for test load magnitudes,
test protocols, and acceptance
criteria for conducting a load
test as a means of evaluating
the safety and serviceability of
concrete structural members
and systems for existing buildings as provided for by ACI
562-19. A load test may be conducted as part of a structural assessment to determine whether an existing building
requires repair and rehabilitation, or to verify the adequacy
of repair and rehabilitation measures applied to an existing
building, or both. This code contains provisions for both a
cyclic load test and a monotonic load test procedure.
An ACI Standard
ACI 563-18
Reported by ACI Committee 563
University of Toronto User.
ACI 318-19—Building Code
Requirements for
Structural Concrete and
Commentary
ACI 563-18—Specifications
The “Building Code Requirefor Repair of Concrete in
ments for Structural Concrete”
Buildings
Specifications for Repair
of Concrete in Buildings
(“Code”) covers the mateThis is a Reference Specifica(ACI 563-18)
rials, design, and construction
tion that the Architect/Engineer
of structural concrete used in
can apply to any construction
buildings and where applicable
repair and rehabilitation project
in nonbuilding structures. The
involving structural concrete
Code also covers the strength
by citing it in the Project Specievaluation of existing concrete structures.
fications. Mandatory requireAmong the subjects covered are: contract documents;
ments and Optional requirements
inspection; materials; durability requirements; concrete
checklists are provided to assist the Architect/Engineer in
quality, mixing, and placing; formwork; embedded pipes;
supplementing the provisions of this Specification, as required
reinforcement details; member design of slab systems,
or needed, by designating or specifying individual project
beams, columns, diaphragms, walls, structural plain
requirements. The first section covers general construction
concrete, construction joints; strength and serviceability;
requirements for all repair work. The second section covers
development and splices of reinforcement; strength evalushoring and bracing of the structure or member to be repaired,
ation of existing structures; provisions for seismic design;
and addresses sequencing of repair work as the structure is
strut-and-tie modeling; and anchoring to concrete.
unloaded and reloaded. The third section covers concrete
The quality and testing of materials used in construction are
removal and preparation of the concrete substrate for repair,
covered by reference to the appropriate ASTM standard speciand defines common equipment and methods. The next
fications. Welding of reinforcement is covered by reference to
five sections cover materials and proportioning of concrete;
the appropriate American Welding Society (AWS) standard.
proprietary cementitious and polymer repair materials; reinUses of the Code include adoption by reference in general
forcement; production, placing, finishing, and curing of repair
building codes, and earlier editions have been widely used in
materials; formwork performance criteria and construction;
this manner. The Code is written in a format that allows such
treatment of joints; embedded items; repair of surface defects;
reference without change to its language. Therefore, backmockups; and finishing of formed and unformed surfaces.
ground details or suggestions for carrying out the requireProvisions governing testing, evaluation, and acceptance of
ments or intent of the Code portion cannot be included.
repair materials as well as acceptance of the repair Work are
The Commentary is provided for this purpose. Some of
included. Sections 9 and 10 incorporate by reference two
the considerations of the committee in developing the Code
other specifications—ACI 503.7 and ACI 506.2—into this
portion are discussed within the Commentary, with emphasis
ACI Standard to cover crack repair by epoxy injection and
given to the explanation of new or revised provisions.
@Seismicisolation
shotcrete, respectively.
@Seismicisolation
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22
Step repair project at government building
4.1—General
Chapter 4 of ACI 562 applies if a jurisdiction has adopted a code that addresses
assessment, repair, and rehabilitation of existing concrete structures such as the
International Existing Building Code (IEBC). Per ACI 562, 1.2.4.2, this chapter
does not apply to existing structures located in jurisdictions that have not adopted
the IEBC. Where Chapter 4 of ACI 562 applies, the LDP has to determine the
design-basis code based on the results of the preliminary assessment (ACI 562, 1.7),
detailed assessment (ACI 562 Chapter 6), and on the criteria in the existing building
code (IEBC) as stated in Section 4.1.2 of ACI 562.@Seismicisolation
The
LDP may choose, however,
@Seismicisolation
23
University of Toronto User.
Overview
Chapter 4 provides the criteria for use of ACI 562 with the IEBC. Section 1.7
specifies a preliminary assessment of deteriorated or damaged existing structures to
determine the extent and significance of damage and deterioration and the reduced
structural capacity of individual existing members and structures. Based upon the
findings of the preliminary assessment, the licensed design professional (LDP) has
to make a decision regarding potentially dangerous structural conditions and the
required extent of further assessment. The findings from the assessment are used
to make a decision regarding the design-basis code for required repairs and IEBC
compliance method.
This chapter establishes limits based on demand-capacity ratios for ultimate strength
design and allowable stress principles to determine if existing members, systems,
or structures are safe or if strengthening, repair, or both, are necessary. The level of
strengthening, repair, or both, is influenced by the calculated demand-capacity limits.
The Project Examples illustrate various types of preliminary assessments and
methods of determining the design-basis code.
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Chapter 4—Basis for Compliance
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
to use the current building code referencing ACI 318-19 for
concrete structures, TMS 402/602-16 for masonry structures, and AISC-16 for steel structures as the design-basis
criteria for all damage states, deterioration, faulty design, or
faulty construction instead of the original building code. This
may be unnecessarily conservative, however, and may lead
to a solution that is cost prohibitive or uneconomical.
The LDP is confronted in the initial stages of a project
with the challenge to determine what design-basis code
criteria applies. This is more prevalent when a structure was
constructed prior to a jurisdiction having adopted a general
building code. The structure may have design and construction that do not satisfy current building code requirements.
ACI 562, with the IEBC, is used to determine if an existing
structure should be rehabilitated or retrofitted to satisfy
the requirements of the current building code. The LDP, in
the absence of mandatory local ordinances, should determine if a seismic evaluation is necessary for potentially
hazardous conditions. Consistent with the IEBC, ASCE/
SEI 41 should be used for evaluation of seismic damage to
members, systems, or structures that are seismically unsafe.
ASCE/SEI 41 may or may not be applicable to nonbuilding
structures. The requirements in ASCE/SEI 41 may apply to
nonbuilding structures, but the LDP should use judgment
as the applicability of these requirements has not been fully
verified for every type of structure. This is particularly true
for nuclear power plants or other structures designed by
nonbuilding standards.
Table 4.1—Design-basis code criteria references for
rehabilitation categories
Rehabilitation category
Additions
Alterations
Changes in occupancy
4.3.2
4.3.3
IEBC Section 405.2.3
IEBC Section 405.2.4
4.5
4.2—Compliance method
A compliance method as per the 2018 IEBC is used for
assessing
the code basis for repair or rehabilitation projects
4.5
is described in this section. The design-basis code for repair
and rehabilitation projects varies based on the extent of alter4.6
ations, additions, or repairs. In general, the original building
IEBC Sections 502, 606, or
code is the design basis for minor alterations without signifiChapter 11
cant changes in load. The current building code serves as
IEBC Section 503;
the design basis for elements subject to major alterations or
Sections 602 and Chapter 7;
significant load changes. It should be noted, however, that
Sections 603 and Chapter 8; or
Sections 604 and Chapter 9
ACI 562-19 1.3.8.1, requires the selection of the existing
IEBC Sections 506, 605, or
building code for assessment and design for seismic considChapter 10
@Seismicisolation
erations. Similarly, the design of repairs subject to elevated
@Seismicisolation
4.6
University of Toronto User.
Potentially dangerous structural
conditions for gravity and wind loads
Potentially dangerous structural
conditions for seismic forces in
regions of high seismicity
Substantial structural damage to
vertical elements of the lateral-forceresisting system
Substantial structural damage to
vertical elements of the gravity-loadresisting system
Damage less than substantial structural damage with strengthening
Damage less than substantial structural damage without
strengthening
Deterioration and faulty construction
with strengthening
Deterioration and faulty construction
without strengthening
Design-basis code
criteria reference
ASCE/SEI 41 states that its provisions do not have to
apply to large nonbuilding structures, such as large tanks
found in heavy industry or power plants, floating-roof oil
storage tanks, and large (greater than 10 ft long) propane
tanks at propane manufacturing or distribution plants.
ACI 562 and IEBC should be used to determine the assessment and design-basis criteria for a structure as shown in
Table 4.1 (ACI 562 Table 4.1.4) unless the local jurisdiction
imposes more restrictive requirements. The IEBC references
in Table 4.1 are to sections in the 2018 IEBC.
The LDP is faced with several questions when confronted
with deteriorated or weakened structures, which he or she
should clarify prior to engaging in the assessment.
ACI 562 4.1.5 and 4.1.6, require that new reinforced
concrete members, added to an existing structure, are
designed and detailed to satisfy the current design code
(ACI 318-19). This also applies to the connections between
the new member and the existing structure. When new
concrete and reinforcing members are integrated with the
repairs, however, the original building code can be used
for design. Detailing of the existing structure, however,
need not meet the current design code if the following
conditions are satisfied:
a. The damage or deterioration to the existing reinforcement
is addressed
b. The repaired work area of the structure has capacity
equal to or greater than demand per ACI 562, 5.2.2, using
the original building code requirements or satisfies the
requirements of ACI 562, 4.5.3, when using allowable
stress design
The LDP should review the development length of existing
reinforcement when cracking is evident near the ends of
reinforcement or in regions where reinforcement splices are
present. Research has shown that the development length
equations from previous versions of ACI 318 may be unconservative for top cast plain reinforcement (Feldman and
Cairns 2017). The LDP should also determine if the structure
has demonstrated statistically acceptable performance based
on historic data, such as acceptable resistance of previous
loads that equal or exceed the loads that would be predicted
for the remaining life of the structure, the LDP may judge
the structure to have demonstrated historic structural reliability. The commentary in ACI 562 lists a few references
that provide guidance in judging acceptable performances.
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24
Useful references for assessing and
evaluating existing concrete structures
ACI 562 Chapter 2 defines potentially
dangerous structural condition as follows:
The following documents are listed in the
commentary of ACI 562, R4.1.6, and may provide
guidance in judging acceptable performance.
• ACI 224.1R, “Causes, Evaluation, and Repair
of Cracks in Concrete Structures”
• ACI 437R, “Strength Evaluation of Existing
Concrete Buildings”
• ACI 437.1R, “Load Tests of Concrete Structures: Methods, Magnitude, Protocols, and
Acceptance Criteria”
potentially dangerous structural condition—
(1) Structural state of existing concrete within a
work area for an individual structural member,
structural system, or structure that meets the definition of dangerous or unsafe, is unstable, has
potential of collapse of overhead components or
pieces (falling hazards), has been determined to
have demand/capacity ratio exceeding the limit
of Section 4.3.2.2, or has potentially hazardous
resistance for seismic events. (2) A limit state of
unacceptably low margin of safety against collapse
without supplemental resistance.
factored load combinations of ASCE/SEI 7. In this chapter,
the term “gravity loads” refers to dead, live, and snow
loads. Reduction factors from ACI 562 Section 5.3 or 5.4,
are used whether a structure is rehabilitated or assessed. If
the demand-capacity ratio, as given in ACI 562 Eq. (4.3.2)
is greater than 1.5, then the structure is considered potentially dangerous and must be strengthened or repaired based
on the current building code.
Uc
> 1.5
φRcn
(ACI 562, Eq. 4.3.2)
where Uc is defined as strength design demand by using
nominal loads of the current building code and factored load
combinations of ASCE/SEI 7 for strength design provisions
(LRFD); Rcn is the current in-place nominal resistance of
the structural member, system, or connection including the
effects of damage, deterioration of concrete and reinforcement, and faulty construction; and φ is the strength reduction factor obtained from Section 5.3 or 5.4 of ACI 562. A
demand-to-capacity ratio greater than 1.5 calculated using
Eq. (4.3.2) represents a condition with limited to no margin
of safety against failure (Stevens et al. 2019). Potentially
dangerous structural conditions requiring immediate attention are reported immediately to the owner per ACI 562,
1.5.2, and to the appropriate authorities when required by
the authorities having jurisdiction per ACI 562, 1.5.2.1.
The LDP may also consider the following to satisfy Eq. (4.3.2):
a. Adding structural redundancies, which are desirable to
ensure the safety of a structural system
4.3—Potentially dangerous structural conditions
b. Providing alternate load paths, redistributing the load, or
The LDP needs to determine if potentially dangerous
limiting the live load such that existing members are not
structural conditions exist by carrying out a thorough
overstressed
assessment of the deterioration or damage to the existing
c. Adding secondary supporting members to relieve overstructure, as discussed in Chapter 1 and 6 of this guide. The
stressed members
risk for collapse of each proposed strengthening procedure
If the demand-capacity ratio, however, is less than 1.5,
should be assessed to determine an economical and safe
then less restrictive requirements are implemented as
repair strategy. The LDP calculates the strength demand
described in Section 4.5 of this guide.
based on the current building code, considering gravity and
Unless addressed by the authority having jurisdiction, for
fluid loads and lateral wind and soil loads but excluding
structures in Seismic Design Categories D, E, and F, the LDP
seismic loads. The governing load is determined
@Seismicisolation
using
should review the structure for potentially hazardous seismic
@Seismicisolation
University of Toronto User.
temperatures and fire needs to satisfy the applicable existing
building code.
The LDP should confirm specific requirements of selected
compliance method which may vary depending upon IEBC
edition. The 2018 IEBC describes three compliance methods:
the prescriptive method, the work area method, and the performance method, which are summarized in The Compliance
Methods in the 2018 IEBC chapter at the end of this guide.
Assessing structural safety, level of structural damage
or conditions with less than substantial structural
damage—In the industry, a quantitative measure or scale
to determine the level of deterioration or damage exhibited
by an existing structure does not exist. There are, however,
processes that can be applied to determine the safety level
of an existing structure. Nevertheless, the LDP is confronted
with several questions that require careful planning and
response. Some of the questions may be:
a. When should an existing structure be strengthened or
repaired?
b. What is an acceptable demand-capacity ratio limit to
consider an existing structure safe?
c. What is the minimum acceptable strengthening or repair
level that is considered safe?
d. When should an existing structure’s capacity be increased?
e. How should an existing structure be evaluated by the
working stress method?
f. When should an existing structure be strengthened or
repaired to the original building code, IEBC, or applicable
existing building code level?
These and other questions that may arise are addressed in
ACI 562-19, 4.3 through 4.5.
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Chapter 4—Basis for Compliance25
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
ACI 562-19 Useful references for potentially
dangerous structural conditions
ACI 562-19 Chapter 2 defines substantial
structural damage as follows:
The following documents are listed in the
commentary of ACI 562 and may provide target
reliability indexes, basic probability theory and
concepts for an assessment using the specific
details of the demand as it relates to the capacity
with the strength reduction factors of Chapter 5 for
concrete structures.
• ASCE/SEI 7, “Minimum Design Loads for
Buildings and Other Structures”
• Galambos, T.V.; Ellingwood, B.R.; MacGregor,
J.G.; and Cornell, C.A., 1982, “Probability
Based Load Criteria: Assessment of Current
Design Practice,” Journal of the Structural
Division, ASCE, V. 108, No. 5, pp. 959-977.
• Ellingwood, B.R., and Ang, A. H.-S., 1972,
“A Probabilistic Study of Safety Criteria for
Design,” Structural Research Series 387, University of Illinois Experiment Station, University of
Illinois at Urbana-Champaign, Champaign, IL.
Substantial structural damage—Except when
using Appendix A, substantial structural damage
per the IEBC shall be - A condition where one or
both of the following apply:
1. In any story, the vertical elements of the lateral
force resisting system have suffered damage
such that the lateral load-carrying capacity of
the structure in any horizontal direction has
been reduced by more than 33 percent from its
predamage condition.
2. The capacity of any vertical gravity load
carrying component, or any group of such
components, that supports more than 30 percent
of the total area of the structure’s floor(s) and
roof(s) has been reduced more than 20 percent
from its predamage condition and the remaining
capacity of such affected elements, with respect
to all dead and live loads, is less than 75 percent
of that required by this code for new buildings
of similar structure, purpose and location.
When using this code as a stand-alone code,
substantial structural damage shall be as defined in
A.4.
there is reason to question the capacity of the structure,
ACI 562 requires that it be assessed by checking one of the
criteria in ACI 562, 4.5.1, 4.5.2, or 4.5.3. These sections
must not be applied in combination with each other. The
demand-capacity ratio of a member, system, or structure is
evaluated in accordance with Eq. (4.5.1):
Uo
> 1.0
φo Rcn
where Uo is the strength design demand determined by using
4.4—Substantial structural damage
the nominal loads and factored load combinations of the
A structure with substantial structural damage, as defined
original building code, excluding seismic loads; foRcn is the
in ACI 562 Chapter 2, is assessed and rehabilitated per 2018
current in-place nominal resistance of the structural member,
IEBC Sections 404.2 through 404.3, or 606.2.2 through
system, or connection including the effects of damage, dete606.2.3 that requires the LDP to submit to the building offirioration of concrete and reinforcement, and faulty construccial the structure’s assessment and whether “the damaged
tion adjusted by the strength reduction factor (fo) of the
building, if repaired to its pre-damaged state, would comply
original building code.
with the provisions of the IBC for wind and earthquake
If Uo/foRcn is greater than 1.0, repairs are required to
loads.” 2018 IEBC has, however, two exceptions; for buildrestore the structure to the pre-damage or pre-deteriorated
ings in SDC A, B, or C, if the substantial damage was not
states based on the original building code. Most existing
due to an earthquake, and for one-and two-family dwellings.
concrete structures with damage less than substantial strucBoth do not need to “be evaluated or rehabilitated with load
tural damage, deterioration, or containing faulty construccombinations that include earthquake effects.”
tion, will provide acceptable safety if restored to the strength
of the original building code based on the material proper4.5—Conditions of deterioration, faulty
ties of the original construction. New concrete members and
construction, or damage less than substantial
connections to existing construction must comply with ACI
structural damage
562, 4.5.1.
For structures having less than substantial structural
For structures with a demand-capacity ratio (Uo/ϕcRcn)
damage but have deterioration or faulty construction @Seismicisolation
and
less than 1.0, strengthening is not required.
@Seismicisolation
University of Toronto User.
conditions. The review should be completed to confirm the
structure is adequate for either the seismic performance level
required by the local authorities, or confirm the structure is
compliant with ASCE/SEI 41 for Structural Performance
Level – Collapse Prevention using Earthquake Hazard
Level, BSE-1. Earthquake Hazard Level BSE-1 has a 20
percent probability of exceedance in 50 years, or a 225-year
return period.
When the local authority having jurisdiction does not provide
requirements for potentially hazardous seismic structural conditions, then the LDP should refer to ATC-78, the IEBC, and
ASCE/SEI 41 appendixes for guidance. The LDP is not required
to assess potentially hazardous seismic conditions for concrete
structures located in moderate to low seismicity regions.
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26
IEBC adopted?
No
Go to
Appendix A
Yes
Yes
Go to Chapter 4
Is structure unsafe for
gravity and wind loads,
Uc / φRcn > 1.5?
No
Report unsafe conditions
to Owner/Jurisdiction
(Section 1.5.2)
Is structure in
SDC D, E, F?
No
Yes
Yes
Is structure unsafe for
seismic forces?
No
Design-basis code is the
current building code and
ASCE/SEI 7
Yes
Substantial structural damage
to gravity-force-resisting
system?
Design-basis code
IEBC Section
404.3 or 606.2.3
Yes
Design-basis code is
the ACI 562 and
ASCE/SEI 41
Substantial structural damage
to lateral-force-resisting
system?
No
No
Report unsafe conditions
to Owner/Jurisdiction
(Section 1.5.2)
Yes
Design-basis code
IEBC Section
404.2 or 606.2.2
Strengthening required?
Uo / φoRcn > 1.0?
Restore structure to
pre-damaged or
pre-deteriorated state
No
Less than substantial structural
damage (Section 4.6)
Section 4.6.1
Strengthening per ACI 562
Chapters 7 through 10
Section 4.6.2
Assessing effects of deflection,
vibration, and levelness
No structural damage
Additions
(Section 4.7)
Alterations
(Section 4.8)
Change in occupancy
(Section 4.9)
Fig. 4.5a—Selecting design-basis code.
For an existing structure that was subjected to known
the original structure is significantly inconsistent with the
loads equal to or higher than specified in the design docucurrent standards, which may result in unacceptable strucments during its service life that has performed satisfactotural safety issues. The references listed under Section 4.3 of
rily, then it should be taken as an indicator that the existing
this guide should be considered in the selection of a relevant
structure has an adequate safety factor and strengthening is
assessment criteria. The applicability of the original building
not required. Figure 4.5a provides a road map for selecting
code for assessing existing structures should be questioned if
the design-basis code.
there are any of the following:
ACI 562 Section 4.5.2 permits the LDP to use alternaa. Increased load intensity
tive assessment criteria using engineering principles for
b. Added loads
members, systems, or structures with deterioration, faulty
c. Changes in load factors, strength-reduction factors, or
construction, or damage less than substantial structural
load combinations
damage when approved by authority having jurisdiction.
d. Modifications of analytical procedures
The LDP should assess whether the demand or capacity
@Seismicisolation
of
e. Changes in determining capacity between the original and
@Seismicisolation
University of Toronto User.
Uc – demand using nominal loads of the current building code and factored load combinations of ASCE/SEI 7 for strength
design provisions
Uo – demand using nominal loads and factored load combinations of the original building code for strength design provisions
Rcn – current in-place nominal capacity of structural member, system, or connection including the effects of damage, deterioration of concrete and reinforcement, and faulty construction
φ – strength reduction factor per ACI 562, Section 5.3 or 5.4
φo – strength reduction factor of the original building code
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Chapter 4—Basis for Compliance27
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
current building codes, such as a change from allowable
stress design to ultimate strength design
f. The benefits received from strengthening or repair do not
justify the incurred cost
ACI 562 defines demand based on the current building code
(Uc) as the effect of nominal gravity loads and lateral wind
and soil loads, excluding earthquake loads, using ASCE/
SEI 7 factored load combinations. ACI 562 defines demand
based on the original building code (Uo*) as the effect of
the original building code nominal gravity loads and lateral
wind and soil loads, excluding earthquake loading, using the
factored load combinations of ASCE/SEI 7. The LDP should
compare the demand based on the current building code (Uc)
to the demand of the original building code (Uo*).
If Uc > 1.05Uo*, then the LDP should determine the
demand-capacity ratios based on the current building
code, Uc/fRcn. If the ratio exceeds 1.1, (Uc/fRcn > 1.1), then
strengthening of the structure to the current building code is
required. Otherwise, strengthening is not required.
If the current building code demand, however, does not
exceed the original building code demand by more than
5 percent (Uc ≤ 1.05Uo*), then the LDP should check the
demand-capacity ratio using the original building code
demand and the current building code capacity. If the ratio
exceeds 1.05 (Uo*/fRcn > 1.05), then the system or member
strength should be restored to its original strength using
the original building code. Otherwise, strengthening is not
required (refer to Fig. 4.5b). For both conditions, the strength
reduction factors are obtained from ACI 562 Chapter 5.
The LDP is often confronted with deteriorated or damaged
structures designed using the working or allowable stress
method that was the only available method for designing
structures prior to ACI 318-63. In 1963, the strength design
method was introduced into ACI 318 next to the working
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28
University of Toronto User.
Uc – demand using nominal loads of the current building code and factored load combinations of ASCE/SEI 7 for strength
design provisions
Uo* – demand using nominal loads of the original building code and factored load combinations of ASCE/SEI 7 for strength
design provisions
Rcn – current in-place nominal capacity of structural member, system, or connection including the effects of damage, deterioration of concrete and reinforcement, and faulty construction
φ – strength reduction factor per ACI 562, 5.3 or 5.4
Fig. 4.5b—Alternate method for evaluating reinforced concrete
@Seismicisolation
structure.
@Seismicisolation
Table 4.5—Assessment conditions for reinforced concrete buildings
ACI 562 Section
Demand/capacity
Design-basis code
Potentially dangerous structural condition, Section 4.3
Gravity and wind load (4.3)
Seismic (4.3)
Uc/fRcn > 1.5
Current building code and ASCE/SEI 7 for factored load combinations
ASCE/SEI 41 and ACI 562
Substantial structural damage, Section 4.4
Gravity and wind load (4.4)
Seismic (4.4)
Section 4.5.1
Section 4.5.2C(a)
Section 4.5.2C(b)
Section 4.5.3
IEBC 404.3 or 606.2.3
IEBC 404.2 or 606.2.2
Deterioration, faulty construction, or damage less than substantial
Original building code
Uo/foRcn > 1.0
New members use current building code
Alternate assessment criteria for deterioration, faulty construction, or damage less than substantial
Uc > 1.05Uo* and
Current building code
Uc/fRcn > 1.1
Uc > 1.05Uo* and
Strengthening not required
Uc/fRcn < 1.1
*
Uc < 1.05Uo and
Original building code
Uo*/fRcn > 1.05
*
Uc < 1.05Uo and
Strengthening not required
Uo*/fRcn < 1.05
1.0 < Uc/fRcn < 1.5
Original building code only used allowable stress design and design service loads
Us/Ra > 1.0
Original building code
Strengthening not required
Us/Ra < 1.0
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Chapter 4—Basis for Compliance29
University of Toronto User.
Chloride extraction performed on historic viaduct
stress method. In 1971, ACI 318 dropped the working stress
then strengthening of a structure is required using the origmethod and retained the strength design method.
inal building code. If the demand-capacity ratio, however, is
ACI 562, 4.5.3, provides provisions to assess such a strucless than 1.0, Us/Ra < 1.0, then strengthening is not required.
ture. The demand-capacity ratio is based on service load
The service load demand includes nominal gravity loads
demand, Us, and resistance using allowable stresses, Ra. If
and lateral wind and seismic forces using load combinations
the demand-capacity ratio is greater than 1.0, Us@Seismicisolation
/R
of the original building code. The LDP should be aware that
a > 1.0,
@Seismicisolation
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
using the allowable stress design method is inconsistent with
the reliability principles of current strength design provisions. Therefore, ACI Committee 562 recommends verifying the structure following ACI 562, 4.5.2, and checking
the seismic resistance using ASCE/SEI 41.
Table 4.5 summarizes the different assessment conditions
that the LDP has to address when analyzing a structure for
repair, rehabilitations, or strengthening.
4.6—Conditions of deterioration, faulty
construction, or damage less than substantial
structural damage without strengthening
For other structures not strengthened using ACI 562, 4.3
through 4.5, the LDP needs to follow ACI 562, 4.6 through
4.9, to determine the design-basis criteria to implement for
strengthening.
For structures with minimal or no damage or faulty
construction that do not require strengthening per
ACI 562, 4.5, the LDP can use Chapters 7 through 10 of
ACI 562 as the design-basis criteria to rectify the shortcomings.
Corroded or damaged reinforcement affects the behavior
of the concrete structure. It may result in concrete cracking,
possible reduction in section capacity resisting the applied
loads, or both. The licensed design professional should evaluate
the effectiveness of the reinforcement per Chapter 7 of ACI 562.
ACI 318, as well as other codes, control predicted design
deflections by either limiting calculated deflections to some
specified allowable limits or specifying a minimum spanto-thickness ratio. These limits, however, are based on past
experience with loads (for example, normalweight concrete
with loads less than approximately 100 lb/ft2 [488 kg/m2]
live load for two-way slabs), boundary conditions, and spans,
among other factors. Structures with aggressive construction
Type 1A embedded galvanic anodes on bridge pier
schedules resulting in heavier-than-planned construction
loads, premature form removal, and accelerated shoring and
re-shoring may result in members or structures with excessive
deflections or having vibration issues that should be assessed
for safety and comfort of the occupants. Deflections exceeding
the code-prescribed design limits may be acceptable to the
owner or user provided the member or structure performance is not adversely affected.
4.7—Additions, 4.8—Alterations, 4.9—Changes in
occupancy
In case a structure receives additions, alterations, or has a
change in occupancy, ACI 562 requires that the LDP assess
and rehabilitate the structure and ensure that any change in
loading, addition, or alteration warrants that the existing structure or member with the addition(s), alteration(s), or changes
in occupancy conforms to the IEBC (refer to Table 4.1).
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30
University of Toronto User.
@Seismicisolation
@Seismicisolation
Tensioning new post-tensioning cables on parking deck repair project
31
University of Toronto User.
Overview
The primary objective of building standards is to limit risk and establish the
safety of structures. Chapter 5 of ACI 562 addresses the licensed design professional (LDP)’s responsibilities for determining the load and strength requirements
throughout the assessment, repair, rehabilitation, or strengthening process, both
relative to the member under investigation and the structure as a whole. The basic
requirements for the determination of design strength ϕRn and required strength U
of existing structural members subject to assessment or repair and rehabilitation
design are described.
Chapter 5 of ACI 562 also addresses loads and factored load combinations, and
specifically the treatment of loading scenarios that may change over the duration
of the repair, rehabilitation, or strengthening work. Unlike new construction, this
work may take place while the structure remains in service. Additional factored
load combinations are provided for repairs with external reinforcing systems to
achieve a minimum level of safety during extraordinary events.
The assessment of existing buildings is different from the design of new buildings because the as-built geometries, in-place materials, and material properties
can be documented as required. Having knowledge of these attributes greatly
reduces the uncertainty associated with the parameters used in the design of reinforced concrete buildings. As such, the strength reduction factors used for design in
ACI 318-19 may, in some cases, be unnecessarily conservative. Chapter 5 of ACI
562 addresses this difference for existing buildings and specifies when increased
strength reduction factors may be used for assessment and repair design. These
alternate strength reduction factors are the same as those in Chapter 27 of ACI
318-19, which applies to strength assessment of existing
@Seismicisolation
structures.
@Seismicisolation
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Chapter 5—Loads, Factored Load Combinations, and
Strength Reduction Factors
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
5.1—General
The minimum level of safety regarding load and strength
requirements for a given project are stipulated in the designbasis code, which should be determined as described in
Chapters 1 and 4 or Chapter 1 and Appendix A of ACI 562,
following the general procedure presented in Chapter 1 of
this guide. When the design-basis code requires use of ACI
318-19 for the assessment or repair design, the load factors,
factored load combinations, and strength reduction factors
are obtained from Chapter 5 of ACI 562. When the designbasis code references other standards, such as the original
building code, that specify loads, factored load combinations, and strength reduction factors that are different than
ACI 318-19, certain sections of ACI 562 Chapter 5 will not
apply. The application of Chapter 5 in ACI 562 is dependent on reference to ACI 318-19 in the design-basis code, as
shown in Fig. 5.1.
As described in ACI 562 Section 5.1.2, it is not permitted
to use load factors and factored load combinations from
the original building code with strength reduction factors
from ACI 562 Chapter 5, or load factors and factored load
combinations from ACI 562 Chapter 5, with strength reduction factors from the original building code. Load factors
and strength reduction factors within a given code are
calibrated to achieve an appropriate level of reliability in
design. Mixing factors from different codes may result in
an unsatisfactory level of reliability. The LDP should exercise judgment in applying loads from current editions of
ASCE/SEI 7, ASCE/SEI 37, or ASCE/SEI 41 to previous
factored load combinations, considering that load magnitudes and combinations may have changed over the years.
Wind loads in particular were changed in recent editions of
these ASCE/SEI standards. Using current wind loads with
factored load combinations, load factors, and strength reduction factors from an earlier code may not yield the desired
level of safety that was intended in the development of the
current wind loads in these standards. If the loads specified in the current building code have increased significantly
from the loads specified in the original building code, then
the demand-to-capacity ratio of a member can be evaluated
using procedures in ACI 562, R4.5.2 or RA.5.2. Generally,
use of current gravity loads with load factors, factored load
For repair and rehabilitation design:
Follow procedures in Chapters 1 and 4
or Chapter 1 and Appendix A to
determine the design-basis code.
No
Is ACI 562-19 part of the
design-basis code?
Only Sections 5.1.1, 5.1.3, 5.1.5, and
5.2.1 are applicable for the repair design.
* Where permitted by the original building
code, allowable stress design (ASD) principles
may be used.
All sections of Chapter 5 are applicable,
in particular:
• Determine loads in accordance with
Sections 5.1.2 and 5.1.4; factored load
combinations in accordance with
Section 5.2.3; and strength reduction
factors in accordance with Section 5.3.
• If an unprotected external reinforcing
system is used, ACI 562 requires that
the required strength of the unrepaired
structure satisfy the factored load
effects determined according to
Section 5.5.2 or 5.5.3.
Fig. 5.1—Flowchart for determination of loads, factored load combinations, and strength reduction factors for repair and
rehabilitation design.
@Seismicisolation
@Seismicisolation
University of Toronto User.
Use the design-basis code to determine the
factored loads, factored load combinations,
and strength reduction factors*.
Yes
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32
combinations, and strength reduction factors from the original building code may be prudent if the design-basis code is
the original building code.
The LDP for the project should use the design-basis code
loads during construction. ACI 562 Section 5.1.3 requires
shoring and temporary construction to be designed to support
loadings that may vary throughout the repair process. When
shoring and temporary construction is required to support
occupied structures and ACI 562 is the design-basis code,
the loadings are specified to conform to ASCE/SEI 7. If,
however, the structure or portion of the structure where
work is performed is unoccupied during the construction
period, then less-stringent temporary design loads could be
specified based on ASCE/SEI 37. ASCE/SEI 37 provides
minimum load requirements during construction, which can
often reduce the demand on shoring and temporary construction based on a probabilistic assessment of the factored loads
and factored load combinations that could occur during the
finite construction period.
Section 5.1.4 of ACI 562 requires the LDP to consider the
unique circumstances involved in assessing and designing
repairs, rehabilitations, and strengthening of existing structures. Several considerations that may not have been specified
or present during the original design and construction may be
applicable, including secondary and service load conditions
such as those mentioned in Section R5.1.5 of ACI 562. These
load consideration requirements are applicable regardless of
the design-basis code used for the assessment or repair design.
reinforcement jacking force for the design of post-tensioned
anchorage zones, respectively, are specified in Sections 5.2.4
and 5.2.5 of ACI 562; these load factors are also consistent
with the design methodology of ACI 318-19.
5.3—Strength reduction factors for repair design
For the repair design, the strength reduction factors, ϕ,
in Section 5.3 of ACI 562 are used when the design-basis
code references ACI 318-19; these factors are consistent
with those provided in ACI 318-19. The strength reduction
factors of Section 5.3 of ACI 562 are used in conjunction
with the loads specified in Section 5.1.4 of ACI 562 and
the factored load combinations specified in ASCE/SEI 7, as
referenced through Section 5.2.3 of ACI 562.
When designing a repair of an existing member or structure, the LDP can use the flowchart presented in Fig. 5.1
as a guide to determine the loads, factored load combinations, and strength reduction factors for the repair design. If
ACI 562 is part of the design-basis code for assessment and
rehabilitation design, then the strength reduction factors of
Section 5.3 of ACI 562 apply. The project examples included
within this guide illustrate how Fig. 5.1 is used.
University of Toronto User.
5.4—Strength reduction factors for assessment
For assessment of a member, the design strength reduction factors, ϕ, in Section 5.4.1 of ACI 562 are used when the
design-basis code references ACI 318-19. The higher strength
reduction factors in Section 5.4.1 of ACI 562 may be used when
the as-built member dimensions and reinforcement location are
5.2—Load factors and load combinations
determined as part of the structural assessment, as defined in
Section 5.2.1 of ACI 562 requires the LDP to consider the
Chapter 6 of ACI 562, and material properties are determined
existing loads on the structure as well as the effects of the
per Section 6.3.5 of ACI 562. These increased strength reducrepair process. For example, removal of concrete can cause
tion factors are consistent with those provided in Chapter 27 of
stresses to be redistributed to other members of the structure
ACI 318-19 and are justified by the improved reliability due
or within the member itself. If shoring is provided in this
to the use of accurate field-obtained material properties and
scenario, the ACI 562 Code requires the LDP to consider the
actual in-place dimensions. If the increased strength reduction
effect of shoring loads transmitted to supporting members
factors of Section 5.4.1 of ACI 562 are used, the assessment
of the existing structure during each phase of the repair.
should be performed using the factored load combinations
Additionally, stresses in the member under repair need to
specified in ASCE/SEI 7, per Section 5.2.3 of ACI 562. Project
be assessed at each stage of the repair process to properly
Example 3 provides a specific example of using the strength
assess the influence of shoring, concrete removal, concrete
reduction factors of Section 5.4 of ACI 562.
replacement, and eventual return to service. If shoring is not
When evaluating a member using material properties
provided, the ACI 562 Code requires the LDP to consider
based on Tables 6.3.1a through 6.3.1c of ACI 562, the
stresses in the remaining elements of the original member
strength reduction factors should not be greater than the
combined with stresses in the repair and original member
factors in Section 5.3 in ACI 562. If the material properacting compositely. The LDP should consider the effects and
ties are estimated based on Tables 6.3.1a through 6.3.1c of
sequencing of the repair process, both on the member being
ACI 562, there is still some uncertainty regarding the actual
assessed and the structure as a whole. Consideration of the
material properties, which is reflected in the lower strength
repair process is applicable regardless of the design-basis
reduction factors in Section 5.3 of ACI 562.
code used for the repair design.
When performing an assessment of an existing member or
Section 5.2.3 of ACI 562 stipulates that the required
structure, the LDP can use the flowchart presented in Fig. 5.4
strength U should be at least equal to the effects of the
as a guide to determine the loads, factored load combinations,
factored load combinations specified in ASCE/SEI 7 for
and strength reduction factors for the assessment. If ACI 562 is
the applicable design loads from the design-basis code.
part of the design-basis code, then the strength reduction factors
The factored load combinations in ASCE/SEI 7 are consisof Section 5.4 of ACI 562 apply. Each of the project examples
tent with those in ACI 318-19. For example, a load factor
included within this guide illustrate how Fig. 5.4 is used.
of 1.0 and 1.2 for the internal load effects due to reactions
For both assessment and rehabilitation design, Sections
induced by prestressing and for the maximum prestressing
@Seismicisolation
5.3.4 and 5.4.3 of ACI 562 specify the same load reduc@Seismicisolation
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Chapter 5—Loads, Factored Load Combinations, and Strength Reduction Factors33
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
tion factor of 0.6 for all plain structural concrete members
independent of the member’s behavior, flexure, compression, shear, or bearing, because plain concrete failures are
usually brittle.
5.5—Additional load combinations for structures
rehabilitated with external reinforcing systems
Section 5.5.1 of ACI 562 is used to determine the
minimum required strength of an existing structure that will
be repaired with an external reinforcing system, including,
but not limited to, bonded fiber-reinforced polymer (FRP),
bonded or anchored steel plates, or external post-tensioning
systems. The minimum required strength, expressed in ACI
562 Sections 5.5.2 and 5.5.3 equations, ensures sufficient
strength of members with external reinforcing systems
when subject to damage by vandalism or fire and elevated
temperatures that may limit the performance of the external
reinforcing system. The LDP may specify protection to
No
exposed reinforcing systems to resist fire, collision, and
vandalism. Repaired members or structures with external
reinforcing systems exposed routinely to elevated temperatures are not addressed in this chapter and the LDP is
referred to Section 7.9 of ACI 562.
The LDP needs to verify that the strengthened
structure or members have at least the capacity to exceed
the effects of the factored load combinations specified
in ACI 562, Sections 5.5.2 and 5.5.3. The factored load
combinations in Section 5.5.2, Eq. (5.5.2a) and (5.5.2b),
are intended to minimize the risk of overload or damage
to the existing unstrengthened members in the case
where, during normal operating conditions, the nonmechanically bonded external reinforcing system is
damaged. This would give the owner ample time to be
alerted of the damage and allow the structure to remain
in service until the damaged external reinforcing system
is repaired.
For assessment purposes: Is
ACI 562-19 part of the
design-basis code?
Yes
Use the factored loads, factored load
combinations, and strength reduction
factors* as specified in the original
building code for the assessment.
Sections 5.1.1, 5.1.3, and 5.1.5 are
applicable during the evaluation.
Yes
Use loads in accordance with
Section 5.1.4, factored load
combinations in accordance with
Sections 5.2.2 and 5.2.3, and strength
reduction factors in accordance with
Section 5.4.1 for the assessment
Have the in-place structural
element dimensions, reinforcement
location, and material properties
been determined in accordance
with Section 5.4.1 and Ch. 6?
No
Use loads in accordance with Section
5.1.4, factored load combinations in
accordance with Section 5.2.3, and
strength reduction factors in
accordance with Section 5.3 for the
assessment.
Fig. 5.4—Flowchart for determination of loads, factored@Seismicisolation
load combinations, and strength reduction factors for assessment.
@Seismicisolation
University of Toronto User.
*Where permitted by the original building
code, allowable stress design (ASD)
principles may be used.
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34
ϕRn ≥ 1.1D + 0.5L + 0.2S
(5.5.2a)
ϕRn ≥ 1.1D + 0.75L
(5.5.2b)
where D, L, and S are the dead, live, and snow loads, respectively, as defined in Chapter 5 of ACI 562; φ is the strengthreduction factor obtained from ACI 562 Section 5.3 or 5.4;
and Rn is the nominal strength of the structure without the
external reinforcement. These equations also serve as a limit
on the amount of strengthening that can be resisted by the
external reinforcement.
Repaired structures with external reinforcement need to
satisfy Eq. (5.5.3) without considering the added external
reinforcement to ensure that the repaired member has sufficient strength during a fire event.
ϕexR ≥ (0.9 or 1.2)D + 0.5L + 0.2S
(5.5.3)
where fex = 1.0; and R is the nominal resistance of the
structure, calculated using the probable material properties during a fire event, determined based on the required
fire rating duration. The dead load factor of 0.9 governs
when the dead load effect reduces the total factored loads
effect. The load effect from fire is a secondary effect caused
by restraint to thermally induced expansion, resulting in
thrust and moment redistribution. Except for simple span
members, the analysis of a member exposed to fire should be
based on a design fire scenario and its effect on the behavior
of the overall structure. The analysis will require accurate
modeling of numerous parameters, including fire characteristics, boundary conditions, connection fixity, heat transfer,
and deformations. A broader discussion regarding the effect
of fire on buildings can be found in NIST Technical Note
1681 (National Institute of Standards and Technology).
Guidance regarding the reduced strength of concrete under
exposure to elevated temperature is provided in ACI 216.1.
The factored load combination given in ACI 562 Section
5.5.3 is based on provisions contained in ASCE/SEI 7. As
indicated in the commentary of ASCE/SEI 7, provisions
regarding loading from extraordinary events are not intended
to replace traditional approaches to ensure fire endurance
(that is, fire ratings specified in model building codes based
on ASTM E119 using full service loads). However, the
provisions of ASCE/SEI 7, and therefore the factored load
combination of ACI 562 Section 5.5.3 might be determined
by the authority having jurisdiction to be acceptable based
on the alternative methods of design and construction
provision contained in model building codes. Therefore, the
LDP responsible for repair of the structure should consult
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Chapter 5—Loads, Factored Load Combinations, and Strength Reduction Factors35
University of Toronto User.
New post-tensioning cables installed on parking
deck repair project
@Seismicisolation
@Seismicisolation
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Hydrodemolition concrete removals on waffle floor slab
with involved parties to determine if use of ACI 562 Section
5.5.3 is a viable approach for satisfying the applicable
building code as relates to fire resistance. A sustained live
load, as in libraries or warehouses, or a live load exceeding
100 lb/ft2 (488 kg/m2) will receive an increased live load
factor of 1.0 in Eq. (5.5.2a), (5.5.2b), and (5.5.3). When
considering the effect of fire on a structure, the loads associated with firefighting operations such as additional water
surcharge and wetted materials need to be included in the
analysis. The commentary to ACI 562 recommends a live
load of 20 lb/ft2 to account for wetted material during firefighting operations.
The provisions of Sections 5.5.2 and 5.5.3 of ACI 562 are
not applicable if ACI 562-19 is not part of the design-basis
code. The strength reduction factors in Section 5.3 or 5.4 of
ACI 562 should be used with the factored loads provided in
Eq. (5.5.2) and (5.5.3) of ACI 562. Project Example 5 illustrates the application of Section 5.5 of ACI 562.
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@Seismicisolation
@Seismicisolation
Impulse-response testing being performed on a bridge pier
6.1—Structural assessment
A structural assessment consists of documenting the current condition of the
structure or member, including the as-built construction and any distress and deterioration. Several assessment tools and approaches are available for use at the judgment of the LDP, including document review, visual survey, material sampling,
laboratory evaluation, and destructive and nondestructive testing. A number of
publications, including those discussed in ACI 562 Section, R6.1.1, and the related
ASTM standards listed in the textbox, are available for guidance and specific
aspects of performing assessments of existing concrete structures. Section 6.1 of
ACI 562 describes that structural assessment must be performed if required by ACI
562, 1.7.5. It consists of structural evaluation and, if necessary, structural analyses.
The goal of a structural assessment is to determine if members or portions of the
structure in their current condition have adequate strength and meet serviceability
requirements. Structural assessment covers the following
@Seismicisolation
three steps:
@Seismicisolation
37
University of Toronto User.
Overview
Chapter 6 of ACI 562 provides requirements for conducting a structural assessment of existing concrete members, portions of a structure, or entire structures.
The provisions are presented in the order in which a structural assessment would
normally be conducted, including provisions for conducting structural evaluation,
obtaining and determining material properties, and performing structural analyses.
Strength assessment by load testing is also addressed. The assessment method and
major tasks that are provided in Chapter 6 and Section 1.7 of ACI 562 are summarized in Fig. 6.
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Chapter 6—Assessment, Evaluation, and Analysis
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Structural Assessment (Ch. 6)
Preliminary Evaluation (Section 1.7)
1. Structural assessment of affected
members (Section 6.2).
1. Review of plans and available
documents (Section 1.7.1).
2. Existing conditions visually or
otherwise assessed for deterioration,
damage, or distress (Section 1.7.2).
2. Obtain material properties as required
to perform assessment (Section 6.3 or
Section 6.4).
3. Preliminary analysis and evaluation to
determine strength based on in-place or
assumed geometry and material
properties (Section 1.7.4).
Perform the following as required
based on the results of the
assessment.
3. Structural analysis of existing
member or structure (Section 6.5).
Is a structural assessment
necessary based on the
requirements of Section 6.2.1
or Section 6.2.2?
Yes
4. Serviceability assessment of member
or structure (Section 6.6).
5. Strength assessment by load testing
if appropriate (Section 6.8).
Based on results of assessment
proceed with design of repair or
rehabilitation if required. Perform
analysis for design in accordance
with Section 6.7.
Fig. 6—Summary of assessment methodology of ACI 562.
1. An investigation to establish the in-place condition of the
structure in the work area, including environment, geometry,
material strengths, reinforcing steel sizes and placement, and
signs of distress
2. An evaluation to define the causes of distress, goals of
the rehabilitation, and criteria for selection of rehabilitation
solution(s)
3. Development of appropriate repair strategies, if required
6.2—Investigation and structural evaluation
If the strength of a structure is not in question or there is no
reason to suspect structural issues, a structural assessment
is not necessary when making improvements to address
strength, serviceability, durability, and fire protection requirements. If a preliminary evaluation (ACI 562, 1.7) determines
that there is reason to question the strength or behavior of
one or more members of the structure, a structural evaluation
@Seismicisolation
@Seismicisolation
University of Toronto User.
No
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38
Is a structural assessment always
required?
Use of lower-bound default material
properties
ACI 562 does not require the LDP to perform a
detailed structural assessment in cases where the
capacity of the structure is known. Consider the
following scenarios when a structural assessment
would not be required:
While in most cases it is conservative to use
the lower-bound values for concrete compressive
strength and steel reinforcement yield strength,
the LDP should use engineering judgment when
selecting historic property values from Tables
6.3.1a through 6.3.1c in ACI 562. In some instances,
assuming higher strengths may be more conservative. For example, when evaluating a beam column
joint, ACI 318-19, 18.7.3.2, requires the net moment
strength of the columns be greater than 6/5 the net
moment strength of the beams, which is meant to
ensure inelastic deformations occur primarily at
the beams instead of the columns during a seismic
event. When performing this analysis, it may be more
conservative to assume higher yield strengths in the
beam reinforcement when evaluating the joint.
Scenario No. 1: A beam at the lower level of a
recently constructed shopping center is impacted
by an errant vehicle. The plans and available documents were reviewed by the LDP as part of the
preliminary evaluation and indicate the beam was
designed to satisfy the required loading. Based on
the preliminary evaluation performed by the LDP,
the damage is limited to cracking and spalling of
the cover at a single beam location. There are no
visible signs of damage to the existing reinforcement. Based on the results of the preliminary
evaluation, the LDP may proceed with the design
of the repair without performing a more detailed
structural assessment or structural analysis of the
existing beam or structure.
@Seismicisolation
@Seismicisolation
University of Toronto User.
Scenario No. 2: An LDP is retained to review
the in-place condition of a parking garage that was
opened approximately 5 years ago and provide
documents for repairs or maintenance. During the
preliminary evaluation, the owner shares that the
manager has recently started using de-icing salts
after receiving complaints regarding ice on the
ramps and parking areas. In addition to replacing
failed sealant joints and performing other routine
maintenance, the LDP is considering a coating
or sealer for durability considerations of the
salt-exposed deck. The preliminary evaluation
performed by the LDP indicates that the garage is
in otherwise good structural condition with no signs
of deterioration or structural deficiency. The LDP
may proceed with the coating system design and
durability repairs without performing a structural
assessment or structural analysis of the existing
deck or garage. In this instance, additional assessment (for example, material sampling to determine
chloride levels in the deck) may be considered
by the LDP, but is not required based on ACI 562
Sections 6.1.2 and 6.1.3. A chain drag survey of the
deck might also be considered prior to performing
any coating repairs.
should be performed (ACI 562, 6.2.1). The licensed design
professional (LDP) may question the capacity of a member
or strength of its constituent materials if the member
exhibits signs of deterioration, such as spalling, corrosion,
or distress, such as wide cracking. As an example, loss of
concrete cross section in a compression member or severely
corroded tension reinforcement in a beam would likely
affect capacity and thus trigger a structural evaluation and
analysis of the affected member. The capacity may also be
questioned if there is reason to believe the in-place geometry or reinforcement is incorrect. The structural evaluation
may be limited to the area identified during the preliminary
evaluation; however, if repairs are required on a member,
the LDP should determine if an assessment is required on
similar members (ACI 562, 6.2.3). If the structural evaluation conducted as part of this assessment determines that the
strength of the structure is in fact not in question, a structural analysis is not required (ACI 562, 6.2.1 and 6.2.2).
The Project Examples illustrate various scenarios for determining if a structural assessment is necessary.
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Chapter 6—Assessment, Evaluation, and Analysis39
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Useful references for performing evaluations of existing concrete structures
The following standards from ASTM International
may provide guidance for performing evaluations of
existing concrete structures.
• ASTM C42/C42M, “Standard Test Method for
Obtaining and Testing Drilled Cores and Sawed
Beams of Concrete”
• ASTM C597, “Standard Test Method for Pulse
Velocity Through Concrete”
• ASTM C803/C803M, “Standard Test Method for
Penetration Resistance of Hardened Concrete”
• ASTM C805/C805M, “Standard Test Method for
Rebound Number of Hardened Concrete”
• ASTM C856, “Standard Practice for Petrographic Examination of Hardened Concrete”
•
•
•
•
ASTM C876, “Standard Test Method for Corrosion Potentials of Uncoated Reinforcing Steel in
Concrete”
ASTM C1383, “Standard Test Method for
Measuring the P-Wave Speed and the Thickness
of Concrete Plates Using the Imapct-Echo”
ASTM C1740, “Standard Practice for Evaluating the Condition of Concrete Plates Using the
Impulse-Response Method”
ASTM D4580/D4580M, “Standard Practice for
Measuring Delaminations in Concrete Bridge
Decks by Sounding”
ASTM D6432, “Standard Guide for Using the
Surface Ground Penetrating Radar Method for
Subsurface Investigation”
6.3—Material properties
Determining the material properties of an existing concrete
member or structure is critical to performing a structural
analysis. ACI 562 Section 6.3 describes the requirements
and various methods for obtaining material properties.
When required by ACI 562, concrete compressive strength
and steel reinforcement yield strength must be determined
(ACI 562, 6.3.2). The concrete compressive strength and
steel reinforcement yield strength used for analysis can be
obtained by one of three methods (ACI 562, 6.3.3):
a. Material properties based on historical information (ACI
562, Tables 6.3.1a through 6.3.1c)
b. From available design drawings, specifications, or
previous testing documentation (ACI 562, 6.3.4)
c. Physical testing of in-place or sampled materials (ACI
562, Section 6.4)
Figure 6.3 summarizes the process for determining material
properties in accordance with ACI 562.
Load test being performed @Seismicisolation
@Seismicisolation
University of Toronto User.
The LDP needs to determine the nature of concerns with
the as-built construction or the structural implications of
distress and deterioration. The structural assessment should
then be tailored to obtain information so that these concerns
can be evaluated and, if necessary, a structural analysis
performed. While there are commonalities between many
structural assessments, it is not unusual for unique information to be required to evaluate specific concerns. If an
analysis is to be performed, the structural assessment should
include, per ACI 562, 6.2.4, documentation of existing
conditions including any construction deficiencies or deterioration as required for the analysis which, as a minimum,
per ACI 562, 6.2.5, includes the following:
a. As-measured structural section properties and dimensions
b. The presence and effect of any alterations to the structure
c. Load, occupancy, or usage changes that are different from
the original design
•
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40
No
No
Has visible material deterioration,
degradation, or distress occurred
(Section 6.3.4)?
Do available drawings,
specifications, and other existing
construction documents provide
sufficient information to
characterize the material
properties (Section 6.3.1)?
Use material properties from either: (a)
historical material property data provided
in Tables 6.3.1a through 6.3.1c* or (b)
physical testing in accordance with
†
Section 6.4 .
Yes
Yes
Use material properties from either: (a)
existing drawings, specifications, or
documentation, or (b) physical testing in
†
accordance with Section 6.4 .
Perform physical testing in accordance
†
with Section 6.4 as required to confirm
material properties (Section 6.3.4C).
* If data is not given in either Table 6.3.1b or 6.3.1c, the historic default value for yield strength should be taken as 27,000 psi (185 MPa) (Section 6.3.6).
†
Locations and numbers of material samples should be defined by the LDP (Section 6.3.5).
Fig. 6.3—Summary of process to determine material properties in accordance with ACI 562, 6.3.
The material properties in the tables are lower limits and may
be conservative for many structures. More accurate material
properties can be obtained by sampling and testing the actual
concrete and steel.
In general, ACI 562 permits the use of material properties
provided in the original construction documents or material
test reports, except in cases where visible material deterioration has occurred (ACI 562, 6.3.4). In cases where material
degradation may have occurred, such as alkali-silica reaction, sulfate attack, delayed ettringite formation, freezingand-thawing damage, or reinforcement corrosion, additional
material testing may be required to verify the current material properties for the purpose of assessing the effects of
material degradation on strength and durability.
The various approaches described in ACI 562 Section 6.3
provide flexibility to the LDP in determining the material
properties of existing construction. When material properties are determined by material sampling and testing and the
as-built element dimensions and reinforcement location are
determined, the LDP can take advantage of higher strength
reduction factors shown in ACI 562, 5.4.1. Example 6.1
highlights the various approaches to determining material
properties and the potential benefit when higher strength
reduction factors can be used.
@Seismicisolation
@Seismicisolation
University of Toronto User.
When dealing with existing structures, previous drawings,
specifications, or test reports are often unavailable. Furthermore, obtaining and testing material samples may not be
possible or desirable for a number of reasons. For example,
destructive sampling is often undesirable in historic structures. Other times, accessibility or building operations may
make sampling difficult or costly to the owner. Accordingly, ACI 562 Tables 6.3.1a through 6.3.1c provide default
historical data for use during the structural analysis. These
tables include concrete material properties from 1900 to
present and steel reinforcement data from 1911 to present.
When the steel grade is unknown, the lowest grade of reinforcement for a given historic period is required to be used
(ACI 562, 6.4.4). If the historic data for the reinforcement is
not included in the tables, a lower-bound yield strength of
27,000 psi (185 MPa) is required to be used (ACI 562, 6.3.6).
In some cases, it may be possible to determine the grade
of reinforcement based off the bar markings from original
fabrication. The Concrete Reinforcing Steel Institute (2010)
has information available regarding current reinforcing bar
marking sequences, as well as markings used with historical
reinforcement. The Wire Reinforcement Institute (2014)
has information available regarding historical data on wire,
triangular wire fabric mesh and welded wire reinforcement.
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Chapter 6—Assessment, Evaluation, and Analysis41
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Example 6.1—Methods for determining material properties
Background
New mechanical equipment is to be installed within
the attic of a historic academic building constructed
in 1930. The concrete framing that supports the
attic space consists of a concrete slab with integral
inverted T-beams. The original construction documents are available and show that the reinforcing
for the 6 in. (150 mm) wide by 12 in. (300 mm)
tall beams consist of two 5/8 in. (16 mm) deformed
diameter bars at top and bottom. No material properties are indicated on the construction documents.
strength or the steel reinforcement yield strength,
which are required for the structural analysis.
Historic values
As an initial check, the LDP uses the historical
data from Tables 6.1a and 6.1b (Tables 6.3.1a
and Table 6.3.1b, respectively, in ACI 562) to
perform an analysis of the existing structure with
its current loading configuration. Based on the
tables, a concrete compressive strength of 2000 psi
(14 MPa) is used for the analysis. A default yield
strength of 33,000 psi (230 MPa) is used for the
steel reinforcement based on the age of construction and the fact that no information is available
regarding the grade of steel.
Based on these values and the strength reduction
factors of ACI 562, 5.3.2, a demand-capacity ratio
of 0.90 was calculated for the existing configuration, indicating the strength of the existing member
is adequate for the current loading. When the additional loading for the new mechanical equipment
is considered, however, the controlling demandcapacity ratio of the beam increases to 1.27,
indicating that the beams require strengthening.
For the analysis using historic values, the strength
Evaluation
The LDP is retained by the owner to evaluate the
capacity of the beams to support the loading from
the new mechanical equipment. ACI 562 is applicable, as described in ACI 562, 1.1.2. In accordance
with ACI 562, 6.2.5, the LDP measures section
dimensions and confirms that the as-built member
geometry agrees with the construction documents.
The LDP also verifies the quantity and cover depth
to the reinforcing bars using a concrete cover meter
(pachometer).
The existing documents do not provide sufficient
information to characterize the concrete compressive
Table 6.1a—Default compressive strength of structural concrete, psi (MPa)* (after ACI 562 Table 6.3.1a)
Time frame
1900-1919
1920-1949
1950-1969
1970-present
Beams
2000 (14)
2000 (14)
3000 (21)
3000 (21)
Slabs
1500 (10)
2000 (14)
3000 (21)
3000 (21)
Columns
1500 (10)
2000 (14)
3000 (21)
3000 (21)
Walls
1000 (7)
2000 (14)
2500 (17)
3000 (21)
Note: Adopted from ASCE/SEI 41-13.
Table 6.1b—Default tensile and yield strength properties for steel reinforcing bars for various periods, psi
(MPa)* (after ACI 562 Table 6.3.1b)
Year
Grade
Minimum
yield, psi
(MPa)
Minimum
tensile, psi
(MPa)
1911-1959
1959-1966
1966-1972
1972-1974
1974-1987
1987-present
Structural†
33 (230)
Intermediate†
40 (280)
Hard†
50 (345)
33,000 (230)
40,000 (280)
55,000 (380)
70,000 (485)
60 (420)
65 (450)
70 (485)
75(520)
50,000 (345)
60,000
(420)
65,000
(450)
70,000
(485)
75,000
(520)
80,000 (550)
90,000
(620)
75,000
(520)
80,000
(550)
100,000
(690)
—
X
X
X
—
X
—
X
—
—
—
—
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Note: Adopted from ASCE/SEI 41-13
*
An entry of X indicates the grade was available in those years. †The terms “structural,” “intermediate,” and “hard” became obsolete in 1968.
@Seismicisolation
@Seismicisolation
X
—
—
—
—
University of Toronto User.
*
Footings
1000 (7)
1500 (10)
2500 (17)
3000 (21)
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42
reduction factors for flexure and shear were 0.90
and 0.75, respectively.
Material testing
Given the outcome of the analysis using historical
properties, the LDP recommends a material sampling
program to better determine the actual material properties. Samples were obtained, tested, and the results
evaluated in accordance with Section 6.4 of ACI
562. Core sampling and testing are to be performed
in accordance with ASTM C42/C42M. The ASTM
procedure provides a standard moisture conditioning
protocol for the concrete core samples and a correction for core length to diameter ratio. For situations
when the core samples do not satisfy ASTM C42
requirements, the procedure in ACI 214.4R can be
followed. The equivalent concrete strength (fceq)
was determined per ACI 562 Eq. (6.4.3.1), and the
equivalent yield strength as determined per ACI 562
Eq. (6.4.6), using the following material properties:
f c (average) = average core strength
ƒceq = equivalent specified concrete strength per ACI
562 Eq. (6.4.3.1)
determined in accordance with ACI 562, 6.3.5,
the LDP can take advantage of increased strength
reduction factors per ACI 562, 5.4. Using the material property test results and increased strength
reduction factors results in a demand-capacity
ratio of 1.06 for the beam when considering the
new mechanical equipment. The strength reduction factors for flexure and shear were 1.0 and 0.80,
respectively.
Rather than proceed with a design to strengthen
the beams, the LDP elects to collect two more
samples for yield strength testing of the reinforcement. The additional samples will improve the coefficient of variation modification factor.The revised
steel reinforcement testing results were calculated
and are shown in Table 6.1e.
The corresponding demand-capacity ratio of the
beam reduces to 0.99 based on the revised testing
results for the steel reinforcement. Thus, the
beams satsify the strength requirement for the new
mechanical equipment.
Table 6.1c—Concrete core results based on
ACI 562 Eq. (6.4.3.1)

 (6.4.3.1)
(kcV ) 2
+ 0.0015 
f ceq = 0.9 f c 1 − 1.28
n


ƒy (average) = average steel yield strength value from tests
ƒyeq = equivalent yield strength of steel reinforcement
per ACI 562 Eq. (6.4.6)
f yeq = ( f y − 3500) exp(−1.3k sV ) (6.4.6, in.-lb)
(6.4.6, SI)
Results
8
f c (average)
6218 psi (42.9 MPa)
V
kc
fceq
0.15
1.10
5095 psi (35.1 MPa)
Table 6.1d—Steel reinforcement results based
on ACI 562 Eq. (6.4.6)
Variable
n
fy (average)
V
ks
fyeq
kc = concrete coefficient of variation modification
factor per ACI 562 Table 6.4.3.1
ks = steel coefficient of variation modification factor
per ACI 562 Table 6.4.6
Results
4
42,225 psi (291.1 MPa)
0.05
2.34
33,261 psi (229.3 MPa)
n = number of sample tests
V = coefficient of variation determined from testing
Results from the use of Eq. (6.4.3) and (6.4.6) in
ACI 562 for this scenario are presented in Table 6.1c
and 6.1d.
The material property test results yield an equivalent specified strength for the concrete of more
than twice the historical value and a comparable
equivalent yield strength for the steel to the historical value. Because the material properties were
Table 6.1e—Revised steel reinforcement
results based on ACI 562 Eq. (6.4.6)
@Seismicisolation
@Seismicisolation
Variable
n
ƒy (average)
V
ks
ƒyeq
Results
6
42,860 psi (295.5 MPa)
0.04
1.69
36,049 psi (248.5 MPa)
University of Toronto User.
f yeq = ( f y − 24)
( −1.3 ksV )
Variable
n
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Chapter 6—Assessment, Evaluation, and Analysis43
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
sampling program. As a minimum, two concrete samples are
required to determine kc and three steel samples are required
to determine ks. The equivalent specified strength obtained
from Eq. (6.4.3.1) can be used in strength equations with the
strength reduction factors from Chapter 5.
ACI 562, 6.4.3.2, permits the use of nondestructive testing
methods for assessment of in-place concrete compressive
strength provided that a valid correlation of the nondestructive
test method is established between the nondestructive results
with data obtained from testing representative core samples.
ACI 228.1R provides information for developing statistical correlations between nondestructive testing and core
test results and the following nondestructive testing methods:
a. ASTM C597, “Standard Test Method for Pulse Velocity
Through Concrete”
b. ASTM C803/C803M, “Standard Test Method for Penetration Resistance of Hardened Concrete”
c. ASTM C805/C805M, “Standard Test Method for Rebound
Number of Hardened Concrete”
d. ASTM C873/C873M, “Standard Test Method for
Compressive Strength of Concrete Cylinders Cast in Place
in Cylindrical Molds”
e. ASTM C900, “Standard Test Method for Pullout Strength
of Hardened Concrete”
f. ASTM C1074, “Standard Practice for Estimating Concrete
Strength by the Maturity Method”
If welding of reinforcement is required as part of repair or
rehabilitation, ACI 562 requires that the carbon equivalent of
the existing reinforcing steel be calculated prior to welding,
as required by AWS D1.4/D1.4M. In general, the lower the
carbon equivalent, the more weldable the steel. Steel with
higher carbon equivalent is susceptible to cracking in the
heat affected zone. Most common reinforcing bars used in
construction are ASTM A615/A615M and ASTM A706/
A706M. Welding of ASTM A615 reinforcing bars should
be approached with caution, as no provisions are included
in AWS D1.4 to enhance its weldability; however, ASTM
A706 reinforcing bars are manufactured with a chemical
Local zone reinforcement installed within the post-tensioned
Preparation for beam section enlargement to add shear
anchorage zone
@Seismicisolation
capacity to the structural member
@Seismicisolation
University of Toronto User.
6.4—Test methods to determine or confirm
material properties
ACI 562 Section 6.4 presents requirements for test methods
to obtain in-place mechanical properties of five different types
of materials: concrete (ACI 562, 6.4.2 and 6.4.3), steel reinforcement (ACI 562, 6.4.4 through 6.4.6), connector steel
(ACI 562, 6.4.7), embedded structural steel (ACI 562, 6.4.8),
and prestressing steel reinforcement (ACI 562, 6.4.9). ACI 562
references ASTM C42/C42M and ASTM C823/C823M for
concrete sample removal and testing, ASTM A370 for testing
yield and tensile strength of steel reinforcement and structural
steel, and ASTM A1061/A1061M for testing prestressing reinforcement. Care should be taken in sampling prestressing steel
as the steel may still be under some tension and significant
energy can be released when the steel is cut. Nondestructive
testing may be used to locate existing reinforcement and other
embedded material in existing concrete members. This is critical
when taking core samples from existing concrete members as
the presence of reinforcement or other foreign material such as
conduits or wood may adversely affect the strength test results.
Core samples should be similar in length-to-diameter ratio as
standard strength cylinders, thus the recommended maximum
length-to-diameter ratio of 2 to 1. Cores with length-to-diameter
ratio of less than 1 are unreliable, yield erroneous test results,
and should be rejected. The minimum acceptable core diameter
per ASTM C42/C42M is 3.70 in. (94 mm). Smaller-diameter
cores are likely to have more variability and a lower strength
(Bartlett and MacGregor 1994b).
ACI 562 provides latitude for the LDP to determine the
appropriate material sampling and testing program for each
particular project, while also providing minimum requirements for sampling, testing, and calculating the equivalent
specified strength of the various materials. The equations
provided for calculating the equivalent specified strength
(Eq. (6.4.3.1), (6.4.6), and (6.4.8) in ACI 562) reflect the
uncertainty of sample standard deviation for a small sample
size. The coefficient of variation modification factors (kc and
ks) provide a means to effectively reduce the equivalent specified strength due to the smaller sample sizes. This provides
additional flexibility to the LDP to determine an appropriate
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44
Unique analysis considerations
Numerous situations are encountered with existing
structures that require unique analysis considerations, both for the existing structure and the
design of repairs. ACI 562 specifies that the LDP
consider the various analysis aspects of each situation. Although not intended to be comprehensive, the
following scenarios present unique analysis considerations for various cases:
• Spalling has occurred at the top side of a continuous girder, resulting in loss of bond at some of
the top longitudinal reinforcing steel. The damage
may have caused loss of development in the reinforcing steel and additional structural demand in
other portions of the existing structure as a result
of redistribution of the negative moments.
• Full-depth slab repair is required to address top
and bottom reinforcing bar corrosion in a parking
deck. During repairs, the unbraced length of the
adjacent columns could significantly increase
composition that is enhanced for welding. ASTM A706 reinforcing bars are typically stamped with a W in the deformation to indicate the bar is weldable. Table 5.2 in AWS D1.4
defines the required carbon equivalent for various size reinforcement. If the carbon equivalent is not less than the value
indicated in Table 5.2 of AWS D1.4, then the bars should be
preheated as required by AWS D1.4 to preclude the formation of microcracking in the heat affected zone.
•
•
evaluated when identified (ACI 562, 6.6.1). Serviceability
concerns may be related to the design strength of a member.
If this occurs, the member should be evaluated as described by
ACI 562 Chapter 6. A service-load-level analysis as described
in ACI 562, R6.5.1, may also be required to evaluate deflections
and expected crack size and distribution.
The LDP should investigate the effect of floor levelness,
vibrations, and deflections on the structural performance and
to determine if it is acceptable to the owner and users of the
structure. These criteria should be established for the structure based upon the intended use of the structure and should
consider the existing material properties, existing geometry
of the members, and the condition of the existing members.
6.7—Structural analysis for repair design
Section 6.7 of ACI 562 specifies the minimum requirements for the structural analysis used for repair design. As
with performing a structural analysis of existing structures,
there are several unique considerations that are not typically
considered during design of new members or structures.
The provisions of ACI 562 are focused on requiring that the
LDP consider the actual performance and behavior of the
repaired system. These considerations include the sequence
of the repair process, the variability of section properties,
and the composite action (or lack thereof) in the repair and
substrate. These provisions are presented in Sections 6.7.1
through 6.7.3 of ACI 562.
ACI 562, 6.7.4, requires several seismic considerations as
part of the analysis for repair design. These provisions are
focused on requiring that the seismic response of the repaired
6.6—Structural serviceability
structure has been considered by the LDP. The particulars
ACI 562 requires that serviceability concerns such as unusual
of seismic rehabilitation, including analysis, are not specificracking, excessive deflections, floor levelness, vibrations,
cally prescribed in ACI 562, as these are addressed through
water infiltration or leakage, and excessive heat exposure
@Seismicisolation
be
reference to ASCE/SEI 41 and ACI 369R.
@Seismicisolation
University of Toronto User.
6.5—Structural analysis of existing structures
Section 6.5 of ACI 562 specifies the minimum requirements for performing a structural analysis of existing structures. The goal of the analysis is to accurately model the
current condition of the structure as a whole and the member
under assessment in particular. This includes accounting for
the as-built geometry and existing material properties, as
discussed in ACI 562, 6.2 and 6.3, respectively. Although the
specific method of analysis is left to the judgment of the LDP,
ACI 562 requires that the analysis consider material degradation, bond loss, redistribution of forces, modified load paths,
and previous repairs or modifications (ACI 562, 6.5.4 through
6.5.6). Material degradation and corrosion of reinforcement
often lead to spalling and loss of concrete bond. Any analysis
of the existing structure should consider the current state of
the structural system, included any associated bond loss. The
LDP is cautioned that member deterioration or damage may
result in redistribution of internal forces that is different than
that assumed in the original design. The redistribution of
forces may be determined by analysis or testing.
•
and temporary bracing of the column may be
required.
Alterations as a result of change of occupancy
will include new openings in a two-way slab. The
demolition for the alteration may result in redistribution of existing moments and shear forces in
the remaining structure.
Damage, deterioration, or repairs of prestressed
concrete structure that may have resulted or will
result in prestressing force release (reference
ACI 562, 7.6.4). Repairs that affect the development
of prestressing steel reinforcement may reduce
member capacity.
Concrete spalling has occurred on a column.
The concrete removal during repair may result
in redistribution of internal forces that are locked
in. The strength of such columns should be
considered in accordance with provision Section
6.5.4 in ACI 562.
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Chapter 6—Assessment, Evaluation, and Analysis45
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
6.8—Strength evaluation by load testing
For some structures, it may be difficult to document the
as-built construction and the current conditions in sufficient
detail to have confidence that a structural analysis reflects
actual structural behavior with a reasonable degree of accuracy. Similarly, the effectiveness of proposed repairs may
need to be confirmed. In such cases, load testing might be an
option to determine if an existing structure requires repair
and rehabilitation or to verify the adequacy or performance
of repair and rehabilitation measures. ACI 562, 6.8, permits
the use of load testing to supplement structural analysis or to
demonstrate the strength of the original or repaired structure. ACI 562, 6.8.1, specifies that load testing needs to
be in accordance with ACI 437.2, which establishes the
minimum requirements for the test load magnitudes, load
test procedures, and acceptance criteria applied to existing
concrete structures. ACI 437.2 was developed specifically
for use with ACI 562 and contains provisions for both a
cyclic load test and a monotonic load test, which provides
the LDP with flexibility in determining which procedure
is best for a particular application. The load test procedure
presented in Chapter 27 of ACI 318-19 presents a similar
monotonic test procedure and acceptance criteria. The
LDP may waive the deflection limit of ℓt/180 set in ACI
437.2 when the tested member is not damaged by excessive deflections or when the residual deflection criteria is
satisfied. If retesting is required because the member or
structure failed the cyclic load test, the LDP can waive the
deflection limit of ℓt/180.
In some cases, in-place load tests in accordance with ACI
437.2 may not be practical or necessary. Accordingly, ACI 562,
6.8.5, permits the use of full or scale models to supplement the
structural analysis. The LDP should document experimental
model analysis results, interpret the results, and correlate the
results with the in-place condition of the structure.
6.9—Recommendations
The structural evaluation performed on a member or structure are the basis for recommending whether the member or
structure should be repaired or rehabilitated. If a member or
structure needs to be repaired or rehabilitated, then the work
should be performed in accordance with ACI 562.
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46
University of Toronto User.
@Seismicisolation
@Seismicisolation
Steel bracing installed prior to concrete removals at core walls, columns, and perimeter walls (plywood sheeting was installed
to protect steel members from damage during the demolition process)
7.1—General
Structural repairs need to be designed so that the repaired structure, including
members and connections, have the required strength and serviceability specified by the design-basis code and ACI 562. A repaired section is considered to be
the combination of the installed repair material(s) and the substrate material(s).
Determination of the design capacity need to consider load factors, load combinations, and strength reduction factors in the design-basis code and ACI 562.
Durability considerations are described in ACI 562 Chapter 8.
7.2—Strength and serviceability
The strength and serviceability behavior of existing concrete structures can be
evaluated using information from the original design and construction. When deterioration is present, however, the strength and stiffness
@Seismicisolation
may no longer be adequately
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47
University of Toronto User.
Overview
The need for structural repairs is based upon the results of the preliminary assessment (ACI 562 Chapter 1) or, when required, a more in-depth structural investigation and assessment (ACI 562 Chapter 6). Design-basis code requirements for
repair design are determined using ACI 562 Chapter 4 or Appendix A. The design
and implementation of structural repairs and the performance of the repaired
members and structure vary significantly from the design, construction, and performance of new members and structures. ACI 562 Chapter 7 specifies factors that
need to be considered in the design of the structural repairs to achieve the intended
performance of the repaired members and structures. The project examples that
accompany this guide further illustrate the unique design considerations in the
development of a structural repair program in accordance with ACI 562 Chapter 7.
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Chapter 7—Design of Structural Repairs
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
predicted using the assumptions from the original design.
Deterioration and changes to member stiffness associated
with repair work may result in the redistribution of internal
forces to other portions of the member or to other members
not anticipated by the original design. The deterioration may
also cause inelastic behavior, with permanent deformations
or cracking. As a result, load redistribution may increase
forces and stresses in portions of members less affected by
deterioration. This behavior should be carefully considered
in the repair and serviceability design process.
While a structural repair is in progress, concrete may be
removed from the structure or reinforcing steel bars may
be unintentionally damaged or even cut during concrete
removal or, in some instances, intentionally cut to achieve
a desired outcome (for instance, when creating openings
in slabs or walls). The result of concrete removal is a
decrease in effective concrete section, which the licensed
design professional (LDP) has to consider for the impact
it may have on the member integrity both during and after
the repair process. Concrete removal may also affect
the development or lateral restraint of reinforcing bars,
possibly resulting in a decrease in the effectiveness of
the reinforcing steel. Damage to reinforcing bars during
concrete removal may affect the bar capacities and may
result in redistribution of the load effects into adjacent bars;
cutting bars may also result in a redistribution of the load
effects into adjacent bars. Thus, the repair process could
7.3—Behavior of repaired systems
In some cases, repairs or strengthening of existing
Fig. 7.1—Buckled vertical reinforcing bars due to a lack of
members or structures are performed by adding new struclateral restraint caused by excessive concrete chipping. @Seismicisolation
tural members. ACI 562, 7.3.1, stipulates the minimum
@Seismicisolation
University of Toronto User.
result in further deformations and redistribution of internal
forces. Dead load and in-service live loads acting on the
structure during repair construction need to be supported
by the remaining portions of the members and structure if
shoring and bracing is not provided.
Excessive concrete removal or damage or deterioration of
reinforcing, particularly for compression members such as
columns, could result in member distress or collapse. The
stress in the remaining concrete could exceed the compressive
strength of the concrete, resulting in crushing of the concrete.
If the unbraced length of reinforcing bars in compression
increases due to excessive concrete removal, one or more bars
could buckle and lose capacity (Fig. 7.1). Contractors need
to be made aware of the importance of concrete removal and
reinforcing ties on the stability of compression members.
As such, the LDP should determine a safe limit for concrete
removal in terms of maximum depth, maximum surface area,
maximum unsupported length of reinforcing bar, or some
other measure. The LDP should also specify these limits and
the monitoring requirements in the repair documents.
Unless measures, such as shoring, are taken before and during
the repair process, the deformations and redistributed forces
will remain locked into the sound portions of the structure.
The LDP should consider the effect of these locked-in internal
forces on the safety of the structure during repairs. Internal
forces and deformations may be reduced in the sound portions
of the members prior to beginning repairs by jacking, shoring,
or bracing the members. Initial bracing and shoring may need
to be adjusted to accommodate construction dead and live loads
that can vary over the course of the repair process. Construction dead and live loads can be later transferred to the repaired
members and other portions of the structure. These concepts are
further explained in Chapter 9 of this guide.
In many repair programs, the sound portions of the existing
members and structure will support most if not all the prerepair and repair dead loads and, perhaps, some pre-repair and
live loads during repairs. After the repair materials have cured
and reached design strength, the repair should act compositely with the remaining portions of the existing structure in
supporting subsequent superimposed dead and live loads.
Accordingly, ACI 562 Sections 7.2.1 and 7.2.2 require
that the LDP develop repair design and construction procedures that consider the stiffness, loading, internal forces, and
deformations of both the existing and repaired structure. The
repair design needs to consider if the distribution of internal
forces and deformations in the members and structure are
significantly affected by the repair process and accommodate
or alter the repair process accordingly. The effect of the repair
process on the stiffness of the structure and member under
repair should also be considered. ACI 562, 7.2.2, requires
the repair design and construction procedures consider the
loadings, the magnitude and redistribution of internal forces,
and deformations of the existing and repaired structure.
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48
strength throughout its depth, removing more of the substrate
concrete will have no effect on the achievable bond strength
and a lower design bond strength may need to be used.
7.4.2 Strength of repair material—The compressive
strength of the repair material is typically not a critical factor
in determining the interface strength between the concrete
substrate and the repair. Repair materials with a higher
strength than the substrate concrete may not result in greater
interfacial bond strength. The shear strength of a concrete
section with a repair or overlay is influenced by the depth of
the compression block in the section and the longitudinal tensile
reinforcement ratio (ρs). In a study by Kim et al. (2016), the
shear strength of composite beams made with combinations
of a high-strength concrete material on either the tensile or
compressive faces was examined. The study indicated the
compressive strength of the overlay material did not affect
the interface strength.
7.4.3 Quality of surface preparation of substrate
concrete and construction procedures—The preparation of the substrate concrete is an important factor
in the success of repair that affects bond strength and
should result in a sound, clean surface with some surface
profile and minimal microfracturing (bruising) of the
substrate. Increased surface roughness of the substrate
improves the shear bond strength between the existing
substrate and added overlay. The construction method in
which a surface is prepared affects the bond between the
two layers. Improperly used concrete removal
equipment may result in poor quality bond, delamination, or both. Abrasive, shot, and water blasting methods
typically do not result in extensive bruising. The level
of bruising damage to existing concrete is directly
related to the preparation tools and methods used (Warner
et al. 1998). The LDP must specify removal limits that may
otherwise compromise the integrity and stability of the
concrete member, if not set, and to prevent potential damage
to embedded reinforcement or other embedded items. In
7.4—Interface bond
general, the contractor determines methods and equipBond between the existing concrete substrate and the
ment to be used when removing or cutting of concrete is
new repair material or overlay, is an essential component
required, unless the LDP limits the weight of equipment that
of successful, durable repairs. ICRI 210.3R discusses bond
the contractor may use during the repair or strengthening
strength in repairs, and ICRI 310.2R focuses on various
operation. If removal methods produce bruised surfaces or
methods used to prepare concrete surfaces to achieve the
microcracking of the prepared substrate, then the contractor
desired performance of concrete repairs. ACI 318, 16.4,
must follow up with secondary removal/surface preparation
concentrates on the determination of the nominal shear
methods to remove the bruised surface layer.
strength at horizontal interfaces in composite members.
When considering which surface preparation technique will
ACI 562, 7.4.1 requires the evaluation of the interface
be best for a job, the LDP must balance the desired outcomes
stresses, shear, and tension across bonded interfaces between
the owner is seeking with practical concerns, including:
the overlay and the existing substrate.
a. Avoiding damage to the structure
Bond strength is influenced by the strength of the substrate
b. Preventing any deterioration of reinforcements
concrete, the strength of the repair material, the quality of
or the bond between bars and existing concrete
the surface preparation of the substrate concrete, construcc. Ensuring the impact of the chosen method
tion procedures, characteristics of the repair materials, and
will not compromise the concrete’s structural
time-dependent factors such as shrinkage of the concrete and
integrity
variations in repair material properties with time.
The advantages of proper surface preparation include:
7.4.1 Strength of substrate concrete—Substrate concrete
a. Smoothing out rough spots
with low strength may be the limiting factor for bond
b. Addressing surface irregularities
strength. If the substrate concrete has consistently
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low
c. Correcting edge curling
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University of Toronto User.
requirements for such systems. Per ACI 562, 1.3.5, new
concrete members are to be designed in accordance with ACI
318-19. ACI 562 requires the repaired structure be designed
to act compositely, with repaired and new members designed
to share loads with the existing members and structure.
ACI 562 also requires the force transfer between the new
member and the existing structure to be considered in the
repair design. The effect of the new member on the existing
structure is to be evaluated and should not compromise the
performance of the existing structural system.
In cases where existing members will be repaired or
strengthened, ACI 562, 7.3.2, requires the LDP to account
for force transfer between the repair section and the existing
structure. Composite action between existing and new
concrete can be achieved by bond, mechanical means, or a
combination thereof. ACI 562 permits the use of ACI 318-19
for the design of force transfer between new and existing
concrete. ACI 318-19 addresses bond between existing and
new concrete in Section 17.5 and shear friction in Section
16.4. Furthermore, design for composite action between
concrete and structural steel members is addressed in ANSI/
AISC 360-10, Chapter I, and bond between concrete and
fiber-reinforced-polymer systems is addressed in ACI 440.2R.
ACI 562 requires that repairs designed to resist structural
loading (that is, structural repairs) must act compositely
with the member or structure being repaired under all limit
states. For example, repairs to columns should maintain
full composite action under service and factored loadings.
When repairs are only needed to improve the durability or
aesthetics of a member, full composite behavior should be
maintained as a minimum under service loads. In situations
where a nonstructural repair could pose a life-safety concern,
as might occur with an overhead or façade repair, the repair
should consider composite behavior under both service
and factored loadings or redundancy through supplemental
means of restraint for loads in excess of service loadings.
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Chapter 7—Design of Structural Repairs49
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
d. Removing unwanted or worn finishes or
coatings
e. Paving the way for more extensive repairs to
your concrete
f. Providing a uniform surface to better accept
any type of new overlay or coating
g. Removing existing coatings, glue removal, or
epoxy demo
7.4.4 Bond material—Overlays are bonded to the existing
concrete substrate by either cementitious material, modified cementitious material, or resin-based material. Good
bonding is achieved by roughening the surface and removing
existing deteriorated, damaged, or contaminated concrete.
The selection and installation of the repair material can be
designed to not be a limiting factor for the bond strength.
Several test methods are available in the industry to measure
the bond strength and are presented in Table 7.4.4.
Each method has its advantages and shortcomings that
should be considered when measuring the bond strength
(ACI 546.3R). The advantage of pulloff tests is that they
can be performed in-place, while the other tests require
removal of samples and testing in a laboratory. If the
composite section is subjected to tension, then reinforcement is added crossing the interface and properly
doweled in the concrete substrate and overlay.
7.4.5 Time-dependent factors—The long-term performance of the bonding procedure should be evaluated.
The effects of the load type, duration, and the in-service
(a) Pulloff test
(b) Splitting test
Fig. 7.4.4a—Tension test.
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50
University of Toronto User.
Fig. 7.4.4c—Direct shear test.
Fig. 7.4.4b—Slant shear test.
Table 7.4.4—Required test methods to measure bond strength
Measured bond in
Tension
Shear and compression
Shear
Test type
Pulloff
Splitting
Slant shear
Direct shear
Test method
ASTM
ASTM C1583/C1583M
ASTM C496/C496M
ASTM C882/C882M
ASTM D6916-06c (Reapproved 2011)
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Figure
7.4.4a(a)
7.4.4a(b)
7.4.4b
7.4.4c
environment on the bond should be considered. The
existing concrete substrate has usually undergone most of
its shrinkage, while the added concrete in the repair has not
yet gone through significant shrinkage. Therefore, differential shrinkage, an important time-dependent factor, occurs
between the two layers resulting in added stress at the
interface. Differential shrinkage strain may be less significant in cases where the overlay is lightweight concrete
as the aggregate may supply moisture for internal curing
resulting in reduced shrinkage.
7.4.6 Shear stress calculation—At a minimum, ACI 562,
7.4.1.1, requires that the calculated horizontal shear strength
to be at least equal to the required bond strength or tensile
strength of the concrete substrate, such that:
vu ≤ fvni
(7.4.1.1)
where vu is the calculated bond demand shear stress based
upon mechanics, Table 7.4.4; φ is the reduction factor
obtained from ACI 562, 5.3.2; and vni is the measured bond
stress from a valid test method. The overlay should be tested
for proper bonding as required by ACI 562, 7.4.2 through
7.4.4, and as presented in Table 7.4.5.
A calculated shear stress of less than 30 psi (0.2 MPa),
from ACI 562, Section 7.4.2, requires qualitative bondintegrity testing only. Some of the nondestructive test methods
are hammer sounding in accordance with ASTM D4580/
D4580M, ground penetrating radar, or impact-echo described
in ACI 228.2R or ICRI 210.4, and impulse response in accordance with ASTM C1740. ICRI 210.3 suggests a minimum
measured tensile bond strength of 100 psi (0.7 MPa) as an
acceptable limit for less-critical applications, whereas a
measured tensile bond strength in the range of 175 to 215 psi
(1.2 to 1.5 MPa) is suggested for structural repair in Volume
10 of The European Standard 1504 series (EN 1504-10).
A calculated shear stress between 30 to 60 psi (0.2 to 0.4 MPa)
in ACI 562, 7.4.3, does not require interface reinforcement;
quantitative testing, however, is required. A shear stress of 60 psi
(0.4 MPa) is calculated from the nominal shear stress; 80 psi
(0.55 MPa), listed in ACI 318-19, Tables 16.4.4.2(c) and (d),
multiplied by the reduction factor ϕ = 0.75 of ACI 562, 5.3.2;
and 30 psi (0.2 MPa) is based on half of the 80 psi (0.55 MPa)
multiplied by the reduction factor ϕ = 0.75. Any test presented
in Table 7.4.4 can be used to determine the adequacy of the
bond between the overlay and substrate. While direct shear
test, splitting tension test, and slant test are performed in a
laboratory, the direct tension pull-off test can be performed on
site, which helps the LDP make informed design decisions.
The relationship between the different test methods is not
directly apparent.
If the calculated shear stress exceeds 60 psi (0.4 MPa) from
ACI 562, 7.4.4, but less than 375 psi (2.6 MPa) from ACI
562, R7.4.6, the LDP should provide minimum interface
reinforcement between the substrate and overlay. Quantitative testing as discussed in ACI 562, 7.4.3, should be specified. Interface reinforcement is calculated per ACI 318-19,
16.4.4.1, to resist the total shear strength when the calculated shear stress exceeds 375 psi (2.6 MPa) and quantitative
testing is not required for this condition.
The LDP should specify in the construction documents
the required testing for the interface reinforcement. Tension
testing in accordance with ACI 355.2, ACI 355.4, and ICRI
210.3 can be performed using the number of tests similar to
the pulloff tests from ACI 562, 7.4.7.
Table 7.4.5—Testing requirements based upon interface bond stress demand (vu)
ACI 562
7.4.2
7.4.5
Testing requirements
Bond-integrity testing
Quantitative bond strength testing
Enlargement systems were used to strengthen the column
footers in the parking structure
@Seismicisolation
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University of Toronto User.
vu
Less or equal to 30 psi (0.2 MPa)
Greater than 30 psi (0.42 MPa)
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Chapter 7—Design of Structural Repairs51
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Example 7.1—Determining bond strength
The LDP checked the horizontal shear between
the existing precast concrete beams and the
new cast-in-place elevated slab. ACI 562,
R7.4.1, refers the LDP to ACI 318-19, 16.4,
for designing the interface for horizontal shear.
ACI 318 has two procedures for checking the
factored horizontal shear strength Vuh. In this
example, both methods are presented.
Background
A parking structure floor was constructed of 12 x
22 in. (300 x 560 mm) precast concrete beams
spanning 28 ft (8.5 m) and spaced at 10 ft (3 m)
on center. The beams support precast concrete
simply supported 5 in. (125 mm) thick slab panels.
The structure is subjected to a live load of 40 lb/ft2
(195 kg/m2) per ASCE/SEI 7 (parking structure).
The beams and slab panels were deteriorated due to
corrosion, delamination, and spalling. The beams
were repaired, but the licensed design professional
(LDP) decided to replace the precast slab panels
with 5 in. (125 mm) thick cast-in-place concrete
slab.
Solution:
The beams are simply supported at both ends.
Vu@d = 20.6 kip, where d = 22 in. (beam) + 5 in.
(slab) – 2.5 in. (cover + db/2) = 24.5 in.
Vu@d = 92 kN, where d = 560 mm (beam) + 125 mm
(slab) – 65 mm (cover + db/2) = 620 mm
ACI 318-19, 16.4.3.1, requires that fVnh ≥ Vu at
all sections, where the strength reduction factor
φ = 0.75, Vnh is the horizontal shear strength
calculated in accordance with ACI 318-19,
16.4.4, and Vu is the factored shear force. From
12 in. × 22 in.
3
ACI 318-19, 16.4.4.2, assuming that the top surface
w=
(
0
.
1
5
kip/ft
)
=
0
.
27
5
kip/ft
144 in.2 /ft 2
of each precast concrete beam was intentionally
roughened:
(300 mm × 560 mm)
w=
(2400 kg/m 3 ) = 403 kg/m = (4 kN/m)
2
(1000 mm/m)
vu = (20.6 kip)(1000 lb/kip)/[(12 in.)(24.5 in.)] =
3
70 psi > φ80 psi = (0.75)(80 psi) = 60 psi
g/m ) = 403 kg/m = (4 kN/m)
Calculations:
It is assumed that the beam has adequate reinforcement to support the weight of wet concrete
slab and construction load during construction and
the total dead and live load during service.
Beam self-weight:
Slab self-weight:
5 in.
w=
(10 ft )(0.15 kip/ft 3 ) = 0.625 kip/ft
12 in./ft
125 mm
(3 m)(2400 kg/m3 ) = 900 kg/m (8.9 kN/m)
1000 mm/m
(3 m)(2400 kg/m3 ) = 900 kg/m (8.9 kN/m)
Live load:
w = (40 lb/ft2)(10 ft) = 0.4 kip/ft
φVnh = φ(260 + 0.6(Av/bvs)fyt)lbvd = (0.75)[260 +
0.6(0.11 in.2)(60,000 psi)/(12 in.)(20 in.)](1.0)
(12 in.)(24.5 in.) = φVnh = 61 kip > Vu@d = 20.6 kip
w = (195 kg/m )(3 m) = 585 kg/m = 5.8 kN/m
2
U = 1.2(0.275 kip/ft + 0.625 kip/ft) + 1.6(0.4 kip/ft)
= 1.72 kip/ft
U = 1.2(4 kN/m + 8.9 kN/m) + 1.6(0.58 kN/m)
= 24.8 kN/m
φVnh = φ(1.8 + 0.6(Avfyt/bws))lbvd = (0.75)[1.8 + 0.6
(71 mm2)(420 MPa)/(300 mm)(500 mm)](1.0)
(300 mm)(620 mm) = 268 kN > 92 kN
Therefore, maximum tie spacing is adequate
to transfer the horizontal shear between the
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University of Toronto User.
w=
vu = (92,000 N)/[(300 mm)(620 mm)] = 0.495 MPa
> φ0.55 MPa = (0.75)(0.55 psi) = 0.4 MPa
Therefore, according to ACI 562, 7.4.4, anchors
between precast beams and cast-in-place slab are
required.
Assume No. 3 dowels are anchored into the
precast beams at 20 in. (500 mm) on center and
hooked into the slab to provide the horizontal shear
transfer between the precast beam and cast-in-place
slab. Use Eq. 16.4.4.2(a) from ACI 318-19.
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52
precast concrete beam and cast-in-place slab.
The maximum tie spacing is calculated from
ACI 318-19, 16.4.7.2, which is the lesser of four
times the least dimension of the supported element
and 24 in. (600 mm)
s = (4)(5 in.) = 20 in. < 24 in., (s = (4)(125 mm)
= 500 mm < 600 mm), therefore, use s = 20 in.
(500 mm) in Eq. 16.4.4.2(a).
Second method ACI 318-19, 16.4.5.1, requires
the LDP to calculate the factored horizontal shear
force from the change in flexural compressive or
tensile force (T) in any segment of the composite
concrete member such that Eq. (16.4.5.1) of ACI
318-19 is satisfied at all locations along the contact
surface.
vuh =
vuh =
(92 kip − 68.8 kip)(1000 lb/kip)
= 23 psi
(12 in.)(7 ft)(12 in./ft)
< 30 psi
vuh =
(401 kN − 301 kN)
= 0.157 MPa
(300 mm)(2125 mm)
< 0.2 MPa
Therefore, per Section 7.4.2 of ACI 562, interface
reinforcement is not required.
Between quarter span and support:
vuh =
Tu@ midspan − Tu@1/ 4 span
(68.8 kip − 0 kip)(1000 lb/kip)
= 68 psi
(12 in.)(7 ft)(12 in./ft)
> 60 psi
bv ls
The moment diagram of a simply supported beam
is parabolic that results in relatively large moment
changes (∆M) near the supports compared to the
mid-third of the beam moment diagram. Therefore,
the LDP could divide the half-span of the beam
into three or more sections; at 1/3 and 1/8, and
calculate the factored horizontal shear stress over
those sections. Due to the large moment change
close to the supports, the factored horizontal shear
stress is expected to be greater close to the supports
compared to the calculated factored horizontal in
the midthird of the span. For this example, however,
it was determined that quarter span was adequate to
illustrate the calculation procedure.
Moment at midspan:
vuh =
(301 kN − 0 kN)
= 0.472 MPa
(300 mm)(2125 mm)
> 0.4 MPa
Therefore, per ACI 562, 7.4.4, interface reinforcement is required and the minimum reinforcement is
provided. No. 3 at 20 in. on center (No. 10 at 500
mm on center) is adequate to resist the horizontal
shear force as shown previously.
Conclusion:
The LDP provided No. 3 (No. 10) dowels over
the full length of the precast concrete beam at
maximum spacing of 20 in. (500 mm) on center.
University of Toronto User.
Mu = (1.72 kip/ft)(28 ft)2/8 = 168.6 ft-kip and
Tu1 = Mu/0.9d = 92 kip
Mu = (24.8 kN/m)(8.5 m)2/8 = 224 kN.m and
Tu1 = Mu/0.9d = 401 kN
Moment at quarter span:
Mu = (1.72 kip/ft)[(14 ft) (7 ft) – (7 ft)2/2]
= 126.4 ft-kip and
Tu1 = Mu/0.9d = 68.8 kip
Mu = (24.8 kN/m)[(4.25 m)(2.125 m) – (2.125 m)2/2]
= 168 kN.m and
Tu1 = Mu/0.9d = 301 kN
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Chapter 7—Design of Structural Repairs53
Fig. 7.4—New cast-in-place concrete slab to existing
precast concrete beam connection.
@Seismicisolation
@Seismicisolation
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Example 7.2—Determining bond strength of overlay to an elevated slab
Background
A nine-story parking structure located in the
Midwest of the United States was constructed of
8 in. thick lightweight concrete flat slabs in 1971.
The design concrete compressive strength was
3750 psi and the reinforcing steel was ASTM
A615 Grade 60. The top surfaces of the decks
were sounded and visually inspected and were
found to be badly deteriorated. The LDP estimated that the extent of deterioration on top side
ranged between 30 to 70 percent. Delamination
and cracking were also observed on the bottom
surfaces of the decks, but less extensive than that
on the top surfaces. Samples were taken from
areas that exhibited deterioration and tested for
chloride content.
Cores were extracted from several areas of the
elevated slab and tested for strength and chloride
content. Tests revealed that the concrete compressive strength of the slab matched the design
concrete compressive strength and that chloride
was present over the full depth of the slab with
excessive concentration levels near the top. Insufficient cover over the reinforcement at various locations was detected throughout the garage.
Fig. 7.2a—Pulloff test.
@Seismicisolation
@Seismicisolation
University of Toronto User.
Procedure:
The LDP determined that the repair would
consist of the removal of 3-1/2 in. (90 mm) of
top of the deck slabs and replace with a bonded
lightweight concrete overlay. There are several
methods for concrete removal; blasting, cutting,
impact milling, pre-splitting, and abrading each
having its advantage and shortcomings. Irrespective of the method used it should be effective,
safe and economical, and should produce minimum
damage to the concrete surface left in place (free of
micro cracks). The contractor and the LDP evaluated the different methods and it was decided to use
hydrodemolition for this job for the following reasons:
a. It results in a rough, irregular surface profile
that provides an excellent bond for all types of
repair materials creating a monolithic repair
b. Minimization or elimination of surface microcracking caused by other methods
c. Exposed aggregates are not fractures or damaged,
thus interlocking wall with the overlay
d. Selectively removing lower strength and deteriorated concrete (delamination)
e. Minimizing vibration to surrounding structure
f. Preserves and cleans reinforcing bars for reuse
and eliminates the need for sandblasting
Robotic equipment was used for this job to ensure
uniform removal of concrete. But prior to the start
of the production work, a mockup was installed
that was extensively tested to ensure the success of
the recommended procedure.
The testing of the mockup slab included:
a. Tensile bond tests by pulloff of the overlay
concrete to the substrate (Fig. 7.2a)
b. Cores comparing the lightweight aggregate of
the substrate and the repair concrete
A total of six tests were performed and the
bond strength was measured (Table 7.2a). The
test results exceeded 100 psi (0.7 MPa) (ACI 562
Section R7.4.2 and ICRI 210.3) and the difference
between maximum and minimum test results was
47 psi (0.32 MPa), or 30 percent.
Once the LDP was satisfied with the test results
and the process was confirmed, the contractor
proceeded with the implementation of the repair
work to the full slab starting with removal of the
slab (Fig. 7.2b).
The LDP requested extensive testing of the
repair work throughout the duration of the project.
The testing for the overlay concrete was similar
to the testing for new cast-in-place concrete.
Pulloff testing in accordance with ASTM C1583
was performed to confirm the adequacy of the
bond of the overlay to the substrate concrete.
The test results of the pulloff test are presented
in Table 7.2b.
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54
The test results were scattered and varied
between 32 psi (0.22 MPa) and 190 psi (1.3 MPa)
or a difference of 158 psi (1.09 MPa) or 83 percent
(Table 7.2b). This is a large scatter and unacceptable. The LDP ordered petrographic testing on
some of the samples. The test results revealed that
the contractor did not remove all debris and loose
material from the substrate surface area, thus
creating a weak bond between the substrate and
overlay (Fig. 7.2c).
Table 7.2a—Test results of the pulloff test of the mockup area
Test parameters
Test No.
A1
A2
A3
B1
B2
B3
Test location
Level P8 Floor slab Mock-up
area A
Level P8 Floor slab Mock-up
area A
Level P8 Floor slab Mock-up
area A
Level P8 Floor slab Mock-up
area B
Level P8 Floor slab Mock-up
area B
Level P8 Floor slab Mock-up
area B
Bond force, lb
(kN)
Bond Strength,
psi (MPa)
Separation plane
900 (4.0)
126 (0.87)
Substrate concrete
790 (3.5)
110 (0.76)
Surface of the substrate concrete
790 (3.5)
110 (0.76)
Surface of the substrate concrete
1125 (5.0)
157 (1.08)
Substrate concrete
1000 (4.5)
142 (0.98)
Surface of the substrate concrete
1000 (4.5)
142 (0.98)
50 percent substrate concrete
50 percent surface of the substrate concrete
Table 7.2b—Test results of the pulloff test of the partial completed work
Test No.
BT-1
BT-2
BT-3
BT-5
Bond force, lb
(kN)
6-29-06
560 (2.5)
79 (0.54)
Substrate concrete
6-29-06
670 (3.0)
96 (0.66)
Substrate concrete
7-08-06
(225) 1.0
32 (0.22)
75 percent interface between
substrate concrete and overlay,
25 percent within substrate concrete
7-14-06
1350 (6.0)
190 (1.31)
Test epoxy media
7-14-06
1350 (6.0)
190 (1.31)
Substrate concrete
Fig. 7.2b—Removal of 3-1/2 in. of slab by hydrodemolition.
Fig. 7.2c—Petrographic of new overlay to existing slab.
@Seismicisolation
@Seismicisolation
University of Toronto User.
BT-4
Test area and location
Level P9 on Column Line
2 between Column Lines G
and H
Level P9 on Column Line
2 between Column Lines K
and L
Level P9 West of Column Line
2 between Column Lines N
and P
Level P9 between Column
Lines 8 and 9 and J and K
Level P9 between Column
Lines 8 and 9 and F and G
Test parameters
Bond strength,
psi (MPa)
Separation place
Date of
placement
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Chapter 7—Design of Structural Repairs55
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Example 7.2—continued
Corrective actions were implemented to improve
the bond strength:
a. Contractor improved methods to the clean
surface of the substrate and to remove all
residue resulting from hydrodemolition
b. Inspectors more closely examined the substrate
surface for suitability to receive bonded overlay
The pulloff tests after the corrective measures
were more consistent and were equal to or exceeded
100 psi (0.7 MPa), with the exception of one test
result as shown in Table 7.2c.
The LDP ordered another set of petrographic testing
on some of the samples. The test results showed that the
bond between the substrate and new overlay is acceptable (Fig. 7.2d).
Conclusion:
The construction phase of the work should be
performed with high-quality workmanship and materials that satisfy the intent of the construction documents to warrant a successful project.
Table 7.2c—Test results of pulloff tests after remedial actions
Test No.
BT-16
BT-17
BT-17A
BT-17B
BT-18
BT-19
Test area and location
Level P9, NWC
Level P9, SWC
Level P9, SWC, 9’ N of Core
BT-17
Level P9D, West, 3’ N of Core
BT-17
Level P8D, West
Level P8D, West, column 2
between N&P
Date of concrete
placement
Not provided
Not provided
Bond force, lb
(kN)
1240 (5.5)
560 (2.5)
Test parameters
Bond strength, psi
(MPa)
174 (1.2)
79 (0.54)
Separation place
Interface zone
Substrate concrete
Not provided
790 (3.5)
100 (0.7)
Interface zone
Not provided
790 (3.5)
100 (0.7)
Interface zone
Not provided
1450 (6.5)
206 (1.42)
Interface zone
Not provided
1350 (6.0)
190 (1.31)
Interface zone
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56
University of Toronto User.
Fig. 7.2d—Proper bond between substrate and
overlay.
@Seismicisolation
@Seismicisolation
University of Toronto User.
7.5—Materials
7.6—Design and detailing considerations
ACI 562, 7.5.1, requires the LDP to evaluate the adequacy
7.6.1 Existing materials, reinforcement detailing, deteof the proposed repair materials. The repair materials are
rioration, and repair considerations—ACI 562, 7.6.1,
selected based on short-term and long-term compatibility
requires that the repair design consider the condition of
with the existing structure and durability in the service
the existing concrete, including the actual compressive
environment. The existing materials in the structure need to
strength and variations in that strength; the current condiconform to the design-basis code (ACI 562, 7.5.2) and repair
tion and types and extent of deterioration of the concrete
materials need to conform to ACI 318-19 or be permitted
(ACI 562, 7.6.2); and the sizes, locations, detailing, and
by ACI 562, 7.5.3. Alternate repair materials should be
current condition of the existing reinforcement (ACI 562,
approved by the LDP and the building official (ACI 562, 1.4
7.6.3). In a reinforced concrete structure, these items are
and 7.5.4).
difficult to determine due to the size and complexity of
A key part of any repair program is the selection of repair
the structure and conditions concealed below the concrete
materials. The remaining existing concrete usually has been
surfaces. A preliminary assessment (ACI 562, 1.7) consisting
in service for many years, so that initial drying shrinkage and
of visual and selective sounding surveys, which are relacreep effects would have occurred. The existing concrete will
tively easy and quick to conduct, are used to locate areas of
be required to respond to changes in the service environment,
possible concrete and steel deterioration along with design
such as variations in loadings and temperatures. Therefore, it
and construction deficiencies. Conditions that are identified
is important that the repair material be compatible with the
in the preliminary assessment are investigated in more depth
existing concrete. Compatibility does not necessarily mean
in structural assessment, evaluation, and analysis (ACI 562
having similar properties, but having properties that result in
Chapter 6). It should be recognized that the preliminary
successful repair performance.
assessment and the structural assessment, evaluation, and
ACI 562 requires that physical properties of the repair
analysis may not identify all deterioration that reduces the
material, such as drying shrinkage in cementitious materials,
capacity or design and construction deficiencies. The goal is
be considered when specifying repair materials. The requireto identify all unsafe and structurally significant conditions.
ments for each repair should be evaluated when selecting mateThe repair design needs to address structurally significant
rials. For instance, if shrinkage cracking is not desirable for a
deterioration such as loss of sound concrete cross section or
given repair, restraint of drying shrinkage could be addressed
concrete strength, and loss of reinforcing steel cross section
by developing sufficient tensile strength in the repair material
or development. Existing reinforcement development length
to avoid cracking or sealing the shrinkage cracks that develop
may be inadequate due to corrosion, mechanical damage,
with a crack treatment or a waterproofing coating. Alternately,
insufficient or loss of concrete cover, delaminated concrete,
a repair material that does not experience significant initial
or other conditions. The current design building code, ACI
shrinkage, such as a polymer concrete, or the addition of
318-19, has new development equations that may require
shrinkage-reducing admixtures could be considered.
longer development lengths than earlier development equaTo perform satisfactorily, a repair material needs to be
tions present in earlier building code versions. ACI 562,
compatible with the long-term concrete behavior and antici4.1.6, states that the LDP may not comply with the current
pated environmental conditions. If the repair material is
building code if two conditions are met:
designed to share load with the existing concrete, it may be
a. Damage or deterioration to existing reinforcedesirable that the repair material have similar or less stiffment is addressed
ness and reduced creep properties. It is also desirable that the
b. The repaired work area of the structure has
repair material have a similar coefficient of thermal expancapacity equal to or greater than demand per
sion so that the existing concrete and the repair material will
Section 5.2.2 of ACI 562 using the original
experience similar strains due to temperature variations in
building code requirements.
the service environment. If the existing concrete and the
The repair design need to also address structurally signifirepair material are expected to behave significantly different
cant deficiencies in the design and construction, such as
in the service environment, the differential strains need to be
inadequate concrete thickness or misplaced reinforcing bars.
accounted for in some manner. Methods that could be used
ACI 562, 7.6.6, requires that the repair geometry consider
include using a lower modulus of elasticity in the repair matethe potential for stress concentrations within the repair and
rial, increasing bond and tensile strength in the repair mateexisting structure. Where possible, reentrant corners and
rial, or periodic crack sealing maintenance to address cracks
other geometric irregularities should be avoided in the repair
that form due to differential strains. It should be noted that
and in the existing member to reduce stress concentrations
the existing concrete properties generally cannot be changed
and the potential for cracking in either the repair or the
and may limit the ability to address differential strains and
existing member.
the projected service life of the repaired members.
7.6.2 Prestressed members and structures—The repair
A detailed list of repair materials for various concrete
of members subject to prestressing forces presents unique
repairs, such as replacements, crack treatments, and surface
challenges. The prestressing force is designed to counter the
treatments, as well as discussions of test procedures, typical
effects of dead and live load strains to effectively impart a
test values, and the selection of repair materials is included
general state of compression throughout the member cross
in ACI 546.3R.
@Seismicisolation
section. If part of the concrete section becomes ineffective due
@Seismicisolation
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Chapter 7—Design of Structural Repairs57
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
be rendered fully ineffective in the case of a cut or fracture.
Some structures are designed with excess prestress and can
tolerate the loss of one or more unbonded tendons with no
significant reduction in the structural capacity; however,
in many other structures, this is not the case. Temporary
support such as shoring or reduced live load of the affected
area(s) should be considered until the adequate structural
capacity is confirmed or restored. End anchorages of many
of the unbonded post-tensioning systems used in the 1960s,
1970s, and 1980s are particularly susceptible to concrete
and tendon deterioration due to water infiltration. Modern,
fully encapsulated, unbonded post-tensioning systems have
significantly less risk of water penetration or corrosion.
Usually, repair of unbonded tendons requires detensioning
as the first step in the repair process. Then the unbonded
tendon can be spliced, strand or anchorages removed and
replaced as needed, and the tendon restressed.
Accordingly, ACI 562, 7.6.4, requires that the effects
of prestressing be considered in the repair design
(ACI 562, 7.6.4.1), including prestressing force release and
construction sequence (ACI 562, 7.6.4.2), and stresses in
remaining concrete (ACI 562, 7.6.4.3). ACI 562, R7.6.4.1,
references various ACI, PTI, and ICRI documents for more
information on this subject.
7.6.3 Post-installed anchors and dowels—ACI 562,
7.6.5, specifies minimum requirements for the design of
post-installed anchors, which is to be in accordance with
ACI 318-19. Extensive testing has been performed on
the behavior and capacity of post-installed anchors and
dowels, which is reflected in Chapter 17 of ACI 318-19.
Factors affecting the selection of the anchor type include
the expected concrete cracking condition (cracked or
uncracked), the duration of design loads, the inclination
of the anchor or dowel installation (downwardly inclined,
horizontal, or upwardly inclined), the concrete strength,
the concrete moisture content, anchor hole size, and the
acceptable failure mode. Post-installed anchors and dowels
should be prequalified by laboratory testing in accordance
with ACI 355.2 or ACI 355.4. Installation procedures
(including cleaning the drilled holes, the moisture condition of the concrete for adhesive anchors, torque magnitude
for mechanical anchors, and curing for adhesive anchors)
and testing and inspection procedures are critical for a
satisfactory installation.
7.7—Repair using supplemental post-tensioning
Supplemental post-tensioning consists of tendons or
bars that are positioned externally along the concrete
members. The external reinforcement may be straight or
draped, and may be positioned inside hollow portions of
members such as hollow-core planks and box girders.
Supplemental post-tensioning is normally used to
increase the member capacity or to resolve a deficiency
by introducing moments and shears to partially offset the
effects of gravity loads. Supplemental post-tensioning
can also be used to decrease member deflection. EssenPlacement of bonded overlay over the parking structure
tially, the supplemental post-tensioning is anchored
created a strengthened deck for the public transportation area
@Seismicisolation
near the ends of the member and held in position along
@Seismicisolation
University of Toronto User.
to deterioration or is removed during the repair, the state of
strain across the member cross section will need to be evaluated considering the remaining, sound concrete section. The
repair design needs to confirm that the remaining concrete
section is not overstressed. The potential for buckling and
instability should also be considered by the LDP. The reduction in sound concrete cross section could also result in a
reduction in prestress force due to shortening of the concrete
member; this loss of prestress force could affect the member
capacity. These later effects are particularly critical in
prestressed joists and beams that have larger prestress forces
than slabs.
Repair of deteriorated reinforcement in prestressed and
post-tensioned structures also has unique considerations.
In structures with bonded reinforcement, forces are transferred to the concrete through a combination of bearing at
the anchorages and bond over the entire length of the tendon.
Bonded reinforcement will become ineffective at locations
subject to deterioration of concrete or at locations where
force transfer is disrupted by debondment, reinforcement
fracture, or intentional modification as part of the repair.
Outside of these areas, the reinforcement may continue to
provide prestress force. The redistribution of internal forces
in these scenarios will need to be carefully considered in the
repair design.
Replacement of bonded tendons is rarely possible.
External post-tensioning is commonly used to restore the
reinforcement forces lost as a result of damaged tendons, as
described in ACI 562, 7.7. There are limited options available for the repair of bonded tendons; for example, repair
of voids in the grout in a bonded tendon can be achieved by
vacuum or pressure grouting. With these methods, specific
grouting procedures and quality assurance measures must be
specified to assure complete filling of the duct.
In structures with unbonded tendons, the prestressing
force is transferred to the concrete at the end anchorages
and at locations where the tendons are deviated from a
straight profile. If an unbonded tendon loses some or all
of its prestress, fractures, or is cut, the entire length of the
tendon experiences a proportional loss of prestress or will
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58
Strengthening with external post-tensioning
A 60 ft (18.3 m) long post-tensioned concrete
beam in a parking structure needs to be strengthened, possibly because one or more tendons have
fractured, the beam has excessive deflection, or
design loads are increasing. Repair options include
enlarging the beam section, externally bonded fiberreinforced-polymer reinforcement, supplemental
steel elements, and external post-tensioning. Of
these options, only external post-tensioning is an
active system that introduces external forces into the
beam, unless an attempt is made to unload the beam
by jacking before one of the other repair options is
installed. After considering serviceability, strength,
durability, appearance, fire rating, constructability,
aesthetics, disruption to garage activities, and cost,
the external post-tensioning option is selected.
In the schematic, the external post-tensioning
introduces upward forces at the beam third points.
This reaction serves to partially offset the effects
of the downward dead and live loads. The external
post-tensioning forces decrease the internal tension
and compression forces due to flexure and the
shear forces. The external post-tensioning forces
and the remaining original post-tensioning forces
are combined and compared to the limits in the
design-basis code (ACI 562, 7.7.2.1). The upward,
reverse effect of the external post-tensioning
also serves to decrease the beam deflection. To
provide a minimum capacity should the external
post-tensioning system fail, the strength of the
unrepaired beam is checked for the load combination in ACI 562, 5.5.1. The horizontal component of
the external post-tensioning at the end anchorages
introduces lateral loads and resulting moments into
the columns. The column capacities and stresses
are checked for these added moments (ACI 562,
Sections 7.7.2 and 7.7.3).
The end anchorages and intermediate saddles are
designed to transfer the post-tensioning force into
the beam. The capacity of the concrete members
is evaluated with respect to the effects of the force
transferred at those locations (ACI 562, 7.7.2.2).
Post-tensioning forces, including some transfer of
post-tensioning forces into the adjacent slab, are
estimated. The amount of effective prestress in the
beam is estimated by the upward deflection of the
beam under prestress (ACI 562, 7.7.4).
The tendon placement and anchorages are fully
detailed on the repair drawings, and the incremental
stressing sequence and monitoring of prestress are
specified (ACI 562, 7.7.5).
The external post-tensioning system is evaluated
for serviceability concerns related to fire and vehicular protection. Protection can be provided through
concrete encapsulation or spray-on fireproofing to
provide the required fireproofing (ACI 562, 7.9).
Concrete encapsulation or supplemental steel
framing can be provided for vehicular protection.
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Chapter 7—Design of Structural Repairs59
University of Toronto User.
the length of the member by intermediate saddles
force into the structure without causing damage in the
or supports.
anchorage zones. The restraint imposed by adjacent
ACI 562, Section 7.7, specifies the minimum requireelements, post-tensioning losses, and the sequencing of
ments for repairs using supplemental post-tensioning.
the post-tensioning repair should be considered.
The effects of the supplemental post-tensioning on the
internal stresses in the member being repaired and on the
7.8—Repair using fiber-reinforced polymer (FRP)
adjacent structural members should be considered, and
composites
the combined stress levels should not exceed prescribed
ACI 562, 7.8.1, permits the use of fiber-reinforced
limits in the design-basis code. The end anchorage zones
polymer (FRP) composites in conformance with ACI
should be designed and detailed to transfer the@Seismicisolation
prestress
440.6 and 440.8. ACI 440.2R discusses the design and
@Seismicisolation
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
detailing of externally bonded FRP systems. ACI 562, 7.8.2,
requires that the unrepaired strength of members with externally applied FRP meet the minimum requirements of ACI
562, 5.5. The minimum strength requirement ensures sufficient strength if the FRP is damaged or otherwise compromised. Unless protection is provided, based on the requirements of ACI 562, 5.5, the use of externally bonded FRP to
resist design dead and live loads of a structure will be limited.
7.9—Performance under fire and elevated
temperatures
ACI 562, 7.9, specifies the minimum requirements for
the performance of repairs under fire and elevated temperatures. The performance of the repairs and the repaired structure should comply with the fire safety requirements of the
applicable building code. The properties of the repair materials, particularly adhesives, at elevated temperatures must
also be considered. ACI 440.2R reports that the physical
and mechanical properties of the resin components of FRP
systems are influenced by temperature and can degrade
at temperatures close to and above their glass-transition
temperature, Tg. Therefore, FRP-strengthened concrete
beams require protection to maintain their strength, to
prevent combustion of the material, and to preserve their
bond with the substrate. An acceptable service temperature
for the element of the structure should not exceed Tg – 27°F
when FRP is used for strengthening. This value accounts
for typical variation in test data for dry environment exposures. Adhesive-bonded FRP reinforcement should not be
used if the maximum service temperature for the element
of the structure exceeds Tg – 27°F. A service temperature
exceeding this limit temperature should be addressed using
an adhesive system with a higher Tg value, using heat protection or insulation systems, or using alternate repair systems.
Similar service temperature considerations apply to adhesivebonded steel reinforcement.
Fire rating of the repaired structure and supplemental fire
protection are permitted, but no supplemental fire protection
may be necessary if the repair satisfies the load combination
in ACI 562, 5.5. Project 8 of this guide addresses two fire
rating/protection scenarios. In Scenario 1, the LDP specified
spray-applied fire-resistant material to protect the applied
FRP. In Scenario 2, fire protection to existing reinforcement with low cover was accomplished by installing a 1 in.
(25.4 mm) concrete jacket to provide additional cover to the
existing reinforcement. Fire resistance or rating of a repaired
system or assembly can be determined through full-scale
testing in accordance with ASTM E119.
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Protective deck coating installed on a floor slab of a parking deck
8.1—General
The desired design service life of the repairs and the repaired structure is established by the licensed design professional (LDP) in consultation with the owner.
As such, the overall solution should consider the desired service life for the repairs
and the expected remaining service life for the structural elements to remain. The
overall solution should also consider maintenance efforts over the design service
life for both the repair and remaining structural elements. The durability of the
repair solution requires compatibility between the materials of the repair and the
existing structure, as well as consideration of the anticipated exposure conditions
over its life span. Service life is discussed in ACI 365.1R.
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Overview
The durability of repairs to existing concrete structures is dependent upon the
properties and characteristics of the existing concrete and the repair materials, as
well as their service environment. Properties and characteristics such as cover of
reinforcing steel, cracks, spalls, protective treatments and coatings, permeability,
corrosion potential, and air-void parameters (for concrete subject to cycles of
freezing and thawing) are typically considered in a durability assessment. Moisture,
freezing-and-thawing cycles, chlorides, chemical attack, and other factors are typically
considered when performing an assessment of the effects of service environment on durability. Chapter 8 of ACI 562 sets forth the durability requirements
and considerations for the repair materials and the repaired structure. The project
examples that accompany this guide illustrate the application of durability considerations in the development of a repair program.
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Chapter 8—Durability
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
8.2—Cover
Concrete cover is one of the primary methods of protecting
reinforcing steel from corrosion and fire and ensuring proper
development of reinforcement. ACI 318, which is frequently
used for concrete design as the design basis code, specifies minimum design cover requirements for different types
of construction and environmental exposures. Other ACI
guidelines provide recommendations for concrete cover for
specific applications and exposure conditions, such as ACI
362.1R for parking garages. As part of a condition assessment, the existing concrete cover should be determined and
compared to the cover requirements in the design basis code.
ACI 562 addresses inadequate concrete cover in repair areas
and elsewhere in the structure by increasing the concrete
cover or employing alternative means (termed “equivalent
cover” in ACI 562) for corrosion (ACI 562, 8.2.2) and fire
protection (ACI 562, 7.9).
Concrete overlays and concrete-encased jackets can be
used to address inadequate concrete cover. Where such solutions are impractical or not cost effective in existing concrete
structures, alternate means of addressing member and structure durability due to shallow concrete cover issues should
be considered. Alternative means of corrosion protection
include the application of waterproof membranes on the
surface of the concrete, corrosion-inhibiting coatings on
reinforcing bars, use of concrete with lower permeability, or
corrosion mitigation technologies such as cathodic protection systems or galvanic protection.
ACI 216.1 contains design and analytical procedures for determining the fire resistance of concrete,
including minimum concrete cover for slabs and beams
to achieve various fire resistance ratings. In cases where
the minimum cover cannot be achieved, alternative
materials such as intumescent coatings or other finish
materials may be used to achieve the required fire rating
(ACI 562, 7.9.5). Alternate methods of fire protection
should be approved by the building official as required
in ACI 562, 1.4.2.
Section 8.2.2 of ACI 562 requires that the influence of the
existing concrete cover on the anchorage and development
requirements for reinforcement be assessed regardless of the
durability method selected. ACI 562 requires anchorage and
development requirements be in accordance with the design
basis code.
Project Example 1 includes considerations for cover
in a typical parking garage slab repair. Project Example 2
illustrates a scenario where cover is built out during repair.
Project Example 3 illustrates a scenario where coatings are
used as an alternate means of corrosion protection.
8.3—Cracks and deterioration of reinforcement
and metallic embedments
Concrete cracking can be caused by load effects and
volume changes are common. Cracking may also be
indicative of structural deficiencies or ongoing deterioration mechanisms. Cracks may be active or inactive. Active
cracks are subject to movement whereas inactive cracks
are not. It is important to determine the cause and nature
of the cracking during the condition assessment. ACI
224.1R discusses the causes, assessment, and repair of
cracks in concrete structures. ACI 503.7 provides a specification for repair of cracks through polymer injection. The
comparative cracking potential of different cementitious
materials can be assessed using ASTM C1581/C1581M.
The influence of cracks on the durability of the repair
and existing concrete structure should be considered by
the LDP. Cracks allow moisture and chemicals to enter
into the concrete and access the reinforcement. Exposure to moisture and chemicals can cause deterioration
of the reinforcement, the concrete, or both. Many repair
programs include treatment of existing cracks and provisions for treating new cracks that may form after the
repairs have been installed. The LDP should select an
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Depending on the owner’s planned use of the structure,
the design service life may range from short-term to longterm. To achieve the desired design service life, the repair
program should address the causes of the distress and deterioration. Deterioration will likely return if its causes are
not accurately determined and addressed. Future routine
maintenance is essential to achieving the targeted design
service life, in addition to the assessment, repair program,
and materials.
ACI 562, 8.1.2, requires the repair program development
consider the compatibility of the repair materials, the interaction of the repair materials with the existing structure, the
durability of the repair materials and the existing structure,
and anticipated maintenance requirements. The expected
service life of the repaired structure is determined in consultation with the owner considering strength, safety, and
serviceability requirements and the available repair budget.
In many situations, the available budget and other factors
limit the extent of repairs that can be completed.
To establish an expected service life for a repaired structure, the LDP should understand both the causes of observed
deterioration and the impact of the repairs on the performance of the structure. ACI 546.3R discusses the various
considerations for how compatibility, interaction, and durability are judged for various repair materials. For example,
in many concrete repair applications, the properties of repair
materials, such as the coefficient of thermal expansion and
creep, should be similar to those of the substrate. In contrast,
the success of many crack repair applications depends on
repair materials that have significantly different properties
from that of the substrate, such as high elasticity and low
modulus of elasticity, which will perform better than the
base concrete in the service environment (ACI 546.3R).
The project examples presented in this guide illustrate
project-specific maintenance recommendations that generally
result in improved service life of the repairs. Additional
discussion of maintenance recommendations is provided in
Chapter 1 of this guide.
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approach for crack treatment that considers the causes of
cracking and the anticipated exposure conditions. Rigid
crack repair materials are generally not effective where
crack widths are likely to widen or experience cyclic
opening and closing due to load effects and restrained
volume change.
Each of the project examples illustrates unique considerations for the effects of cracks on durability and particular
examples of how cracks are considered in the repair design.
The following documents may provide guidance
for the causes, assessment, and repair of concrete
structures.
• ACI 201.2R, “Guide to Durable Concrete”
• ACI 222R, “Protection of Metals in Concrete
Against Corrosion”
• ACI 222.2R, “Corrosion of Prestressing Steels”
• ACI 423.4R, “Corrosion and Repair of
Unbonded Single Strand Tendons”
• ACI 423.8R, “Report on Corrosion and Repair of
Grouted Multistrand and Bar Tendon Systems”
• ACI 546R, “Concrete Repair Guide”
• ICRI 310.1R, “Guide for Surface Preparation for
the Repair of Deteriorated Concrete Resulting
from Reinforcing Steel Corrosion”
• ICRI 510.1, “Guide for Electrochemical Techniques to Mitigate the Corrosion of Steel for
Reinforced Concrete Structures”
• The Concrete Society TR 50, “Guide to Surface
Treatments for Protection and Enhancement
of Concrete”
• NACE SP 0187-2017-SG, “Design for Corrosion Control of Reinforcing Steel in Concrete”
• NACE SP 0290-2007, “Impressed Current
Cathodic Protection of Reinforcing Steel in
Atmosherically Exposed Concrete Structures
• NACE SP 0408-2014, “Cathodic Protection
of Reinforced Steel in Buried or Submerged
Concrete Structures”
• NACE 01101-2018-SG, “Electrochemical
Chloride Extraction from Steel-Reinforced
Concrete—A State-of-the Art Report”
364.3T, and ACI RAP-8 provide further information on
the anodic ring (halo) effect. In such cases, the LDP might
consider galvanic anodes to reduce the risk of premature
corrosion due to the ring anode effect. Dissimilar materials that might result in galvanic corrosion are also to be
considered. ACI 222R discusses strategies for avoiding
galvanic corrosion. If electrochemical protection systems
are recommended, the impact of the cost of these systems
on the life cycle of the repaired members and the structure
as a whole should be considered. ACI 546.3R discusses
corrosion protection and material compatibility in the
development of repair solutions.
Project Example 1 illustrates several durability considerations and various options for corrosion protection as
part of a representative parking garage repair. Project
Examples 2 and 3 also include corrosion considerations
and mitigation strategies for each specific case.
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8.4—Corrosion
Corrosion of embedded reinforcement is a common
cause of concrete distress and deterioration in many environments. The documents listed in the textbox discuss the
causes, assessment, and repair of reinforcement corrosion
in concrete structures. There are a number of methods for
addressing reinforcement corrosion. These include locations
where the reinforcement is in contact with repair materials
as well as in locations where the reinforcement remains
embedded in the existing concrete. ACI 562, 8.4, requires
that corrosion be considered in developing a durable repair
strategy. The level of damage to existing reinforcement due
to corrosion, including mild and prestressing steel, should
be assessed to determine its effects on member strength and
bond and development of the reinforcement.
For locations where reinforcement will be in contact
with repair concrete, various methods such as corrosionresistant reinforcement coatings, galvanic anodes, and
replacement concrete materials with enhanced properties (such as corrosion-inhibiting admixtures, additional
concrete cover, surface treatments, or coatings) can be used
in combination or individually to provide a cost-effective
and durable repair. For locations where reinforcement will
remain embedded in existing concrete, crack treatments,
surface treatments or coatings, surface-applied penetrating
corrosion inhibitors, active cathodic protection, galvanic
protection, chloride extraction, realkalization, and other
measures warrant consideration. A cost-effective repair
program usually includes some combination of these
measures. For further discussion of corrosion mitigation
measures, refer to ACI 546R and The Concrete Society
Technical Report 50. Information about the design, monitoring, and maintenance of cathodic protection systems
can be found in NACE SP0187, NACE SP0290, NACE
SP0408, and NACE 01101.
ACI 562 requires that the specified repair materials
and reinforcement be compatible with respect to the
existing concrete materials and reinforcement, as well
as other building materials that remain. Therefore, the
new materials should not adversely affect the durability
of the existing materials. For example, a difference in
electrical potential can arise in existing reinforcement
that is continuous between the repair area and existing
concrete, and that potential can accelerate reinforcement
corrosion at the perimeter of the repair. This phenomenon is termed “the ring anode effect”. ACI 546R, ACI
Useful references on the causes,
assessment, and repair of reinforcement
corrosion in concrete structures
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GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
8.5—Surface treatments and coatings
Most types of concrete deterioration, including cyclic
freezing-and-thawing deterioration, reactive aggregates,
and corrosion of embedded reinforcement require the
ingress of moisture into the concrete. Surface coatings
and treatments, sealant joints, and other waterproofing
considerations such as flashings can be effective at limiting
moisture and chemical penetration into the concrete and
therefore reduce the potential for concrete deterioration.
For repair projects where the concrete is already contaminated with chloride or other chemicals and the deterioration processes are already occurring, surface coatings and
treatments can be effective remedies to reduce the ongoing
deterioration of elevated structures that can dry over time.
This is accomplished by limiting the ingress of additional
moisture into the concrete. For concrete that is saturated,
however, surface membranes can actually accelerate deterioration, as indicated in ACI 562, R8.5.1. The use of surface
coatings should be assessed for each project by the LDP
prior to specifying them to alleviate deterioration mechanisms. Surface treatments can also help reduce penetration
of moisture into cracks. For instance, elastomeric coatings can be effective in bridging moving cracks whereas
penetrating epoxy or methacrylate sealers can penetrate
and fill narrow nonmoving cracks.
Surface treatments, sealant joints, and coatings have
a finite service life, and require maintenance to ensure
continued effectiveness. These systems also generally
require replacement or repair during the service life of the
structure. Cracks that may limit the effectiveness of surface
treatments and coatings should be assessed and may require
special treatment before the selected surface treatment or
coating is installed.
Project Examples 1, 2, and 3 provide case studies where
the use of surface treatments were considered for improved
durability.
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Hydrodemolition used to remove deteriorated concrete on the supported level of a parking structure
9.1—General
The licensed design professional (LDP) needs to communicate the owner’s
requirements in clear, well-understood, and coordinated construction documents
to the contractor. Accordingly, the contractor is to safely and properly implement
the repair, rehabilitation, and strengthening work for the structure to perform
as intended. The cost of formwork can be greater than half the total cost of the
concrete structure. Therefore, this investment requires careful thought and planning by the LDP when designing and specifying the structure and by the contractor
when designing and constructing the formwork. The contractor needs to abide
by the construction documents to ensure that work is performed as intended, that
testing and inspection are coordinated and performed as specified, and any deviation from the construction documents or unexpected findings during construction
are properly communicated to the LDP. The construction documents for repair,
rehabilitation, and strengthening should specify, if applicable, specific temporary
shoring and bracing requirements, specific jacking requirements, project-specific
inspection, testing, and field observation requirements.
9.2—Stability and temporary shoring requirements
ACI 562, 9.2.1, 9.2.2, 9.2.3, and 9.2.4, require that temporary shoring and bracing
provisions for the project be described in the contract
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documents. Shoring, bracing,
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Overview
Repair of existing structures presents challenges that may not be encountered in
new construction. Chapter 9 of ACI 562 highlights three construction considerations
specific to repair projects: stability and temporary shoring, temporary conditions, and
environmental issues.
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documents. ACI 562 requires the temporary shoring or
bracing remain in place until the member is repaired. Continuity of the structure and the required strength of the repair
should also be considered prior to removal of the shoring.
The shoring and bracing requirements developed by the
specialty engineer should consider the following during
each phase of the assessment and repair:
a. In-place conditions and superimposed loads due to repair
construction or continued building operations
b. Displacement compatibility between existing members
and temporary shoring or bracing
c. Global stability of the structure and stability of compression elements or bracing members, including changes in
unbraced length
d. Lateral forces determined by generally accepted engineering principles or as required by the current building
code
e. Stiffness of the shoring and bracing systems as required
to prevent excessive displacement of existing braced
members
f. The impact of shoring or bracing loads transmitted to other
areas of the existing structure
g. Redistribution of loads and internal forces in members
subject or adjacent to repair
h. The effects of section loss or material degradation on
structural member capacity
i. Specified camber to ensure completed work is within the
tolerance limits
j. Constructed formwork dimensions should result in
concrete members having dimensions within the specified
dimensional tolerances
Section 6.0 of Project Example 1 illustrates how the provisions of ACI 562 Chapter 9 might be used to assess stability
and temporary shoring requirements during the assessment
and repair process for a parking structure. Section 5.3 of
Project Example 2 illustrates the process of considering
stability and temporary shoring during a typical balcony
repair project. Section 6.3 of Project Example 3 illustrates
the process of considering stability and temporary shoring
for concrete removal on compression members.
9.3—Temporary conditions
ACI 562 stipulates loads and load factors during the
assessment and repair construction process, including the
design of shoring and other temporary construction, be in
accordance with ASCE/SEI 7 for buildings occupied during
the construction period, and ASCE/SEI 37 for buildings
that will be unoccupied during the construction period. ACI
562 requires the design strength of the existing structure
or member exceed the required strength for all phases of
the assessment and repair process. For example, if during
the assessment unsafe conditions are identified, it may be
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or both is needed to address concrete distress or deterioration that has reduced the structural capacity or stiffness of
one or more members below safe levels. Temporary shoring
or bracing may also be required to support the existing
structure or structural elements, depending on the means
and methods adopted by the contractor to execute the repair.
For example, the concrete repair process frequently involves
the removal of unsound and, as necessary, sound concrete in
preparation for the installation of repair materials. Consequently, at one or more stages of the repair process, member
structural capacity or stiffness may be reduced below design
safety factors, necessitating temporary shoring and bracing.
Likewise, complete demolition of one or more structural
members can diminish the strength or stability of nearby
members that relied on the demolished member(s) for continuity or bracing. For example, shoring may be warranted at
slabs or beams adjacent to areas where concrete removal is
being performed, prior to the removal of concrete, to minimize the introduction of stresses into these elements due to
redistribution of moments.
ACI 562 requires the design of temporary shoring and
bracing to be performed by an LDP. The LDP responsible
for shoring and bracing design will typically be a specialty
engineer retained by the contractor. The specialty engineer
will develop the details of the shoring and bracing system in
conformance with the requirements specified on the contract
documents developed by the LDP for the repair and to suit
the contractor’s means and methods. In accordance with
ACI 562, 9.2.1a, 9.2.2a, 9.2.3, and 9.2.4, the LDP for the
repair need only provide the information necessary to design
the shoring and review the shoring design to verify design
intent and loads imposed on the structure. For example, for
a structural alteration that requires removal of an existing
column, the LDP for the repair might provide the shoring
loads and locations on the contract documents, and require
the contractor to submit a design for the shoring for review
and approval.
In accordance with ACI 562, the specialty engineer
will determine where shoring or bracing is necessary
to maintain global and individual member capacity and
stability, including bracing of compression members.
Conditions requiring temporary shoring or bracing may be
identified during the assessment of the structure, prior to
repairs, or when conditions become apparent during repair
construction. As discussed in Section 7.2 of this guide, it
is essential that the LDP specify in the repair documents
where it is known that shoring or bracing is required, and
that the LDP clearly specify limitations on the extent of
concrete removal before the specialty engineer is notified
to determine if shoring or bracing might be necessary. The
contractor should notify the LDP if damage observed during
construction is more severe than anticipated by the contract
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Shoring due to failure of columns during repair
A high-rise façade repair project involved removing
and replacing unsound concrete on exposed concrete
columns and slab edges. As much as 20 to 30 percent
of the concrete on some columns was removed and
replaced following a structurally safe sequence
determined by the LDP. During concrete removal on
one floor, four columns collapsed and the corner of
the building dropped 3/4 in. (19 mm).
The LDP was immediately notified and the corner
of the affected floor as well as several floors above
and below were shored (ACI 562, 9.2.2f and 9.2.8).
The owner and the authorities having jurisdiction
were also notified (ACI 562, 1.5.2). The shoring
layout and system were designed to transfer the
entire dead and live load in the collapsed columns
out of the columns above the affected floor and
back into the columns below the affected floor.
The increased shears in the adjacent beams were
considered (ACI 562, 9.2.1a, 9.2.2a, 9.2.2d, 9.2.3,
9.2.4, and 9.2.7).
A structural assessment was performed on the
affected members (ACI 562, 6.2.1 and 6.2.2).
Visual, destructive, and nondestructive testing
were performed as part of the structural assessment. Evaluation of removed core samples determined that over 50 percent of the column concrete
had been patched with mortar (in other words,
no coarse aggregates) and the interior column
surfaces had then been painted, concealing the
patches. The patch material crumbled during
coring and was deemed to be very weak. No further
strength testing was deemed necessary by the LDP
(ACI 562, 6.3.5). Ultrasonic testing and additional
coring of other columns determined that the extensive patching was limited to these four columns (ACI
562, 6.2.3). The poor-quality repair mortar resulted
in significantly reduced column strength, and the
resulting collapse. Assessment of the surrounding
members and other areas did not indicate any other
structural damage as a result of the collapse.
The full section of concrete and poor-quality
repair mortar was removed at the affected columns
and rebuilt using quality ready mixed concrete.
The LDP determined that the design strength for
the replacement concrete would be the same as
the original column concrete design strength (ACI
562, 7.5). Per ACI 562, 1.2.4.5, 4.1.5, A.2.5, and
A.4.1, the replacement columns were reinforced
and detailed consistent with the requirements of the
current building code. The predicted shortening of
the rebuilt columns due to the application of loads
and creep; the transfer of axial forces and moments
into the new column sections; and the adverse
effects of the column replacements on the adjacent
portions of the structure were assessed and considered acceptable (ACI 562, 7.2, 7.3, and 7.4). After
the concrete had reached its design compressive
strength, the shoring was removed and the façade
repair program continued. The new columns had
the same fire resistance as the existing structure
(ACI 562, 7.9). Because it was not feasible to raise
the corner of the floors 3/4 in. (19 mm), the corner
portions of the affected floor slabs were repaired
with a leveling course.
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GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
necessary to provide temporary shoring and bracing prior to
the repair phase.
9.4—Environmental issues
ACI 562 requires the contract documents assign the
contractor or other designated party responsibility for all
specified environmental remediation measures, reporting of
any new conditions encountered, and control of all construction debris, including environmentally hazardous materials.
Known environmentally hazardous materials and legally
required handling and disposal procedures are to be included
in the contract documents.
Section 8.0 of Project Example 1, Sections 6.0 and 8.0 of
Project Example 3, and Section 10.0 of Project Example 5
illustrate environmental concerns during repair projects
including the control of water with debris on the site, the
control of construction dust and debris, and the disposal of
construction debris.
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Inspector examining the externally bonded fiber-reinforced polymer (FRP) system installed on the bottom of a concrete beam
10.1—General
Quality assurance measures are planned, such as systematic activities that
confirm the quality of materials and workmanship used in the work. These activities
typically include inspections, testing of repair materials, and other construction
observations as necessary to determine if the work conforms to the requirements
specified in the contract documents. ACI 562 requires that testing and inspection
requirements of the general existing building code or local jurisdiction be described
in the contract documents.
Quality assurance requirements are included in the contract documents by
the licensed design professional (LDP) either through reference to the existing
building code or through specified testing and inspection requirements applicable
to the project. The LDP should consider the minimum
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Overview
Repair and rehabilitation work is sensitive to quality. Deficiencies in surface
preparation, repair material installation, or repair material curing can cause the
repair or rehabilitation work to fail prematurely or not perform as intended.
Studies such as CON REP NET 2004 indicate that 80 percent of concrete repairs
will continue to perform satisfactory after 5 years, but that after 10 years, the
percentage of repairs exhibiting satisfactory performance drops to 30 percent. An
earlier study completed by the U.S. Army Corps of Engineers (COE ) (McDonald
and Campbell 1985) determined that 50 percent of the repairs completed on COE
projects are not performing properly. The COE attributed the failure of repairs
to a combination of design, material specification, and construction errors. Thus,
quality assurance and quality control during construction are essential for the
success of a repair or rehabilitation program.
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GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
local jurisdiction, the structural importance of the repairs,
the desired service life for the repairs, and the associated
costs of the various inspections or tests.
Each of the project examples illustrate representative
quality assurance programs customized for each of the
project scenarios.
10.3—Testing of repair materials
ACI 562, 10.3, requires that the LDP specify in the
contract documents repair material tests and test frequencies, test reporting requirements, and the time period that the
testing agency must retain the test records. The LDP should
review the existing building code and general building
code, or other requirements adopted by the local jurisdiction governing the repair or rehabilitation construction, and
provide appropriate reference to the applicable testing provisions of these requirements in the contract documents. In the
absence of any requirement from the local jurisdiction, ACI
562 requires that the test records be retained by the testing
agency for a minimum of 3 years beyond completion of
construction. ACI 546.3 and ICRI 320.2R discuss various
tests of repair materials, including bond strength, dimensional behavior, durability properties, mechanical properties, and constructability properties. As with all components
of the quality assurance program, the importance of the
tested property, the desired service life for the repair, and
the associated costs of the test should be considered when
developing the testing requirements. In general, testing for
all the listed properties is not practical. Each of the project
examples illustrate representative testing requirements for
each of the project scenarios.
10.4—Construction observations
As required in ACI 562, 10.2.2, the LDP needs to include
project-specific testing and inspection requirements in the
contract documents. Section 10.4.1 of ACI 562 requires
that construction observations be performed as specified in
the contract documents. Inspections as specified in ACI 562
Sections 10.2 and 10.3 are intended to verify the quality of
materials installed, workmanship used, and compliance of the
work to the intent of the construction documents. Observations as specified in ACI 562, 10.4, are intended to verify critical assumptions used in the design of the rehabilitation work.
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10.2—Inspection
ACI 562, 10.2.1, requires that the inspection and testing
meet the minimum inspection requirements of the existing
building code or as required by the local jurisdiction. For
jurisdictions that have adopted the IEBC, Section 109 of
the 2018 IEBC provides the minimum inspections required
by the building code official for work where a permit is
required. Additionally, special inspections are required per
Section A109.3.8 of the 2018 IEBC. Special inspections
are to be provided by the owner or owner’s representative
and include continuous and periodic inspections or verifications for construction. The required special inspections and
verifications for concrete construction are provided in Table
1705.3 of the 2018 IBC. The inspections should be performed
by an LDP, a qualified inspector or individual, or a combination thereof per recommendations by the LDP to the owner.
The LDP should develop repair construction documents that specify the inspections required by the existing
building code, as well as supplemental inspections and
tests that are appropriate to the project. ACI 562, 10.2.2,
requires that the LDP include project-specific testing and
inspection requirements in the contract documents. The
repair inspectors should be qualified individuals who are
experienced in this type of work and have been certified as an
ICRI Concrete Surface Repair Technician – Grade 1, or as an
ACI Concrete Construction Special Inspector (ACI C630).
The ICRI Concrete Surface Repair Technician Certification Program consists of a two-tiered online educational
training program with the second tier providing full certification, qualifying the individual to perform pre- and postplacement inspections and testing on concrete repairs. The
ACI Concrete Construction Special Inspector program qualifies a person to inspect and record the results of concrete
construction inspection based on codes and job specifications. These programs meet the repair inspector qualifications discussed in ACI 562, R10.2.2.
As required by ACI 562, 10.2.3, the project-specific
requirements are to state that existing conditions and
reinforcement shall not be concealed with materials that
preclude visual inspection before completion of the inspection,
unless the LDP determines that only representative repair
locations need be inspected. Unanticipated conditions are
often uncovered during construction. The repair inspector
should inform the LDP so that the LDP could assess the
situation and determine what actions should be taken before
proceeding with the repair or strengthening construction.
In addition to the commentary provided in ACI 562,
R10.2.2, numerous publications are available that discuss
various methods and considerations for quality assurance inspections. ACI 546R discusses particular quality
assurance and control measures for concrete repair, and
ICRI 210.4 discusses the use of nondestructive evaluation methods for purposes of quality assurance during
repair. Additionally, ACI 311.1R and ACI 311.4R provide
guidance on quality control, inspection, and testing procedures for concrete. Each of the project examples illustrate
representative inspection requirements for each of the
project scenarios.
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GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Chapter 11: Commentary References
Restoration of a lock in Florida
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71
University of Toronto User.
Overview
Chapter 11 of ACI 562 provides the full document titles for references presented
in the commentary portion of ACI 562. These references include building codes,
guides, reports, standards, and various other published materials and are presented
to the LDP for additional information and resources on a given topic. As these
references are not all written with mandatory language, the references are not
considered part of the code requirements of ACI 562 unless referenced specifically
within the body of the ACI 562 code language. The standards that are referenced
within the code text of ACI 562 are listed in Chapter 3 of ACI 562.
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71
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Shoring of prestressed beam due to corrosion of prestressed reinforcement.
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72
University of Toronto User.
Cast-in-place shear block with anchored external post-tensioning
to strengthen beam.
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73
University of Toronto User.
The LDP is confronted in the initial stages of a project
with the challenge to determine what design-basis code
criteria applies. This is more prevalent when a structure
was constructed prior to a jurisdiction having adopted a
general building code. The structure may have design and
construction elements that do not satisfy the original or
current building code requirements based on the preliminary assessment in ACI 562 Section 1.7 and the detailed
assessment of ACI 562 Chapter 6. Accordingly, the LDP
will use Appendix A of ACI 562 to determine if an existing
structure should be rehabilitated to satisfy original design
requirements or strengthened to satisfy requirements of
the current building code. ACI 562 Appendix A is used to
determine if an existing structure should be repaired, rehabilitated, or retrofitted to satisfy the requirements of the
current building code.
When a jurisdiction has not adopted a standard for the
assessment of structures for seismic resistance as well
as for the repair or strengthening or retroft of individual
members, systems, or structures, the LDP should make the
determination if seismic assessment is required by using
ACI 562 Appendix A.3.3. ACI 562 and ASCE/SEI 41 should
be used for evaluation of seismic damage to members,
systems, or structures that are seismically unsafe. ASCE/
A.1—General
SEI 41 may or may not be applicable to nonbuilding strucAppendix A of ACI 562 applies if a jurisdiction has not
tures. Its requirements may apply to nonbuilding structures
adopted a code that addresses assessment, repair, and rehasuch as pipe racks, steel storage racks, structural towers
bilitation of existing concrete structures such as the Interfor tanks and vessels, piers, wharves, and electrical powernational Existing Building Code (IEBC). Per ACI 562,
generating facilities, but the LDP should use judgment, as
1.2.4.2, Appendix A also applies if a jurisdiction has adopted
the applicability of these requirements has not been fully
ACI 562 as the only existing building code. It can also be used
verified for every type of structure. ASCE/SEI 41 states,
to supplement Chapter 34 in the 2012 and previous versions of
however, that its provisions do not have to apply to large
the IBC.
nonbuilding structures, such as large tanks found in heavy
industry or power plants, floating-roof oil storage tanks,
A.2—Design-basis code criteria
and large (greater than 10 ft [3 m] long) propane tanks at
Where Appendix A of ACI 562 applies, the LDP has to
propane manufacturing or distribution plants.
determine the design-basis code based on the criteria stated
ACI 562 Appendix A should be used to determine the
in ACI 562, A.2.1. The LDP may choose, however, to use the
assessment and design-basis criteria for a structure, as
current building code referencing ACI 318-19 as the designshown in Table A.2 (ACI 562 Table A.2.3) unless the local
basis criteria for all damage states, deterioration, faulty
jurisdiction imposes more restrictive requirements.
design, or faulty construction. The LDP should discuss this
The LDP is faced with several questions when confronted
option with the owner before using it as it may be unnecwith deteriorated or weakened structures, which should be
essarily conservative and may lead to a solution that is not
clarified before engaging in the assessment.
cost-effective or economical.
ACI 562, A.2.4 and A.2.5, require that any new reinforced
concrete member added to an existing structure should be
designed and detailed to satisfy the current building code
(ACI 318). This also applies to the connections between new
Chapter 4 and Appendix A of ACI 562 are compamembers and the existing structure. Consequently, when the
rable. The reader may perceive similarities in the
original building code is used as the design-basis criteria for
code text between them, which is mirrored in this
repairs, rehabilitation, and strengthening, new concrete or reinguide text as well. Major changes, however, occur
forcing members built integrally with the existing concrete strucin A.4—Substantial structural damage, A.7—
ture, or both, must be designed using the original building code.
Additions, A.8—Alterations, and A.9—Change in
In the case where the design-basis criteria for the design
occupancy.
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of repairs to existing structures is the original building code,
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Overview
Appendix A of this guide provides the criteria for use of
ACI 562 to assess and strengthen existing concrete structures when a jurisdiction has not adopted an existing building
code. In this case, Chapter 4 of ACI 562, which is used to
assess and strengthen existing structures when a jurisdiction has adopted an existing building code, does not apply.
Section 1.7 of ACI 562 specifies a preliminary assessment of
deteriorated or damaged existing structures to determine the
extent and significance of damage and deterioration and the
reduced structural capacity of individual existing members
and structures. Based on the findings of this assessment, a
compliance method is selected by the licensed design professional (LDP) to determine the design basis code.
This appendix establishes limits based on demandcapacity ratios for ultimate strength design and allowable
stress principles to determine if existing members, systems,
or structures are safe or if strengthening, repair, or both,
are necessary. The level of strengthening, repair, or both, is
influenced by the calculated demand-capacity limits.
Project Example 1 illustrates a type of preliminary assessment and method of determining the design basis code and
how to apply Appendix A of ACI 562.
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Appendix A—Criteria when Using ACI 562 as a Stand-Alone Code
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Table A.2—Design-basis code criteria references for rehabilitation categories
Rehabilitation category
Potentially dangerous structural conditions for gravity and wind loads
Potentially dangerous structural conditions for seismic forces in regions
of high seismicity (Seismic Design
Category D or higher)
Substantial structural damage to vertical
members of the lateral-force-resisting
system
Substantial structural damage to vertical
members of the gravity-load-resisting
system
Damage less than substantial structural damage, deterioration, and faulty
construction with capacity increase
Damage less than substantial structural damage, deterioration, and faulty
construction without capacity increase
Sections of this code to use for the assessment criteria
Preliminary code of the design-basis criteria used with
this code
A.3.2
A.3.3
For potentially dangerous structures, current building
code* supplemented by ASCE/SEI 41 for seismic if the
structure is in Seismic Design Category D or higher
A.4
Current building code* for substantial structural damage
A.4
Current building code* for substantial structural damage
A.5
Current building code*
unless compliant with Sections A.5.1, A.5.2 or A5.3 for
the original building code†
A.6
This code, Chapters 8 through 10
Additions
A.7
Alterations
A.8
Changes in occupancy
A.9
Current building code*
unless compliant with Section A.7 for the original
building code†
Current building code*
unless compliant with Section A.8 for the original
building code†
If rehabilitation is required, then use the current
building code*
Note: Section and chapter numbers refer to ACI 562. Wording such as “this code” also refers to ACI 562.
*
Current building code is as per 1.2.2.
†
Original building code is as per 1.2.3.
The LDP should determine if the structure has
demonstrated statically acceptable performance based on
historical data, such as acceptable resistance of previous
loads that equal or exceed the loads that would be predicted
for the remaining life of the structure. The LDP may judge
the structure to have demonstrated historic structural reliability. The following references provide guidance in
judging acceptable performances.
The design basis code for repair and rehabilitation projects varies based on the extent of alterations, additions, or
repairs. In general, the original building code is the design
basis for minor alterations without significant changes in
load. The current building code serves as the design basis
for elements subject to major alterations or significant load
Useful references for assessing and
changes. For evaluation of seismic resistance and rehabilitaevaluating existing concrete structures
tion design, ACI 562 requires that ASCE/SEI 41 needs to
The following documents are listed in the commenapply per Section 1.3.8.1. Similarly, the design of repairs
tary of ACI 562 Section RA.2.4 and may provide
subject to elevated temperatures and fire should satisfy the
guidance in judging acceptable performance.
applicable existing building code.
• ACI 224.1R, “Causes, Evaluation, and Repair
In the industry, a quantitative measure or scale to determine the
of Cracks in Concrete Structures”
level of deterioration or damage exhibited by an existing structure
• ACI 437R, “Strength Evaluation of Existing
does not exist. There are, however, processes that can be applied
Concrete Buildings”
to determine the safety level of an existing structure. Neverthe• ACI 437.1R, “Load Tests of Concrete Strucless, the LDP is confronted with several questions that require
tures: Methods, Magnitude, Protocols, and
careful planning and response. Some of the questions may be:
Acceptance Criteria”
a. When should an existing structure be strengthened or
@Seismicisolation
repaired?
@Seismicisolation
University of Toronto User.
detailing of the existing reinforcement does not need to
comply with the current building code requirements if the
following conditions are satisfied:
a. The damage or deterioration to the existing reinforcement
is addressed
b. The repaired work area of the structure has capacity equal
to or greater than demand per ACI 562 Section 5.2.2 using
the original building code requirements or satisfies the
requirements of ACI 562 Section A.5.3 when using allowable stress design
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74
ACI 562 Chapter 2 defines potentially dangerous
structural condition as follows:
potentially dangerous structural condition—
structural state of an individual structural member,
structural system, or structure with instability,
potential collapse of overhead components or
pieces (falling hazards), noncompliance with fire
resistance ratings or demand to capacity ratio limits
above acceptable limits defined in this code.
b. What is an acceptable demand-capacity ratio limit to
consider an existing structure safe?
c. What is the minimum acceptable strengthening or repair
level that is considered safe?
d. When should an existing structure’s capacity be increased?
e. How should an existing structure be evaluated by the
working stress method?
f. When should an existing structure be strengthened or
repaired to the original building code or applicable
existing building code level?
These and other questions that may arise are addressed in
ACI 562, A.3 through A.5.
ACI 562-19 useful references for potentially
dangerous structural conditions
The following documents are listed in the
commentary of ACI 562-19 and may provide
target reliability indexes, basic probability theory,
and concepts for an assessment using the specific
details of the demand as it relates to the capacity
with the strength reduction factors of Chapter 5 for
concrete structures.
• ASCE/SEI 7-16, “Minimum Design Loads for
Buildings and Other Structures”
• Galambos, T.V.; Ellingwood, B.R.; MacGregor,
J.G.; and Cornell, C.A., 1982, “Probability
Based Load Criteria: Assessment of Current
Design Practice,” Journal of the Structural
Division, V. 108, No. 5, pp. 959-977.
• Ellingwood, B.R.; MacGregor, J.G.; Galambos,
T.V.; and Cornell, C.A., 1982, “Probability
Based Load Criteria: Load Factors and Load
Combinations,” Journal of the Structural Division, V. 108, No. 5, pp. 978-997.
• Ellingwood, B.R., and Ang, A. H.-S., 1972,
“A Probability Study of Safety Criteria for
Design,” Structural Research Series No. 387,
Engineering Experiment Station, University of
Illinois at Urbana-Champaign, Champaign, IL.
The LDP may also consider the following to satisfy
Eq. (A.3):
a. Adding structural redundancies which are desirable to
ensure the safety of a structural system
b. Providing alternate load paths, redistributing the load, or
limiting the live load such that existing members are not
overstressed
c. Adding shoring to support members and to relieve overstressed members
If the demand-capacity ratio is less than 1.5, however, then
less-restrictive requirements are implemented as described
in A.4 through A.9 of this guide.
Potentially dangerous structural conditions in Seismic
Design Category (SDC) D, E, and F structures, as deterUc
(A.3)
mined per ASCE/SEI 7, are assessed using ASCE/SEI 41.
> 1.5
φRcn
The design-basis criteria for rehabilitation design and
where Uc is defined as strength design demand by using nominal
construction of potentially dangerous structures are
loads of the current building code and factored load combinaASCE/SEI 41 and ACI 562.
tions of ASCE/SEI 7 for strength design provisions (LRFD); Rcn
Unless addressed by the authority having jurisdiction,
is the current in-place nominal capacity of structural member,
for structures in SDC D, E, and F, the LDP should review
system, or connection including the effects of damage, deteriothe structure for potentially hazardous seismic conditions.
ration of concrete and reinforcement, and faulty construction;
The review should be completed to confirm the structure is
and φ is the strength reduction factor obtained from Section 5.3
adequate for either the seismic performance level required
or 5.4 of ACI 562. A demand-capacity ratio greater than 1.5
by the local authorities, or confirm the structure is compliant
calculated using Eq. (A.3) represents a condition with limited
with ASCE/SEI 41 for Structural Performance Level –
to no margin of safety against failure. Potentially hazardous
Collapse Prevention using Earthquake Hazard Level, BSE-1.
structural conditions requiring immediate attention should be
Earthquake Hazard Level BSE-1 has a 20% probability of
reported to the owner per ACI 562, 1.5.2.
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exceedance in 50 years, or a 225-year return period.
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University of Toronto User.
A.3—Potentially dangerous structural conditions
The LDP needs to determine if potentially dangerous structural conditions exist by carrying out a thorough assessment
of the deterioration or damage to the existing structure, as
discussed in Chapters 1 and 6 of this guide. The risk for collapse
of each proposed strengthening procedure should be assessed
to determine an economical and safe repair strategy. The LDP
calculates the strength demand based on the current building
code, considering gravity and fluid loads and lateral wind and
soil loads but excluding seismic loads. The governing load is
determined using factored load combinations of ASCE/SEI 7.
In this appendix, the term “gravity loads” refers to dead, live,
and snow loads. Reduction factors from ACI 562, 5.3 or 5.4,
are used whether a structure is rehabilitated or assessed. If the
demand-capacity ratio, as given in Eq. (A.3) (ACI 562-16,
Eq. (A.3.2)), is greater than 1.5, then the structure should be
strengthened or repaired based on the current building code
75
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APPENDIX A
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
When the local authority having jurisdiction does not
provide requirements for potentially hazardous seismic
structural conditions, then the LDP should refer to ATC-78,
the IEBC, and ASCE/SEI 41 appendixes for guidance. The
LDP is not required to assess potentially hazardous seismic
conditions for concrete structures located in moderate to low
seismicity regions.
A.4—Substantial structural damage
A structure determined safe should be assessed to decide
if the sustained damages are substantial. If a jurisdiction has
not adopted IEBC, the IEBC definition of substantial structural damage cannot be used.
The ACI 562 approach to substantial structural damage is
based upon the requirements presented in the IEBC, with
some modifications added to enhance clarity. When substantial structural damage has occurred, ACI 562 requires the
structure be strengthened to satisfy current code requirements. ACI 562 focuses on substantial structural damage to
lateral-force-resisting systems and to gravity-load-resisting
systems. Gravity load per ACI 562 is considered to consist
of dead load D, live load L, and snow load S.
A lateral-force-resisting system of a structure is considered to have substantial structural damage if the vertical
members in any story, shear walls, or columns of the lateralforce-resisting system are damaged such that the lateralforce-resisting nominal capacity of the structure, ∑Rcn,
in any horizontal direction is reduced by more than
33 percent from its predamaged condition, ∑Rn, as presented
by Eq. (A.4a) (ACI 562 Eq. (A.4.1a)).
∑ Rn
≥ 1.25 (A.4b)
∑ Rcn
The gravity-load-resisting system of a structure should
also satisfy the condition such that ratio of the factored
gravity load of the current building code, ∑Uc, to the
in-place vertical design capacity, ∑Rn, of these damaged
members is greater than 33 percent per Eq. (A.4c) (ACI 562
Eq. (A.4.1c)).
∑ Uc
≥ 1.33 (A.4c)
∑ Rcn
Equations (A.4a), (A.4b), and (A.4c) use the reduction
factors of ACI 562 Chapter 5.
A.5—Conditions of deterioration, faulty
construction, or damage less than substantial
structural damage
This section addresses reinforced concrete structures that
are safe, have less than substantial structure damage, but
have deterioration or faulty construction and there is reason
to question the capacity of the structure. Accordingly, assessment is performed by checking one of the criteria in ACI 562
Sections A.5.1, A.5.2, or A.5.3.
ACI 562 requires that demand-capacity ratio of a member,
system, or structure be assessed in accordance with Eq.
(A.5) (ACI 562 Eq. (A.5.1)).
Uo
> 1.0
φo Rcn
(A.5)
where Uo is the strength design demand determined by using
the nominal loads and factored load combinations of the
original building code, excluding seismic loads, and foRcn is
the capacity adjusted by the strength reduction factor (fo) of
the original building code.
If Uo/fRcn is greater than 1.0, the LDP is permitted
to repair and restore the structure to the predamaged or
predeteriorated states and satisfy the original building
code requirements. Most existing concrete structures
with damage less than substantial structural damage,
deterioration, or containing faulty construction, will
provide acceptable safety if restored to the strength of
the original building code. The LDP is permitted to use
material properties of the original construction when
designing the repair or rehabilitation work to existing
concrete structures. New members or connections to
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University of Toronto User.
∑ Rn
(A.4a)
≥ 1.5
∑ Rcn
A gravity-load-resisting system is considered to have
substantial structural damage if any wall, column, or a group
of vertical members of the gravity-load-resisting system
having a tributary area greater than 30 percent of the total
area of the structure’s floor(s) or roof(s) are damaged such
that the total vertical nominal capacity, ∑Rcn, is reduced by
more than 20 percent from its predamaged condition, ∑Rn,
as presented in Eq. (A.4b) (ACI 562 Eq. (A.4.1b)).
For substantial structurally damaged structures, the
design-basis code is the current building code demands
supplemented by ACI 562 for existing structures and ASCE/
SEI 41 for seismic design provisions for the following:
a. Lateral-force-resisting system in both directions for the
case of substantial structural damage in either direction
from lateral force
b. Vertical member of the gravity-load-resisting system for
the case of substantial structural damage from gravity
loads
Structures assigned to SDC D, E, and F per ASCE/SEI 7
with substantial structural damage caused by earthquake are
assessed or rehabilitated for load combinations that include
earthquake effects. The level to which a structure is assessed
or rehabilitated is based on seismic design provisions of
ASCE/SEI 41. When the objective is life safety, use ASCE/
SEI 41 Earthquake Hazard Level BSE-1E and use BSE-2E
when the objective is to prevent the collapse of the structure.
The design-basis code for new members and connections to
existing members is the current design building code. Structures with substantial structural damage caused by wind
should be assessed or rehabilitated using load combinations
that include the current building code gravity and wind loads.
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76
77
Fig. A.5a—Selecting design basis code.
existing members, however, should be designed to
satisfy the current building code.
For structures with a demand-capacity ratio of less than
1.0 (Eq. (A.5)), strengthening is not required.
For an existing structure that was subjected to known loads
equal to or higher than specified in the design documents
during its service life but has performed satisfactorily, it
should be taken as an indicator that the existing structure has
an adequate safety factor and strengthening is not required.
Figure A.5a provides a road map for selecting the designbasis code.
ACI 562 Section A.5.2 provides alternative assessment
criteria for structures with deterioration, faulty construction,
or damage less than substantial structural damage. The LDP
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University of Toronto User.
Uc – Demand using nominal loads of the current building code and factored load combinations of ASCE/SEI 7 for strength
design provisions
Uo – Demand using nominal loads and factored load combinations of the original building code for strength design provisions
Rcn – Current in-place nominal capacity of structural member, system, or connection including the effects of damage, deterioration of concrete and reinforcement, and faulty construction
Rn – Nominal capacity of structural member, system, or connection excluding the effects of damage, deterioration of concrete
and reinforcement, and faulty construction
φ – Strength reduction factor per ACI 562 Section 5.3 or 5.4
φο – Strength reduction factor of the original building code
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APPENDIX A
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
University of Toronto User.
should assess whether the demand or capacity of the origACI 562, A.5.3, provides provisions to assess such a
inal structure is significantly inconsistent with the current
structure. The demand-capacity ratio is based on service
standards, which may result in unacceptable structural
load demand, Us, and resistance using allowable stresses,
safety issues. ASCE/SEI 7, Galambos et al. (1982a, b), and
Ra. If the demand-capacity ratio is greater than 1.0 (Us/Ra >
Ellingwood and Ang (1972) should be considered in the
1.0), then strengthening of a structure is required using
selection of a relevant assessment criteria. The applicathe original building code. If the demand-capacity ratio,
bility of the original building code for assessing existing
however, is less than 1.0 (Us/Ra < 1.0), then strengthening
structures should be questioned if any of the following
is not required.
conditions exists:
The service load demand includes nominal gravity loads
a. Increased load intensity
and lateral wind and seismic forces using load combinations
b. Added loads
of the original building code. The LDP should be aware
c. Changes in load factors, strength-reduction factors, or
that using the allowable stress design method is inconsisload combinations
tent with the reliability principles of current strength design
d. Modifications of analytical procedures
provisions. Therefore, the structure should be verified
e. Changes in determining capacity between the original and
following ACI 562, A.5.2, and the seismic resistance should
current building codes, such as a change from allowable
be checked using ASCE/SEI 41. The LDP may restore a
stress design to ultimate strength design
member or system to the capacity of the original building
f. The benefits received from strengthening or repair do not
code using the material properties of the original construcjustify the incurred cost
tion. New members, however, must satisfy the requirements
The LDP may use a probabilistic approach of loads and
of current building code.
capacities to show that the structure has adequate reliTable A.5 summarizes the different assessment condiability indexes or may use an assessment procedure based
tions the LDP may consider when analyzing a structure for
on demand-capacity ratios that are derived from the basic
repair, rehabilitation, or strengthening. The alternate assessengineering principles as presented in current standards.
ment criteria, Section RA.5.2, are included in the table even
ACI 562 defines demand based on the current building
though they are not code requirements. However, the LDP
code (Uc) as the effect of nominal gravity loads and lateral
will likely find these criteria useful in situations where
wind and soil loads, excluding earthquake loads, using
significant differences exist between the original design
ASCE/SEI 7 factored load combinations. ACI 562 defines
loads and current design requirements.
demand based on the original building code (Uo*) as the
effect of the original building code nominal gravity loads
A.6—Conditions of deterioration, faulty
and lateral wind and soil loads, excluding earthquake
construction, or damage less than substantial
loading, using the factored load combinations of ASCE/
structural damage without strengthening
SEI 7. The LDP has to compare the demand based on the
For structures not strengthened using ACI 562, A.3
current building code (Uc) to the demand of the original
through A.5, the LDP should follow ACI 562, A.6 through
building code (Uo*).
A.9, to determine the design-basis criteria to impleIf Uc > 1.05Uo*, then the LDP has to determine the demandment for strengthening. For structures with minimal or
capacity ratios based on the current building code, Uc/fRcn.
no damage or faulty construction that do not require
If the ratio exceeds 1.1(Uc/fRcn > 1.1), then strengthening
strengthening per ACI 562, A.5, the LDP can use Chapof the structure or member to the current building code is
ters 7 through 10 of ACI 562 as the design-basis criteria
required. Otherwise, strengthening is not required.
to rectify the shortcomings.
If the current building code demand, however, does not
Corroded or damaged reinforcement affects the behavior
exceed the original building code demand by more than
of the concrete structure. It may result in concrete cracking,
5 percent (Uc ≤ 1.05Uo*), then the LDP should check the
possible reduction in section capacity resisting the applied
demand-capacity ratio using the original building code
loads, or both. The LDP should evaluate the effectiveness of
demand and the current building code capacity. If the ratio
the reinforcement per Chapter 7 of ACI 562.
exceeds 1.05(Uo*/fRcn > 1.05), then the system or member
ACI 318, as well as other codes, control predicted deflecstrength should be restored to its original strength using
tions by either limiting calculated deflections to some
the original building code. Otherwise, strengthening is not
specified allowable limits, or specifying a minimum spanrequired (refer to Fig. A.5b). For both conditions, the strength
to-thickness ratio. These limits, however, are based on past
reduction factors are obtained from ACI 562 Chapter 5.
experience with loads (for example, normalweight concrete
The LDP is often confronted with deteriorated or
with loads less than approximately 100 lb/ft2 [488 kg/m2]
damaged structures designed using the working or allowlive load for two-way slabs), boundary conditions, and spans,
able stress method that was the only available method for
among other factors. Structures with aggressive construction
designing structures prior to ACI 318-63. In 1963, the
schedules resulting in heavier-than-planned construction
strength design method was introduced into ACI 318 next
loads, premature form removal, and accelerated shoring and
to the working stress method. In 1971, ACI 318 dropped
reshoring may result in members or structures with excessive
the working stress method and retained the strength
deflections or having vibration issues that should be assessed
design method.
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Uc – Demand using nominal loads of the current building code and factored load combinations of ASCE/SEI 7 for strength
design provisions
Uo* – Demand using nominal loads of the original building code and factored load combinations of ASCE/SEI 7 for strength
design provisions
Rcn – Current in-place nominal capacity of structural member, system, or connection including the effects of damage, deterioration of concrete and reinforcement, and faulty construction
φ – Strength reduction factor per ACI 562 Section 5.3 or 5.4
Fig. A.5b—Alternate method for evaluating reinforced concrete structure.
A.7—Additions
Structures without structural damage, deterioration, or
faulty construction and receive additions, undergo alterations, or there are changes in occupancy, need to satisfy the
provision of Sections A.7, A.8, or A.9 of ACI 562.
In a case where a structure is receiving additions such as
new columns, beams, or a new expansion to the existing
structure, the LDP should evaluate the gravity load
demands of the existing gravity-load-resisting systems
and members with the additions based on the current
building code and the original building code. If the gravity
load demands based on the current building code, Uc, are
greater than 5 percent than the demands based on the original building code, Uo, then the design-basis criteria is the
current building code with ACI 562 for the assessment and
design of existing systems and members and ACI 318 for
the design of new members.
If an addition results in a decrease in the gravity-loadresisting systems and members’ capacity, Rn, using ACI
562, then the LDP needs to ensure that the in-place capacity
exceeds the current building code demand, Uc.
If the vertically self-supporting addition is dependent on
the existing structure for lateral-force resistance, then the
design-basis code for the existing lateral force-resisting
system with the new addition is the current building code
supplemented by ASCE/SEI 41 for seismic assessment
and design.
ACI 562 provides an exception to the aforementioned
guidance to new additions by allowing the LDP to use
the original building code for the assessment and designbasis criteria of the lateral-force-resisting system if the
calculated demand-capacity ratio of the existing structure based on the original building code increased by 10
percent is at least equal to the demand-capacity ratio of
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tions exceeding the maximum allowed by code, however,
may be acceptable to the owner or user, provided the member
or structure performance is not adversely affected.
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APPENDIX A
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Table A.5—Assessment conditions for reinforced concrete buildings
ACI 562 Section
Demand/capacity
Design-basis code
Potentially dangerous condition, Section A.3
Gravity and wind load A.3
Current building code and ASCE/SEI 7 for factored load combinations
Uc/fRcn > 1.5
Seismic A.3
ASCE/SEI 41 and ACI 562
Substantial structural damage, Section A.4
Gravity load
∑ Rn
≥ 1.25
∑ Rcn
A.4.1b
and
and
∑ Uc
≥ 1.33
φo Rcn
Current building code demand supplemented by requirements of ACI 562
A.4.1c
∑ Rn
≥ 1.5
∑ Rcn
Lateral-force-resisting system
A.4.1a
Seismic
Section A.5.1
Section A.5.2C(a)
Section A.5.2C(b)
Current building code demand supplemented by ASCE/SEI 41
ASCE/SEI 41—Earthquake Hazard Level BSE-1E with the Basic Performance
Objective of “Life Safety” for Risk Category I, II, or III (ASCE/SEI 7) and of
“Immediate Occupancy” for Risk Category IV
Deterioration, faulty construction, or damage less than substantial
Original building code,
Uo/foRcn > 1.0
new members use current building code
Alternate assessment criteria for deterioration, faulty construction, or damage less than substantial
Uc > 1.05Uo* and
Current building code
Uc/fRcn > 1.1
*
Uc > 1.05Uo and
Strengthening not required
Uc/fRcn < 1.1
Uc < 1.05Uo* and
Original building code
Uo*/fRcn > 1.05
*
Uc < 1.05Uo and
Strengthening not required
Uo*/fRcn < 1.05
—
Original building code only used allowable stress design and design service loads
Us/Ra > 1.0
Original building code
Strengthening not required
Us/Ra < 1.0
Section A.5.3
Condition
Design-basis code
For existing structure and addition:
Uc > 1.05Uo
Current building code w/
Decrease in gravity-load-resisting systems and member capacity due to
addition
Addition depends on existing building for lateral-force resistance
Exception:
Uc/Rn (w/addition) ≤ 1.1Uo/Rn (w/o addition)
the existing structure, including the addition based on the
current building code; refer to Table A.7.
A.8—Alterations
In case a structure undergoes alterations such as creating
an opening in an elevated slab, removing a beam, or change
in the load path, the LDP should evaluate the gravity load
demands of the existing gravity-load-resisting systems and
members with the alterations based on the current building
code and the original building code. If the gravity load
Existing members: ACI 562
New members: ACI 318
Rn (existing structure + addition) per ACI 562 > Uc per current building code
Current building code supplemented by ASCE/SEI 41
Original building code for any lateral-force-resisting member
demands based on the current building code are greater than
5 percent than the demands based on the original building
code, then the design-basis criteria is the current building
code with ACI 562 for the design of existing systems and
members and ACI 318 for the design of new members.
Increasing member sizes or creating openings in a slab
may increase or decrease the design lateral loads on a
structure and may result in a structural irregularity, as
defined in ASCE/SEI 7.
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Table A.7—Design-basis code for different addition requirements to existing structures
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Removing deteriorated concrete
Column after repair
Framing in place ready for repair material
81
APPENDIX A
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Table A.8—Design-basis code for different alteration requirements to existing structures
Condition
Design-basis code
For existing structure and alteration:
Uc > 1.05 Uo
Current building code w/
Decrease in gravity-load-resisting systems and members capacity due to
alteration
Alteration results in structural irregularity and increase in lateral loads or
decreases lateral capacity
Exception:
Uc/Rn (w/alteration) ≤ 1.1Uo/Rn (w/o alteration)
ACI 562 provides an exception to the aforementioned
guidance of structural alterations by allowing the LDP to use
the original building code for the assessment and designbasis criteria of the lateral-force-resisting system if the
calculated demand-capacity ratio of the existing structure
based on the original building code increased by 10 percent
is at least equal to the demand-capacity ratio of the existing
structure, including the alterations based on the current
building code; refer to Table A.8.
A.9—Changes in occupancy
When a change in use or occupancy is proposed by
the owner, the LDP should review the demand resulting
Existing members: ACI 562
New members: ACI 318
Rn (existing structure + alteration) per ACI 562 > Uc per current building
code
Current building code and ASCE/SEI 41
Original building code for any lateral-force-resisting member
from the new use or occupancy using the appropriate
current building code mandated loads compared to
the demands determined using the original building
code demands.
The change in use or occupancy is acceptable if the structure is evaluated and shown to comply with current building
code or rehabilitated. The rehabilitation of the existing
structure should be performed in accordance with ACI 562
and the current building code. ACI 318 should be used for
the design and connection of new members to the existing
structure. Seismic design criteria, when required, should be
obtained from ASCE/SEI 41.
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University of Toronto User.
Overview
any statement within this document in the format of “Section
After the publication of ACI 562, the next logical step was
x.x” refers to a section within ACI 563, “Specification for
to publish a standard that covers the specification of repair
Repair of Concrete in Buildings,” directing the reader where
of existing concrete structures. Hence, the publication of
the relevant information can be found.
ACI 563, “Specification for Repair of Concrete in Buildings.” The architect/engineer (A/E) should cite ACI 563 in
General
any construction repair and rehabilitation project involving
Complete specifications and good quality workmanship
structural concrete in the project specifications. It is worth
are fundamental to the success of construction and duramentioning that ACI 318 and ACI 562 use licensed design
bility of concrete repair work. Owners need assurance from
professional (LDP) when referring to the person in charge
A/Es and contractors that the repaired concrete structures
of the design new structures or repair and strengthening of
will achieve the intended design life expectancy as desired
existing structures, whereas ACI 301 and ACI 563 use the
by owners. Therefore, to achieve lasting and durable repair
term architect/engineer (A/E).
work of structures beyond the design phase, sound, clear,
Each technical section of ACI 563 is written in the threeand applicable project specification is required that allows
part section format of the Construction Specifications Instifor an effective quality management program to be impletute, as modified by ACI (Suprenant 2019):
mented. This can be achieved at two levels: the design level,
1. Part 1 covers general administrative requirements such as
were the A/E produces specifications that are specific and
definitions, submittals, referenced standards, and acceptance
address the actual conditions present in the project and
criteria
provides requirements for the contractor; and at the execu2. Part 2 addresses products and materials
tion level, where the contractor ensures that the personnel
3. Part 3 deals with execution
performing the work are well trained, adept, and are familiar
ACI 563 is divided into 10 sections, Notes to Specifier,
with the type of work to be performed.
Mandatory Requirements Checklist, and Optional Satisfied
The A/E should include only pertinent provisions to the
Requirements Checklist. The first section covers general
project in the project specifications and not reference the
construction requirements for all repair work, including
entire ACI 563 document and have the contractor search for
terminology (Section 1.3) and referenced standards (Section
the relevant sections in the document; otherwise, it may lead
1.4). The second section includes shoring and bracing
to confusion, frustration, and possible conflicts.
of the structure or members to be repaired, and addresses
It is in the best interest of the contractor to have the workers
sequencing of repair work as the structure is unloaded and
properly trained in the execution of the Work to be applied.
reloaded. The third section deals with concrete removal and
Many material producers/suppliers provide training on the
preparation of the concrete substrate for repair and defines
application of their material. ICRI has developed certificates
common equipment and methods. The fourth section covers
to ensure that workers are familiar and able to perform repair
formwork performance criteria and construction, shoring,
work satisfactorily.
and backshoring. Section 5 focuses on the different types
of reinforcement and reinforcement supports. Section
Section 1—General requirements
6 covers materials and proportioning of concrete, duraThis section addresses general information for repair work
bility of concrete, trial mixtures, and concrete compressive
in existing concrete structures. It states that this specificastrength determination. Section 7 covers placing, finishing,
tion governs if there is conflict with referenced material and
and curing of repair materials; treatment of joints; repair of
testing standards. The contractor, however, is permitted to
surface defects; mockups; embedded items; and finishing
submit alternative requirements to any provision in this
of formed and unformed surfaces. Provisions governing
specification for consideration. The specification claritesting, evaluation, and acceptance of repair materials as
fies language how to interpret language when “and,” “or,”
well as acceptance of the repair work are included. Section 8
“may,” or “will” are used. For example, when two or more
includes proprietary cementitious and polymer repair mateitems are connected by “and,” then all conditions, requirerials. Sections 9 and 10 incorporate by reference two other
ments, events, or connected items apply, whereas connected
specifications—ACI 503.7, “Specification for Crack Repair
items, conditions, requirements, or events connected by “or”
by Epoxy Injection,” and ACI 506.2, “Specification for
only apply to one item. “May” or “will” are for information
Shotcrete,” respectively. To help the specifier, Mandatory
purposes to the contractor only (Section 1.2).
and an Optional requirements checklists are provided at the
The specification further states that the user should interend of the specification standard.
pret the provisions with the plain meaning of the words
In this chapter, where appropriate, the text will reference
and terms used. For example, the phrase “as indicated in
specific sections within the specification to help the reader
the contract documents” (Section 1.2.1.8) means that the
better navigate the specification and become familiar and
specifier included the provision requirements in the contract
get better understanding of the document content. Therefore,
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documents. The phrase “unless otherwise specified” (Section
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Appendix B—Repair Guide
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Example B.1a—Language used in
the specification as a direction to the
contractor
EXAMPLES
1) Field bending of reinforcing bars partially
embedded in concrete shall not be permitted, except
as indicated in contract documents
2) Owner will furnish, as indicated in the contract
documents, all required rights to use the lands upon
which the work occurs.
3) Unless otherwise specified in the contract documents, construct formwork so concrete surfaces
conform to the tolerance limits of ACI 117.
4) Concrete for slab-on-ground shall be 4000 psi
unless otherwise specified
5) If specified, admixtures shall be subjected to
the following limitations: …
6) Foundation shall consist of portland cement
concrete, and reinforcement if specified on the
plans …
The contractor is not only required to protect the members
or structure itself but must also protect adjacent properties
and public, especially if exterior repair work is involved
(Fig. B.1b and B.1c), as well as the work itself. For example,
protecting concrete work while curing from mechanical
disturbances or environmental conditions if exposed to high
temperature variations, sunlight, wind, and other conditions.
University of Toronto User.
Preinstallation conference
After the signing of the construction contract and before
the commencement of construction, it is important that
all parties meet, discuss the project, and address all issues
related to the project. A successful project must have proper,
clear, and transparent communication between all parties.
Therefore, having a preinstallation conference, also termed
“preconstruction meeting” or “project start-up meeting,” is
essential to set the project on a path that promises a wellorganized and successful project and provides a platform
for effective communication between all involved parties.
The preinstallation conference or preconstruction meeting
will set expectations and will help to ensure that issues will
be addressed on time, minimizing downtime and resolving
disagreements that may arise during construction through
the established lines of communication, saving owner both
time and money.
1.2.1.9) means that the specifier may have included an alterIt is the A/E’s responsibility to prepare a comprehennative to the default requirement in the contract documents.
sive agenda to the project and distribute to all involved
The phrase “if specified” (Section 1.2.1.10) means that the
parties designated representatives ahead of time (Section
specifier may have included a requirement in the contract
1.6). At the meeting, the A/E should facilitate the discusdocuments for which there is no default in the specification
sion to ensure that all parties involved fully understand the
(Example B.1a).
goals and objectives for the repair project and the expected
requirements to achieve them. It will also serve as setting the
General procedures
ground rules for the project for defining the lines of commuThis section addresses construction loads, protection, and
nication, the coordination of inspections, the handling of
completed repair work. It is imperative for the contractor to
nonconformances, and the chain of command.
protect the structure and its content during the work. The
At the preinstallation conference, several items are usually
contractor is directed not to overload the structure by propdiscussed at length and ground rules are set for the duration
erly distributing repair materials stored in the vicinity of
of the project, such as the submittal schedule and turnaround
construction work. Equipment and other construction loads
of the shop drawings and request of information (RFI)
should be strategically located such that its effects do not
responses’ timeframe. For example, what is the process/
exceed the capacity of the member, thus jeopardizing the
procedure when a shop drawing or submittal is rejected
capacity of the supporting member or, in extreme cases, the
or declined? This will help move the project forward and
capacity of the structure itself (Fig. B.1a). Sometimes, due
realize a successful project while minimizing surprises.
to construction sequencing or extent of repair, the stability
From the contractor’s perspective, the meeting creates
of a member or capacity is compromised. The contractor
an opportunity for the contractor to discuss special project
should consult the A/E to alleviate this unsafe condition
features and requirements; to understand the design intent of
by designing for temporary shoring, bracing, or both
the repair work; to have specific details or repair sequencing
(Section 1.5.2).
clarified by the A/E; and to propose alternate details, repair
The material delivered to the job site should be in conformaterials, or both, to be used on the project to reduce or
mance with the specifications. Often, the contractor will
minimize future conflicts.
propose alternates to the specified materials and, if approved
Although on small projects the issues can be handled as the
by the A/E, then the alternate materials can be used. It is
project progresses, the preconstruction meeting, however, is
therefore required that any material delivered to the job site
a chance to handle these important issues in a more formal,
should be clearly marked with legible and intact labels with
less haphazard, and less painful way.
manufacturers’ name, brand name, lot number, and identiIn summary, the preinstallation conference is used to
fying contents of containers to be easily identified by the
establish the line of communication between all involved
inspector and compared to the specified material in the
parties, to define items to be inspected, to outline how to
contract documents or approved alternate.
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handle nonconformances, and to determine the chain of
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84
85
Fig. B.1a—Construction load during change of occupancy work of Frederick Douglass Building,
University of Rochester, Rochester, NY (photo courtesy of University photo/J. Adam Fenster).
command in the project as a whole. It ensures that the project
proceeds efficiently. Refer to Example B.1b for a preinstallation meeting agenda sample (ACI 132R and ICRI 110).
Fig. B.1c—Sidewalk debris containment and overhead
protection for workers and pedestrians underneath (photo
courtesy of Superior Scaffold Services).
d. What are the expectations from the QA/QC programs?
The first step in the QA/QC program is to develop an
organizational chart and assign the responsibilities to individuals. This will provide a roadmap of the process for easy
reference. QA and QC are sometimes used interchangeably
but they have different practices and meanings (refer to
Example B.1c).
Quality assurance, quality control, testing, and
inspection
The preinstallation conference is the first step in the
quality assurance and quality control (QA/QC) program. At
the preinstallation conference, matters and issues related to
QA/QC are raised and addressed (Section 1.8):
Quality assurance (QA)
a. Who is responsible for the QA/QC program?
ISO 9000 (2005a) defines QA as, “part of quality manageb. How will the parties involved solve the problems that
ment focused on providing confidence that quality requirearise? Who must be notified and when? What is the
ments will be fulfilled.” In other words, it is the process in
procedure?
which a construction company provides the best possible
c. How often should the QA/QC team meet to discuss project
product to an owner. QA is planned and developed prior to
status and quality issues?
@Seismicisolation
any construction activity and is performed during the dura@Seismicisolation
University of Toronto User.
Fig. B.1b—Sidewalk overhead pedestrian and traffic protection (photo courtesy of CityRealty by CityRealty Staff).
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APPENDIX B
Example B.1b—Preinstallation meeting agenda example
University of Toronto User.
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GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
86
87
Example B.1c—Differences between QA and QC programs (Sam-solutions.com)
Quality assurance and quality control comparison chart
QA
QC
A managing tool
A corrective tool
Process-oriented
Product-oriented
Proactive strategy
Reactive strategy
Prevention of defects
Detection of defects
Everyone’s responsibility
Testing team’s responsibility
Performed in parallel with a project
tion of a construction project to ensure that the project meets
the quality standards. It provides the owner with a sense
of comfort that all the agreed-upon methods, approaches,
and techniques will be implemented as agreed upon and
will possibly be modified during the course of a project,
as deemed necessary, to prevent mistakes, omissions, or
substandard practices.
To achieve this goal, the QA program must rely on welldeveloped and complete project specifications and contract
documents specifying what should be tested and the
frequency of tests, which activities require certified workers,
and which tests require certified technicians. The QA process
has both advantages and disadvantages.
Disadvantages of quality assurance
a. Time-consuming; it adds more time to a project schedule
for periodical meetings and implementing the process. It
also requires time to train the workers.
b. High cost; to train and implement the process will add to
the cost of the project.
In conclusion, the value of implementing a QA program
outweighs the inconveniences and cost of implementing one.
the authority, given as a signed letter by the owner, to stop
work if construction is substandard and does not meet the
minimum standard requirements and installed material deviated from the specifications, or did not pass the specified test
standards.
In general, for a project without a QC program, the
final inspection that contractors and owners usually
do, also termed as “walk-through,” is at the end of a
project. The concern with such an approach is that the
contractor/subcontractor has to fix any shortcoming
when encountered. This will result in expensive repairs
and a delay in project delivery that generally supersedes
the additional cost had the contractor implemented a
robust QC program. A QC program has both advantages
and disadvantages.
Advantages of quality control
a. Develops quality-conscious construction workers, which
helps achieve a better product and a satisfied owner.
b. Minimizes owner complaints and can result in a repeat
client.
c. Reduction in construction cost, as the substandard
construction quality and consequently rework is reduced.
d. Improvement in performance; workers are familiar with
the work and avoid the common errors. This will result in
reduced inspection costs.
e. Updates and changes can be introduced to projects and
plans without much difficulty or effort.
f. Improves the relationship between employer and
employees.
Disadvantages of quality control
a. Increase in project cost due to:
1. Training workers to better perform tasks related to
the project
2. More labor hours/employees are needed to maintain a
QC program resulting in added time to the process
Quality control (QC)
b. Hiring inspectors to oversee the process and perform the
ISO 9000 defines quality control as “A part of quality
required inspections.
management focused on fulfilling quality requirements.”
c. It does not encourage all workers to be responsible for
While QA concentrates on the process of construction,
quality.
QC deals mainly with the end or finished product. It ensures
In conclusion, a QC program is a reactive approach to
that the defects or shortcomings at the construction phase
ensure that a constructed project meets the owner’s expecare detected early on so that corrective actions are taken.
tations and conforms to the defined standards. Failure to
It helps ensure that the owner receives a structure that is
detect defective work or material will not prevent rejection
usable and functional. Therefore, it is the QC’s manager
if a defect is discovered later and does not obligate the A/E
responsibility to ensure that the QC plan is implemented
for final acceptance. QC is considered as the final checkpoint
and followed closely. The QC manager should @Seismicisolation
also
have
before the delivery.
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University of Toronto User.
Advantages of quality assurance
The benefits of quality assurance are significant:
a. Prevents substandard construction as well as errors in
construction at early stages; this will save time, money,
and effort on reworking faulty workmanship and meeting
owner’s expectations.
b. Workers understand the importance of quality work, or
lack thereof and the consequences associated with it.
c. Helps create teamwork within an organization rather than
supervision. It is a path for securing a smooth and tranquil
end result of a project.
d. Builds trust between contractor and owner, providing the
contractor an edge over others in a competitive market.
Performed after the final product is ready
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APPENDIX B
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Testing and inspection
To ensure that QA and QC programs are properly implemented and performing as planned, testing and inspection of material and of the work must be performed as
work progresses by trained and often certified personnel
(ACI 563 Mandatory Requirements Checklist) (Example
B.1d). It is up to the contractor to ensure and verified by
the owner’s testing agency that the certificate of the person
performing the work is valid and conforms to the type of
test to be performed.
The contractor must submit test data, test results, and
documentation on proposed repair material to be used per
construction contract documents for review and approval by
the A/E. These submittals are properly logged, documented,
and must remain accessible for the duration of the project.
The contractor is permitted to propose alternate repair
materials from what was specified by the A/E. The contractor
must provide reasons for the substitution, demonstrate
compliance of substituted repair materials with the specified
performance criteria, and what impact the alternate repair
materials may have on the project schedule and overall cost
for approval by the A/E.
As work progresses, repair materials and operations are
tested and inspected to verify that work is being performed
in accordance with approved procedures, manufacturer’s
instructions, specific instructions from A/E if given, or reference standards cited in contract documents (Section 1.8.1).
Accordingly, the contractor must coordinate and schedule
with the owner’s testing agency and provide them with
minimum 24 hours advance notice before performing tests
on specific work to allow ample time for the testing agency
for review of project requirements and assigning the appropriate personnel to perform inspection and testing (Section
1.8.2.2(b)). On the day of the testing, the contractor must
arrange for safe access to the location where test is to be
performed, assist in obtaining and handling samples at the
project site, and provide easy access and sources to water
and electrical power.
ACI 563 Mandatory Checklist table lists minimum tests
that must be performed. The A/E may specify additional
tests, if needed, to ensure proper installation of the repair
material and work (Examples B.1e and B.1f).
The owner’s testing agency will report test and inspection results of the work to owner, A/E, contractor, and repair
material supplier within 7 days after tests and inspections
have been performed (Section 1.8.3.2(c)). After reviewing
test results, the owner may choose to verify the test results
of proposed concrete mixture, test samples of production
materials at plants or stockpiles for compliance with contract
documents, collect samples of fresh concrete and test as
Example B.1d—Mandatory Requirements Checklist
Section/Part/Article
1.8.2.1
Example B.1e—Required tests to be performed per ACI 563
Section/Part/Article
1.8.3.2(a)
1.8.3.3(c)
1.8.3.3(d)
1.8.3.3(e)
1.8.3.3(g)
1.8.3.3(h)
1.8.3.3(i)
1.8.3.4(a)
1.8.3.4(b)
1.8.3.4(c)
1.8.3.4(d)
1.8.4.1
1.8.4.2
1.8.7.1(a)
1.8.7.1(b)
1.8.7.1(c)
Tests to be performed by owner’s testing agency
Sample and test fresh and hardened repair materials
Collect samples of production materials at plants or stockpiles
Obtain samples of fresh concrete
Concrete strength test
Testing proprietary materials
Examine completed repairs for cracking and sound repairs
Direct-tension bond testing of prepared surfaces and completed repairs
Inspect batching, mixing, and delivery operations
Inspect forms, foundation preparation, surface preparation, reinforcement placement, and repair material placing, finishing,
and curing operations
Sample repair material at point of placement and other locations as directed by A/E
Review manufacturer’s report for each shipment of repair materials
Hardened concrete strength
Nondestructive testing
Concrete air-content
Concrete slump
Concrete temperature
@Seismicisolation
@Seismicisolation
University of Toronto User.
Notes to Specifier
Indicate the required certifications and experience for every repair material, when deemed necessary and possible alternate
credentials and experience. Examples of possible field personnel include, but are not limited to:
a. ACI Concrete Field Testing Technician - Grade I
b. ACI Adhesive Anchor Installation Inspector
c. ACI Concrete Construction Special Inspector
d. ACI Masonry Field Testing Technician
e. CSA-Based Concrete Construction Special Inspector (Canada Only)
f. CSA-Based Concrete Field Testing Technician - Grade I (Canada Only)
g. ICRI Concrete Surface Repair Technician—Grade 1
h. ICRI Concrete Slab Moisture Testing Technician—Grade 1
i. NACE Coatings Inspector Program, Levels 1 through 3
j. SSPC Concrete Coating Inspector
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88
indicated in contract documents, or conduct concrete strength
test on hardened concrete at no cost to the contractor unless
test results by contractor’s testing agency were flawed, did
not meet the acceptance criteria specified in the construction
contract documents, or both.
If test results are found flawed or work is not in compliance
with the contract documents, the owner’s testing agency and
its representatives do not have the authority to revoke, alter,
relax, enlarge, or release requirements of contract documents, nor to accept or reject any portion of work (Section
1.8.3.2(b)).
If tested concrete compressive strength did not achieve the
specified strength in the contract documents, the contractor is
required to verify the actual concrete strength by extracting
cores from the work area and test them no earlier than 48
hours after drilling or last wetting and no later than 7 days
after the cores were drilled from the structure (Section
1.8.4.3(a)). At least three representative cores should be
extracted from each area of in-place concrete that is considered potentially deficient. The A/E determines the location
of cores to limit damage to the strength of the structure.
If, before testing, cores show evidence of having been
89
damaged after or during removal from the structure, replacement cores should be taken (Section 1.8.4.3(b)). The holes of
the extracted cores should be filled with low-slump concrete
or mortar of strength equal to or greater than the original
concrete by the contractor and provide moist curing for at
least 3 days, unless otherwise specified (Section 1.8.4.3(c)).
The acceptance criteria for the tested cores is provided
in Section 1.8.6 and detailed information is presented in
Section 6.
Example B.1g elucidates the method for evaluating the
concrete cores. ACI 214R and ACI 214.4R provide a method
for proper evaluation. Every average of three consecutive
strength tests equals or exceeds fc′. Strength of concrete is
acceptable if no strength test result falls below fc′ by more
than 500 psi (3.5 MPa) when fc′ is 5000 psi (35 MPa) or
less, or by more than 0.10 fc′ when fc′ is more than 5000 psi
(35 MPa), and average compressive strength of the cores is
at least 85 percent of fc′, and no single core is less than 75
percent of the specified compressive strength fc′.
Nondestructive in-place tests are not acceptable as the
sole basis for accepting or rejecting concrete. The use of
the rebound hammer or the pulse-velocity method may be
Example B.1f—Required inspection to be performed per ACI 563
Section/Part/Article
1.8.2.2(f)
1.8.2.2(g)
1.8.2.2(h)
1.8.2.2(i)
1.8.2.2(j)
1.8.3.2(a)
1.8.3.4(a)
1.8.3.4(b)
1.8.3.4(e)
Inspection to be performed by owner
Surface preparation
Reinforcement
Work in progress to verify that work is being performed in accordance with approved procedures
Completed work
Bracing and shoring
Fresh and hardened repair materials
Additional testing and inspection services
Batching, mixing, and delivery operations
Forms, foundation preparation, surface preparation, reinforcement, embedded items, reinforcement placement, and repair
material placing, finishing, and curing operations
Testing or inspection operations as required by A/E
Acceptable test results
Test No.
1
2
3
4
5
Individual cylinders
No. 1, psi (MPa)
No. 2, psi (MPa)
4110 (28.3)
4260 (29.4)
3840 (26.5)
4080 (28.1)
4420 (30.5)
4450 (30.7)
3670 (25.3)
3820 (26.3)
4620 (31.9)
4570 (31.5)
Average test, psi (MPa)
4185 (28.9)
3960 (27.3)
4435 (30.6)
3745 (25.8)
4595 (31.7)
Average of three consecutive tests,
psi (MPa)
—
—
4193 (28.9)
4047 (27.9)
4258 (29.4)
Average test, psi (MPa)
3585 (24.7)
4015 (27.7)
4040 (27.9)
4780 (33)
3250‡ (22.4)
Average of three consecutive tests*,
psi (MPa)
—
—
3880† (26.8)
4278 (29.5)
4023 (27.7)
Low test results, not acceptable
Test No.
1
2
3
4
5
Individual cylinders
No. 1, psi (MPa)
No. 2, psi (MPa)
3620 (25)
3550 (24.5)
3970 (27.4)
4060 (28)
4080 (28.1)
4000 (27.6)
4860 (33.5)
4700 (32.4)
3390 (23.4)
3110 (21.4)
All cores are above 75 percent of the specified compressive strength greater than 4000 psi (28 MPa) (Section 1.8.6.2).
*
Average concrete compressive strength of three consecutive cores is low, but above 85 percent of fc′ (Section 1.8.6.2).
†
@Seismicisolation
One test result is more than 500 psi (3.5 MPa) below the specified concrete
compressive strength (Section 1.8.6.1(b)).
@Seismicisolation
‡
University of Toronto User.
Example B.1g—Example of core test results
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APPENDIX B
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Example B.1h—Decision for approval of repair work
ACI 563 Section No.
1.9.1.1
1.9.1.2
Condition
Concrete repair work fails to meet one or more requirements of contract documents but if
repaired, work is in compliance
Concrete repair work to meet one or more project requirements and cannot be brought into
compliance
permitted by A/E to evaluate uniformity of in-place concrete or to
select areas to be cored or tested by other in-place test methods.
For additional information, refer to Chapter 6 of this guide.
Repair work approval is contingent that completed work
is in conformance with the specification and contract documents. ACI 563 Section 1.9 provides criteria for approval of
repair work. Example B.1h summarizes those requirements:
In case concrete repair work is rejected, the contractor
must submit a proposed method, repair material, and modification needed to correct work shortcomings and to satisfy
the requirements in the contract documents.
Terminology related to concrete repair work is provided
in Section 1.3
Decision
Accepted
Rejected
University of Toronto User.
as required by ACI 563 Section 2.1.2, signed and sealed
calculations by the specialty engineer (Section 2.2.2.2), and
shoring layout shop drawings to be reviewed by the A/E. The
calculations may specify the construction loads per ASCE
37 if the repair work area is unoccupied and must specify
construction loads per ASCE/SEI 7 if the repair work area
is occupied. Conservatively, ASCE/SEI 7 may, however, be
used for all load conditions irrespective of occupancy status.
The specialty engineer must consider the load effects on the
structure and parts thereof occurring throughout the duration
of the repair work and establish that all loadings supported
by the shoring and bracing system are safe.
The shoring layout shop drawings must show the arrangement of equipment for shoring, inclusive of installation
Section 2—Shoring and bracing
details, maintenance requirements, and permitted changes.
ACI 347R defines shoring as the vertical or inclined
The contractor must submit sequencing requirements of
support member or braced frame designed to carry the
shoring installation and removal, concrete removals, surface
weight of the formwork, concrete, and construction loads,
preparation, repair installation, curing, and minimum
and defines bracing as a structural member used to provide
concrete strength at removal for A/E’s approval.
lateral support for another member, generally for the purpose
Per ACI 563 Section 2.2, the specialty engineer can select
of ensuring stability or resisting lateral loads.
the shoring system that provides economy, safety, and reliShoring and bracing provide support to beams and floors
ability to a project. The shoring system can be manufacin a building to prevent collapse if a beam, column, or wall is
tured pre-engineered components where manufacturers of
removed, or if the structure’s vertical framing system, lateral
shoring equipment develop descriptive literature and strucframing system, or both, have been compromised. Theretural performance data that helps the specialty engineer in
fore, this requires careful attention and planning by the A/E
the design of the shoring system (Example B.2a). It also
by clearly identifying the shortcomings in the existing strucprovides installation procedures and safety data that helps
ture, what modifications will occur, and which members will
the contractor in the installation and removal of the shoring
be removed or altered. ACI 563 Section 2.1.1.1 places the
system per the manufacturer’s requirement (Section 2.2.2.3).
responsibility of design, installation, stability, and removal of
The specialty engineer may select to design the shoring
shoring and bracing on the contractor’s engineer or a specialty
system that are not a premanufactured system.
engineer hired by the contractor. Therefore, it is prudent that
Irrespective of what system the specialty engineer selects,
the specialty engineer interacts with the A/E to understand the
the calculations must be prepared following the state, local,
structural behavior of the system, what will be removed and
and federal codes; ordinances; and regulations pertaining to
when, and what will be added to the existing structure.
shoring and bracing. The specialty engineer must consider
The specialty engineer must consider the deficiencies
when designing and preparing the shoring shop drawings
within the structure and unsafe structural conditions, if
design and layout following safety requirements by the
present, including the effect of loads and deflection requireSafety and Health Regulations for Construction, Standard
ments during repair, and must consider the effects of compat-29 CFR (2020).
ibility of deformations on the shoring system and supported
The installation and removal must be in accordance with
and supporting structural members while maintaining stability
the sequencing shown in the shop drawings and reviewed by
of the structure and structural members when designing the
the A/E. This information must be complete, accurate, and
shoring and bracing systems. Must also consider redistribuclearly stated. As part of the QA/QC program, the contractor
tion of forces in the structure as a result of member removal or
must submit documentation of inspections and certifications
addition and deformation of a member. A member may require
required from specialty engineer as specified by 2.1.2.1(d).
jacking during repair to restore its levelness or to remove a
The specialty engineer must inspect the shoring and
supporting member. The specialty engineer must account for
temporary bracing before the start of the repair/strengththis jacking load and its effect on the existing concrete strucening work and at appropriate intervals throughout the
ture and shoring (Section 2.1.1.2(a)).
process, and certify that they, as installed, meet the intent
As part of the QA program, the specialty engineer must
of the design. During construction and per ACI 563 Section
take into consideration the safety of the structure and submit,
@Seismicisolation
2.3, the contractor must survey the shoring elevation and
@Seismicisolation
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90
91
Example B.2a
Minimum information furnished by the preengineered manufacturer shoring manufacturer
may provide the following list:
a. Provide education and training related to the
product
b. Implied warrantees to the end user (contractor)
when equipment is selected, installed, and used
properly by the contractor’s competent person:
i. Application guide
ii. Tabulated data (structural limitations)
iii. Assembly instructions
iv. Installation sequence
v. Identify safety issues
vi. Maintenance and repair
Fig. B.2a—Shoring of beams at Norristown, PA, Main Street
parking garage in Montgomery County (photo courtesy of
Superior Scaffolding Services).
stability to ensure that the shores did not move or displace
due to construction activities. If such movement or displacement occurs, the contractor must stop the work in the area
and adjust the shores/bracing and inspect shoring and
temporary bracing before the repair process commences
again. The contractor can remove erected shoring or bracing
when repair or strengthening work is complete, added new
materials have attained the specified strength, and existing
members work together to support the applied loads.
University of Toronto User.
Section 3—Concrete removal and preparation for
repair
This chapter covers the partial removal of concrete for
repair and preparation of substrate to receive repair material.
Fig. B.2b—Bracing of columns at Harvard Towers Parking
Proper surface preparation of existing concrete is essential
Garage, Cambridge, MA (photo courtesy of Simpson
for achieving a successful project (ACI 515.3R). Therefore,
Gumpertz & Heger).
before any concrete removal work begins, it is recommended
that the A/E, contractor, and owner hold a preconstruction
coating with limited thickness (thin), a smoother CSP of 2
meeting; refer to Section 1, Preinstallation conference, of
to 4 is appropriate. When using thicker self-leveling and
this Appendix. In the preinstallation conference, one of the
polymer overlays, the appropriate CSP will range from 4 to
issues that the parties involved will address is the means
6 (Fig. B.3b).
proposed to achieve the recommended concrete surface
There are several methods that can be used for surface
profile (CSP); the equipment the contractor is proposing to
preparation. The main goal, however, is to minimize damage
use on the job to achieve the CSP; and the methods planned
to the existing structure. An effective method for concrete
to remove the debris, laitance, and bond-inhibiting material
removal, however, may not be effective or appropriate for
to achieve the suggested bond between the existing substrate
a specific surface preparation requirement. For example,
and the new overlay as directed by the A/E in the contract
some concrete removal methods leave the concrete surface
documents. In the meeting, the method and frequency of
too rough or irregular for the intended repair material such
testing the bond strength between the existing substrate and
as membrane coatings. In these cases, removal methods
the new overlay should also be discussed.
specifically intended for the final surface preparation may
ICRI developed a concrete surface profile (CSP) (310.2R)
be required. Therefore, in the preinstallation conference/
system to measure the acquired roughness of the repaired
meeting, the contractor should present the means and
concrete surface. The CSPs are rated from 1 to 10; with 1
methods proposed for concrete removal such that damage to
being the smoothest, nearly flat, and 10 being the roughest,
the structure and bruised surfaces on the concrete substrate is
close to 1/4 in. (6 mm) amplitude (Fig. B.3a). These clasminimized (3.2.1.1). The equipment proposed for use should
sifications are accepted industry criteria to help guide the
be selected based on the area of concrete to be removed,
contractor verify the proper texture achieved for successful
the orientation of the member, its suitability to produce the
bonding of the overlay or coating. Generally, when using
required CSP, and the capacity of the structural member that
a thick overlay, the CSP needs to be higher. When
@Seismicisolation
using a
will support the equipment.
@Seismicisolation
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APPENDIX B
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
ACI 563 Section 3.2.1 does not restrict the contractor
to a specific method for the removal and roughening of
the concrete substrate. ACI 563 lists several methods for
concrete removal, including concrete breakers (Section
3.2.1.3); hydrodemolition (Section 3.2.1.4); and scarifying,
scabbling, and milling/rotomilling (Section 3.2.1.5). Each of
the listed methods has its advantages and shortcomings that
should be considered before implementing such a method.
Concrete breakers vary in size, weight, and type of tip
based on the application and type of structure. It depends on
the level of concrete surface preparation whether it is partial
or full-depth concrete removal. To minimize bruising to the
concrete surface in partial depth removal, the contractor
should use sharp tips on breaker equipment (Section 3.2.1.3).
This will dictate the size and weight of the equipment to
be used. In general, for handheld concrete breakers, the
Fig. B.3a—Concrete surface profiles (image courtesy of Graco Contractor).
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92
University of Toronto User.
Fig. B.3b—Possible surface profiles to be used with various protective systems (image courtesy
of ICRI 310.2R).
@Seismicisolation
@Seismicisolation
Fig. B.3c—Handheld concrete breaker chipping concrete
cover off brick wall.
a. Roughened surface to 1/4 in. (6 mm) amplitude with aggregate undamaged
93
Fig. B.3d—Hydrodemolition of concrete wall (image
courtesy of CVM).
b. Machined roughened surface 1/4 in. (6 mm) amplitude
with aggregates cut through
Fig. B.3e—Roughened concrete surface.
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APPENDIX B
University of Toronto User.
Fig. B.3f—Roughening concrete surface using scarifier (image courtesy of ConcreteHire).
recommended weight should be limited to 15 lb (6.8 kg)
When using the hydrodemolition method, the contractor
equipment (Fig. B.3c).
must address how water is collected or providing runoffs.
Hydrodemolition uses high-pressure water to break and
Scarifiers, also called surface planers or milling machines,
remove concrete (Fig. B.3d). Unsound concrete can be
remove concrete faster and more aggressively than grinders
quickly and efficiently removed creating a highly rough and
(Fig. B.3f). Equipment choices range from small handheld
bondable surface. Concrete that is still sound is left ready
units with 2 to 3 in. (50 to 75 mm) cutting widths to manual
to be bonded with a new surface (Fig. B.3e). Concrete that
push or self-propelled walk-behind machines with working
has become delaminated or contaminated by chloride can
paths of 4 to 16 in. (100 to 400 mm). Cutting depths are
be removed, leaving behind concrete that still has@Seismicisolation
integrity.
adjustable on most machines, with some models achieving
@Seismicisolation
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Fig. B.3h—Concrete surface roughening using rotomilling
(image courtesy of NovaPave).
Fig. B.3g—Scabbler on concrete (image courtesy of
TrelawnySPT).
up to 1/4 in. (6 mm) of material removal in one pass. A
scarifier generally leaves behind a rough finish and may
create ridges in the concrete. On jobs where a smoother
finish is required, the contractor needs to grind the surface
after scarifying.
Scabbling is a technique that involves applying cutting
heads powered by pistons to the substrate at right angles to
remove rigid coatings and deteriorated concrete that is less
than 1/4 in. (6 mm) in thickness (Fig. B.3g). The resulting
surface texture ranges from CSP 7 to CSP 9. Scabbling can
cause microcracks in the concrete that negatively affects the
ability of the substrate to bond with a new surface. Contractors usually combine this method with either abrasive blasting,
high-pressure water blasting, or shotblasting to improve bond.
Both milling and rotomilling can remove the thickest
surfaces for the most involved surface preparation project
(Fig. B.3h). This method results in a coarse, fractured aggregate surface that is usually CSP 9, the highest measure of
texture on the CSP scale. Because this process involves
heavy machinery and a high level of impact, it is only used
in limited cases.
The A/E may specify in the contract documents to the contractor
to produce a mockup of the work so that the owner, contractor,
and A/E can agree on repair procedure, quality of repairs, and
the post-repair aesthetics before starting the repair program. This
step will reduce unrealistic expectations as to the performance
and appearance of the repair areas (Section 3.1.3.2). Mockups
are usually a sample of the work performed on a limited area
of the repair project with the proposed equipment and material.
Field testing mockups of selected removal techniques can help
determine the best procedures to use for the repair. The contractor
will check the validity of removing the debris, laitance, and other
loose material before applying the overlay (Section 3.2.2) and
notify the A/E before beginning concrete removal and surface
Section 4—Formwork
preparation per the contract documents (Section 3.3.2.1).
ACI 563 Chapter 4 covers the design, construction,
The specifications require the contractor to follow the
and treatment of formwork to support, confine, and shape
Contract Document requirements when it comes to the @Seismicisolation
area
repair materials to required dimensions. ACI 347R defines
@Seismicisolation
University of Toronto User.
and depth of concrete removal unless the contractor comes
across additional delamination or fractured or unsound
concrete in adjacent areas, in which case the contractor must
notify the A/E for direction (Section 3.3.2.2). The contractor
should avoid directly striking reinforcement with impact tools
used for concrete removal so as not to damage and jeopardize
the structural integrity of the member (Section 3.3.2.2(a)).
ACI 563 directs the contractor to provide perpendicular
edges and avoid reentrant corners at the perimeter of the repair
area, saw cut to a depth of 0.50 to 0.75 in. (12 to 20 mm), and
must ensure not to cut or damage embedded reinforcement or
other embedded items, obtaining uniformity of depth (Section
3.3.2.2(b)) (Fig. B.3i). Assessments performed onsite are critical at this stage of a repair project. Contractors must often
perform inspections to identify cracked, delaminated, spalled,
disintegrated, and otherwise unsound concrete for removal. If
embedded reinforcing bars or other embedded items are too
close to the surface to provide the perpendicular edge cut, the
contractor must notify the A/E for direction before proceeding
(Section 3.3.2.2(b)).
Methods listed in ACI 563 Section 3.2.2 for cleaning
concrete surface and reinforcement are abrasives and shotblasting, compressed air, high- and ultra-high-pressure
water jetting, low-pressure water cleaning, and vacuum
approaches. All equipment must be operated so not
to damage reinforcing bar, other embedded items, or
adjacent concrete.
It is important for the contractor to ensure that the
completed work satisfies the requirements of the contract
documents by performing the pull-off test to measure the
bond strength between the existing substrate and the new
overlay (Fig. B.3j). This test is usually done at the mockup
level so that adjustments to the work can be done before fullscale construction and after completion of the work (Section
3.1.3) (refer to Example 7-2 of this guide).
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94
Fig. B.3i—Preferred sawcut perimeter with few reentrant
corners.
95
Fig. B.3j—Pull-off test.
University of Toronto User.
a. Shop drawings for engineered-designed formwork signed
formwork as the total system of support for freshly placed
and sealed by a specialty engineer (Section 4.1.2.2(a))
concrete, including the mold or sheathing that contacts the
b. Design calculations for engineered design formwork,
concrete as well as supporting members, hardware, and
shoring, reshoring, and backshoring signed and sealed by
necessary bracing.
specialty engineer (Section 4.1.2.2(b))
The cost of formwork can comprise most of the repair work
c. Manufacturer’s product data sheet for form ties and
cost. This investment requires planning by the A/E when
anchors to existing concrete (Section 4.1.2.2(c))
designing and specifying the structure and by the specialty
d. Product data sheet for expansion joint materials (Section
engineer when designing and constructing the formwork.
4.1.2.2(d))
Hence, it is imperative that the Contactor and specialty engie. Product data sheet for waterstop materials and splices
neer work closely together on the design of formwork and
(Section 4.1.2.2(e))
shoring. The layout, design, and construction of formwork
Section 4.2 specifies products requirements for formwork
should be the responsibility of the specialty engineer. This
material, location of construction, expansion, and contracis fundamental to the achievement of safe and economical
tion joints, and type of form-facing materials required to
formwork design and of the required formed surface quality
produce the required appearance and texture. If the design or
of the concrete. Some of the items that the contract docudesired finish requires special attention, the A/E can specify
ments should consider and clarify are:
in the contract documents the formwork materials and any
a. Who will design the formwork?
other feature necessary to attain the objectives.
b. Who will design shoring and the reshoring system?
Hence, all formwork should be well planned before
c. Who will inspect the specific features of formwork and
construction begins, designed for strength and serviceability,
when will the inspection be performed?
and investigated for system stability and member buckling.
d. What reviews, approvals, or both, will be required for:
The safety of formwork is particularly significant in formi. Formwork drawings, calculations, or both
work construction because it supports concrete during its
ii. Post-tensioning support
plastic state and until concrete becomes structurally selfiii. Reshoring design
supporting. In addition to the adequacy of the formwork,
iv. Formwork preplacement inspection
special structures require consideration of the behavior of
e. Who will give such reviews, approvals, or both?
existing structural members that are used to support formACI 563 Chapter 4 is divided into three sections; General,
work and other construction loads. Although the safety
Products, and Execution. In Section 4.1.2, the specification
of formwork is the responsibility of the contractor, the
directs the Contactor to submit as a minimum the following:
A/E should review the formwork, including drawings and
a. Form-facing material if different from what is specified in
calculations by including this requirement in the contract
4.2.1.1 and 4.1.2.1(a)
documents. Formwork for unusually complicated strucb. Construction and contraction joint layout if different from
tures, structures whose designs were based on a particular
the contract documents (Section 4.1.2.1(b))
method of construction, structures in which the forms impart
c. Testing for formwork removal if methods other than fielda desired architectural finish, certain post-tensioned struccured cylinders is proposed (Section 4.1.2.1(c))
tures, folded plates, thin shells, or long-span roof structure
d. Shoring and backshoring procedure, including drawmust receive special attention by the A/E during the review
ings signed and sealed by a specialty engineer (Section
process.
4.1.2.1(d))
When designing formwork and shoring, the Specialty Engie. Data on formwork release agent or form liner proposed for
neer should follow all state, local, and federal codes, ordiuse with each formed surface (Section 4.1.2.1(e))
nances, and regulations pertaining to forming and shoring
Section 4.1.2 further compels the Contactor to submit the
before submitting the signed and sealed calculations and shop
following information before installing shoring or formwork:
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drawings to A/E for review. The design calculations should
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APPENDIX B
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
show that formwork can withstand the repair material pressures, pressure resulting from placement, and consolidation
procedures to maintain specified tolerances (Section 4.2.2.2).
ACI 563 Section 4.2.2.3 does not allow for use of earth cuts as
forms for vertical and sloping surfaces and limits the deflection of exposed repair material surface to view to 1/240 of
span between structural members of formwork.
Section 4.3, Execution, covers construction and erection
of formwork, removal of formwork, and strength of repaired
material required for formwork removal. The contractor
should, before placement of cementitious repair material,
inspect the formwork to ensure that the erected formwork
is watertight to prevent any leakage of the repair material
that may adversely affect strength and appearance of final
product. Also, the contractor should ensure that there are
no loose or deleterious material within the formwork that
may affect the final appearance and quality of the concrete
surface (Section 4.3.1.3). If the A/E does not call for
specific materials or accessories, the Specialty Engineer can
choose any materials that meet the contract requirements.
The specification, however, specifies a minimum of, Class
B for surfaces exposed to view and Class D for concrete
surfaces that will be permanently concealed (Section 4.3.1.5
and Example B.4a). The A/E should specify the tolerances
so that the contractor will know precisely what is required
and can compensate for deflections and anticipated settlements in formwork during concrete placement. It should
be noted that tolerances normally found in construction
specifications, such as those in ACI 117, are for the as-built
concrete members and not the formwork used to shape these
members. Therefore, formwork should be constructed with
such dimensions so the resulting concrete members are
within the specified dimensional tolerances (Fig. B.4a). The
contractor should set and maintain concrete forms, including
any specified camber, to ensure completed work is within
the tolerance limits (Section 4.3.1.7).
Wedges are typically used for final alignment before repair
material placement and telltale devices are installed on
shores or forms to stabilize and secure the erected formwork
in position before the final check and to detect formwork
movements during concrete placement. Formwork should
be anchored to the shores below so that undesired movement of any part of the formwork system is prevented during
concrete placement. Such anchoring and bracing should be
installed in such a way as to allow for anticipated take-up,
settlement, or deflection of the formwork members (Sections
4.3.1.8 and 4.3.1.9). After securing the formwork in place
and before repair material placement, the contractor should
ensure that the formwork surfaces and embedded objects are
clean from all foreign material and formwork surfaces are
sprayed with the approved material that prevents bond with
the repair material (Sections 4.3.1.14 and 4.3.1.15).
Formwork can be removed when the repair cementitious material has attained the minimum strength to support
its self-weight and will not result in damage to the repair
material (Sections 4.3.2.1). If the repaired member, however,
will support construction loads, then formwork should
remain until concrete has attained the specified compressive
strength in the contract documents and verified by testing
specimens field cured in the same manner as repair material
they represent (4.3.2.5 and 4.3.4.1).
All repaired surfaces must be true and even, free of open
or rough spaces, depressions, or projections. Immediately
after the removal of forms, all bulges, fins, form marks, or
other irregularities that, in the judgment of the A/E, will
adversely affect the appearance or function of the structure
Class of surface
A
1/8 in. (3 mm)
B
1/4 in. (6 mm)
C
1/2 in. (13 mm)
D
1 in. (25 mm)
Example B.4b
Concrete surface category (CSC) levels (ACI 117)
are specified for individual parts of the structure
to reflect the Owner’s needs, desires, and budget.
Possible examples include:
• Basement walls: CSC1
• Industrial structures: CSC1 or CSC2
• Electrical and mechanical rooms: CSC1 or
CSC2
• Stairwells: CSC1, CSC2, or CSC3
• Commercial building exteriors: CSC3
• High-end commercial building exteriors: CSC3
or CSC4
•
Religious structures or museums: CSC3 or
CSC4
• Monumental or landmark structures: CSC4
where:
CSC1 is for concrete surfaces in areas with low
visibility or of limited importance
CSC2 is for concrete surfaces where visual
appearance is of moderate importance
CSC3 is for concrete surfaces that are in public
view or where appearance is important
CSC4 is for concrete surfaces where the exposed
concrete is a prominent feature of the completed
structure or visual appearance is important
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University of Toronto User.
Example B.4a—Permitted abrupt or gradual irregularities in formed surfaces as measured within a 5 ft (1.5 m)
length with a straightedge
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96
Fig. B.4a—Formwork for beam cross section enlargement
(image courtesy of Pullman, A Structural Technologies
Company).
must be removed. All form bolts and ties must be removed
to a minimum depth of 1 in. (25 mm) below the surface of
the repair. The cavities produced by form ties and all other
holes of similar size and depth must be thoroughly cleaned.
Holes resulting from form bolts or straps that pass through
the wall must be entirely filled with mortar to form a dense,
well-bonded unit. ACI 347.3R defines four quality levels of
formed concrete surfaces and provides methods to achieve
and evaluate them (Example B.4b). These quality levels are
identified by three surface finish categories: 1) form facing;
2) concrete surface void ratio; and 3) characteristics of formfacing materials (Fig. B.4b).
97
Fig. B.4b—General view of formed repaired surface with
unacceptable number of voids.
University of Toronto User.
using normal handling tools and machines, such as slings,
are usually acceptable and must be kept off ground and, if
stored outdoors, then they must be covered. Epoxy-coated
bars, however, require additional precaution to protect the
coating from damage due to collision or dragging. Some of
measures that the contractor can take are by using bare chains
and cables, using spreader bars or strong backs with multiple
pick-up points to minimize sagging, using synthetic slings
to reduce damage to coating, and placing wood and plastic
between bars when shipping. Epoxy-coated bars should
be stored off ground on timber cribbing or wooden boards
Section 5—Reinforcement and reinforcement
and should remain from mud, debris, and other deleterious
supports
material. Other requirements apply to other types of bars,
ACI 563 Section 5, Reinforcement and reinforcement
such as stainless steel bars or galvanized bars, but irrespecsupports, covers material selection by specifying the grade
tive of the type, bars should be stored elevated from the
of bars determining its yield strength, ultimate strength,
ground and stored indoors or under cover to protect them
chemical composition, and percentage of elongation. It also
from the elements (Section 5.1.3.2 and Example B.5).
covers fabrication tolerances, proper placement of the bars
The contractor must comply with the reinforcement
in the right place, maintaining tolerances of new steel reingrades, types, and sizes as indicated in the contract docuforcement and reinforcement supports, and methods acceptments. Each bar requires identification marks to be rolled
able for repair of existing reinforcement to remain.
into the surface of one of its sides (Section 5.2.1.1)
The contractor is required to submit bar data and bar place(Fig. B.5b). If welding is required, then the contractor must
ment drawings of reinforcement for approval by the A/E
follow the requirements of AWS D1.4/D1.4M.
(Section 5.1.2). The data are in the form of manufacturer’s
ACI 563 Section 5.3 covers the execution work of
certified test report, which accompanies each shipment of
preparing, placing, cutting, field bending and straightening,
reinforcing bars. The mill reports certify that the reinforcing
and preheating of bars. New and existing bars must be free
bar conforms to the project specifications and reveals the
of contaminants deleterious to the bond and existing bars
chemical composition of the reinforcing bar and mechanical
must have minimum deformation for proper bonding, otherproperties (Fig. B.5a). The drawings should also include
wise the contractor must inform the A/E on the status of
length and location of splices. If mechanical splices are used
existing reinforcement for any modifications to the original
on the job, the contractor must submit type and coating of
design (Section 5.3.2.2). To maintain the specified cover of
sleeves, bolts, and nuts for approval (Sections 5.1.2.1(b)
the bars required by the contract documents, the contractor
through (d)). The submitted placement drawings should also
must provide supports or what is normally termed “chairs.”
include request for field cutting if required, including locaPlacing reinforcement in the right place and keeping it
tion and type of bar to be cut and reason for the field cutting
there during concrete placement is critical to the structure’s
(Section 5.1.2.1(h)).
performance (Section 5.3.3.3). Placing bars on supports,
The contractor must properly handle and store reinforcehowever, is not enough. Bars must be secured in place to
ment and protect it from soil, petroleum products, or other
prevent displacement during construction activities and
materials that will inhibit its bond to concrete (Section
concrete placement. This is usually accomplished with tie
5.1.3.1). There are different ways of handling and storing
wires. For epoxy-coated bars, PVC or similar ties are usually
bars, depending on type. For example, typical black bars,
used (Fig. B.5c(a) and (b)).
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APPENDIX B
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Sometimes it is necessary to move or relocate new reinforcement beyond the specified placing tolerances to avoid
interference with existing reinforcement, conduits, or
embedded items. The contractor must submit a proposed
plan for the alternate spacing to the A/E to approve the relocation of new bars beyond the placement tolerances (Section
5.3.3.2).
The contractor is permitted to bend or straighten reinforcing steel bars partially embedded in concrete in the
field. Bar sizes No. 3 through 5 may be cold bent the first
time, provided bar temperature is above 32°F (0°C) (Section
5.3.3.8). For other bar sizes, bars must be preheated before
bending or straightening. Heat is applied such that it does
not harm bar material or cause damage to concrete. The
minimum preheat length is usually five bar diameters in
each direction from center of bend provided preheating
is not extended below the concrete surface. Maintain bar
preheat temperature of 500°F (260°C) at concrete interface
and between 1100 and 1200°F (593 and 649°C) away from
concrete until bending or straightening is complete. Allow
bar to cool down slowly. Artificial cooling methods can
be used when bar temperature falls below 600°F (316°C)
(Section 5.3.3.8(a)). This method is consistent with ACI 301
Section 3.2.2.8. ACI 318 Section 26.6.3.2, however, does
not allow bending unless shown in the construction documents or permitted by the A/E. The commentary in ACI 318
further elaborates that tests have shown that ASTM A615
Grade 40 and 60 bars can be cold bent and straightened up
to 90 degrees, provided the minimum diameter provided in
Section 25.3 is maintained. ACI 318 Section 26.6.3.2 further
explains that heating of bars up to 1500°F may be necessary
if cracking or breakage is encountered and bars should be
spliced outside the bend region. Field-bending or straight-
Example B.5—Simple steps save time and effort (ACI 347R):
a.Order the reinforcing bar with the construction
schedule in mind.
b. When reinforcing bar is delivered to the site,
check the shipping list or manifest, dray ticket,
or loading sheet as each bundle is unloaded.
c.Save time by hoisting the bundles of bars
directly from the truck to the area on the structure where the bars are going to be placed.
d. Put bundles in an area with easy access for
rehandling. Make sure the reinforcing bar
is placed on timbers to keep it away from or
standing water.
e.
Keep stockpiles orderly. Straight bars are
usually stored by sizes and by lengths for
easy identification. Stockpile similar bent bars
together.
f. Make sure all bar tags are at the same end for
quick identification. When bars are removed,
make sure the bar tag stays with the bundle and
does not get lost.
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98
University of Toronto User.
Fig. B.5a—Sample of certified mill test report
(image courtesy of CRSI).
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@Seismicisolation
ening of zinc-coated (galvanized) or epoxy-coated bars is
permissible, but damage to coating must be repaired.
Section 6—Conventional concrete mixtures
ACI 563 Chapter 6, Conventional concrete mixtures,
covers the requirements for materials, proportioning,
producing, and delivery of concrete prepared from constituent materials. The A/E conveys those requirements through
the contract documents in the form of specifications to the
contractor to perform the work as intended. The A/E should
be aware that specifications for concrete mixtures can be
either prescriptive or performance-based. When prescriptive specifications are used, the A/E assumes responsibility
for the prescribed materials and process to meet the performance requirements by including clauses for means and
methods (Example B.6). Performance specifications, on the
other hand, are a set of instructions that address requirements
for mechanical and functional properties of the concrete.
This method requires the designer to clearly specify the test
methods that are needed to be performed, ensure that the
specified requirements are achievable by the method the
contractor chooses, and that the specified requirements are
measurable and enforceable, satisfying the relevant testing
standards. Performance-based specification puts the respon-
sibility on the contractor to achieve the requirements specified in the contract documents.
ACI 563 requires the contractor to submit to the A/E
concrete mixture proportions and characteristics, field test
records used to establish the required average compressive
strength, and documentation indicating that the proposed
concrete proportions will produce an average compressive strength equal to or greater than the specified average
compressive strength (Section 6.1.2). For a repair job, the
contractor must submit data on concrete materials per specified ASTM standards—that is, cementitious material type,
aggregates, water and ice source, and admixtures. As part of
the QC program, the A/E must maintain records verifying
that materials used are the specified and accepted types
and sizes and are in conformance with the requirements of
Section 6.2.1, while the contractor must ensure that concrete
production and delivery conform to the corresponding
ASTM standards. If the contractor proposes changes of one
or more of the materials used in a mixture design, new field
data, data from new trial mixtures, or other evidence must
be submitted to the A/E for approval that the change will
not adversely affect the relevant properties of the concrete
before changes are made.
When concrete is mixed at the job site, the contractor
should store cementitious material and other material related
(a) Chair supporting a bar. Note: bar not post- (b) Chair supporting a bar and strands. Strands are
tensioning tied to chair.
tied to chair, while bar is not yet.
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@Seismicisolation
University of Toronto User.
Fig. B.5b—Bar identification (image courtesy of CRSI).
Fig. B.5c—Typical bar chairs.
99
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APPENDIX B
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
University of Toronto User.
Section 6.2.2 directs the contractor to ensure that the cementitious material content is adequate to satisfy the specified
Sections with dimension h
Temperature in 24 hours
requirements for strength, water-cementitious materials ratio
a. < 12 in. (300 mm)
50°F (10°C)
(w/cm), durability, finishability, and placement constraints of
b. 12 in. (300 mm) ≤ h < 36 in. (900 mm)
40°F (4°C)
the project. The specification permits the contractor to lower
c. 36 in. (900 mm) ≤ h < 72 in. (1800 mm)
30°F (–1°C)
the cementitious material content contingent upon verificad. h ≥ 72 in. (1800 mm)
20°F (–7°C)
tion that concrete mixtures with lower cementitious material
content will meet the specified strength requirements and will
produce concrete with equal finish quality, appearance, durability, surface hardness, and placeability. The contractor must
Example B.6—Prescriptive specification
submit a history of the proposed modified mixture design or,
for an interior reinforced concrete building
by evaluating the proposed mixture, by placing concrete in a
beam
representative location at the project site using project mateConcrete shall be a minimum of 4000 psi (28 MPa)
rials, equipment, and personnel.
concrete compressive strength with a maximum
Section 6.2.2.5 sets limitations on the maximum delivw/cm of 0.4 and a minimum cement content of
ered concrete temperature of 95°F (35°C), unless the A/E
3
3
600 lb/yd (9611 kg/m ), a maximum fly ash content
specifies a different temperature when placing concrete. If
of 10 percent by mass of cementitious material, and
the ambient temperature from midnight to the following
a maximum slump of 4 in. (100 mm).
midnight is expected to be less than 40°F (4°C) for more
Discussion:
than three successive days, concrete should be delivered to
The concrete compressive strength, 4000 psi
meet the minimum temperatures noted in Table B.6 immedi(28 MPa), is the critical characteristic in this
ately after placement.
prescriptive specification. The beam is protected
Durability—Architect/Engineers strive to design
from exposure; therefore, the low w/cm limit is
concrete that is durable and can withstand extreme envinot required for durability. Listing the minimum
ronmental conditions without deterioration or damage.
cementitious content is not necessary to meet
Therefore, properly designed, proportioned, transported,
strength requirements. Limiting fly ash content to
placed, finished, and cured concrete can provide decades
10 percent is possibly to ensure rapid strength gain
of service with little or no maintenance; however, certain
for form stripping, which is an issue of means and
conditions or environments exist that can lead to premature
methods of construction and should not be included
concrete deterioration. There are various factors that influin the specification.
ence the durability of concrete and should be considered in
In addition, the specification is in contradiction in
the context of the environmental exposure of the concrete.
requesting 4000 psi (28 MPa) concrete compresThe specification sets durability requirements such as
sive strength with low w/cm (0.4).
sulfate resistance, freezing-and-thawing resistance, low
permeability, corrosion protection of reinforcement, and
shrinkage limits to protect concrete from such exposures.
For example, it is essential that concrete of an exposed
reinforced concrete bridge girder resists water and chloride
and other chemical migration for its longevity and proper
service (Fig. B.6).
Use of fibers—The use of steel fibers and macrosynthetic
fiber-reinforced concrete must be based on fiber-reinforced
concrete’s flexural performance requirements as indicated in
the contract documents when tested and calculated in accordance with ASTM C1609/1609M, ASTM C1399/C1399M,
or ASTM C1550 (Sections 6.2.2.8 and 6.2.2.9).
Proportioning—Section 6.2.3 provides direction to the
contractor to analyze statistically existing data of field test
records within the past 12 months and that span no less than
60 days for a class of concrete within 1000 psi (7 MPa) of
Fig. B.6—Bridge girder damage due to chemical migration
that specified in the contract documents to justify its use.
(image courtesy of Helpiks).
When test data are not available, the contractor must provide
to the concrete mixture in a dry place, protecting them from
data form trial mixtures using the specified material requiregetting contaminated. In addition, aggregates should be
ments in the contract documents (Section 6.2.3.1).
stored and handled in a way to prevent segregation and avoid
Execution—Durable concrete is not obtained by using
mixing with other materials or other sizes of aggregates and
good materials and proper mixture proportioning alone, but
to protect stored admixtures against evaporation or damage
also by appropriate placement practices and workmanship
(Section 6.1.4).
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that are essential to the production of durable concrete.
@Seismicisolation
Table B.6—Minimum concrete temperature
immediately after placement
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100
Section 6.3 provides direction to the contractor for the
mixing and placement of concrete when concrete is readymixed or site-produced. Sections 6.3.2.1 and 6.3.2.2 direct
the contractor when and how to adjust the slump and what
measurements to take when the maximum concrete discharge
time, drum revolution, or both, have exceeded the requirements set in ASTM C94/C94M.
101
Example B.7—Surface finish criteria
Surface Finish-1.0 (SF-1.0)
a. No formwork facing material is specified
b. Patch voids larger than 1-1/2 in. (38 mm) wide
or 1/2 in. (13 mm) deep
c. Remove projections larger than 1 in. (25 mm)
d. Tie holes need not be patched
e. Surface tolerance Class D as specified in ACI
117
f. Mockup not required
University of Toronto User.
Section 7—Handling and placing of conventional
concrete
Section 7 covers the handling and placing of cast-in-place
and precast concrete, and localized partial-depth concrete
repairs.
The requirements for handling and placing of concrete
on a repair project are identical to the conventional placeSurface Finish-2.0 (SF-2.0)
ment of concrete. Therefore, this section will not cover
a. Patch voids larger than 3/4 in. (20 mm) wide or
these requirements in detail. The contractor, however, must
1/2 in. (13 mm) deep
still submit data to the A/E for approval (Section 7.1.2.1(a)
b. Remove projections larger than 1/4 in. (6 mm)
through (f)), such as field control test data; qualifications
c. Patch tie holes
of finishers; shop drawings of placing, handling, and
d. Surface tolerance Class B as specified in ACI
construction methods and data; placement notifications;
117
and preplacement requirements. The contractor must also
e. Unless otherwise specified, provide mockup of
submit data to the A/E on the conveying equipment type to
concrete surface appearance and texture
be used on the repair job and proposed methods for removal
of stains, rust, efflorescence, and surface deposits (Section
Surface Finish-3.0 (SF-3.0)
7.1.2.2). Also, data must be submitted to the A/E when the
a. Patch voids larger than 3/4 in. (20 mm) wide or
contractor proposes alternatives, such as construction and
1/2 in. (13 mm) deep
contraction or expansion joint locations and layout, underb. Remove projections larger than 1/8 in. (3 mm)
water placement, initial and final curing methods, and
c. Patch tie holes
coated ties.
d. Surface tolerance Class A as specified in ACI
Products—Section 7.2 specifies the material that should
117
be used on a repair job. For example, water when used for
e. Provide mockup of concrete surface appearcuring must be potable (Section 7.2.1.1). Seawater or water
ance and texture
containing contaminants that may discolor concrete is
prohibited (Fig. B.7). Membrane-forming curing compounds
that conform to ASTM C309 or ASTM C1315 are acceptable except for silica-based liquid surface densifiers that are
prohibited from use (Section 7.2.1.2).
Execution—Section 7.3 covers the actual concrete work
such as preparation, placement, and curing of concrete,
finishing formed surfaces, finishing unformed surfaces,
sawed joints, curing and protection, and repair of surface
defects. It provides a road map for the contractor to perform
the work, requiring the contractor to complete the following
tasks before placing concrete in forms or against prepared
concrete (Section 7.3.1.2):
a. Comply with surface preparation requirements in Section
3.
b. If formwork is used, comply with formwork requirements
Fig. B.7—Concrete discoloration due to curing with contamspecified in Section 4.
inated water.
c. Remove snow, ice, frost, water, and other foreign materials, if present, from surfaces against which concrete will
be placed, and from reinforcement and embedded items.
The specification directs the contractor to take precautions
d. Comply with reinforcement placement requirements specwhen placing concrete in wet, cold, or hot weather. Additional
ified in Section 5; position and secure in-place expansion
precautions should be taken by maintaining minimum and
joint materials, anchors, and other embedded items.
maximum reinforcement, embedded material, and formwork
e. Provide properly conditioned concrete surface substrate as
surface temperatures that will be in contact with concrete for
indicated in contract documents in Section 3. @Seismicisolation
cold and hot weather concrete placement (Section 7.3.2.1).
@Seismicisolation
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APPENDIX B
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Section 7.3.3 lists the acceptable surface finishes of placed
concrete (Example B.7). Section 7.3.7 provides direction to
the contractor for repairing surface defects.
Sections 9 and 10
These two chapters incorporate two other standards into
this standard by reference: ACI 503.7, “Specification for
Crack Repair by Epoxy Injection,” and ACI 506.2, “Specification for Shotcrete.”
Notes to Specifier (nonmandatory)
ACI 563-18 lists nonmandatory Notes to the Specifier.
Those notes are provided to help the A/E determine how to
use ACI 563 in a project Contract Document. It advises the
A/E to reference or incorporate the reference specification
in its entirety in the project specification (Example B.NS).
Copying sections, parts, or paragraphs into the project specification may take them out of context or may change their
meaning. It also directs the A/E to determine which standard
controls when two standards are referenced in the project
document that are in conflict.
The Notes to the Specifier include two checklists for
the A/E to use in incorporating ACI 563 into the concrete
specification. The first of these checklists, the Mandatory
Requirements Checklist, indicates specific qualities, procedures, and performance criteria that the specifier must define
in a project specification. The second, the Optional Requirements Checklist, identifies choices and alternatives that the
specifier can include as requirements in a specification.
Checklists
ACI 563 has a mandatory and nonmandatory requirements checklist. It is recommended that the A/E references
ACI 563 when the project is designed in accordance with
ACI 562; this assures the designer that the requirements that
are in ACI 562 are written in specification language. The
A/E must specify the items in the Mandatory Requirements
Checklist as the information is required on any project. The
A/E also needs to review ACI 563 Sections 1 through 8 to
determine which of the special concrete requirements are
needed for the specific project.
The Optional Requirements Checklist allows the A/E to
determine if alternative tolerances or other specification
items should be included in the contract documents. These
items should be adjusted to the needs of a particular project
by including those selected alternatives or additions as
mandatory requirements in the Project Specification.
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University of Toronto User.
Section 8—Proprietary cementitious and polymer
repair materials
Section 8 covers properties, proportioning, mixing,
and use of proprietary cementitious and polymer repair
materials. The contractor must submit the following to the
A/E for approval before proceeding with repair:
a. Repair material manufacturer (RMM) product data sheets
and certifications with performance data; collected data
must follow nationally standardized test methods whenever possible and provide sufficient detail to allow verification of the data within reasonable testing variation. such
as precision and bias used in ASTM test methods
b. Material safety data sheets (MSDS) or safety data sheets
(SDS)
c. Product samples
d. Aggregates
The contractor must submit supplemental testing data to
ensure the specified material conforms with the specified
requirements not included in the RMM product data sheet.
The contractor must also prepare mockups to demonstrate
that workers have mastered the construction techniques to
the manufacturer’s representative satisfaction and to the
approval of the A/E and owner that the product conforms
to the specified requirements in the contract documents.
If the contractor proposes alternate material than what
was specified in the contract documents, then the contractor
must submit new field data, data from new trial mixtures,
or other evidence that the substituted repair material
conforms to the specified performance criteria as indicated
in the contract documents. The data must be submitted at
least 7 days in advance for acceptance before changes are
made, unless continuation of the work is accepted by the
A/E with the alternative material(s). The contractor must
provide a rationale for the substitution. If the substituted
products have properties that deviate from the specified
performance in the contract documents, then it cannot be
used without a written approval by the A/E and owner
(Section 8.1.4).
As part of the QC, the material production and delivery
must follow the manufacturer’s requirements. Testing and
inspection of the repair material must be performed as indicated in the contract documents and test records must be
saved for future reference (Section 8.1.6).
During the execution of the repair work, the contractor
must notify the A/E in writing before proceeding if there are
deviations between the contract documents surface preparation requirements and the RMM’s written instructions
(Section 8.3.2). The contractor, however, must follow the
RMM’s written instructions for batching, mixing, placing,
and curing of repair materials (Section 8.3.3). If there is any
deviation from the RMM’s instruction, the contractor must
obtain approval from the A/E before proceeding with the
repair work.
The repair material must be installed within the time
frame specified, finished, and cured in accordance with the
RMM’s written instructions and as indicated in the contract
documents. As part of the QA/QC, the manufacturer’s
representative must be available at the job site advising the
contractor on the proper use, handling, and application of the
material until the manufacturer’s representative is confident
and assured that the workers have mastered the work and
understand how to apply it.
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102
103
ACI 503.7-07
An ACI Standard
Specification for Shotcrete
Specification for Crack Repair
by Epoxy Injection
An ACI Standard
Reported by ACI Committee 503
ACI 506.2-13(18)
Reported by ACI Committee 506
Example B.NS—Referencing specifications into a construction document
References
The specification listed below forms a part of this specification.
American Concrete Institute (ACI)
563-18—Specification for Repair of Concrete in Buildings
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APPENDIX B
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The first 11 chapters and Appendix A of this guide describe
the chapters and Appendix A of ACI 562 and provide additional information about the background and application of
the provisions. Section numbers in these chapters correspond
to the ACI 562 section number of that is being described.
Appendix B of this guide describe the chapters of ACI 563.
The following eight project examples illustrate how the
requirements of ACI 562 can be applied to satisfy the code
provisions for typical repair project scenarios.
For convenience, the relevant sections of ACI 562 are
listed to the top right of each corresponding paragraph of the
Project Example text. The Project Examples are based on
real projects. Because ACI 562 was not available at the time
the projects were actually performed, they have been modified to reflect compliance with ACI 562, assuming that ACI
562 was accepted by the local jurisdiction having authority
over the project.
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Project Examples
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104
Description of structure
Chapter 2
Investigation of the structure shows it is a two-story, enclosed parking structure
located in the northern United States. The parking structure, constructed in the
1960s, measures approximately 240 x 150 ft (73.2 x 45.7 m) in plan, as shown in
Fig. 12.1. The lower level is on ground, and the middle level and roof consist of reinforced concrete flat slabs with drop panels. The middle-level deck is 9 in. (225 mm)
thick with 10 ft-0 in. x 10 ft-0 in. x 2-1/4 in. (3 m x 3 m x 57 mm) drop panels
centered around 2 ft-6 in. x 2 ft-6 in. (750 x 750 mm) reinforced concrete columns.
The slab is covered with 1 in. (25 mm) asphalt topping. No design information or
drawings were available.
Project initiation and objectives
Table A.2.3
At the middle-level deck, the owner noted potholes and unevenness in the
asphalt topping and water leakage through cracks. A few small pieces of concrete
had fallen from the underside of the slab. The project was initiated to determine
the current condition of the parking structure and to develop a plan for repair of
ACI 562-19 provision numbers applying to each section of text are shown in red at the top right of each paragraph.
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105
University of Toronto User.
Fig. 12.1––Middle-level deck plan showing Slab Area 1 with approximately 60 percent delaminated or
spalled top surface concrete and Slab Area 2 with approximately 10 to 20 percent delaminated or spalled
top surface concrete.
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Chapter 12: Project Example 1—Typical Parking Structure Repair
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
the parking structure deterioration using the assessment and design criteria in
Table A.2.3.
Governing building codes
Based on discussions with the building officials, the building codes adopted by
the jurisdiction were determined.
Jurisdiction—Northern U. S. city.
Original building code—1961 Uniform Building Code (1961 UBC).
Current building code—2015 International Building Code (2015 IBC).
Existing building code—Not adopted.
1.2.3
1.2.2
1.2.1
1.1.2
ACI 562 supplements the existing building code, which is normally the International Existing Building Code (IEBC) and the 2015 IBC Chapter 34, and governs in
all matters pertaining to concrete members in existing buildings, except wherever
ACI 562 is in conflict with requirements in the 2015 IEBC, in which case the 2015
IEBC governs.
1.2.4, A.2
The design-based criteria are determined based on the assessment criteria in
Chapter 4, if the IEBC is used, and in Appendix A, if ACI 562 is used without the
IEBC. Because the repairs are intended to increase the structural safety (strength)
by remediating the observed deterioration and Appendix A does not conflict with
Chapter 34 of the 2015 IBC, design-basis criteria of Appendix A apply.
A.3
a. Section A.3 – 2015 IBC supplemented by ACI 562-19, excluding detailing of the
existing reinforcement.
b. Section A.5.3 – 1961 UBC supplemented by ACI 562-19.
A.5.3
A.5.2
c. Section A.5.2 – 2015 IBC supplemented by ACI 562-19, excluding detailing of
the existing reinforcement.
A.5.2, A.5.3
1961 UBC uses allowable stress design and service loads. An option, which
was chosen by the licensed design professional (LDP), was to use Section A.5.2
of ACI 562-19 and the 2015 IBC supplemented by ACI 562 as a check for the
Section A.5.3.
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1.7.1, 1.7.3, A.3, A.5.3, A.5.2
Design-basis codes—Based on a preliminary assessment as described in
Section 1.7 and considering the requirements of Sections A.3, A.5.3, and A.5.2 of
ACI 562 and the existing building code, the design-basis code was determined to
be as follows:
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106
Preliminary assessment
1.7.1, 1.7.3
No documents were available for review, and the design-basis code for
the preliminary assessment was assumed for purposes of practicality to be
the current building code, 2015 IBC, that references ACI 318-14. The LDP
is to use judgment to determine if a preliminary assessment is necessary and
how to make their assessment considering the minimum requirements of
ACI 562-19.
Investigation of existing site conditions
1.7.4
Existing structural geometry—The existing structural geometry, including typical
dimensions and member sizes, was measured on-site as part of the investigation.
1.7.1, 1.5.3
Existing concrete condition––On the top surface of the middle-level deck, the
asphalt topping was removed, exposing the top concrete surface. Exposed concrete
surfaces were visually surveyed for types and patterns of distress and deterioration
(ACI 201.1R). Concrete surfaces were selectively sounded by chain drag, hammer
tapping, or tapping with a reinforcing bar to estimate the extent of delaminated
concrete. The pattern of deterioration suggested that deicing salts had been transported into the parking structure by vehicles causing corrosion-related deterioration particularly in areas near the parking structure entrance and where vehicles are
most apt to park. Concrete powder samples were procured from the upper portion
of the middle-level slab and tested for chloride content (ACI 364.1R). Samples
were removed from areas near the parking structure entrance/primary parking
area that exhibited deterioration as well as areas farther removed from these areas
where less or no deterioration was exhibited. The purpose of this testing was to
ascertain the level of chloride contamination at the level of the reinforcement. The
following concrete distress and deterioration was documented.
Typical types of observed concrete deterioration are illustrated in Fig. 12.2.
1.7.1, 1.7.4
Reinforcement—The reinforcing layout and condition were documented at
a few typical locations by measurement of exposed bars, magnetic survey, and
exploratory chipping to expose bars. No. 7 @ 7-1/2 in. (No. 22 @ 190 mm) on
center and No. 7 @ 15 in. (No. 22 @ 380 mm) on-center bars were determined
in column strips for top and bottom reinforcement, respectively. No. 7 @ 18 in.
(No. 22 @ 450 mm) on center were determined @Seismicisolation
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middle strips top and bottom
University of Toronto User.
a. The underside of the roof slab was determined to be in generally good condition.
b. The top surface of the middle-level slab had two areas with distinctly different
levels of concrete deterioration, as shown in Fig. 12.1. Slab Area 1, consisting
of approximately half of the slab surface and located near the parking structure
entrance/exit and the main drive aisle, was approximately 60 percent delaminated
or spalled due to corrosion of the embedded reinforcement. The regions around
the columns were completely delaminated or spalled. Slab Area 2, consisting
of the remainder of the middle-level slab, was 10 to 20 percent delaminated or
spalled.
c. The underside of the middle-level slab was 10 to 20 percent delaminated or
spalled due to corrosion of the embedded reinforcement, with greater damage
observed in Slab Area 1.
d. Just above the slab, the bases of columns had small areas of delamination due to
corrosion of the embedded reinforcement mostly in Slab Area 1.
e. The upper portion of the middle-level slab was heavily contaminated with chloride, greatly exceeding the corrosion threshold value (ACI 222R), particularly in
areas that were delaminated, spalled, or cracked.
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GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Fig. 12.2––Typical concrete deterioration details.
reinforcement, respectively. Cover was measured at 3/4 in. (19 mm). Surface
corrosion and some section loss were documented for the top slab bars in Slab
Area 1 (ACI 364.1R).
Findings of preliminary assessment
1.7.4
The following determinations were made based on the preliminary assessment:
RA.5.2
A comparison of the nominal loads in the 1961 UBC and the 2015 IBC shows no
changes in these nominal loads for the parking structure.
U c = U o*
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Capacity and demand of existing structure
1.7.4, 6.2.1, Table 6.3.2a, Table 6.3.2b, 1.7.3, A.3, A.5.3, A.5.2
A preliminary assessment was performed to estimate the existing capacity
of the middle-level slab and the columns, including the impact of the observed
deterioration. Rather than sampling and testing to determine the concrete and
steel properties, the concrete compressive strength was assumed to be 3000 psi
(21 MPa) and the yield strength of the reinforcing bars was assumed to be 33,000 psi
(230 MPa) in accordance with Tables 6.3.2a and 6.3.2b of ACI 562. The demand for
the middle-level slab and the columns were analyzed based on nominal loads and
procedures in the 1961 UBC for ACI 562, Section A.5.3, and in the 2015 IBC for
ACI 562, Section A.3 and A.5.2.
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108
Chapter 2
where Uc is defined as demand using nominal loads of the current building code
and factored load combinations of ASCE/SEI 7 for strength design provisions
(LRFD); and Uo* is the demand using nominal loads of the original building code
and factored load combinations of ASCE/SEI 7 for strength design provisions
(LRFD).
5.3
Without deterioration when using strength design provisions, the middle-level
slab and the columns have capacity greater than demand with strength reduction
factors of Section 5.3 of ACI 562 and using the 2015 IBC and 1961 UBC nominal
loads along with ASCE/SEI 7 load factor combinations.
Area 1
A.3.2
As there was substantial documented top surface concrete deterioration in
Slab Area 1 but significant effort would be necessary to accurately determine the
structural effects of this deterioration, approximately 60 percent of the top slab
reinforcing bars were conservatively judged to be debonded at delaminations
(Fig. 12.3) and therefore structurally ineffective.
ACI 562 requires that the licensed design professional determines if the slab is
potentially dangerous (ACI 562, Section A.3.):
Column strip negative moment region:
The slab capacity with no deterioration or delamination was calculated for the
negative column strip region to be: fRn = 344 ft-kip (466 kN·m). This is greater
than the factored applied load calculated at: Mu,cs– = 285 ft-kip (386 kN·m) for
the same region. However, because 60 percent of the reinforcement is considered
to be ineffective, this results in a slab capacity of: fRcn = 137 ft-kip (186 kN·m).
Evaluating the demand-capacity ratio of the column strip negative moment region:
A.3.2
Uc/fRcn = 285 ft-kip/137 ft-kip = 2.1 > 1.5
(Uc/fRcn = 386 kN·m /186 kN·m = 2.1 > 1.5)
Demand (Uc)
Mu,cs– = 285 ft-kip
(386 kN·m)
Design capacity
fRn = 344 ft-kip
(466 kN·m)
Actual capacity
fRcn = 137 ft-kip
(186 kN·m)
Demand/capacity Uc/fRcn
285 ft-kip/137 ft-kip = 2.1 > 1.5
(386 kN·m/186 kN·m = 2.1 > 1.5)
Column strip positive moment region:
It was determined conservatively that 20 percent of the bottom slab area was
deteriorated and accordingly reinforcement in that area was debonded. The slab
capacity with no deterioration or delamination was calculated for the positive
column strip region to be: fRn = 133 ft-kip (180 kN·m).
This is greater than the factored applied load calculated at: Mu,cs+ = 123 ft-kip
(167 kN·m) for the same region. But due to deterioration, the slab capacity was
reduced by 20 percent to: fRcn = 106 ft-kip (144 kN·m). Without repairs, however,
the negative moment not resisted by the column strip is redistributed and added to
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As indicated in Section A.3.2 of ACI 562, an element or structure with a demand/
capacity ratio of greater than 1.5 is considered unsafe and requires shoring or other
measures.
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Chapter 12: Project Example 1—Typical Parking Structure Repair109
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Fig. 12.3––Effects of unsound concrete on reinforcing steel development. ℓd = tension development
length, per ACI 318-05.
Uc = Mu,cs+ = 123 ft-kip + (285 ft-kip – 137 ft-kip) = 271 ft-kip
(Uc = Mu,cs+ = 167 kN·m + (386 kN·m – 186 kN·m) = 367 kN·m)
Evaluating the demand-capacity ratio of the column strip positive moment
region:
A.3.2
Uc/φRcn = 271 ft-kip/106 ft-kip = 2.56 > 1.5
(Uc/φRcn = 367 kN·m /144 kN·m = 2.5 > 1.5)
Therefore, the slab is structurally unsafe.
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the column strip positive moment region increasing the positive bending demand
on the slab to:
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110
Demand (Uc)
Mu,cs+ = 271 ft-kip
(367 kN·m)
Design capacity
fRn = 133 ft-kip
(180 kN·m)
Actual capacity
fRcn = 106 ft-kip
(144 kN·m)
Demand/capacity Uc/fRcn
271 ft-kip/106 ft-kip = 2.56 > 1.5
(367 kN·m /144 kN·m = 2.55 > 1.5)
If the negative column strip bending capacity is repaired, then the positive
column strip bending demand need not include any redistribution of negative
moment to the positive moment except for redistributed moment that is locked in,
and the positive bending demand is:
Uc = Mu cs+ = 123 ft-kip (167 kN·m) and
Uc/φRcn = 123 ft-kip/106 ft-kip = 1.16 < 1.5
(Uc/φRcn = 167 kN·m /144 kN·m = 1.16 < 1.5)
With the demand-capacity ratio of the column strip negative bending at 2.56
(2.55), the slab is currently considered to be structurally unsafe.
There was substantial deterioration of the top reinforcement near the columns
in Area 1, which rendered the slab shear capacity determined using the 1961 UBC
provisions to be structurally insufficient.
v = V / bjd (from 1961 UBC)
A.3.2
Area 2
Current concrete deterioration has little or no effect on the allowable member
capacities in Slab Area 2 and of the columns. The factored applied moment at
the negative column strip is Mu,cs– = 285 ft-kip (386 kN·m) and the capacity for
that section is fRn = 344 ft-kip (466 kN·m). Assuming that only 20 percent of
the reinforcement is unbonded, then the capacity is reduced to fRcn = 275 ft-kip
(373 kN·m) resulting in demand-capacity ratio of:
A.3.2
Uc/fRcn = 285 ft-kip/275 ft-kip = 1.04 < 1.5
(Uc/fRcn = 386 kN·m/373 kN·m = 1.03 < 1.5)
The slab in Area 2 is therefore considered safe.
Demand (Uc)
Mu,cs– = 285 ft-kip
(386 kN·m)
Design capacity
fRn = 344 ft-kip
(466 kN·m)
Actual capacity
fRcn = 275 ft-kip
(373 kN·m)
Demand/capacity Uc/fRcn
285 ft-kip/275 ft-kip = 1.04 < 1.5
(386 kN·m /466 kN·m = 1.03 < 1.5)
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A.3.2
Following ACI 562-16 Section A.3 requirements, the demand-capacity ratio
(Uc/fRcn) for both bending moment and shear varies with the extent of damage.
As an estimate of the shear strength in Area 1, h was used for plain concrete from
ACI 318-14, Chapter 14 as the depth from the bottom of the slab to the delamination layer, Table 14.5.5.1 shear strength equations, and a strength reduction factor
of 0.6 for plain concrete, which resulted in an effective two-way shear capacity of
approximately 60 percent of the strength calculated without delamination. Where
concrete is delaminated in Area 1 at the critical shear boundary, the section shear
capacity can be considered as having dropped significantly and accordingly the
demand-capacity ratio for shear is likely approaching or at 1.5. Therefore, the
structure in Area 1 is considered unsafe (Uc/fRcn >1.5).
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Chapter 12: Project Example 1—Typical Parking Structure Repair111
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Column strip positive moment region:
It was determined conservatively that 15 percent of the bottom slab area was
deteriorated and accordingly reinforcement in that area was debonded. If deterioration did not exist, the slab capacity in that region was calculated to be: fRn =
133 ft-kip (180 kN·m). The slab capacity must be reduced by 15 percent to
113 ft-kip (153 kN·m) and additional moment demand from the negative region of
the top slab must be added to determine the current condition.
Mu,cs+ = 123 ft-kip + (285 ft-kip – 275 ft-kip) = 133 ft-kip
(Mu,cs+ = 167 kN·m + (386 kN·m – 373 kN·m) = 180 kN·m)
This will result in a demand-capacity ratio:
Uc/fRcn = 133 ft-kip/113 ft-kip = 1.18 < 1.5
(Uc/fRcn = 180 kN·m/153 kN·m = 1.18 < 1.5)
A.3.2
Per ACI 562 Section A.3.2, the section is safe and further assessment per
Sections A.4 through A.9 is required.
Demand (Uc)
Mu,cs+ = 133 ft-kip
(180 kN·m)
Design capacity
fRn = 133 ft-kip
(180 kN·m)
Actual capacity
fRcn = 113 ft-kip
(153 kN·m)
Demand/capacity Uc/fRcn
133 ft-kip/113 ft-kip = 1.18 < 1.5
(180 kN·m /153 kN·m = 1.18 < 1.5)
Per the commentary for the definition of damage, deterioration from aging should
not be considered as damage. The columns had only small localized concrete deterioration and the check of Section A.5.2 of ACI 562 was not done in this example.
A.5.3
For Area 2, the slab is considered safe per ACI 562, Section A.3.2, and accordingly Section A.5.3 or A.5.2 may be checked to determine if strengthening is
required. The following table lists the demand and capacity at critical sections in a
typical interior two-way slab of the parking structure using Eq. (RA.5.3).
Column
strip
Middle
strip
Reinforcement
A s–
As +
A s–
As +
Demand, Us
As,req’d in.2 (mm2)
12.5 (8065)
6.8 (4387)
5 (3226)
5 (3226)
Capacity, Ra
As,prov. in.2 (mm2)
13.5 (8710)
7.2 (4645)
6 (3871)
6 (3871)
Us / Ra
0.93 < 1
0.94 < 1
0.83 < 1
0.83 < 1
The slab two-way shear capacity was calculated at 89 psi (0.61 MPa), which is
less than the allowable required by code of 0.03fc′ = 90 psi (0.62 MPa) and therefore, increasing slab shear punching strength was not required.
A.5.3
ACI 562 Section A.5.3 commentary states that, “using the allowable design is
inconsistent with the reliability principles of current strength design provisions. To
adequately address safety, consideration should be given to verification using A.5.2
and a check of seismic resistance using ASCE/SEI 41.”
Seismic resistance is not an issue in the region and was excluded from the
analysis.
ACI 562 Sections A.5.1, A.5.2, or A.5.3 per Table A.2.3 were used to verify the
structural adequacy in Area 2. This was not required to be performed at Area 1 because
it was already determined to be unsafe and would be repaired to be in compliance
with the current code.
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Location
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112
Report to owner
The owner was notified of the safety concerns. Shoring was promptly
installed to support Slab Area 1 to address the safety concern and to allow
continued access to the parking structure until repairs could be installed. Also,
loose concrete was promptly removed from the underside of the slabs. As
immediate safety concerns were promptly addressed, it was not necessary to
notify the authorities having jurisdiction.
The LDP considered the following factors:
1.5.3
a. Based on the simplifying preliminary assumption made by the LDP that the top
slab reinforcement in Slab Area 1 is over 60 percent debonded and ineffective,
the slab was deemed unsafe.
b. As no excessive cracking or deflections were noted, the slab is apparently still
performing satisfactorily despite the extensive deterioration and, therefore,
the preliminary assumption is conservative particularly for areas with little to
minimal deterioration.
c. Structural elements outside of Slab Area 1 have some concrete deterioration but
were not considered by the LDP or authorities having jurisdiction as unsound or
structurally deficient.
A.2.4, A.2.5, RA.5.1
d. Code changes in detailing and other requirements make it difficult, if not impossible, to bring existing concrete structures into full compliance with current code
requirements. Although Area 1 has unsafe structural conditions, the structure
has demonstrated historical structural reliability having been in service for more
than 50 years, is located in a region where seismic activity is minimal, and is
to be repaired; therefore, full compliance with detailing requirements was not
necessary.
The LDP determined, and the authorities having jurisdiction agreed, that the
design basis code should be 1961 UBC, with the provision that where possible, the
slab in Slab Area 1 should be brought into conformance with the requirements of
the current building code 2015 IBC.
STRUCTURAL ASSESSMENT
6.1.1, 6.2.2, 6.2,3, 6.2.4
Existing structural geometry—The existing structural geometry was documented in more detail than was done for the preliminary assessment (4.1.1).
a. All column spacing, column dimensions, and drop panel dimensions were
measured.
b. The slab thickness was determined with ground-penetrating radar and confirmed
by physical measurements at holes drilled through the slab.
6.4.2.1, 6.4.3.1
Concrete strength—Concrete core samples were extracted and tested in compression to determine the slab concrete compressive strength. The strength values were
consistent with the strength assumed in the preliminary analysis.
6.2.4, 6.4.4.1
Reinforcing steel layout and strength—Reinforcing steel spacing and cover
were determined with ground-penetrating radar and confirmed at exposed bars
and exploratory openings. Exposed reinforcing bars were examined for identification marks that might indicate the steel yield strength. No marks were found.
Additional areas were investigated for reinforcing layout, sizes and, cover using
magnetic survey, cover meter, and exploratory chipping to expose bars. The extent
of measurement of expanded from the preliminary measurements and the results
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Existing conditions
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Chapter 12: Project Example 1—Typical Parking Structure Repair113
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
were consistent with the preliminary findings. Therefore, the same assumptions for
the preliminary assessments were used for the final assessments.
6.4.5.1
Coupons were removed from reinforcing bars and tested in tension to determine
the steel yield strength. Strength values were consistent with the strength assumed
in the preliminary analysis.
Structural analysis for repair design
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1.3.8.2, 5.2.3
Loads factors and load combinations—The loads, load factors, and load combinations are as specified in ASCE/SEI 7-10.
6.5.1, 6.5.2, 6.5.3, 6.5.5, 6.5.7, 6.7.1, 6.7.2, 6.7.3
Analysis—In the preliminary assessment, the direct design method was used to
determine the elevated slab moments, whether the slab was safe, and if strengthening was required. For the final assessment, a three-dimensional finite element
model was developed to confirm the preliminary assessment findings, to evaluate the proposed repair procedure, and to assess the repaired system potential
performance.
For the current state, the LDP used the actual reduced slab thicknesses due to
delamination and the actual material properties obtained from in-place testing
removing eight cored cylinders. The LDP took caution not to drill through existing
reinforcement by locating the bars before drilling. Additional nondestructive
testing was performed using rebound hammer to collect additional data. Correlation was established between the nondestructive data and test results obtained from
the extracted cylinders.
The finite element analysis confirmed the preliminary assessment calculation
for Area 1 and Area 2. The calculated demand of the gravity loads based on the
current design code to the obtained capacity from the software output exceeded
1.5 for Area 1 indicating an unsafe condition. For Area 2, the demand-capacity
ratio calculated per A.5.1 did not exceed 1.0; therefore, the structure did not
require strengthening.
The elevated slab was then reanalyzed considering the structural repair process,
including the effects of the sequence of shoring for Area 1, load application, and
material removal for both areas. The final finite element analysis assumed that the
replacement concrete would be fully bonded to the existing concrete and, hence,
there would be full composite action between repair materials and existing materials. The demand-capacity ratio of both repaired areas (Areas, 1 and 2), obtained
from the final analysis, was below 1.0; therefore, the repair design deemed theoretically satisfactory. Note that the asphalt overlay was removed and replaced with
concrete overlay. The difference in the material unit weight was considered in the
final finite element analysis.
7.4.1, 7.4.1.1
Bonding of the new concrete to the existing concrete was critical to satisfactory
performance of the repaired structure. The horizontal shear demand at the interface
of the repair and existing concrete was calculated based on the loads and combinations described previously. ACI 562 Section 7.4.1 requires the bond strength
demand to be at least equal to the bond strength capacity (nu ≥ fnni).
Shear was calculated at face of columns and at face of drop panels, change
in slab thickness. Based on the applied load, the ultimate shear stress at face
of columns and at face of drop panels were calculated at 22 and 28 psi (0.15 and
0.19 MPa), respectively.
7.4.1.2
These stress values were compared to the shear stress values in Table 7.4.1.2 of
ACI 562. Because the calculated ultimate stress values were smaller than 30 psi
(0.21 MPa), interface reinforcement was not required and bond-integrity testing as
specified in the construction documents must be performed.
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As part of the field assessment, pulloff testing of the substrate determined that
the substrate had adequate strength to achieve the required bond strength. Based on
required bond strength, the LDP concluded that the required bond could be attained
by chemical or mechanical means with proper surface preparation and repair material application (ICRI 310.1R discusses surface preparation for repair of deteriorated
concrete). Therefore, no supplemental reinforcement was required. Refer to Example
7.2 of this guide for more detailed information on the testing requirements, and
pulloff test to ensure adequacy of the bond between overlay and substrate.
Area 1
6.5.4
While the extent of debonding of the top reinforcing steel was unclear, the
analysis also considered the possible redistribution of load effects and resulting
increases in concrete and steel stresses due to the deterioration and subsequent
installation of shoring, as follows:
a. It was assumed that approximately 60 percent of the negative moment capacity
had been lost, and the increased steel and concrete stresses in the positive
moment region were calculated.
b. It was then assumed that the shoring supported the slab during construction, such
that no loads from construction were resisted by the slab.
c. When construction had been completed and the shoring removed, it was assumed
that the topping weight and design live load were supported by the repaired
composite section. The capacity of the repaired section was examined and determined to have adequate strength to resist design loads.
Area 2
University of Toronto User.
6.5.4
The extent of debonding area of the top reinforcing steel was substantially
smaller than what was observed in Area 1; therefore, redistribution of load effects
was not considered and subsequently installation of shoring was not considered:
a. It was assumed that approximately 20 percent of the negative moment capacity
had been lost, and the increased steel and concrete stresses in the positive
moment region were calculated and found to be negligible.
b. When the construction was completed, it was assumed that the topping weight
and the design live load were supported by the repaired composite section. The
capacity of the repaired section was examined and determined to have adequate
strength to resist the design loads.
A.3.2, A.5.1
Consideration of punching shear––The LDP understood the 1961 UBC considered only vertical shear, or punching shear, transfer from the slab to columns.
Newer codes, such as ACI 318-14 referenced by the current building code (2015
IBC), specified that a portion of the unbalanced slab moments must be transferred into the column by eccentricity of the shear, thus increasing the maximum
punching shear.
A.2.4, A2.5, RA.5.1
A close visual inspection of the top and bottom surfaces of the middle-level slab
around the first interior columns, where the unbalanced slab moments are greatest,
did not detect any cracking that might be indicative of distress due to inadequate
punching shear capacity. Although ACI 318-14 predicts an inadequate punching
shear capacity at some columns, the LDP determined that because the slab prior
to deterioration had performed satisfactorily for 50 years, and that it was being
repaired back to original strength, that it was unnecessary to bring the punching
shear capacity into conformance with provisions of the current building code.
1.5.3.a, 1.5.3.b, 1.5.3e, 1.5.3g
The LDP provided the owner with a basis of design report providing a description
of the structure, identifying the structural system, and listing the codes used for the
design and construction of the structure. The basis of design report also included
documentation of unsafe structural conditions in the
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work area as presented previ@Seismicisolation
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GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
ously and identified members that required strengthening. Strengthening options
were presented to the owner along with the advantages and disadvantages of each
option along with the recommendation of the LDP.
DESIGN OF STRUCTURAL REPAIRS AND DURABILITY
Slab area 1
Slab repairs were designed according to the provisions of the 1961 UBC. Two
repair options for deteriorated concrete on the top surface were discussed with the
owner:
1. Removal and replacement of deteriorated concrete only on the top slab surface.
2. Removal and replacement of the top 3 to 4 in. (75 to 100 mm) of concrete in the
entire area.
Option 2 was recommended for the reasons described in the following.
Option 2 advantages––
University of Toronto User.
8.4.3, 8.4.4
a. Chloride-contaminated concrete around the top reinforcing mat is to be removed
and replaced with uncontaminated concrete with low permeability, improving
durability and reducing future maintenance.
7.5.2
b. The new concrete will have similar or slightly enhanced properties compared to
the existing concrete.
7.3.2, 7.3.3, 7.4
c. After concrete removal work has been completed, the exposed concrete surfaces
will be cleaned and a suitable bonding procedure will be used to attain the
minimum required bond strength and ensure composite behavior under service
loads. Surface roughness of the exposed concrete surfaces will be specified per
a Concrete Surface Profile number from ICRI Guideline No. 310.2R or some
other means.
7.3.2, 8.4.2, 8.4.4
d. Existing reinforcing bars, except for those embedded in columns, are to be
removed and replaced with new epoxy-coated reinforcing bars, replacing bars
with reduced cross-sectional area. Because the new bars are uncontaminated and
coated with epoxy, their resistance to corrosion is much improved, improving
durability and reducing future maintenance of the slab system. Existing bars to
remain are to be cleaned and coated with a corrosion-inhibiting material.
8.2.1, 8.2.2
e. Top reinforcing bars with shallow cover can be relocated downward in the slab
for increased corrosion protection cover. This is assuming that the slab still has
adequate calculated shear capacity with a decreased effective depth, and that
additional bars are added as necessary to provide adequate calculated flexural
capacity.
7.6.3.3
f. New reinforcing bars are to be fully encapsulated and developed in the replacement concrete.
7.1.1, 7.2.1, 7.2.2
g. The repaired slab will have similar or greater strength and stiffness to the originally constructed sections.
8.5.1
h. Due to the new uncontaminated concrete with low permeability, and the epoxycoated reinforcement, new surface coatings such as a traffic-bearing elastomeric
coating or a surface sealer were not recommended, reducing initial and maintenance costs.
i. The new slab will have similar or enhanced fire resistance rating compared to
that of the existing slab.
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116
7.9.1, 7.9.2, 7.9.3
j. The higher initial cost of this repair option will be at least partially offset by
lower future maintenance costs.
k. As this repair area is at the parking structure entrance, less future maintenance also
equates to fewer, shorter parking structure closures and less user inconvenience.
Option 2 disadvantages—
7.3.2, 7.3.3, 7.6.3.3
a. The perimeter of the partial-depth replacement area must be located and detailed
to account for shear and moment transfer and reinforcing steel development.
9.2.5, 9.2.6
b. The slab will need to be shored prior to the slab removal and remain shored until
the new slab concrete has been placed and cured.
c. Cracks that may form in the replacement concrete should be sealed.
8.3.1
d. This repair option has a higher initial cost as compared to Option 1.
Slab Area 2 and columns
Replacement of deteriorated concrete only was recommended in this slab area,
as the partial-depth replacement option recommended for Slab Area 1 was not a
cost-effective approach for the limited concrete deterioration in this area. Similarly, the columns have very limited concrete deterioration and only replacement
of deteriorated concrete was recommended.
This limited approach has the following advantages and disadvantages.
University of Toronto User.
Advantages––
a. Only deteriorated concrete is to be removed and replaced, limiting repairs and
repair costs to current requirements.
7.6.6
b. Reentrant corners will be avoided in both the repair and existing concrete.
7.3.2, 7.4
c. After concrete removal work has been completed, the exposed concrete surfaces
will be cleaned and a suitable bonding procedure used to attain the minimum
required bond strength and ensure composite behavior under service loads.
Surface roughness of the exposed concrete surfaces will be specified per a
Concrete Surface Profile number from ICRI Guideline No. 310.2R or some other
means.
8.4.2, 8.4.4
d. Existing reinforcing bars that are exposed in removal areas will be cleaned and
coated with a corrosion-inhibiting material to reduce ongoing corrosion in and
around the replacement concrete areas.
7.6.3.1, 8.4.2, 8.4.4
e. New epoxy-coated reinforcing bars will be lapped with existing bars that are
exposed in removal areas and that have lost structurally significant crosssectional area.
8.4.1, 8.4.4
f. Discrete galvanic anodes will be installed around the perimeter of slab concrete
replacements to reduce corrosion in the existing concrete around the concrete
replacements. To function properly, the anodes must be attached to uncoated
portions of the reinforcing bars in the removal areas before the bars are coated
with a corrosion-inhibiting material.
8.2.2
g. As much of the existing concrete will remain, the as-built reinforcing steel cover
generally will not be modified.
7.5.2
h. The replacement concrete will have similar or slightly enhanced properties
compared to the existing concrete.
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Chapter 12: Project Example 1—Typical Parking Structure Repair117
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
7.6.3.3
i. The existing and new reinforcing bars will be developed in the existing concrete,
the repair concrete, or both.
7.1.1, 7.2.1, 7.2.2
j. The repaired sections will have similar strength and stiffness to the originally
constructed sections.
8.3.1, 8.3.2
k. Existing cracks will be addressed prior to the installation of the traffic-bearing
elastomeric coating. New cracks that may form in the replacement concrete
may be sealed by the traffic-bearing elastomeric coating or will be addressed by
future maintenance repairs.
8.5.1, 8.5.2
l. A traffic-bearing elastomeric coating will be applied on the repaired slab surface
to drastically reduce moisture penetration into the slab concrete and reduce
ongoing corrosion activity in the remaining existing concrete and concrete
replacements. The membrane will extend several inches up the column bases
so that moisture on the deck surface cannot directly access the column concrete.
7.9.1, 7.9.2, 7.9.3
m. The repaired slab will have similar or enhanced fire resistance rating compared
to that of the existing slab. This repair approach has a relatively low initial cost
but periodic maintenance repairs will be necessary. It is a very cost-effective
approach to address the present condition of the parking structure.
7.2.2
n. Analysis of the middle-level slab determined that the slab concrete remaining
after the assumed extent of removal of deteriorated concrete can safely support
the dead and construction live loads during the repair installation and its portion
of the long-term dead and live loads after the repairs have been completed.
Disadvantages—
Slab soffit repairs
1.5.1, 1.6.1
The replacement of deteriorated concrete only was recommended on the slab
soffit throughout the supported slab areas.
Construction specifications
The LDP prepared contract documents that specified repair materials satisfying
governing regulatory requirements and conveyed necessary information to perform
the work.
The LDP used ACI 563 as a source for construction specifications. The specification sections that were referenced included:
Section 1—General requirements
Section 2—Shoring
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and bracing
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University of Toronto User.
8.4.3
a. Except at repair locations, chloride-contaminated concrete will remain in place,
resulting in some ongoing corrosion activity with concrete and steel deterioration requiring periodic maintenance repairs. The corrosion reduction measures
incorporated into the repair program should significantly reduce ongoing corrosion activity and periodic repair requirements.
9.2.2, 9.2.5
b. The LDP must establish limits for concrete removal and monitor the removal
work so that shoring can be installed before the load limits are exceeded.
9.2.2, 9.2.5, 9.2.6, 10.2.3
c. The LDP must monitor the concrete removal work for loss of reinforcing steel
development and possible short-term and long-term structural implications, and
for possible structurally significant loss of reinforcement cross-sectional area, as
determined by the LDP. The LDP must determine if unsafe conditions may exist
and if temporary shoring should be installed.
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118
Construction
9.2
The LDP monitored the construction for unexpected conditions that may affect
the short-term or long-term safety of the structure. Temporary shoring or bracing
may be necessary (Sections 6.2.1 and 6.2.4).
9.4.1
Environmental issues, such as allowing water with debris to flow into floor
drains or off of the site and disposal of construction debris, will be specified in
conformance with local ordinances.
Quality assurance
1.5.1, 10.2.1, 10.2.2, 10.4.1
The repair specifications included quality assurance and control measures for
material approvals and field verification of quality. The specified quality control
measures and construction observations were performed during the construction,
including the following:
a. Review of material submittals and reinforcement shop drawings for Slab Area 1.
b. Visual inspection of the work in progress.
c. Sounding of concrete surfaces to remain to determine if all loose concrete was
removed prior to repair.
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University of Toronto User.
Section 3—Concrete removal and preparation for repair
Section 5—Reinforcement and reinforcement support
Section 6—Conventional concrete mixtures
Section 7—Handling and placing of conventional concrete
Section 9—Crack repair by epoxy injection
The repair work did not require any formwork, therefore, Section 4—Formwork,
was not referenced. Based on the size of the repairs, a conventional concrete was
specified by the LDP in place of a proprietary material or shotcrete.
ACI 563, “Specifications for Repair of Concrete Buildings,” addresses conditions
that are unique to the project. The standard has mandatory and nonmandatory requirements checklists at the end of the standard to help the specifier submit as complete a
specification as possible. For the parking structure slab repair, only a few sections from
the mandatory checklists are extracted to include in the Project Contract Document:
a. Section 1.5.1.1—State the maximum dead and live loads and any temporary
reduction in loads, to be permitted during repair and after completion of repair
program, in concert with the requirements of 2.1.1.1.
b. Section 1.5.4.1—Show the demarcation line of the project location, specific
work areas, and adjacent construction.
c. Section 1.8.2.1—Identify work to be performed by certified personnel.
d. Section 3.1.1.2—Provide the surface profile and remove laitance, debris, and
bond-inhibiting materials.
e. Section 3.1.3.1—Indicate testing locations, type, number, and frequency of tests.
f. Section 3.2.1.1—Select the means and methods for concrete removal that will
minimize damage to the structure and bruised surfaces on the concrete substrate
that remains within and adjacent to the work areas.
g. Section 3.2.1.5—State the required surface profile.
h. Section 3.3.1.1—Show the required depth of concrete removal.
i. Section 3.3.4.2—Indicate that tensile pull-off tests shall be performed at specified locations in accordance with ASTM C1583/C1583M.
j. Section 5.2.1.2(b)—Indicate ASTM specification to which epoxy-coated reinforcing bars are to conform.
k. Section 6.2.2.6(d)—State the chloride exposure classification for are of work.
l. Section 6.2.2.7—Indicate the specified concrete compressive strength fc' for the
work.
m. Section 7.1.2.2—List the information in 7.1.2.2(a) to 7.1.2.2(g) that is to be
submitted.
n. Section 9—Repair of cracks by epoxy injection in accordance with ACI 503.7.
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Chapter 12: Project Example 1—Typical Parking Structure Repair119
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
10.2.3
d. Observation of the prepared concrete surfaces and of the concrete placement and
curing operations.
10.3.1
e. Testing of repair concrete, including slump, temperature, and compressive
strength.
f. Bond strength testing of in-place repair concrete to confirm that the bond strength
was in accordance with Table 7.4.1.2 of ACI 562.
PROJECT CLOSE-OUT
Periodic maintenance
R1.5.3k, 8.1.2
Periodic maintenance requirements were discussed with the owner during the
selection of the most appropriate repair concepts. A schedule of recommended
monitoring and possible maintenance requirements was provided to the owner at
the conclusion of the repair construction, including the following:
a. Periodic inspections every 3 to 5 years to monitor the condition of the parking
structure.
b. Limited concrete deck repairs every 5 years.
c. Limited repair of the traffic-bearing elastomeric coating every 3 to 5 years to
address areas of high wear such as near the parking structure entrance/exit.
d. Top coating the traffic-bearing elastomeric coating and restriping the parking
structure every 15 to 20 years.
Record documents
1.6.3, 1.5.3d, R1.5.3j
The owner was provided with copies of the project and construction documents
and the recommended monitoring and maintenance program.
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120
University of Toronto User.
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Description of structure
The structure is a 28-story residential tower located in the northern United States.
The building, constructed in the 1970s, measures approximately 80 x 90 ft (24.4 x
27.4 m) in plan, as shown in Fig. 13.1. The north and south elevations are cast-inplace reinforced concrete shear walls with 1 in. (25 mm) deep reveal strips at every
floor line. The east and west elevations consist of exposed slab and column edges
with glass-and-metal curtainwall infills. Several tiers on the east and west elevations have reinforced concrete balconies that cantilever out from the building. The
original design drawings were available.
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Chapter 13: Project Example 2—Typical Façade Repair
University of Toronto User.
Fig. 13.1—Plan of residential tower.
ACI 562-19 provision numbers applying to each section of text are shown in red at the top right of each paragraph.
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GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Project initiation and objectives
The owner had noted spalled areas of concrete and exposed corroded reinforcing
bars on all elevations. The project was initiated to determine the current condition
of the concrete façade, identify unsafe conditions, and develop a plan and schedule
for façade maintenance.
Governing building codes
Based on discussions with the local building officials, as well as the information
available on the original design drawings, the building codes adopted by the
jurisdiction were determined as follows.
Jurisdiction—Northern U.S. city
Original building code—1973 municipal code
Current building code—2013 municipal code
Existing building code—Not adopted
1.2.3
1.2.2
1.2.1
LDP interpretation: The repairs proposed will not exceed this threshold, therefore the municipal code provisions for new construction are not applicable as the
design-basis code.
No change in use was proposed.
LDP interpretation: The compliance criteria for the determination of the designbasis code for change in use as set forth in the municipal code are not applicable.
“Every existing building shall be so constructed and maintained as to
support safely the loads prescribed in” the current building code.
LDP interpretation: The floors were well maintained and there was no condition of deterioration or other reasons to suggest that the capacity of the floors had
been impaired over time.
The original building code specified a live load of 40 lb/ft2 (1.91 kN/m2) for
“dwelling units or sleeping rooms.” No specific loading provisions were provided
in the original building code for balconies. A design review indicated that the
balconies had been designed for a live load of 40 lb/ft2 (1.91 kN/m2). The current
building code specified a live load of 100 lb/ft2 (4.81 kN/m2) for balconies of
residential units. Because the previsions of the current building code applicable
to existing structures
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specified that the structure should safely support the floor
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University of Toronto User.
1.1.2, 1.7.3, 1.2.4.2, A.2.1, A.2.4
Design-basis code—Because the local jurisdiction has not adopted an existing
building code, the design-basis code will be determined in accordance with ACI 562
Section 1.7.3. A preliminary assessment was performed using ACI Appendix A and
Chapter 6. It was determined that the structure was in compliance with the version
of ACI 318 referenced in the original building code (1973 municipal code). The
assessment also determined that the structure was safe. Therefore in accordance
with Section A.2.4, the repairs could be designed in accordance with the version of
ACI 318 used for the original construction and ACI 562.
It should be noted that requirements pertinent to existing buildings contained
in the current building code must also be checked by the licensed design professional (LDP). A review of the two chapters for existing construction from the 2013
municipal code yielded the following pertinent provisions relative to the determination of the design-basis code.
“Any building over 80 ft (24.4 m) in height that is altered or repaired,
the cost of which in any 30 months exceeds 50 percent of the reproduction cost of the building, shall comply with the requirements,” for new
construction of high-rise buildings.
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122
loads in the current building code, the building code official was consulted. It was
concluded that it was satisfactory for the balconies serving single units, which were
unlikely to experience loads approaching 100 lb/ft2 (4.81 kN/m2), to be designed
for the live load in the original building code, As such it would not be necessary to strengthen the balconies to meet the current building code requirement for
live load. Because it is frequently an overwhelming burden for building owners to
upgrade structural elements to current design load requirements, this approach is
not uncommon if it is unlikely that the structural elements will actually experience
the larger current design loads associated with the current code.
The following provisions in the current building code for exterior walls of
existing buildings were also checked by the LDP.
“It shall be the duty of the owner of every building regardless of height to
maintain the building’s exterior wall in a safe condition.”
For unsafe conditions of exterior walls, the owner is obligated, “to take appropriate precautionary measures, which may include the erection of a construction
canopy and effect such repairs or reinforcements in a timely manner to remediate
such unsafe conditions.”
LDP interpretation: In this scenario, the primary structural system also serves
as the exterior wall; as such, the exterior concrete must be maintained in a safe
condition and unsafe conditions must be made safe. Furthermore, as confirmed
with the building official, the original building code should be used as the designbasis code for exterior concrete repairs.
1.2.4.2
Therefore, the design-basis code is the original building code, which for this
scenario is the 1973 municipal code along with ACI 562.
Preliminary observations and assessment
University of Toronto User.
1.5.1, 1.7.1
The LDP visually surveyed the façade from the ground with binoculars. Based
on this survey, two locations on each elevation were selected for tactile inspection
from a suspended swing stage. Surveys from the swing stage included close-up
visual inspections and hammer sounding of concrete for delaminated and loose
concrete. The span of the swing stage and width, length, and configuration of the
building was such that nearly all exterior vertical concrete surfaces were visually
examined from a close proximity.
1.7.1, 6.4.1.1
Approximately 5 percent of the balconies were also accessed by swing stage or
through the residential units, and the topside and underside concrete surfaces and
concrete handrails were visually surveyed and sounded for delaminated and loose
concrete.
6.1.1, 6.4.1.1, 6.4.1.2, 8.3.1, 8.4.3
In addition, samples of concrete, consisting of six 2 in. (50 mm) diameter core
samples and 10 concrete powder samples were obtained for laboratory investigation of chlorides, carbonation, and concrete quality. The objective of the sampling
plan was to obtain information that can be used to evaluate the condition of the
concrete and the constructions, and to corroborate observed satisfactory performance, or to document and explain distress or failure. The sampling plan was
specific to the structure and the needs of the LDP to make informed designs about
repair solutions, and generally followed the provisions of ASTM C823/C823M.
Concrete cores were obtained and tested in accordance with ASTM C42/C42M.
The purpose of the cores was to determine the quality of the concrete cover and
depth of penetration of chlorides and carbonation. As such, the depth of the cores
extended to approximately 1 in. (25 mm) beyond the reinforcing bars. The depth
of reinforcing was measured at selected locations. ASTM C1152/C1152M was
consulted for the obtaining of concrete powder samples. The original design drawings and maintenance history of the building were@Seismicisolation
also
thoroughly reviewed.
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Chapter 13: Project Example 2—Typical Façade Repair123
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Observed concrete conditions
Typical types of observed concrete deterioration are described in the following
and illustrated in Fig. 13.3 and 13.4.
(a) Concrete spalls with exposed reinforcing bars at a reveal in a shear wall.
(b) Concrete spall with exposed reinforcing bars and
delaminated loose concrete at slab edge.
Fig. 13.3—Typical small isolated areas
of deteriorated concrete on balconies.
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University of Toronto User.
Fig. 13.2—Typical types of concrete deterioration.
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North and south shear walls––The concrete deterioration on the north and south
shear walls mainly consisted of numerous small delaminations and spalls at the
location where reinforcing bars crossed beneath the reveal strips, resulting in
shallow cover. A few larger areas of delaminations, approximately 100 to 200 ft2
(9.3 to 18.6 m2) in area each, were noted; generally, in these areas the wall reinforcing bars had been misplaced with shallow cover.
East and west slab and column edges––The exposed slab and column edges had
small areas of concrete delaminations and spalls, most typically at locations where
reinforcing bars were located close to the surface.
Balconies––The top and edge balcony surfaces were 10 to 20 percent delaminated. The balcony soffits were delaminated over 5 percent or less of their
surface. Delaminations and spalls typically occurred at isolated locations where
reinforcing bars were located close to the surface. The metal handrails were
in generally good condition with a few small areas of localized corrosion and
peeling paint.
Reinforcing bars––Reinforcing bars, typically No. 5 (No. 16) bars, exposed at
spalls and locations where loose concrete was removed exhibited minor surface
corrosion and the bar deformations remained clearly visible. Typically, the
exposed bars had 1 in. (25 mm) or less of concrete cover. The cover was further
reduced locally, sometimes too little or no cover, at the location where the bar
crossed a reveal or near slab edges and corners. The exposed reinforcing bars
were generally associated with slab bars that were provided with a 180-degree
hook at the slab edge.
1.5.2, 1.7.2
Unsafe conditions––Areas of loose concrete were identified by the LDP and
removed as part of the swing stage inspection. The owner was notified of these
unsafe conditions and advised that additional areas of loose concrete were likely
present in areas not accessed by the LDP. The owner elected to have a contractor
promptly remove all remaining loose concrete from the entire façade. It was therefore not necessary to notify the authorities having jurisdiction as unsafe conditions
had been eliminated.
Findings
Spalled and delaminated concrete was mostly limited to locations where reinforcing bars were placed too close to the surface and located in carbonated concrete.
The loss of concrete was limited to the depth of the steel in an area slightly wider
than the bar at these locations. In limited instances, the small areas of spalled and
delaminated concrete combined to form larger areas of concrete loss with shallow
depth that did not extend behind the bars. Steel reinforcement had not experienced
appreciable section loss.
1.7.1, 1.7.2, 1.7.4, A.2.3
Assessment of the structural implications associated with the spalled and delaminated concrete by the LDP concluded that there was no substantial structural
damage and, in fact, the observed distress and deterioration were of no consequence to the structural integrity of the members being assessed or the building as
a whole.
The current depth of carbonation in the concrete had only reached and affected
reinforcing bars with shallow cover. As the depth of carbonation increases, more
reinforcing bars may be affected. An anti-carbonation coating could be considered
to greatly reduce the rate of carbonation.
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Laboratory findings
Petrographic examination of concrete core samples revealed that the concrete
was of good quality with good durability characteristics. Neither the slab nor the
wall concrete had elevated chloride contents, but the concrete was carbonated to a
depth of approximately 1/2 in. (13 mm) below the concrete surface.
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Structural assessment and repair design
Shear wall reveal strip repairs
It is very difficult to repair concrete over shallow reinforcing bars in a durable,
yet visually acceptable manner. In some locations, ends of bars or hooks at the ends
of bars could be cut off, but at most locations the end hooks were necessary for
the development of the reinforcing bars and could not be removed. The following
approaches were discussed with the owner and are illustrated in Fig. 13.4:
Approach 1: Build out the concrete replacement so that a minimum
concrete cover of 1 in. (25 mm) is attained. This procedure results in the
most durable repair, but results in build-outs in the concrete surface that
may not be visually acceptable. The tops of the build-outs would be sloped
downward and outward to shed water.
Approach 2: Install a repair material, such as cementitious or polymer
mortar, flush with the existing concrete surface. This procedure eliminates
build-outs in the concrete surface. However, it is difficult to find a repair
material that can be applied at thicknesses less than 1 in. (25 mm) (and
perhaps much thinner at some locations) over the reinforcing bars and
that will not crack or debond in an exterior northern environment. If the
material cracks, subsequent reinforcing bar corrosion may cause the repair
material to debond, creating a hazard of falling material.
Approach 3: Remove unsound concrete and clean and coat the exposed
reinforcing
@Seismicisolation
bars with a corrosion-inhibiting material. As no concrete or
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University of Toronto User.
7.2.2, 9.1c, 9.2
Concrete columns exposed as façade elements are commonly part of the gravityload-carrying system and may be part of the lateral-load-carrying system. Consequently, the effect of concrete and reinforcing steel deterioration and the repair
procedures on the ability of the columns to carry loads must be evaluated. Fortunately, on some façade repair projects such as this example, the extent of concrete
and steel deterioration is relatively minor and of minimal structural consequence.
However, the LDP must be cognizant of the role of the column in the structure
and must specify appropriate bracing and shoring measures and repair procedures.
Refer to 7.2 and 9.1 of this guide for considerations related to column deterioration
and repair.
5.1.2
The extent of the deterioration for this example does not have structural implications to the affected members or the building as a whole. Furthermore, the designbasis code does not require structural upgrades to satisfy current building code
requirements. Hence, the factored loads, factored load combinations, and strength
reduction factors of ACI 562 Chapter 5 are not applicable to this project.
6.2.1, 6.2.2
Based on visual observations of the structure, the LDP determined there was no
reason to question the design strength of affected members or the structure. Therefore, a structural analysis and evaluation was not required per ACI 562 Chapter 6.
1.3.7.1, 7.3.3
The primary purpose of the repair is to restore the concrete façade to its original cross section for durability and aesthetic purposes. In accordance with the
design-basis code, the repair shall also remediate unsafe conditions associated
with falling hazards.
7.5.1, 7.5.2, 8.1.1, 8.1.2
The specifics of the repair design will consider the existing construction,
including the reinforcing bars with shallow cover; properties of the repair materials, including adhesion, shrinkage, and thermal movement; installation procedures, including curing requirements and environment conditions; and performance in the service environment, including durability and corrosion resistance,
per ACI 562 Section 7.5. The LDP selected the repair materials and developed the
installation procedures based on the experience of the LDP as well as ACI and
ICRI documents on concrete repair.
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University of Toronto User.
@Seismicisolation
Fig. 13.4—Repair options at concrete delaminations
and spalls at shear wall reveal strips.
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GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
North and south walls away from reveal strips and east and west
slab and column edges
The owner generally elected to build out concrete replacements in these areas to
provide a minimum concrete cover of 1 in. (25 mm), similar to at the reveal strips,
as the most durable repair. A slab edge build-out is illustrated in Fig. 13.5. The
owner felt that the build-outs would not be that visible from the ground and would
not be aesthetically objectionable.
Balcony repairs
8.4.1, 8.4.2, 8.4.3
The balconies had limited areas of concrete deterioration, primarily due to
shallow concrete
@Seismicisolation
cover. To maintain aesthetics and uniform walking surfaces,
@Seismicisolation
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other material replacement will be performed, this procedure will leave
depressions in the concrete surface at the shallow reinforcing bars.
Unavoidable imperfections in the coating application, particularly at the
interface between the bars and the concrete, will result in unsightly rust
stains over time. This coating would need to be maintained to prevent
corrosion of reinforcing that could lead to continued delamination of
concrete.
The existing concrete is not uniform in appearance. As such, the repair concrete
mixture will need to be carefully controlled to minimize an uneven, blotchy
appearance. For Approaches 1 and 2, it will be difficult and costly to match the
appearance of the repair concrete to that of the adjacent existing concrete. Alternatively, the owner could consider covering the façade with a somewhat breathable
architectural coating that would result in a uniform appearance, and also reduce
water and carbon dioxide penetration into the concrete. This coating would need to
be reapplied periodically to maintain an acceptable appearance.
After discussing the various repair approaches and the associated advantages and
disadvantages, the owner elected to go with Approach 1 and build-out the concrete
replacements for better durability. The owner also elected to coat the façade for
improved durability and appearance.
8.2.2, 8.4.2, 8.4.4, 7.4, 7.5.1, 7.5.2, 7.6.3.2
In this repair approach, unsound and, as necessary, sound concrete was removed
to provide minimum patch depths and minimum gaps behind the reinforcing
bars. The concrete and steel surfaces were cleaned by wire brushing and the steel
surfaces were coated with a corrosion-inhibiting material for improved corrosion
resistance. To achieve the best quality of the installed repairs, removal areas on
vertical surfaces were formed and placed using bird mouths (small angled extensions from the face of the formwork to allow placement of concrete) so that
the plastic replacement material did not have to resist gravity. The bird mouths
produce small extensions of concrete from the surface that are ground off after
form removal. Use of a proprietary latex-modified concrete with 3/8 in. (9.5 mm)
coarse aggregate provided a suitable replacement concrete with good bond to the
existing concrete. The selected material could be mixed in small batches and placed
in locations that generally did not exceed 3 ft2 (0.3 m2) in surface area. Proprietary
materials generally are manufactured with good quality control, reducing the risk
of batching problems at the site. Further, the material exhibited minimal shrinkage
cracking. The build-outs increased the concrete cover at the shallow reinforcing
bars, improving the durability of the replacements.
8.3.1, 8.5.1, 8.5.2
The architectural coating of repaired areas decreased the surface permeability of
the repair concrete and sealed non-moving cracks, which improved the durability
of the repair. (Non-moving cracks are generally formed as a result of shrinkage
during the curing process.) Coating of the remainder of the façade provided a
uniform surface appearance and provided improved durability for areas with
shallow cover that had yet to experience delaminations or spalls. Moving cracks
were routed and sealed prior to application of the architectural coating.
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128
concrete cover could not be increased in replacement areas by building up the
replacement material. Thus, the recommended repair was to remove the deteriorated concrete and install replacement concrete in the removal areas flush with
the surface.
The concrete delaminations and spalls were relatively small and isolated and
had no effect on the structural capacity of the balconies. No unsound concrete
extended into the residential units. No shoring was necessary during the repairs.
While concrete deterioration was limited and isolated on this project, on some
projects, cantilever balconies can have significant top surface deterioration near
the building wall and even into the building interior, resulting in reduced structural
capacity. It may be necessary to shore such balconies for one or more levels below
during the repair process.
7.6.3.2, 8.1.3, 8.5
Unsound and, as necessary, sound concrete was removed to provide minimum
removal depths and minimum gaps behind the @Seismicisolation
reinforcing
bars. The exposed
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University of Toronto User.
Fig. 13.5—Built-out replacement at balcony slab edge.
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Chapter 13: Project Example 2—Typical Façade Repair129
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
concrete and steel surfaces were cleaned by sandblasting and the steel surfaces
were coated with a corrosion-inhibiting material for improved corrosion resistance. To achieve the best quality of the installed repairs, removal areas on vertical
surfaces were formed and placed using bird mouths. Removal areas on overhead
surfaces were formed and cast by dry packing so that the plastic replacement material did not have to resist gravity. A proprietary portland cement concrete with 3/8 in.
(9.5 mm) coarse aggregate was used for top surface and edge concrete replacements. A proprietary latex-modified concrete with 3/8 in. (9.5 mm) coarse aggregate was used on overhead concrete surfaces for increased bond to the existing
concrete. The selected materials could be mixed in small batches and placed in
locations that generally did not exceed 3 ft2 (0.3 m2) in surface area. Proprietary
materials generally are manufactured with good quality control, reducing the risk
of batching problems at the site.
8.4.1, 8.5.1, 8.5.2
It was also recommended, and the owner agreed, to coat the top surface and edges
of the balconies with a traffic-bearing elastomeric coating and coat the balcony
soffits with the architectural coating used on the façade. The surface coating along
with a corrosion-inhibiting coating on reinforcing bars serve to improve durability
of the balconies, particularly at locations of shallow concrete cover. The trafficbearing elastomeric coating will significantly reduce moisture penetration into
the balcony concrete and reduce the potential for future corrosion activity in the
remaining existing concrete and the replacement concrete. The traffic-bearing elastomeric coating will require periodic maintenance over its lifetime.
8.3.1
The surfaces to receive an architectural coating were cleaned by pressure washing
and the architectural coating was applied, all per the recommendations of the
coating manufacturer. On top and edge balcony surfaces to receive a traffic-bearing
elastomeric coating, the surfaces were cleaned by sandblast, existing cracks were
also filled with sealant, and the coating was installed, all per the recommendations
of the coating manufacturer.
Performance under fire and elevated temperatures
Contract specifications
1.6.1, 9.4.1
The LDP prepared contract documents that specified repair materials that satisfied governing regulatory requirements and that conveyed necessary information
to perform the
@Seismicisolation
work. The LDP determined and specified limits of concrete removal
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University of Toronto User.
7.9
Except at the reveal strips where the concrete replacements will be built out,
increasing the fire protection, the repairs will restore the concrete structural
elements to their original as-built condition. The LDP determined that exterior
façade elements were unlikely to be exposed to design fire conditions due to a lack
of nearby flammable materials. Also, the limited small areas of concrete replacements would have no effect on the overall fire resistance of the structure and, even
if repair areas with inadequate fire resistance were enhanced, adjacent unrepaired
sections might still have inadequate fire resistance. Therefore, the LDP determined
that the concrete repairs did not need any special detailing to enhance their fire
resistance, and the authorities having jurisdiction agreed.
1.5.3, 1.5.3a, R1.5.3b, 1.5.3h, 1.5.3e
The LDP provided the owner with a basis of design report providing a description
of the structure, identifying the structural system, listing the codes used for the design
and construction of the structure, and the design-basis code that will be used for the
repair work. The basis of design report also included documentation of structural
conditions in the work area as presented above and identified members that required
repair. The report noted that the structure was safe and that substantial structural
damage was not present. The LDP presented the owner with three approaches for the
repair of the structure of which the owner selected one to perform the repair work.
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130
areas to ensure that no members would be overstressed. The contract documents
also instructed the contractor to be responsible for the control of all construction
debris, including environmentally hazardous materials.
The LDP used ACI 563 as a source for construction specifications. The specification sections that were referenced included:
Section 1—General requirements
Section 3 —Concrete removal and preparation for repair
Section 4 —Formwork
Section 5 —Reinforcement and reinforcement support
Section 8 —Proprietary cementitious and polymer repair material
The repair work did not require any shoring and bracing, therefore, Section 2—
Shoring and bracing, was not referenced. Based on the size of the repairs, latexmodified concrete was specified by the LDP in place of a conventional concrete.
ACI 563, “Specifications for Repair of Concrete Buildings,” addresses conditions that are unique to the project. The standard has mandatory and nonmandatory
requirements checklists at the end of the standard to help the specifier submit as
complete a specification as possible. For the parking structure slab repair, only few
sections from the mandatory and nonmandatory checklists are extracted to include
in the Project Contract Document:
a. Section 1.5.4.1—Show the demarcation line of the project location, specific
work areas, and adjacent construction.
b. Section 1.8.2.1 —Identify work to be performed by certified personnel.
c. Section 3.1.1.2—Provide the surface profile and remove laitance, debris, and
bond-inhibiting materials.
d. Section 3.2.1.1 —Select the means and methods for concrete removal that will
minimize damage to the structure and bruised surfaces on the concrete substrate
that remains within and adjacent to the work areas.
e. Section 3.3.1.1—Show the required depth of concrete removal.
f. Section 4.2.2.6—Specify appearance and texture required.
g. Section 5.2.1.2(b)—Indicate repair coating, application procedures, and coating
repair approval process.
h. Section 8.1.2.1(a)—Review the submittal list and indicated the testing required
to be submitted.
Construction
Quality assurance
1.5.3d
The repair specifications included quality assurance and control measures for
material approvals and field verification of quality. The specified quality control
measures and construction observations were performed during the construction,
including the following:
a. Review of material submittals.
10.2.3
b. Visual inspection of the work in progress.
1.5.1, 10.2.1, 10.2.2, 10.4.1
c. Sounding of concrete surfaces to determine if all loose concrete was removed
prior to repair.
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9.1, 9.2.1, 9.2.2, 9.2.3, 9.2.4, 9.2.5
Based on the assessment by the LDP, the observed distress and deterioration
was of no consequence to the structural integrity of the members being repaired.
Consequently, while temporary shoring is sometimes necessary on balcony repair
projects, it was not required on this project. Nonetheless, the contract documents
required the contractor to notify the LDP when removal amounts exceeded the
maximum areas expected for this project. This allowed the LDP to assess global
and individual member stability, if required, for these areas.
Areas of unsound concrete to be removed and replaced were identified by
hammer tapping the concrete surfaces.
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d. Observation of removal areas to ensure that excessive removal or damage to
steel was not occurring.
10.2.3
e. Observation of the prepared concrete surfaces, the applied corrosion-inhibiting
coating, and the concrete placement and curing operations. This monitoring is
particularly important in the early stages of the repairs so that a minimum level
of quality can be established.
10.3.1
f. Testing of repair concrete, including slump, temperature, air content, and
compressive strength.
10.2.1, 10.2.2
g. Sounding of cured replacements to verify that the replacements are bonded
to the substrate. As none of the concrete replacements were of structural
significance, the LDP determined that bond pulloff testing was not necessary,
but that the replacements should be sounded for debonding.
10.3.1
h. Prior to installation of the traffic-bearing elastomeric coating, the vapor
emissions of representative concrete replacements on top balcony surfaces
were tested to verify that the emissions were less than that recommended by
the coating manufacturer.
PROJECT CLOSE-OUT
Periodic maintenance
Record documents
1.6.3, 1.5.3d, 1.5.3j, 1.5.3k
The owner was provided with copies of the project and construction documents
as well as the recommended monitoring and maintenance program.
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R1.5.3k
Periodic maintenance requirements were discussed with the owner during the
selection of the repair approach, and a schedule of recommended monitoring and
possible maintenance requirements was provided to the owner at the conclusion of
the repair construction, including the following:
1.5.3j
a. In conformance with the current building code, inspections for unsafe façade
conditions from ground level are required every 2 years and close-up inspections
from a swing stage are required every 4 years. Findings of the periodic façade
inspections are to be reported to the building code official.
b. If unsafe conditions are found, the owner should take appropriate precautionary
measures in a timely manner to remediate such unsafe conditions.
c. Cleaning and maintenance of the coated façade surfaces are recommended every
10 to 15 years (depending on performance of the coating) to maintain a satisfactory appearance and assure continued integrity of the coating.
d. Top coating the traffic-bearing elastomeric coating is recommended every 10 to
20 years (depending on performance of the elastomeric coating) to maintain a
satisfactory appearance and assure continued integrity of the coating.
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Description of structure
The 300,000 ft2 (28,000 m2) facility, shown in plan in Fig. 14.1, is a two-story
structure constructed in the 1920s. Until 1971, the supported train deck included
train tracks and loading platforms. The train deck was then converted into parking
and loading facilities for a postal distribution center. As part of an adaptive reuse
project, the train deck will be reconfigured into a multimodal transportation hub
servicing light rail commuter trains, Class 1 rail trains, and buses. The facility is
listed on the National Register of Historic Places.
The train deck, shown in cross section in Fig. 14.2, is constructed of a two-way,
21 in. (530 mm) thick reinforced concrete slab with drop panels that spans between
reinforced concrete columns with capitals. The train deck is covered with 23 to
60 in. (580 to 1500 mm) of granular fill and is divided into four areas by northsouth expansion joints. The top surface of the train deck is protected with a waterproofing system applied directly to the deck. The self-adhering rubberized sheet
waterproofing system was installed in 1993. The asphalt-paved lower, or ground,
level of the facility is used for automobile parking and storage.
The reinforced concrete columns are typically spaced 21 ft (6.4 m) apart in both
orthogonal directions and are 12 to 15 ft (3.7 to 4.6 m) tall. The majority of the
columns are 30 in. (760 mm) in diameter, and approximately two-thirds of the
columns had original or supplemental steel jackets installed on the bottom third of
the columns for impact protection and in response to corroded reinforcing steel and
concrete deterioration that was apparent many years ago.
ACI 562-19 provision numbers applying to each section of text are shown in red at the top right of each paragraph.
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133
University of Toronto User.
Fig. 14.1—Grid layout of train deck.
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Chapter 14: Project Example 3—Adaptive Reuse of Historic Depot
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Fig. 14.2—Typical cross section.
Project initiation and objectives
Governing building codes
Based on discussions with the building officials, as well as the information available on the original design drawings, the relevant building codes adopted by the
jurisdiction were determined as follows.
Jurisdiction—northern U.S. city.
1.2.3
Original building code—Proposed Standard Building Regulation for the Use of
Reinforced Concrete (ACI 1910 with Chicago ruling of 1915 for flat slab design).
In response to the need for uniform design standards for flat slab construction, the
Chicago Building Commission in 1915 adopted the Flat Slab Ruling (commonly
referred to as the Chicago Ruling), which gives formulas for the design of flat slab
structures. As described in the Thirteenth Proceedings of the Annual Convention
of the American Concrete Institute, the ACI Committee on Reinforced Concrete
and Building
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Laws took up the proposed changes offered in the Chicago Ruling
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1.7
Prior to undertaking the adaptive reuse project, the owner needed to evaluate the
condition of the train deck structure and columns, which after 80 years of service
exhibited areas of freezing-and-thawing damage and corrosion-related concrete
deterioration. The evaluation was required to determine the structural adequacy
of the deck and columns to support the new multimodal transportation hub and
determine appropriate repairs, as necessary. The owner also established a desired
50-year service life for the rehabilitated concrete structures. The evaluation and
repair design was executed per the guidance offered in ACI 562.
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Preliminary observations and evaluation
1.3.1, 1.3.2, 1.7.1
The track deck and columns exhibited deterioration consistent with 90 years
of exposure to a harsh northern climate. Deterioration was most prevalent along
expansion joints, at column bases, and along exposed slab edges. To understand the
extent and impact of deterioration of the structural capacity of the existing structure, the LDP recommended that an investigation and assessment be performed.
Concrete conditions
1.7.2
All surfaces of the track deck soffit and supporting columns were visually
surveyed and selectively sounded by hammer tapping. In addition, selective areas
were identified for in-depth study. The expanse of the train deck and potential for
significant cost and disruption associated with removing
@Seismicisolation
the fill to expose the top
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and included these in their 1917 proposed revisions to the 1910 Standard Building
Regulation for the Use of Reinforced Concrete. An article by the assistant engineer for the project published in the December 17, 1921, edition of Railway Age
describes the design of the track structure.
1.2.2
Current building code—2015 International Building Code (2015 IBC), which
references ACI 318-08.
1.2.1
Existing building code—2015 International Existing Building Code (2015
IEBC).
1.1.2, 1.4.1
ACI 562 supplements the 2015 IEBC and the 2015 IBC Chapter 34 and governs
in all matters pertaining to concrete members in existing buildings, except wherever ACI 562 is in conflict with the requirements in the 2015 IEBC, in which cases
the 2015 IEBC governs.
1.2.4
Design-basis code—Because the local jurisdiction has adopted an existing
building code, Sections 1.2.4.1, 1.2.4.2, and 1.2.4.4 of the ACI 562 code directs the
licensed design professional (LDP) to determine the design-basis code in accordance with ACI 562, Chapter 4.
4.1
Per ACI 562 Section 4.1, the design-basis code was determined based on criteria
set forth in the existing building code, which for this project example is the 2015
IEBC. The IEBC contains specific requirements that determine when existing
structures should be upgraded to satisfy the requirements of the current building
code. Per Chapter 11 of the 2015 IEBC, the repair, alteration, addition, restoration, and change of occupancy of a historic structure should comply with the work
classifications described in Chapter 4 of the 2015 IEBC. The work classification
was considered a Level 3 Alteration given that more than 50 percent of the aggregate building was planned for major renovations as part of the adaptive reuse.
The occupancy classification would remain unchanged. Therefore, the existing
structural elements supporting gravity loads (per 707.4 of the 2015 IEBC) need to
comply with the existing building code.
The design-basis code was therefore established as the 2015 IBC. This code
specifies the applicable gravity and lateral loads used for the evaluation and the
rehabilitation design. Live loads not covered by the 2015 IBC are required to be
determined in accordance with a method approved by the building official. For
the determination of truck and railroad loading requirements, the LDP received
approval from the building official to supplement the design-basis code with
AASHTO and AREMA (American Railway Engineering and Maintenance-ofWay Association) codes, respectively. As the facility was on the National Register
of Historic Places, the LDP also had to consider the Secretary of the Interior’s
Standards for the Treatment of Historic Properties.
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Chapter 14: Project Example 3—Adaptive Reuse of Historic Depot135
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
The following types of concrete distress and deterioration were noted in the train
deck slab:
a. Localized areas of freezing-and-thawing deterioration were identified in the top
surface of the train deck slab; no corrosion-related distress was observed at the
top slab surface.
b. The condition of the deck soffit varied widely. Corrosion-related delaminations
and spalls@Seismicisolation
were
prevalent at expansion and construction joints and at drains and
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University of Toronto User.
deck surface dictated the scope of the selective opening and concrete sampling
program. In consultation with the owner and contractor, the LDP recommended
four study areas based on their condition from best to worst, as assessed through
visual inspection and nondestructive testing. The selected areas were also representative of the most common design features across the 6 acre (24,000 m2) site. The
fill was removed from each study area, which included at least one structural bay.
The steel jackets were also removed to expose the lower portion of the columns.
1.7.2
The exposed areas of the top deck surface were visually examined and sounded
by chain dragging and hammer tapping. Because the waterproofing membrane may
affect the acoustic emission from a chain drag survey, the LDP predominately relied
on hammer sounding results to quantify the extent of damage. In-depth examination was performed at selected areas of the deck and columns, including materials
sampling for laboratory testing of concrete quality through petrographic examination, chloride content analysis, carbonation testing, and strength testing. In-place
measurement of corrosion potentials and corrosion rates was also performed.
Samples of steel reinforcing bars were removed and tested to determine appropriate properties to use in the analysis. The waterproofing membrane was in fair
condition. Refer to ACI 364.1R for more detailed information on the evaluation of
concrete structures.
1.7.2
The LDP originally anticipated that delaminations and spalling on the deck
underside could be quantified for estimating repair areas based on the visual survey,
confirmed by delamination surveys in the four study areas. The white paint on
the deck underside was expected to highlight distress in the underlying concrete.
Based on this expectation, the area of distress was first calculated from the visual
survey notes. However, during the close-up inspections and sounding of the deck
study areas, it became clear that numerous delaminations were present that were
not visually identifiable from ground level. Thus, to provide a more accurate basis
for quantifying distress, the LDP selected and hammer sounded 18 bays outside
of the deck study areas. These included several bays for each condition state from
best to worst based on the visual assessment.
1.7.4, 1.7.5, 6.3.5, 6.4.2.1
The material sampling program included the removal of 60 cores. The LDP
selected core locations to ensure that all elements and areas of the structure were
represented and to permit further investigation of conditions of interest. Based
on the preliminary evaluation by the LDP and the robust design of the original
structure, concrete strength was not a significant limiting factor in the adaptive
reuse. Thus, lower-bound values of concrete strength would be sufficient for determining safety of the repaired structure. As such, it was concluded that an exhaustive concrete coring program was not required for the determination of concrete
strength.
However, information collected through the material sampling program was
required to assess the cause and extent of observed concrete deterioration and to
guard against distress mechanisms that might limit the durability of repairs or unrepaired areas that appeared good at the time of the assessment. The LDP selected
concrete cores located both inside and outside of the in-depth study areas. Core
locations were selected to be representative of the various conditions observed. The
findings of the laboratory analysis of concrete and steel samples yielded consistent
results and indicated that further sampling was not required.
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136
openings in the deck. This included areas of original concrete and locations that
had been previously repaired with shotcrete patches.
c. Hammer sounding of the deck soffit detected significantly greater quantities of
delamination than suspected based on visual examination.
d. Corrosion potential and corrosion rate testing indicated that moderate corrosion
was occurring at the deck soffit, particularly around joints, drains, and openings
in the deck. Little if any corrosion activity was detected at the top of the deck.
The following distress and deterioration were noted on the columns:
a. Many of the columns without jackets had deteriorated concrete that extended
1 to 2 ft (0.3 to 0.6 m) above the pavement.
b. Localized areas of corrosion-induced concrete deterioration were noted above
the steel jackets.
c. Steel jacket corrosion was variable, ranging from minor surface corrosion to
heavy rust scaling.
d. Some of the steel jackets were split along vertical seams, which was most likely
associated with the expansion of columns due to the corrosion of embedded
reinforcement.
Material evaluation findings
1.5.3, 8.4.3
Carbonation depth and chloride contents were obtained to evaluate the durability
of the concrete against corrosion-related damage from embedded steel reinforcement. Petrographic examination of concrete samples was used to evaluate concrete
quality and deterioration. The laboratory testing demonstrated that the concrete
quality and composition was typical for site-batched concrete construction of the
early twentieth century. Specific observations included:
a. Typical to above-typical compressive strengths, as described in Section 5.2.2
b. Carbonated concrete beyond the reinforcing steel at the deck underside and
columns
c. Chloride levels in the deck near joints and drains were above the corrosion
threshold values presented in ACI 222R
d. High chloride levels at the column bases (ACI 222R)
e. Highly porous concrete not intentionally air entrained
Summary
University of Toronto User.
1.5.3, 1.5.3a
The LDP provided the owner with a basis of design report that summarized
the findings from the preliminary evaluation. The basis of design report included
a brief description of the age of construction, gravity-load structural system, the
original building code used to design the structure, and historical overview of the
uses the structure was subjected to.
The basis of design report documented the shortcomings in the structure, such as
the existing porous, non-air-entrained concrete being susceptible to damage from
cyclic freezing and thawing. Minor to moderate depths of freezing-and-thawing
damage have occurred in areas throughout the structure where existing concrete
surfaces are exposed and subject to water saturation during freezing conditions.
The most severe deterioration has occurred at the deck underside, particularly
along construction joints and near expansion joints, and at the bases of columns
due to chloride contamination of the concrete. The high level of carbonation
reduces the pH of the concrete and destroys the passive film on the reinforcement,
which encourages corrosion. Future freezing-and-thawing damage deterioration
was likely in exposed portions of the structure, unless protection from quantities of
water sufficient to saturate the concrete is provided. Additional corrosion-related
deterioration was also expected if the chloride-contaminated and carbonated
concrete was not addressed. The LDP addressed these issues to meet the project
objective for a 50-year service life.
@Seismicisolation
@Seismicisolation
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Chapter 14: Project Example 3—Adaptive Reuse of Historic Depot137
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Structural assessment
Requirement for structural assessment
6.2.2
A structural assessment was performed to determine the gravity and lateral load
effects associated with the new loadings proposed for the adaptive reuse. Specifically, the concrete columns and slab structure were evaluated for truck and rail loadings. Deteriorated portions of individual members would be repaired, so that any
strength reduction due to the deterioration was not considered in the assessment.
Existing properties
Structural analysis
5.2.3, 5.1.3
Loads—The applicable gravity, wind, and seismic loads were determined using
the design-basis code. The dead loads were based on the documented self-weight of
the existing structure
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and the weight of the proposed fill and additions associated with
@Seismicisolation
University of Toronto User.
1.7.1, 1.7.2, 1.7.4, 6.2.4
Existing structural geometry—The existing structural geometry was obtained
from the original construction documents and verified through field measurements.
Column spacings, column dimensions, and drop panel dimensions were measured.
The slab thickness was confirmed by physical measurements at core holes drilled
through the slab. Fill depths were measured at exploratory openings.
6.3.2, 6.3.3, 6.4.2.1, 6.4.3.1, 5.1.3
Concrete strength—Concrete core samples were extracted from the train deck
and the columns and tested in compression to determine properties for use in the
analysis. A total of 60 cores were removed, with 26 tested in compression. Ten cores
from the slab and 10 cores from the columns were tested. The average strength of
the deck cores was 8130 psi (56 MPa), with a range of 4790 to 9980 psi (33.0 to
68.8 MPa) and a standard deviation of 1500 psi (10.3 MPa). Based on Eq. (6.4.3.1)
in ACI 562, the equivalent specified concrete strength was approximately 6600 psi
(45.5 MPa). The average strength of the column cores was 5070 psi (35.0 MPa),
with a range of 3070 to 8580 psi (21.1 to 59.2 MPa) and a standard deviation of 1560 psi
(10.8 MPa). Based on Eq. (6.4.3.1) of ACI 562, the equivalent specified concrete
strength was approximately 3900 psi (26.9 MPa). The equivalent specified concrete
strengths are significantly greater than the default value of 2000 psi (13.8 MPa) for
slabs and columns in Table 6.3.1a in ACI 562.
The historic documents indicated that each slab bay was batched on-site, which
could produce variable concrete properties throughout the depot. The sample
size was considered relatively small given the extensive quantity and method of
batching. As such, the LDP elected to use lower-bound concrete strengths of 5000 psi
(34.5 MPa) for the slabs and 3000 psi (20.7 MPa) for the columns in the structural assessment, which are greater than the values presented in Table 6.3.1a. The
visual survey of concrete and the 30 additional cores suggested generally consistent quality from the sampled areas, which represented conditions varying from
good to poor. The structural analyses yielded suitable results to accommodate the
owner’s objectives for the reused structure. As such, a more costly and thorough
concrete sampling program was not deemed necessary.
6.4.4.1
Reinforcing steel layout and strength—Reinforcing steel spacing and cover were
determined by magnetic surveys and confirmed at inspection openings on the train
deck and the columns. The field measurements were in good agreement with the
design drawings.
6.4.5.1, 6.4.6
Reinforcing bar samples were obtained from deck and columns and tested in
tension to determine the steel material properties. The bars were determined to be
intermediate grade reinforcing steel with a yield strength of 40,000 psi (276 MPa).
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138
Structural analysis findings
5.1.3, 9.2.1, 9.2.2
Gravity load effects—The structural analysis, which was based on the requirements of the design-basis code and the project load criteria, determined that the
structure had adequate calculated capacity to support the gravity loads from the
proposed adaptive reuse. Analysis of the structure under repair, which considered
concrete removal when determining member limit states, indicated that shoring
was not required to support dead loads and construction live loads.
Live load effects—The structural analysis indicates that the existing track
deck did not have adequate flexural capacity to support the Cooper E-80 trainaxle loading (AREMA code), but was sufficient for lighter Cooper loadings. The
Cooper E-80 loading was the most severe load case required by the project criteria.
The track deck was found to be adequate for the light rail and bus loadings anticipated in the adaptive reuse. The columns had adequate capacity to support E-80
loadings, and thus by extension the lighter rail and bus loadings.
Lateral load effects—The lateral-load-resisting system was slab-column frames
in both orthogonal directions. The original structure was designed for wind load
effects, but seismic loads were not considered in the 1920s. The wind load effects
from the design-basis code were relatively modest for the two-story structure and
by structural engineering judgment and analysis did
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not control the design.
@Seismicisolation
University of Toronto User.
the adaptive reuse. Live loads were prescribed by the project load criteria, including
a series of train axle loads and bus uniform and axle loads. The uniform load for
platform areas was based on the requirements of the 2015 IBC. Impact factors and
braking forces were estimated based on the provisions of AREMA codes.
1.3.8
Wind and seismic loads were determined in conformance with the requirements
of the 2009 IEBC. The 2015 IEBC references ASCE/SEI 41-2013 for the seismic
evaluation of existing buildings and ASCE/SEI 41-2013 for the seismic rehabilitation of existing buildings.
5.1.3
Loads during the construction and repair process were also considered and
evaluated in accordance with ASCE/SEI 37-2014, as the structure was unoccupied
during the construction period.
6.5.1
Load factors and load combinations—The load factors and load combinations
were determined based on the requirements of the 2005 AREMA Manual in conformance with the project design criteria, which were at least equal to the effects of
factored load combinations specified in ASCE/SEI 7-2005.
6.5.2, 6.5.3
Analysis—A portion of the train deck was modeled as uncracked concrete
sections using finite element modeling. The model included the support columns
and appropriate boundary conditions. A linear elastic analysis was performed.
The analysis was in general conformance with the 2005 AREMA Manual and was
consistent with general industry practice.
6.7.1
Because all unsound deck and column concrete was planned for repair before the
construction on top of the train deck was installed, the effects of the concrete deterioration were not included in the finite element model for evaluating the adaptive
reuse. An analysis was also performed to determine if the train deck and column
concrete remaining after the assumed extent of removal of deteriorated concrete
could safely support the dead and construction live loads during the repair installation and its portion of the long-term dead and live loads after the repairs had been
completed.
5.1.2, 5.2.2
Flexural and shear capacities were calculated based on the requirements of the
2005 AREMA Manual, which as a supplement to the design-basis code took precedence over the provisions of Section 5.4 in ACI 562.
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GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Recommended repair program
Train deck rehabilitation
Based on the assessment and evaluation work, the LDP recommended widespread repairs to the deck underside, whereas only localized repairs at the deck top
surface were necessary. Future periodic maintenance of the deck underside was
also anticipated to achieve the desired 50-year service life. Measures to protect the
topside of the
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repaired deck from future water ingress through full-depth cracks
@Seismicisolation
University of Toronto User.
6.7.4.3, 1.7.3
A basic check of the seismic demands and column capacities was performed
by the LDP to understand the overall magnitude of the seismic risk and if a more
detailed seismic analysis would be required. The effort of the LDP here was considered a preliminary analysis. Per ACI 562 Section 1.7.3, the LDP was permitted to
assume a design-basis code and selected the Equivalent Lateral Force Procedure
in ASCE/SEI 7-2010.
A typical column was checked for its tributary seismic mass using the seismic
requirements in ASCE/SEI 7-2010. The ground motion values SDS and SD1 were
obtained from the USGS Design Maps website using the project latitude and
longitude coordinates, a soil classification of D (stiff soil), a risk Category of I,
and a seismic importance factor of 1. The SDS and SD1 values placed the structure
in the Seismic Design Category A, which defines the applied lateral forces to be
0.01W per story (that is, the lateral force applied at the top of the column is 0.01
× the tributary dead load that the column supports). Comparing this demand with
the flexural capacity of a typical column the demand to capacity ratio (DCR) was
calculated to be approximately 1.5 percent. Given the low seismic demand, the
LDP decided that no further seismic evaluations were necessary.
Note that the evaluation of the structure using the procedures of ASCE/SEI 31 yields
a similar conclusion. Under this analysis, the structure and assessment allow for the
use of the Low Seismicity Checklist per Section 3.6 of ASCE/SEI 31. The two checklist items for structural components were both found to be compliant. Load path was
compliant because the slab and columns and retaining walls allow for transfer of inertial
forces to the foundations. Wall anchorage was compliant to satisfy the forces calculated
in the referenced Quick Check Procedure. No further analysis was therefore required.
Seismic Design Category—To determine the detailing requirements in the 2015 IBC
it was necessary to determine the Seismic Design Category of the structure (2015 IBC,
Section 1908.1.2). As noted previously, the computed SDS and SD1 values place the
structure in Seismic Design Category A (2015 IBC Table 1613.5.6 (1) and (2)). For
Seismic Design Category A structures, the requirements of Chapter 21 of ACI 318-14
did not apply (2015 IBC Section 1908.1.2; ACI 318-14 Section 21.1.1.3).
6.5
Lateral-load-resisting system—The capacities of the as-built slab and column
frame members were calculated based on provisions of the 2015 IBC. The seismic
demands were extremely small relative to the member capacities. In fact, the calculations demonstrated that, due to the relatively large dead loads, the columns under
seismic loadings remained elastic. The slab also had adequate calculated capacity
to resist the moment and shear effects of the design load combinations.
As-built detailing—The as-built detailing did not strictly conform to the requirements of the 2015 IBC and ACI 318-14, excluding Chapter 21. It would be
prohibitively expensive to bring the as-built detailing into conformance with the
requirements of the design-basis code. As the existing structure has performed
satisfactorily for 90 years with no visible signs of structural distress, and as the
adaptive reuse would not significantly increase the structural loadings, the LDP
determined that no structural rehabilitation was necessary for the adaptive reuse.
It should be noted that the Chicago Ruling of 1915 was one of the first guides
published for flat slab design. Flat slab design at the time was a relatively new
concept that yielded structures with very robust reinforcement schemes. The
authorities having jurisdiction concurred with this assessment.
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140
and joints were determined to be critical to prolonging the life of the repairs and
the repaired structure.
The execution of localized repairs was determined to be considerably more cost effective than complete deck replacement. However, complete deck replacement at areas of
severe deterioration, such as expansion joints, was cost effective and considered.
Repairs recommended for the train deck:
a. Partial-depth topside and underside surface repairs
b. Full-slab-thickness repairs, primarily along expansion joints and near drains
c. Removal and repair of all underside slab deterioration not addressed by fullslab-thickness repairs
d. Crack and construction joint sealing
e. New expansion joint seals
f. New drains
g. Topside waterproofing/deck protection
Of these, the buried fully adhered waterproofing with an unbonded concrete topping
was likely the most durable in this application. Bonded overlays (concrete or polymer
resin) would be designed similar to those used in bridge deck rehabilitation and protection. An exposed traffic-bearing waterproofing membrane
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was also considered, but the
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University of Toronto User.
The partial-depth surface repairs and full-slab-thickness repairs would include
removal of unsound concrete and sufficient sound concrete to create minimum
replacement depths and gaps around exposed reinforcing bars, and restoration of
the structural cross section at the repair areas. Because chloride contamination was
limited to deteriorated areas where the concrete would be removed as part of the
repair process, supplemental corrosion mitigation such as galvanic anodes were
not considered to be of significant value in these deck repairs.
8.4.3
Given the level of underside concrete deterioration, significant areas of the
deck soffit required repair. The areas to remain are known, based on testing, to be
carbonated to the level of reinforcing steel. As such, future corrosion-related deterioration of these areas should be anticipated. Several alternatives were considered,
as described in the following paragraphs, to address the long-term durability of
these areas. The historic character of the structure also required that soffit repairs
be developed to mimic the plank formwork look of the original, existing surface.
8.2.2, 8.5
Elimination of water and chlorides will slow the rate of embedded steel corrosion.
The adaptive reuse recommendations for the train deck included the new deck joints and
drains and the removal and replacement of the entire topside waterproofing, which would
eliminate water ingress from the top surface. The LDP also recommended coating the
deck soffit with a breathable surface sealer to limit water and chloride ingress. Both of
these treatments will slow the rate of deterioration and extend the life of original concrete
areas to remain. Nonetheless, periodic maintenance of the deck soffit should be expected.
8.4.7
Electrochemical realkalization of the original concrete areas to remain was also considered to mitigate future corrosion-related damage due to the carbonated concrete. The
realkalization process restores the alkalinity of carbonated concrete, thereby increasing its
pH to levels that will slow the corrosion rate. The cost and benefits of this treatment did
not justify its use in the context of other treatments proposed as part of the adaptive reuse.
8.5.1, 8.5.2, 8.3.1, 8.4.1
The elimination of water leakage through the deck was critical to achieving the
desired service life for the repaired structure. Several topside waterproofing/deck
protection strategies were developed for the owner’s consideration:
a. Buried, fully adhered, flexible, monolithic waterproofing with unbonded
concrete wear course
b. Bonded, high-performance concrete overlay
c. Bonded, thin, polymer-resin-based overlay
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LDP determined that this system would not have the desired durability for this project
as it would require significant maintenance and repair due to wear.
The owner selected the buried, fully adhered, flexible, monolithic waterproofing
with an unbonded concrete wear course as the system that best protected the structure for purposes of achieving the desired 50-year service life. This waterproofing
system served to improve the durability of both the repaired and original train
deck concrete and mitigate leakage at locations where new cracks could form after
the repair program was completed. Installation of the new waterproofing required
removal of 23 to 60 in. (580 to 1500 mm) of fill, removal of the existing waterproofing and preparation of the deck to receive the new waterproofing membrane.
The LDP developed details and specifications for this work. The LDP also
designed a variable thickness concrete protection course to protect the membrane
and improve sub-surface drainage beneath the fill.
The LDP presented the following alternatives for the owner’s consideration:
1. Fully welded structural steel jacket with sacrificial galvanic anodes (Fig.
14.3 and 14.4). The steel jacket would provide structural confinement, so spiral
reinforcement that might corrode in the future would not require repair and would
be a barrier to future water and chloride infiltration, which should reduce future
corrosion rates. The sacrificial galvanic anodes would provide long-term protection against anticipated ongoing corrosion of original column reinforcement that
would remain embedded in chloride-contaminated concrete. Based on consultations with various product and material manufacturers and personal experience, the
LDP estimated that this repair would have a service life of approximately 50 years.
2. Structural steel jacket with corrosion-inhibiting admixture (Fig. 14.3
and 14.4). The repair was similar to Alternative 1. The new concrete included a
corrosion-inhibiting admixture and the galvanic anodes were omitted. The corrosion-inhibiting admixture would help reduce corrosion of the spiral reinforcement,
but was not expected to be effective in preventing ongoing corrosion of the vertical
bars that remain embedded in chloride-contaminated concrete. The estimated
service life is lower because there is not a direct means to mitigate the anticipated
ongoing corrosion of existing vertical reinforcement. Based on consultations with
various product and material manufacturers and personal experience, the LDP estimated that this
@Seismicisolation
repair would have a service life of approximately 20 to 30 years.
@Seismicisolation
University of Toronto User.
Column rehabilitation
Several constraints limited the rehabilitation options for the columns. The columns
were reinforced with tightly spaced spirals (pitch of less than 3 in. [75 mm]) that would
complicate the removal of chloride-contaminated concrete. To gain access behind
the vertical bars for concrete demolition and replacement, the spirals would need
to be removed. This would create the potential for buckling of vertical bars under
construction loads. Shoring was not feasible from a cost and scheduling perspective
due to the extensive work associated with timber foundations and other rehabilitation
work in the area of the columns. A solution that left the vertical bars in chloridecontaminated concrete with protection provided by alternative corrosion mitigation
strategies was required. The steel jackets had been installed for impact resistance
and in response to corroded reinforcing steel and concrete deterioration that was
apparent many years ago. Split seams in some of the jackets and continued corrosion of the column reinforcement indicated that the reinforcing steel corrosion activity
has continued. Accordingly, the LDP judged that the steel jackets had or were close to
reaching their effective service life. Therefore, the rehabilitation option would also need
to include provisions for impact protection of the column bases.
Five foot (1.5 m) tall steel and concrete jackets were considered for impact
protection. Installation of the new jackets would require removal of existing steel
jackets, removal of chloride-contaminated concrete to the depth of the exterior
of the vertical reinforcing bars, installation of new fully grouted steel jackets or
bonded reinforced concrete jackets that extended to the column bases, and corrosion mitigation measures.
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142
3. Concrete jacket with sacrificial galvanic anodes (Fig. 14.3 and 14.5). New
horizontal hoop reinforcement included in the concrete jacket provided additional
structural confinement so existing spiral reinforcement that might corrode in the
future would not require repair. New reinforcement would be epoxy-coated to
provide resistance to future corrosion. Sacrificial galvanic anodes were recommended to provide long-term protection against anticipated ongoing corrosion of
existing column reinforcing bars that remain embedded in chloride-contaminated
concrete. The concrete jacket would protrude 2 to 3 in. (50 to 75 mm) beyond
the column surface, altering the column appearance. Based on consultations with
various product and material manufacturers and personal experience, the LDP estimated that this repair would have a service life of approximately 50 years.
4. Concrete jacket with corrosion-inhibiting admixture (Fig. 14.3 and 14.5).
The repair was the same as Alternative 3, except it did not include galvanic anodes
and the new concrete included a corrosion-inhibiting admixture. The corrosioninhibiting admixture would help reduce corrosion of the spiral reinforcement, but
was not expected to be effective in preventing ongoing
@Seismicisolation
corrosion of the vertical
@Seismicisolation
University of Toronto User.
Fig. 14.3—Column jacket repair concept.
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Chapter 14: Project Example 3—Adaptive Reuse of Historic Depot143
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Fig. 14.4—Steel jacket repair concept: Alternate 1 (shown); and Alternate 2 (as noted).
Concrete repair details
7.4, 7.5.1, 7.5.2, 7.4.1.1, 7.4.1.2, 7.4.5, 7.4.6
Bonding of the new concrete to the existing concrete was considered critical
to satisfactory performance of the deck soffit repairs, particularly with regard to
underside repairs becoming loose and falling in the future. The research and test
results for various repair materials were reviewed to develop appropriate project
material specifications
@Seismicisolation
and procedures for concrete replacement. The horizontal
@Seismicisolation
University of Toronto User.
bars that remain embedded in chloride-contaminated concrete. The estimated
service life was lower because there was not a direct means to mitigate the anticipated ongoing corrosion of original vertical reinforcement. Based on consultations
with various product and material manufacturers and personal experience, the LDP
estimated that this repair would have a service life of approximately 20 to 30 years.
If galvanic anodes were used in the column repairs, the size and spacing of the
anodes would be determined in consultation with the anode manufacturer. The size
and spacing of anodes would be dependent on the amount of reinforcement to be
protected, the desired service life extension, and the severity of the environment.
Localized, conventional, partial-depth concrete surface repairs would also be
required above the new jackets at some columns. Because these repairs were
expected to be generally small, localized removal of concrete behind vertical bars
could be performed and the column cross section restored.
The owner selected corrosion mitigation Alternative 1, fully welded structural
steel jackets with sacrificial galvanic anodes, as the option that best met the 50-year
service life criteria and maintained the historic character of the structure.
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Fig. 14.5—Concrete jacket repair concept: Alternate 3 (shown); and Alternate 4 (described).
In addition to the items discussed previously, the concrete repairs included the
following features:
a. Reentrant corners were avoided in both the repair and existing concrete.
7.6.6, 7.3.3, 7.4
b. After concrete removal work was completed, the exposed concrete surfaces
were cleaned and prepared to receive the repair material. To achieve composite,
monolithic behavior, replacement concrete was bonded to existing substrate
using chemical or mechanical means, or both.
8.4.4
c. Existing reinforcing bars that were exposed in concrete removal areas were
cleaned and coated with a corrosion-inhibiting material to reduce future corrosion in and around the concrete replacements, except in areas where galvanic
anodes were installed.
8.4.4
d. New epoxy-coated reinforcing bars were lapped with existing bars that were
exposed in removal areas and had lost structurally
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significant cross-sectional
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University of Toronto User.
shear demand at the interface of the repair and existing concrete was calculated based
on the loads and combinations described previously; vu = 45 psi (vu = 0.31 MPa). The
calculated design interface shear stress was verified by performing pulloff tests and a
mean capacity of 100 psi (0.7 MPa) was determined with the specified surface preparation, such that vu ≤ fvni is satisfied. As part of the field assessment, pulloff testing
of the substrate determined that the substrate had adequate strength to achieve the
required bond strength. Based on the required bond strength, the LDP concluded that
the required bond could be attained by chemical or mechanical means with proper
surface preparation (ICRI 310.1R, ICRI 320.2R, and ICRI 210.3R) and repair material application. Therefore, no supplemental reinforcement was required.
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Chapter 14: Project Example 3—Adaptive Reuse of Historic Depot145
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Contract specifications
1.5.1, 1.6.1, 9.4.1, 10.2.2
The LDP prepared contract documents that specified repair materials that satisfied governing regulatory requirements and that conveyed necessary information
to perform the work, including environmental considerations.
The LDP used ACI 563 as a source for construction specifications. The specification sections that were referenced included:
Section 1—General requirements
Section 2—Shoring and bracing
Section 3—Concrete removal and preparation for repair
Section 4—Formwork
Section 5—Reinforcement and reinforcement support
Section 6—Conventional concrete mixtures
Section 7—Handling and placing of conventional concrete
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area. The epoxy coating was used as a corrosion-reduction measure. Uncoated
bars were used in areas where galvanic anodes were installed.
8.2.2
e. Because much of the existing concrete was scheduled to remain, the as-built
reinforcing steel cover would generally not be modified. The corrosion reduction measures incorporated into the repair program were therefore developed to
reduce future corrosion activity, offsetting any shallow cover issues.
8.1.1, 8.1.2, 8.1.3
f. The replacement concrete was developed to have similar or slightly enhanced
properties compared to the existing concrete and, in particular, was required to
have adequate air content for freezing-and-thawing resistance.
7.6.3.3
g. The existing and new reinforcing bars were developed in the existing concrete,
the repair concrete, or both.
h. Deck soffit repairs were formed with planks to simulate the appearance of the
original concrete surface and cast with concrete. Replacement concrete was
generally cast from the top deck surface through core holes.
7.1.1, 7.2.1, 7.2.2
i. The repaired sections were designed to have similar strength and stiffness to the
originally constructed sections.
7.9.1
j. The repaired slab was designed to have similar fire resistance rating compared to
that of the existing slab.
8.5.1, 8.5.2
k. The column surfaces, including the steel jackets, were coated to limit future
moisture penetration into the concrete and corrosion of the steel jackets. Appropriate coatings were selected in consultation with the architect and coating
suppliers.
9.1c, 9.2.1c
l. The LDP established limits for concrete removal and required monitoring of
the removal work. If these limits were exceeded, the contractor was required
to engage a licensed engineer to verify the integrity of the structure or design
shoring, as necessary.
9.2.5
m. The LDP required monitoring of the concrete removal work for loss of reinforcing steel development and possible short-term and long-term structural
implications, and for possible structurally significant loss of reinforcement
cross-sectional area.
n. The LDP required the contractor to notify the LDP if unsafe conditions were
encountered or if the in-place reinforcement was different than shown on the
contract documents. If unsafe conditions were encountered, additional temporary shoring was specified for installation.
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146
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Section 8—Proprietary cementitious and polymer repair materials
Section 9—Crack repair by epoxy injection
Based on the size of the repairs, conventional concrete and proprietary cementitious and polymer repair materials were specified by the LDP in place of a proprietary material or shotcrete.
ACI 563, “Specifications for Repair of Concrete Buildings,” addresses conditions that are unique to the project. The standard has mandatory and nonmandatory
requirements checklists at the end of the standard to help the specifier submit as
complete a specification as possible. For the adaptive reuse of a historic structure,
the main sections from the mandatory and nonmandatory checklists are extracted
to include as a minimum in the Project Contract Document:
a. Section 1.5.1.1—State the maximum dead and live loads and any temporary
reduction in loads, to be permitted during repair and after completion of repair
program, in concert with the requirements of 2.1.1.1.
b. Section 1.5.2—Designate Owner-approved work areas and schedule
requirements.
c. Section 1.5.4.1—Show the demarcation line of the project location, specific
work areas, and adjacent construction.
d. Section 1.8.2.1—Identify work to be performed by certified personnel.
e. Section 1.8.2.2(d)—Point out specific repair procedures that require review and
approval.
f. Section 1.8.2.2(e)—Specify submittal of component materials, repair material
mixture proportions or batch requirements, and concrete supplier’s or repair
material manufacturer’s QC program.
g. Section 1.8.3.2.(d)—Determine frequency of sampling and whether sampling
will be performed on a random basis. Indicate testing requirements in accordance with critical design performance requirements.
h. Section 2.3.3.2—State whether specialty engineer inspection is required.
i. Section 3.1.1.2—Provide the surface profile and remove laitance, debris, and
bond-inhibiting materials.
j. Section 3.1.3.1—Indicate testing locations, type, number, and frequency of tests.
k. Section 3.1.3.1(a)—Determine if pulloff strength testing is required and provide
the minimum pulloff strength.
l. Section 3.2.1.1—Select the means and methods for concrete removal that will
minimize damage to the structure and bruised surfaces on the concrete substrate
that remains within and adjacent to the work areas.
m. Section 3.1.2.4—Specify whether high-pressure water for concrete removal by
hydrodemolition is permitted to be used for the project and permitted locations.
n. Section 3.2.1.5—State the required surface profile.
o. Section 3.3.1.1—Show the required depth of concrete removal in Contract
Documents.
p. Section 3.3.4.2 –— Indicate that tensile pull-off tests shall be performed at specified locations in accordance with ASTM C1583/C1583M.
q. Section 4.1.2.2—Review the submittal list and indicate in Contract Documents
the items to be submitted.
r. Section 5.2.1.1—Specify required grades, types, and sizes of reinforcing bars.
s. Section 5.3.3.7—Indicate locations of splices.
t. Section 6.2.2.6(d)—State the chloride exposure classification for are of work.
u. Section 6.2.2.7—Indicate the specified concrete compressive strength, fc′ for the
work.
v. Section 7.1.2.2—List the information in 7.1.2.2(a) to 7.1.2.2(g) that is to be
submitted.
w. Section 8.1.2.1—Indicate which repair products require samples, and the quantity and size(s) of samples required.
x. Section 9—Repair of cracks by epoxy injection in accordance with ACI 503.7.
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Chapter 14: Project Example 3—Adaptive Reuse of Historic Depot147
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Construction
9.1b, 9.4.1
The LDP monitored the construction for unexpected conditions that could affect
the short-term or long-term safety of the structure. The contractor was required to
notify the LDP if reinforcement with 10 percent or more loss of cross-sectional
area (ACI 364.10T) was encountered. Temporary shoring or bracing may be necessary (Section 7.1.3). Environmental concerns, such as limiting water with debris
to flow into floor drains or off of the site and disposal of construction debris, were
specified in conformance with local ordinances.
Quality assurance
10.2.1, 10.2.2, 10.4.1
The repair specifications included quality assurance and control measures for
material approvals and field verification of qualities. The specified quality control
measures and construction observation were performed during the construction,
including the following:
a. Review of material submittals.
10.2.3
b. Visual inspection of the work in progress.
c. Sounding of concrete surfaces to determine if all loose concrete was removed
prior to repair.
10.2.3
d. Observation of the prepared concrete surfaces prior to placement of repair
materials, and of the concrete placement and curing operations (ICRI 310.1R
discusses surface preparation for repair of deteriorated concrete).
10.3.1
e. Testing of repair concrete, including slump, temperature, air content, and
compressive strength.
f. Bond strength testing of in-place repair concrete to confirm assumption of full
composite action between repair materials and existing materials.
g. Electrical connectivity testing of the column reinforcing steel and the galvanic
anodes.
h. Moisture testing by an ICRI-certified floor moisture technician prior to the installation of coatings and waterproofing (ICRI Concrete Surface Repair Testing
Technician).
Periodic maintenance
1.5.3k
Periodic maintenance requirements were discussed with the owner during the
selection of the most appropriate repair concepts, and a schedule of recommended
monitoring and possible maintenance requirements was provided to the owner at
the conclusion of the repair construction, including the following:
a. Periodic inspections of the train deck soffit and columns every 3 to 5 years to
monitor the condition of the concrete
b. Limited concrete deck soffit and column repairs every 5 years
c. Injection of leaking train deck cracks every 5 to 10 years
d. Coating repair or recoating of concrete and steel jacket surface treatments
Record documents
1.6.3, 1.5.3d, 1.5.3j
The owner was provided with copies of the project and construction documents
and the recommended monitoring and maintenance program.
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PROJECT CLOSE-OUT
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148
Description of structure
The facility consists of an 11-story office building over a two-story, 100,000 ft2
(9300 m2) parking structure supporting an open-air plaza. The building is located
in the northern United States, and construction was completed in 2013.
The supported garage slab is a reinforced concrete flat plate, and the plaza slab
is a reinforced concrete flat slab with drop panels.
Project initiation and objectives
Shortly after construction was completed and the certificate of occupancy
was obtained excessive deflections and top surface cracking were noted on the
supported garage slab. Crack maps of the supported garage slab are shown in Fig. 15.1.
The project was initiated to determine the causes of the cracking and deflections
and the overall safety of the as-built structure.
Governing building codes
The building codes adopted by the jurisdiction were determined.
Jurisdiction—Northern U.S. city.
Original building code—2009 International Building Code (2009 IBC).
Current building code—2018 International Building Code (2018 IBC).
1.2.3
1.2.2
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Chapter 15: Project Example 4—Parking/Plaza Slab Strengthening
University of Toronto User.
Fig. 15.1—Supported garage slab with top surface cracking mapped.
ACI 562-16 provision numbers applying to each section of text are shown in red at the top right of each paragraph.
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GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
1.2.1, 1.4.1
Existing building code —The jurisdiction had adopted the International Existing
Building Code (2018 IEBC).
1.1.2, 1.3.1
ACI 562 supplements the existing building code and governs in all matters
pertaining to concrete members in existing buildings, except wherever ACI 562
is in conflict with the requirements in the existing building code in which case the
existing building code governs.
1.2.4, 4.1
Design-basis code—Based on a preliminary evaluation as described in Section 4
of this example and considering the requirements of the existing building code,
the design-basis code was determined to be the 2009 IBC and, by reference,
ACI 318-14.
Preliminary evaluation
Document review
1.7.1
The design drawings, construction documents, and various reports were available and reviewed by the licensed design professional (LDP). The construction
documents and reports confirmed that the concrete and reinforcing bars met the
specified material properties.
Existing site conditions
Strength of as-built structure
1.7.3, 1.7.4
Preliminary analysis—A preliminary analysis was performed for a few locations of the supported garage slab and the plaza slab to estimate the decrease in the
as-built strength compared to the design strength due to the documented construction deficiencies; that is, the decreased drop panel thicknesses and the increased
concrete cover over the top reinforcing bars. The 2009 IBC was assumed to be the
design-basis code for the purposes of the preliminary evaluation.
Effects of shallow drop panels—The shallow drop panel condition on the plaza
slab decreased the effective depth of the slab reinforcement d, the distance from
the extreme compression fiber to the centroid of the longitudinal tension reinforcement, from the design value of 26 3/4 in. (680 mm) to the as-constructed value of
18 3/4 in. (475 mm), a decrease of approximately 30 percent. In accordance with
ACI 318-14 Section 10.3, the slab flexural capacity is calculated as follows
φM@Seismicisolation
= φ (As)(fy)(d){1 – [(ρ)(fy) / (2 (0.85)(f'c ))]}
n@Seismicisolation
University of Toronto User.
1.7.1, 1.7.2
Existing structural geometry—The existing structural geometry, including
typical dimensions and member sizes, was measured on site. The thickness of the
drop panels in the plaza slab was measured to be approximately 6 in. (150 mm)
compared to the design thickness of 14 in. (355 mm), as shown in Fig. 15.2.
1.7.1
Existing concrete condition—The top surface cracks on the supported garage
slab were mapped (Fig. 15.1) and the top surface elevations were surveyed to
document the slab deflections.
1.7.1
Reinforcement—The reinforcement layout in the garage slab was documented
using ground penetrating radar (GPR) supplemented by exploratory chipping at
isolated locations to expose reinforcing bars and confirm the GPR findings. The
investigation revealed areas having over 4 in. (100 mm) of concrete cover to the
top reinforcing bars compared to the as-designed cover of 0.75 in. (19 mm), as
shown in Fig. 15.3.
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150
where φ is the strength reduction factor for tension-controlled flexural sections; Mn
is the nominal flexural strength of the section; As is the area of steel reinforcement;
fy is the specified yield strength of the reinforcement; ρ is the steel reinforcement
ratio, As/bd; and f′c is the specified concrete compressive strength.
The slab flexural capacity is directly and indirectly related to d. The measured
decrease in d resulted in a calculated flexural deficiency of 30 to 40 percent.
4.3.1, 4.5.1
The calculated demand-capacity ratio of nominal loads of the current building
code and factored load combinations of ASCE/SEI 7 to the current in-place nominal
capacity of the plaza slab adjusted by the reduction factor in ACI 562 Section 5.4 was
1.3, which is less than 1.5 (Uc/fRcn = 1.3 < 1.5). The LDP assessed the structural
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Chapter 15: Project Example 4—Parking/Plaza Slab Strengthening151
University of Toronto User.
Fig. 15.2—Illustration of as-designed drop panel thickness on plaza slab compared to as-built drop panel
thickness.
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GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
24” TO 30”
(610 TO 760 mm)
10”
(250 mm)
3/4” (19 mm)
CLEAR COVER
3/4” (19 mm)
CLEAR COVER
AS-DESIGNED
24” TO 30”
(610 TO 760 mm)
2” TO 4” (50 TO 100 mm)
CLEAR COVER
(3” [75 mm] COVER
DEPICTED HERE)
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10”
(250 mm)
152
3/4” (19 mm)
CLEAR COVER
AS-BUILT
Fig. 15.3—Illustration of as-designed concrete cover compared to as-built concrete cover for top reinforcing bars of supported garage slab.
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slab by calculating the demand-capacity ratio using the strength design demand
determined using the nominal loads and factored load combinations of the original
building code and the structural slab capacity adjusted by the strength reduction
factor of the original building code (Uo/fRcn = 1.18 > 1.0). Therefore, repairs are
needed to restore the plaza slab to its pre-damaged state.
The slab punching shear capacity is calculated in accordance with ACI 318-14
as follows
fVn = φ(4)(√f′c)(bo)(d)ACI 318-14 Eq. (22.6.9.6) (in.-lb units)
fVn = φ(0.33)(√f′c)(bo)(d)ACI 318-14 Eq. (22.6.9.6) (SI units)
where φ is the strength reduction factor for shear; Vn is the nominal punching shear
strength of the section; and bo is the perimeter of the critical section for shear in
slabs.
Refer to Fig. 15.4 for an illustration of bo and d.
Compliance method and design-basis code
4.2.1
Compliance method—For this project, the LDP elected to use the prescriptive
compliance method in the 2012 IEBC, Chapter 4, which was previously Chapter
34 of the IBC. Specific minimum construction work requirements are prescribed
in this chapter.
4.1.2, 4.1.4
Design-basis code—The construction deficiencies do not constitute substantial
structural damage, as defined by the 2012 IEBC. Therefore, the design-basis
code for the required strengthening repairs was the 2009 IBC.
1.5.3.1, 1.5.3.1a, 1.5.3.1b, 1.5.3.1c, 1.5.3.1h, 1.5.3.1i
Basis of design report—The LDP presented the owner with a basis of design
report in which a description of the building was reported; unsafe structural conditions as determined by the preliminary evaluation were listed; and a slab plan with
cracks mapped was included in the report as well as the main calculations validating that the existing elevated slabs were unsafe in their present condition. The
design-basis code used for the strengthening of the elevated slabs was also listed
in the basis of design report.
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The slab punching shear capacity is also directly related to d. The measured
decrease in d resulted in a calculated shear deficiency of 30 percent.
Effects of excessive cover—The excessive cover for the top reinforcing bars
in the supported garage slab similarly decreased the slab d from the as-designed
dimension of 8-3/4 in. (220 mm) to as little as 5-3/4 in. (145 mm), a decrease of
approximately 35 percent. Again, the flexural and punching shear capacities were
adversely affected, with a calculated flexural deficiency of 15 to 45 percent and a
calculated shear deficiency of 18 to 46 percent.
1.5.2, 1.7.2, 4.3.1, 5.4.1
Safety concerns—The LDP determined that the cracking and deflections of the
supported garage slab and the gross deviations of the construction from the design
were significant safety concerns. The LDP determined that both the supported garage
slab and the plaza slab had sufficient calculated capacity to support the estimated
dead loads, but did not have sufficient calculated capacity to support the estimated
dead loads and the design live loads, even if the strength reduction factors for evaluation permitted by Section 5.4 of ACI 562 were used. The LDP advised the owner
that the supported garage slab and the plaza should be immediately removed from
service or shored to grade. Accordingly, the owner elected to remove both slabs from
service. The owner deemed it prudent to notify the authorities having jurisdiction of
the temporary measures that had been taken due to the structural deficiencies.
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Chapter 15: Project Example 4—Parking/Plaza Slab Strengthening153
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Structural assessment
Requirement for structural assessment
6.2.1
Structural deficiency—A structural assessment was necessary due to the structural deficiencies determined in the preliminary analysis.
Structural assessment
6.2.4, 6.2.5
Existing structural geometry—The existing structural geometry was documented in more detail than was done for the preliminary evaluation (Section 4.2.1).
a. All column spacings, column dimensions, and drop panel dimensions were
measured.@Seismicisolation
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Fig. 15.4—Illustration of effects of steel bracket or reinforced concrete column capital on punching shear
capacity, φVn, of slab.
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154
b. The slab thickness was determined with GPR. The reliability of the measurements was confirmed by physical measurements at several holes drilled through
the slab.
6.3.4
Concrete strength—The concrete compressive strength was assumed to be the
design strength, as confirmed by the construction testing laboratory reports that
were available.
Reinforcing steel layout and strength—
a. Reinforcing steel spacing and cover were determined at all locations with GPR
and confirmed at exploratory openings. Bar sizes were also measured at the
exploratory openings.
6.3.4
b. The reinforcing steel tensile strength was assumed to be the design strength, as
confirmed by the mill certificates in the construction records.
Structural analysis
5.1.2
Load factors and load combinations—The load factors and load combinations
were as specified in 2009 IBC and, by reference, ACI 318-14.
6.5.2
Analyses of slab designs—The supported garage slab and the plaza slab were
analyzed as two-dimensional plates. These analyses were performed to confirm
the accuracy of the computer models and the adequacy of the original slab designs.
6.5.3, 6.5.7
Analyses of as-built slabs—The two-dimensional plate models were modified
to reflect the documented as-built construction. The supported garage slab and the
plaza slab were then analyzed to determine locations with inadequate calculated
structural capacity and the magnitude of the calculated capacity deficiency.
Strengthening concepts
Two strengthening concepts were considered by the LDP and reviewed with the
owner.
Strengthening Concept 1
Strengthening Concept 2
Strengthening repairs—The strengthening repairs would include the following
activities.
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7.4.4, 8.2.1
At locations with excessive concrete cover—On the supported garage slab, the
top portion of the slab concrete would be removed and reconstructed with new top
bars correctly placed and vertical shear connectors crossing the bond line between
the existing and new concrete, as illustrated in Fig. 15.5.
6.7.1
After the removal work, but before the reconstruction work, the slab would be
unloaded by jacking so that the entire slab design load, including dead load and
live load, would be transferred to the new repaired slab after the repairs have been
installed, cured, and the jacks removed.
This approach would restore the supported garage slab to its as-designed configuration, thus restoring its design capacity.
7.3.1.1
At locations with thin drop panels—For the plaza slab, steel brackets would be
installed on the columns at the underside of the slab. The steel brackets would
move the critical punching shear section further from the column, increasing the
perimeter of the section, bo, and thus the punching shear capacity (Fig. 15.4). The
brackets also would move the critical negative moment section further from the
column, decreasing the design negative moment to the moment capacity of the slab
section with the reduced drop panel thickness (Fig. 15.6).
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Chapter 15: Project Example 4—Parking/Plaza Slab Strengthening155
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Fig. 15.5—Illustration of Strengthening Concept 1.
a. Reinforced concrete column capitals (Fig. 15.7) would be constructed on the
columns at the underside of both supported slabs. At a few short span conditions where there was no positive moment, supplemental drop panels would be
constructed on the underside of the supported garage slab.
7.3.1.1
b. At a few locations on the underside of the plaza slab, carbon-fiber-reinforcedpolymer (CFRP) laminate installed by manual lay-up (laminate) would be
installed as supplemental flexural reinforcement to allow some moment redistribution from the negative moment regions at the columns.
Assessment of strengthening concepts
The preliminary details of the strengthening concepts were determined based
on the findings of structural analyses performed in Section 5.0, and cost estimates
were obtained for both strengthening concepts. Strengthening Concept 2 was estimated to cost approximately 20 percent of the estimated cost of Strengthening
Concept 1. Other
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factors such as construction scheduling and sequencing were not
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These repairs have the following effects on the structural capacity.
a. Punching shear capacity—The column capitals move the critical punching shear
section further from the columns, increasing the perimeter of the section and the
punching shear capacity (Fig. 15.4). The supplemental drop panels increase the
effective slab depth, further increasing the punching shear capacity (Fig. 15.8).
b. Design negative moment—The column capitals also move the critical negative moment section further from the columns, decreasing the design negative
moment (Fig. 15.6). The supplemental drop panels increase the effective slab
depth, increasing the negative moment capacity (Fig. 15.8).
c. Moment redistribution—The CFRP reinforcement on the underside of the slab
increases the positive moment capacity of the slab and allows some redistribution of negative moments to the positive moment regions.
6.8.1
Load test—The effectiveness of this repair concept would be verified by
load test.
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156
RSLAB = (1/4) wℓ1ℓ2 – Slab reaction into column
Mu-A-B– = MCL– – RSLAB ℓA-B + (1/2) wℓA-B2 ℓ2 = MCL– – (1/2) wℓA-Bℓ2 (ℓ1/2 – ℓA-B)
Mu-REP – = MCL– – RSLABℓREP + (1/2) wℓREP2 ℓ2 = MCL– – (1/2) w ℓREPℓ2 (ℓ1/2 – ℓREP)
Fig. 15.6—Illustration of effects of steel bracket or reinforced concrete capital on design negative moment, Mu, of slab.
substantially different for the two concepts on this project. Using cost as the key
differentiator, the owner elected to pursue Strengthening Concept 2.
Structural analysis for repair design
6.6.1, 6.7.1, 6.5.4, 7.2.2, 7.4.1.1, 6.7.3
The effects of the repair process and the installed repairs were analyzed using
the two-dimensional plate models of the as-built slabs. The analysis considered the
current condition of the slabs, including the cracking, the deflected shape, and the
stresses in the slab due to dead loads. The stress increases due to live load in the
repaired existing slabs were also evaluated. The adequacy of the bond strength at
the interface between the repair material and the existing concrete was evaluated
based on Section 16.4.5.1 of ACI 318-14.
The analysis assumed full composite action at the repair material interface.
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where ℓ1 is the length of the slab span in the direction of the moments being determined, measured center-to-center of supports;
ℓ2 is the length of the slab span perpendicular to l1, measured center-to-center of supports; and MCL– is the negative moment
at column centerline
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Chapter 15: Project Example 4—Parking/Plaza Slab Strengthening157
University of Toronto User.
Fig. 15.7—Illustration of column capital in Strengthening
Concept 2.
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158
Fig. 15.8—Illustration of effect of increasing drop panel thickness on d, distance from extreme compression fiber to centroid of
longitudinal tension reinforcement, and hence on punching shear capacity and negative moment capacity of slab.
Design of structural repairs and durability
University of Toronto User.
7.1.1, 7.2.2, 7.3.1, 7.5.1, 7.5.2
The strengthening requirements of the repairs were determined based on the
findings of the analyses of the original design, the as-built construction, and the
repair design. The stiffening effects of the repairs were also evaluated. The repair
design included the following details and considerations.
7.3.1, 7.4.4, 7.6.5, 7.5.1
a. The column capitals were designed and detailed to integrate and act compositely
with the columns and the slab above. The column surfaces were intentionally
roughened and hoop reinforcement was included in the capitals to transfer forces
into the columns by shear friction. Self-consolidating concrete (SCC) was used
to facilitate filling of the forms to the slab soffit.
7.3.3, 7.3.3.1, 7.4.4, 7.6.5, 7.5.1
b. The supplemental drop panels were also designed and detailed to integrate and
act compositely with the columns and slab above. Reinforcing steel extended
between the column capitals and the drop panels, and the capitals and drop
panels were placed monolithically. Epoxy-grouted dowels were installed in the
slab soffit to transfer the horizontal flexural shear by shear friction. SCC was
used to facilitate filling of the forms to the slab soffit.
7.8.1, 7.8.2, 1.4.2, 7.4.2, 7.5.1, 7.5.2, 7.9.1, 7.9.3, 7.9.4, 7.9.5, 8.3.1, 8.3.2
c. The CFRP sheets were designed as a supplemental strengthening measure,
based on the recommendations of ACI 440.2R. The structural strength of the
repaired slab was adequate to carry the factored loads specified in the current
building code without the CFRP sheets. The CFRP sheets were used to increase
the calculated slab positive moment capacity to account for the increased positive moments due to moment redistribution that occurred before the repairs were
installed, and to limit further deflections from these moments. CFRP reinforcing
was not a preapproved material in the local jurisdiction, so the design philosophy, product information, and design calculations were presented to the authorities having jurisdiction for approval. The contractor was required to select a
CFRP system possessing an Evaluation Service Report (ESR) to verify that the
system complied with code requirements as per ACI 440.2R. The CFRP sheets
were detailed and bonded to the slab soffit per the
@Seismicisolation
manufacturers recommenda@Seismicisolation
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tions and ACI 440.2R. Bond pulloff testing was performed to verify the bond.
The authorities having jurisdiction required that the CFRP sheets be coated with
intumescent paint, even though the CFRP sheets would likely debond before the
paint became effective in the event of a fire.
8.5.1
d. The injection of epoxy into cracks on the top surface of the supported garage
slab was requested by the owner and also served to increase the slab stiffness
and seal the cracks against intrusion of water and deicing salts into the concrete,
improving the durability of the slab.
8.1.1, 8.1.2, 8.1.3
e. A traffic-bearing elastomeric coating was applied on the top slab surface in the
negative moment regions around the columns on the supported garage slab to
prevent the intrusion of water and deicing salts into cracks that may not have
been sealed and to minimize the intrusion of water and deicing salts into the
concrete and improve the durability of the slab.
f. As the column capital and drop panel repairs and the CFRP reinforcement were all
installed on the undersides of the slabs, the repairs are not directly exposed to the
harsh top slab surface service environment and the repairs were judged to be durable.
Photographs of the repairs in progress are shown in Fig. 15.9 to 15.12.
Contract specifications
University of Toronto User.
1.6.1, 9.1c
The LDP prepared contract documents that specified repair materials that satisfied governing regulatory requirements and conveyed necessary information to
perform the work. The contract documents included the minimum requirements for
shoring and bracing for all phases of the repair project, including requirements for
the contractor to submit shoring documents that were signed and sealed by an LDP.
The LDP used ACI 563 as a source for construction specifications. The specification sections that were referenced included:
Section 1—General requirements
Section 2—Shoring and bracing
Section 3—Concrete removal and preparation for repair
Section 4—Formwork
Section 5—Reinforcement and reinforcement support
Section 6—Conventional concrete mixtures
Section 7—Handling and placing of conventional concrete
Section 9—Crack repair by epoxy injection
Based on the size of the repairs, conventional concrete and proprietary cementitious and polymer repair materials was specified by the LDP in place of a proprietary material or shotcrete.
ACI 563, “Specifications for Repair of Concrete Buildings,” addresses
conditions that are unique to the project. The standard has a mandatory and
nonmandatory requirements checklists at the end of the standard to help the
specifier submit as complete a specification as possible. For the adaptive
reuse of a historic structure, the main sections from the mandatory and
nonmandatory checklists are extracted to include as a minimum in the Project
Contract Document:
a. Section 1.5.1.1—State the maximum dead and live loads and any temporary
reduction in loads, to be permitted during repair and after completion of repair
program, in concert with the requirements of 2.1.1.1.
b. Section 1.5.2—Designate Owner-approved work areas, and schedule requirements.
c. Section 1.5.4.1—Show the demarcation line of the project location, specific
work areas, and adjacent construction.
d. Section 1.8.2.1—Identify work to be performed by certified personnel.
e. Section 1.8.2.2(d)—Point out specific repair procedures that require review and
approval. @Seismicisolation
@Seismicisolation
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160
Fig. 15.10—New supplemental drop
panel with capital at various stages of
construction: (top) reinforcement and
dowels; (middle) formwork with port
holes; and (bottom) completed drop
panel and capital.
f. Section 1.8.2.2(e)—Specify submittal of component materials, repair material
mixture proportions or batch requirements, and concrete supplier’s or repair
material manufacturer’s QC program.
g. Section 1.9.2.1—Indicate if tolerances different from those in ACI 117.
h. Section 2.3.3.2—State whether specialty engineer inspection is required.
i. Section 3.1.1.2—Provide the surface profile and remove laitance, debris, and
bond-inhibiting materials.
j. Section 3.1.3.1—Indicate testing locations, type, number, and frequency of tests.
k. Section 3.2.1.1—Select the means and methods for concrete removal that will
minimize damage to the structure and bruised surfaces on the concrete substrate
that remains within and adjacent to the work areas.
l. Section 3.3.1.1—Show the required depth of concrete removal in Contract
Documents.
m. Section 4.1.2.2—Review the submittal list and indicate in Contract Documents
the items to be submitted.
n. Section 4.3.4.2—Establish if alternative methods for evaluating repair material
strength for formwork removal are permitted.
o. Section 5.2.1.1—Specify required grades, types, and sizes of reinforcing bars.
p. Section 6.2.2.6(d)—State the chloride exposure classification for are of work.
@Seismicisolation
@Seismicisolation
University of Toronto User.
Fig. 15.9—New supported parking
and plaza slab capitals at various
stages of construction: (top) reinforcement consisting of hoops plus
supplemental shrinkage reinforcement; (middle) pumping self-consolidating concrete (SCC); and (bottom)
completed capital.
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Chapter 15: Project Example 4—Parking/Plaza Slab Strengthening161
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Fig. 15.11—CFRP strip repair: (top) installation; and (bottom) installed and
painted sheets.
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162
University of Toronto User.
Fig. 15.12—Epoxy
injection of cracks on top surface of supported garage slab.
@Seismicisolation
@Seismicisolation
q. Section 6.2.2.7—Indicate the specified concrete compressive strength, fc′ for the
work.
r. Section 7.1.2.2—List the information in 7.1.2.2(a) to 7.1.2.2(g) that is to be
submitted.
s. Section 9—Repair of cracks by epoxy injection in accordance with ACI 503.7.
Construction
9.1a, 9.1c, 9.2.1a, 9.2.6
The contract documents required the contractor to monitor the construction for
any conditions that were not consistent with the available information or that might
affect the short-term or long-term safety of the structure, including the possible
need for temporary shoring or bracing.
9.4.1
Requirements for environmental issues, such as allowing water with debris to
flow into floor drains or off of the site and disposal of construction debris, were
specified in conformance with local ordinances.
Quality assurance
Load test
6.8.1
After the repairs had been installed, a representative portion of the repaired
supported garage slab was evaluated by load testing to demonstrate the strength of
the repaired slab. The test area was selected based on typical repairs in the area and
ease of setting up and running the test.
Test procedure
6.8.1, 1.1.2, 1.4.1
ACI 562 references ACI 437.2 for load testing. The 2009 IBC, the design-basis
code, references ACI 318-14, which includes Chapter 20, “Strength Evaluation of
Existing Structures.” Based on ACI 562 Sections 1.1.2
@Seismicisolation
and 1.4.1, ACI 562 governs
@Seismicisolation
University of Toronto User.
1.5.1, 10.2.1, 10.2.2, 10.4.1
The repair specifications included quality assurance and control measures for
material approvals and field verification of quality. The specified quality control
measures and construction observations were performed during the construction,
including the following:
a. Review of material submittals and reinforcement shop drawings.
10.2.3
b. Visual inspection of the work in progress at critical stages of the repair.
c. Observation of the prepared concrete surfaces and comparison with ICRI
concrete surface profiles (ICRI 310.2R) to verify that minimum roughness had
been achieved.
d. Observation of the installed reinforcement.
e. Periodic inspection and pullout testing of epoxy-grouted dowels in the slab soffit
in accordance with ACI 355.4.
f. Observation of the concrete placement and curing operations.
10.3.1
g. Testing of repair concrete, including slump flow, air content, temperature, and
compressive strength.
h. Impact-echo testing to verify the continuity between the slab soffit and the new
capitals (Fig. 15.13).
i. Observation of the surface preparation and installation of the CFRP sheets.
j. Bond strength testing of installed CFRP sheets (ASTM D7522/D7522M).
Impact-echo testing was performed on the top slab surface over drop panel and
capital repairs to detect possible gaps between the slab soffit and the repairs. Some
areas with gaps were detected (Fig. 15.13). Open joints between the slab soffit and
drop panel and capital repairs were injected with epoxy (Fig. 15.14) to fill the joints
and bond the repairs to the soffit. Continuity was confirmed by impact-echo testing.
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164
University of Toronto User.
Fig. 15.13—Impact-echo testing of joint between slab soffit and capital: (top) test in progress; and (bottom)
field notes of areas with open joints to be injected with epoxy.
for all matters pertaining to evaluation and shall govern when in conflict with other
referenced standards. Accordingly, the monotonic load test procedure described in
ACI 437.2 was used for the evaluation. The monotonic load test was selected after
consultation with the contractor’s available means, methods, and familiarity with
the monotonic test. The test procedure included the following details.
Loading—The test load magnitude (TLM) was calculated per ACI 437.2 Section
4.2.2.
@Seismicisolation
@Seismicisolation
TLM = 1.3 (DW + DS)
TLM = 1.0DW + 1.1DS + 1.6L + 0.5 (Lr or S or R)
TLM = 1.0DW + 1.1DS + 1.6 (Lr or S or R) + 1.0L
where Dw is load due to self-weight of the concrete structural system; Ds is superimposed dead load other than self-weight of structural system; L is live load due
to use and occupancy of the building; Lr is roof live load produced during maintenance by workers, equipment, and materials or by moveable objects or people; S is
snow load; and R is rain load.
Fig. 15.14—Epoxy leakage from injection of gap between slab soffit and capital.
Δr < Δ1/4 or Δ1 < 0.05 in. (1.3 mm) or Δ1 < ℓt/2000
and
@Seismicisolation
@Seismicisolation
University of Toronto User.
The test loads were applied by hydraulic jacks (Fig. 15.15) that reacted against
the soffit of the plaza slab. Back-up shoring was installed underneath the supported
garage slab. The jack arrangement included two interior panels of the supported
garage slab (Fig. 15.16).
Instrumentation—Instrumentation included load cells (Fig. 15.15) to measure
the load applied by the jacks; cable-extension transducers (Fig. 15.17) to measure
vertical deflections; strain gauges (Fig. 15.17) to measure the strain in individual
reinforcing bars; Whittemore strain gauges to measure strains in the concrete; and
linear variable differential transformers (LVDTs) for measuring crack widths. All
of the instrumentation was wired to a data acquisition system.
Test setup—The test setup is shown in Fig. 15.18.
Test procedure—The test procedure (ACI 437.2 Section 5.3) consisted of
applying the load in four equal increments; holding the load after each increment
for deflection measurements; holding the total load for 24 hours; and releasing the
load as quickly as practicable.
Acceptance criteria—The acceptance criteria (ACI 437.2 Section 6.3) included
the following items
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Δ1 < ℓt / 180
where Δ1 is the measured maximum deflection; ℓt is the shorter span under load for
a two-way slab; and Δr is the measured residual deflection.
Fig. 15.15—Load application: (left) jacks at plaza slab soffit, on towers; and (right) close-up of jack with
load cell (arrow) on top.
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Fig. 15.16—Arrangement of jacks. @Seismicisolation
@Seismicisolation
Test results
The load results are summarized as follows:
a. Δ1 = 0.558 in. < 1.63 in.  passed test (Δ1 = 14.2 mm < 41.4 mm  passed test)
b. Δr after 24 hours: 0.125 in. < 0.139 in. (Δ1 / 4) passed test (3.2 mm < 3.5 mm
(Δ1 / 4)  passed test)
The repaired structure passed the load test.
The measured maximum deflection from the load test corresponded with calculated deflections based on the gross moment of inertia, Ig, in the negative moment
regions where surface cracks had been injected and the cracked moment of inertia,
Icr, in the positive moment regions that had not been injected.
@Seismicisolation
@Seismicisolation
University of Toronto User.
Fig. 15.17—Instrumentation: (top) cable-extension transducer; and (bottom)
strain gauge on reinforcing bar.
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Fig. 15.18—Test setup. (Note: data acquisition equipment in lower right corner.)
PROJECT CLOSE-OUT
Periodic maintenance
1.5.3k
The LDP recommended that a visual inspection of the repaired structure be
performed 1 year after the repair installation to verify that no unanticipated behavior
had occurred. The LDP also recommended periodic monitoring and maintenance
of crack repairs, traffic bearing membranes, and CFP. The northern climate dictated
that these durability maintenance issues be monitored.
Record documents
1.6.3, 1.5.3d, 1.5.3j
The owner was provided with copies of the project and construction documents
and the recommended monitoring and maintenance program.
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@Seismicisolation
Description of structure
The facility is a water treatment plant in the northern United States. The plant
includes a concrete framed structure that houses water treatment tanks and a pump
room. The plant began operation in 2018 and is not accessible to the general public.
The roof over the steel tank area (Fig. 16.1) includes 43 precast, prestressed
concrete double tees and the roof over the pump room includes five double tees.
The double tees are generally 12 ft (3.7 m) wide and 28 in. (710 mm) deep, and
span from 59 to 72 ft (18.0 to 21.9 m). In the west bay, the double tees are 24 in.
(610 mm) deep and span approximately 31 ft (9.4 m). Along the south side of the
facility the double-tee widths decrease to 8.5 ft (2.6 m). The ends of the double tees
are dapped, as shown in Fig. 16.2. For the 28 in. (710 mm) deep double tees, the
daps are typically 16.5 in. (420 mm) long by 10.5 in. (267 mm) deep.
The steel tank area measures approximately 230 x 132 ft (70.1 x 40.2 m) in plan,
and the adjacent pump room measures approximately 62 x 60 ft (18.9 x 18.3 m) in
plan, as shown in Fig. 16.3.
Project initiation and objectives
Shortly after construction, the owner’s personnel observed a wide diagonal crack
in the stem at the end of a double tee (Fig. 16.4). Further inspections revealed fine
diagonal cracking at the ends of other double-tee stems. A temporary retrofit was
designed and installed for the severely cracked member as an emergency safety
measure. The owner then retained a licensed design professional (LDP) experienced in the investigation and repair of problems with existing structures to determine the cause of the cracking, assess any structural implications, and develop
long-term repair details, as necessary.
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Chapter 16: Project Example 5—Precast/Prestressed Double-Tee Repair
University of Toronto User.
Fig. 16.1—Precast, prestressed double-tee roof members over steel tank area.
ACI 562-19 provision numbers applying to each section of text are shown in red at the top right of each paragraph.
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169
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GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Fig. 16.2—Dapped ends of double tees.
Governing building codes
Based on discussions with the building officials, the building codes adopted by
the jurisdiction were determined.
Jurisdiction—Northern U.S. city
Original building code—2009 International Building Code (2009 IBC)
Current building code—2018 International Building Code (2018 IBC)
1.2.3
1.2.2
1.2.1
Existing building code—The jurisdiction has adopted the 2018 International
Existing Building Code (2018 IEBC)
1.1.2, 1.4.1, 1.4.2
ACI 562 supplements the existing building code and governs in all matters
pertaining to concrete members in existing buildings, except wherever ACI 562 is
in conflict with the requirements in the existing building code in which cases the
2012 IEBC @Seismicisolation
governs.
@Seismicisolation
University of Toronto User.
Fig. 16.3—Roof plan over steel tank area and pump room, showing double tee layout.
1.2.4
Design-basis code—Because the jurisdiction has adopted a general existing
building code, ACI 562 Section 1.2.4 specifies that the design-basis code shall be
determined in accordance with ACI 562 Chapter 4 or Appendix A. If a jurisdiction
has adopted the IEBC, as in this example, Chapter 4 applies.
4.2
The Prescriptive Method was selected for compliance. The Prescriptive Method
(2018 IEBC Chapter 4) allows existing materials in use to remain in use unless
determined to be unsafe. New and replacement materials as permitted for new
construction may be used. Under repair scenarios, vertical gravity load-carrying
components that have sustained substantial structural damage are required to be
rehabilitated to comply with the current building code. Snow loads are required
to be considered if the substantial structural damage was caused by snow load
effects. Existing gravity load-carrying members are permitted to be designed using
original design loads. Undamaged gravity load-carrying members receiving loads
from the rehabilitated member are required to be shown to have sufficient capacity
to carry the design loads of the rehabilitation design.
1.7.1
A preliminary assessment was performed to investigate the extent of structural
damage, from which a determination of the design basis requirement could be
made.
Preliminary assessment
1.7.1
The precast concrete shop drawings, including erection plans, individual precast
piece drawings, connection details, and design calculations were available and
reviewed by the LDP.
Existing site conditions
Design strength of existing structure
1.7.1, 1.7.2, 1.7.3
The precast concrete shop drawings and design calculations were reviewed. The
loads were in accordance with the original building code. The design shear strength
of a typical double-tee stem end was based on the procedures of ACI 318-08, as
referenced by the 2009 IBC. The as-designed shear strength was confirmed to be
adequate for the design load effects.
Findings of preliminary assessment
6.2.1
Initially, a wide diagonal crack was noted at the end of only one double-tee beam.
A temporary retrofit had been installed at this location. The preliminary assessment
documented relatively fine diagonal cracks at the ends of many of the other tee
beam ends and confirmed that the as-designed shear strength was adequate. At
this point, it was unclear if the fine diagonal cracks were indicative of unusual
structural behavior and, perhaps, a structural deficiency,
@Seismicisolation
or if the cracks were just
@Seismicisolation
University of Toronto User.
1.7.1
Existing structural geometry—The layout and dimensions of the double tees
were determined to be in conformance with the precast concrete shop drawings.
1.7.1, 1.7.2
Existing concrete condition—Accessible double-tee stem ends were visually
inspected from various walkways and catwalks. Binoculars and ladders were used
where appropriate. Over 75 percent of the double-tee stem ends were observed. It
was determined that the stem adjacent to the daps had an apparent concrete shear
cracking problem, as illustrated in Fig. 16.4 and 16.5.
1.7.1
Reinforcement—The precast concrete shop drawings detailed the prestressing
steel and vertical reinforcement in the stems, and the reinforcement at the ends.
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normal concrete behavior. The owner reported no excessive loads, including snow
loads, that could have caused the observed damage.
1.7.2, 1.7.5, 6.2.2, 6.2.3, 4.5, 4.5.1, 6.1.1
The LDP recommended to the owner that further investigative studies be performed
to verify the as-built construction and determine the structural implications of the
Shear crack
Splitting
Fig. 16.4—Diagonal shear and longitudinal splitting cracks observed at end of
double-tee stem.
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University of Toronto User.
Fig. 16.5—Typical types of cracking observed at ends of@Seismicisolation
double-tee
stems.
@Seismicisolation
cracking. The LDP notified the owner that the diagonal cracks might be indicative
of a potential safety concern. The LDP recommended that a structural assessment
per ACI 562 Section 6.1.1 be performed as soon as possible. The LDP recommended that the structural assessment include both a structural assessment and
structural analysis. As the cracks were relatively fine at this time, the LDP recommended that the crack widths be visually monitored and determined that temporary shoring was not necessary given the timing of the investigation and potential
repairs would take place between April and October to minimize the likelihood of
snow load.
Design-basis code
1.2.4, 1.7.1
Based on the work completed by the LDP, there was reason to suspect that the
as-built construction may differ from the precast concrete shop drawing details.
The condition did not meet the definition of substantial structural damage as
given in IEBC. Accordingly, the LDP concluded that repairs could be designed to
restore the members to their original design capacity based on material properties
and design strengths applicable at the time of original construction. (2012 IEBC
Section 404.4). Therefore, repairs would be required to meet the requirements of
the original building code (2009 IBC), which references ACI 318-08.
Structural evaluation
Existing site conditions
@Seismicisolation
@Seismicisolation
University of Toronto User.
6.2.4
Existing structural geometry—The existing structural geometry was documented in more detail than was done for the preliminary assessment (Section 1.7).
a. Double-tee spans, widths, and stem depths and widths were measured.
b. The flange thicknesses were determined with ground-penetrating radar (GPR)
that was calibrated by physical measurements at holes drilled through the flange.
6.1.1, 6.2.4, 8.1.2
GPR uses electromagnetic waves that are transmitted into the member to discern
internal objects within the concrete. The waves reflect off material interfaces and
the optical reflections are processed to determine the location and depth of reinforcing bars. Reflected waves off of the back side of the member can also be used
to determine the member thickness (ACI 228.2R-13).
6.3.1
Reinforcing steel layout and strength—Reinforcing steel spacing and cover were
determined with GPR and confirmed at exploratory openings (Fig. 16.6 and 16.7).
The steel yield strength was assumed to conform to the steel grades specified on
the precast concrete shop drawings.
6.2.4
The location of the reinforcing steel was determined at 41 stem ends. At five
of the stem ends, the vertical reinforcement started within 10 in. (255 mm) of the
dapped end. At the other 36 locations, or almost 90 percent of those inspected,
the vertical reinforcement started 1 ft-6 in. to 7 ft-7 in. (0.46 to 2.31 m) from the
dapped end, with most of the reinforcement starting 4 to 6 ft (1.2 to 1.8 m) from the
dapped end. A typical GPR scan and marked-up dapped end illustrating the location of the first vertical reinforcing bar is shown in Fig. 16.8. The as-built construction is illustrated in Fig. 16.9.
6.3.4
Concrete strength—Concrete cylinder tests performed during fabrication indicated that the concrete achieved its design strength. No visible deterioration of
the concrete was observed. The concrete strength was therefore assumed to be
5500 psi (37.9 MPa), as shown in the shop drawings.
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Fig. 16.6—Ground-penetrating radar (GPR) survey in progress.
Reinforcing bar
Fig. 16.7—Vertical reinforcement exposed at exploratory opening along shear
crack.
Structural analysis for evaluation
Load factors and load combinations—The load factors and load combinations
were as specified in the 2009 IBC, which references ACI 318-08.
6.5.2
Analysis—The shear strength at the as-constructed beam ends was calculated
according to the provisions of ACI 318-08. It was determined that the calculated
shear strength provided by the concrete alone was less than the design shear force,
necessitating shear reinforcement per the provisions of ACI 318-08. Accordingly,
the original design included vertical reinforcing steel at the ends of the double-tee
stems adjacent to the daps.
The GPR testing found that vertical reinforcing was mislocated or missing.
Consequently,
@Seismicisolation
the stems had inadequate calculated strength that resulted in the
@Seismicisolation
University of Toronto User.
Shear crack
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174
Start of
vertical
Fig. 16.8—Gap at end of stem before start of vertical reinforcement: (top) GPR
scan of cracked double-tee stem shown in Fig. 16.4 (WWR is welded wire reinforcement); and (bottom) markup of vertical reinforcement on double-tee stem.
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Fig. 16.9—Illustration of as-built double-tee stem construction, showing gap from
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end of dap to start of vertical reinforcement.
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GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
observed diagonal cracking. The absence of vertical reinforcement also meant that,
after cracking had initiated, there was inadequate steel to limit the crack widths.
As shown in Fig. 16.9, the ends of the double-tee stems also have vertical,
C-shaped hanger bars adjacent to the daps. In many locations the bottom horizontal hook extensions of the hanger bars had little concrete side cover. Small
side cover results in less concrete resistance to splitting along the bond length of
the hook, causing splitting cracking of the concrete at lower than anticipated bond
stresses. The splitting cracking reduces the development of the bar and the transfer
of stresses between the bar and the surrounding concrete. Based on the side cover
measured on some beams, ACI 318-08 provisions were used to predict the likelihood of the observed horizontal splitting cracking. Well-detailed vertical reinforcement along the hanger bar bottom hooks would limit the splitting crack widths. The
absence of this reinforcement meant that, after cracking had initiated, there was no
steel to limit the crack widths.
Structural safety
Repair/replacement options
1.5.3f, 1.5.3g
Four repair/replacement options were considered:
1. Complete replacement of the double-tee roof with new precast members
2. Strengthening of the double-tee ends by concrete jacketing
3. Strengthening of the double-tee ends with steel plates
4. Strengthening of the double-tee ends with carbon fiber-reinforced polymer
(CFRP)
Repair/replacement Option 1
This option included the complete removal of the roof over the steel tank
area and the pump room and the installation of a new double-tee roof and a new
roofing system. This option would be very disruptive to operations as a temporary
protection/weatherproofing platform would need to be constructed underneath the
existing roof structure and all attachments to the underside of the double tees such
as lights, conduits, and pipes would need to be temporarily relocated. Also, the
existing facility and grounds caused staging difficulties for the large crane necessary for the @Seismicisolation
removal
and replacement of the double tees.
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University of Toronto User.
1.5.1, 4.3.1, 1.5.2, 1.7.2
The observed diagonal cracking at the ends of most of the double-tee stems and
the mislocated or missing vertical reinforcement in these areas made it difficult to
reliably assign a concrete shear capacity at these locations. However, as shown in
Fig. 16.9, there were horizontal reinforcing bars in the dapped end, attached to the
bearing plate, and vertical hanger bars that extended across the diagonal cracks,
providing a nominal shear transfer mechanism and some ductility at the cracks.
The horizontal reinforcement and vertical hanger bars provided some ductility at
the double-tee ends and prevented the complete failure of the double tees. The
owner was advised of the precarious and unsafe nature of the present structural
conditions, and the urgency of addressing the unsafe conditions. The owner was
also advised that if repairs were delayed, the double-tee stems should be visually
surveyed and monitored for increased distress on a monthly basis. The recommendation was also made to limit roof live and snow loads by removing accumulated
snow.
1.5.3a, R1.5.3b, 1.5.3c, R1.5.3d, 1.5.3e
The LDP provided the owner with a basis of design report providing a description of the structure, identifying the structural system, and listing the codes used
for the design and construction of the structure. The basis of design report also
included documentation of unsafe structural conditions in the work area as presented
previously and identified members that required strengthening. Four rehabilitation
options were presented to the owner along with the advantages and disadvantages
of each option along with the recommendation of the LDP.
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Repair/replacement Option 2
This option consisted of constructing reinforced concrete jackets at the ends of
the double-tee stems, as shown schematically in Fig. 16.10. The jackets would
increase the stem width from 6 in. (150 mm) to 12 to 15 in. (305 to 380 mm). The
new reinforcement would provide the vertical shear capacity and confinement steel
that was lacking at numerous existing tee stems.
7.4, 7.5.2
This work would require significant field labor to prepare the concrete surfaces,
place the reinforcement, form the jackets, and then place the concrete. Enclosed
temporary work platforms would be necessary at the ends of the double tees to
access the undersides of the double-tee stems and contain dust and other debris
from the construction activities. As an alternate, a permanent catwalk was also
considered. In either case, the cost for the temporary work platforms or new
catwalk was substantial.
7.3.1.1
This option would require additional engineering considerations and analysis of
the original design. For example, the concrete jackets would add dead weight to
the double-tee stem ends and thus the cast-in-place girders that support the double
tees would have to be evaluated for the additional loads.
Repair/replacement Option 3
7.5.2
This option consisted of installing steel-plate assemblies at the ends of the
double-tee stems, as shown schematically in Fig. 16.11. The assemblies would
provide the necessary shear capacity and confinement at the ends of the double-tee
stems.
7.3.1.1
This work would require field labor to install the plate assemblies. The various
plates would have to be sized so that one or two iron workers could handle them.
Enclosed temporary work platforms would be necessary at the ends of the double
tees to access the undersides of the double-tee stems and contain dust and other
debris from the construction activities. As an alternate, a permanent catwalk was
also considered. In either case, the cost for the temporary work platforms or new
catwalk was substantial.
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Fig. 16.10—Schematic of Repair/replacement Option 2, reinforced concrete jacket.
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Fig. 16.11—Schematic of Repair/replacement Option 3, steel-plate assembly.
8.1, 8.4.1, 8.4.6
As the environment may have elevated humidity, corrosion protection would
need to be considered for the exposed as well as the concealed steel surfaces. A
high-quality paint system could be applied, but periodic maintenance would be
expected. Alternately, stainless steel plates could be used; in this case, however,
workers with experience in stainless steel fabrication and welding would have to
be employed.
Repair/replacement Option 4
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7.5.2
This option consisted of installing externally bonded, CFRP strips at the double-tee
stem ends, as shown schematically in Fig. 16.12. This repair would be relatively
easy to install over open water tanks; very lightweight, thereby not affecting
supporting structural elements; and could be finished with a surface coating to
enhance the aesthetics of the beam end repair area and maintain the overall appearance of the structure.
This work would require trained field labor experienced with FRP installation to
prepare the concrete surfaces and install the CFRP strips. Enclosed temporary work
platforms would be necessary at the ends of the double tees to access to the undersides of the double-tee stems and contain dust and other debris from the construction activities. As an alternate, a permanent catwalk was also considered. In either
case, the cost for the temporary work platforms or new catwalk was substantial.
7.4.1, 7.4.2
The success of a CFRP system relies on adequate bond to the substrate. The risk
of bond failure could be mitigated with a good quality assurance/quality control
program, including selection of a proven, high-quality repair system and an experienced installation contractor, regular observation of the installation, and testing
for debonding and bond strength of the installation. Once properly installed, the
CFRP strips would be expected to perform throughout the anticipated service life
of the structure.
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178
Fig. 16.12—Schematic of Repair/replacement Option 4, carbon fiber-reinforced polymer (CFRP) reinforcement.
7.9
A second concern is damage to the repair due to fire. Considering the lack of
flaMmable material housed or generated in the treatment process, the possibility of
a fire in this facility appeared quite low. A natural gas pipeline in the facility could
create a torch effect if the pipe ruptures, but existing emergency shut-offs mitigate
this occurrence. Heat shields/deflectors could also be considered at repair areas
above this pipeline.
DESIGN OF STRENGTHENING REPAIRS
Structural analysis for repair design
6.7.1, 7.2.1, 7.2.2
The structural analysis for repair followed the provisions of the 2009 IBC to determine the repair design forces. The means and methods for the CFRP installation require
minimal equipment and construction loadings. Nonetheless, the effect of these loads
were evaluated to assess the safety of the double-tee members during construction.
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University of Toronto User.
Evaluation of repair/replacement options
The costs of each of the repair/replacement options were estimated. Options 1
and 4 had similar estimated costs and Options 2 and 3 also had similar estimated
costs that were approximately double the estimated costs of Options 1 and 4. The
cost to access the repair areas for Options 2, 3, and 4 included temporary scaffolding or a new catwalk system represented over 40 percent of the repair cost,
and was the primary factor that caused the costs between Option 1 and 4 to be so
closely related despite the fact that Option 1 included the complete removal and
replacement of the double-tee members. Based on cost and interruption to operations, the owner elected to pursue Option 4.
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Design of strengthening repairs
7.8.1, 7.8.2
Design provisions—The structural design of the CFRP repairs was in conformance with the provisions of ACI 440.2R. The provisions of ACI 440.2R are based
on the provisions of ACI 318.
5.5, 7.8.2
Strength of existing members—The cracks at the ends of the double-tee stems
would be injected with epoxy to restore the sections to their uncracked condition.
For rehabilitation achieved with external reinforcing systems, ACI 562 requires
that the structural members without rehabilitation have capacity to equal or
exceed the effects of the load combinations specified in ACI 562 Sections 5.5.2
and 5.5.3.
5.5.2
The nominal shear strength, (Vn)unc, of the existing unstrengthened concrete
sections were calculated and were found to exceed the minimum strength required
by ACI 562 Eq. (5.5.2a) and (5.5.2b).
(φVn)unc > 1.1D + 0.5L + 0.2S
(5.5.2a)
(φVn)unc > 1.1D + 0.75L (5.5.2b)
where φ is the strength reduction factor for shear; D is the dead load effect; L is the
live load effect; and S is the specified snow load.
These load combinations are intended to minimize the risk of overload or damage
to the existing unstrengthened elements in the case where, during normal operating
conditions, the external reinforcement is damaged. This would allow the structure
to remain in service until the damage to FRP is repaired.
5.5.3
To ensure adequate member strength during a fire event, ACI 562 requires
that strength of the structural member without externally applied CFRP satisfy
ACI 562 Eq. (5.5.3)
fex Rn > (0.9 or 1.2)D + 0.5L + 0.2S (5.5.3)
fVn = φ (Vc + Vs + ψfVf)
where Vc is the nominal shear strength provided by the concrete; Vs is the nominal
shear strength provided by the reinforcing steel, in this case ‘0’; ψf is the additional CFRP strength reduction factor, suggested as 0.85 by ACI 440.2R-08; and Vf
is the nominal shear strength provided by the CFRP stirrups.
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University of Toronto User.
where fex = 1.0; and Rn is the nominal resistance of the structure, calculated using
the reduced material properties due to effects of fire, determined based on the
required fire rating duration. The dead load factor of 0.9 governs when the dead
load effect reduces the total factored loads effect. Considering the lack of flammable material housed or generated in the treatment process, the possibility of a
fire in this facility appeared quite low. Based on these conditions, it was concluded
that fire evaluation is not required for this application.
4.3.1
As there was no roof live load expected during the repair installation, the LDP
determined that shoring would not be necessary to prevent recracking of cracked
sections after epoxy injection and before the CFRP repairs were installed. The
owner was advised not to access the roof while repairs were curing.
7.1.1, 7.5.1, 7.5.2
Strength of repaired members—The nominal shear strengths, Vn, of the repaired
members were calculated as suggested by ACI 440.2R-08 Eq. (11-2)
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180
The nominal shear strength provided by the concrete was calculated by
ACI 318-08 Eq. (11-3)
Vc = 2 ( fc′ ) bwd
Vc = 0.17 ( fc′ ) bwd
(in.-lb units)
(SI units)
where fc' is the concrete compressive strength; bw is the stem width; and d is
distance from the extreme compression fiber to the centroid of the longitudinal
tension reinforcement.
The nominal shear strength provided by the CFRP stirrups was calculated as
suggested by ACI 440.2R Eq. (11-3)
Vf = (Afv ffe (sin α + cos α) dfv) / sf
where Afv is the area of CFRP shear reinforcement with the spacing sf; ffe is the
effective stress in the CFRP; α is angle of inclination of the CFRP shear reinforcement relative to horizontal; dfv is the effective depth of the CFRP shear reinforcement; and sf is the horizontal spacing of the CFRP shear reinforcement.
The effective stress in the CFRP was calculated as suggested by ACI 440.2R-08
Eq. (11-5)
ffe = εfe Ef
where εfe is the effective strain in the CFRP reinforcement attained at failure; and
Ef is the tension modulus of elasticity of CFRP.
For bonded U-wraps, the effective strain in the CFRP reinforcement attained at
failure is calculated as suggested by ACI 440.2R-08 Section 11.4.1.2
εfe = κν εfu < 0.004
The design rupture strain was calculated as suggested by ACI 440.2R-08
Eq. (9-4)
εfu = CE εfu*
where CE is an environmental reduction factor—0.95 for carbon fiber in internal
exposures (ACI 440.2R, Table 9-1); and εfu* is the ultimate rupture strain of CFRP
reinforcement.
DESIGN OF STRUCTURAL REPAIRS AND DURABILITY
Development and bond of CFRP strips
7.6.3.3
Development—To develop the effective stress in the CFRP, the active bond
length Le was calculated as suggested by ACI 440.2R-08 Eq. (11-8)
Le = 2500 / (ntfEf)0.58 (in.-lb units)
Le = 23,300 / (ntfEf)0.58 (SI units)
where n is the number of plies of CFRP reinforcement; tf is the nominal thickness of
one ply of CFRP reinforcement; Ef is the tensile modulus
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of elasticity of the CFRP.
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University of Toronto User.
where κν is a bond reduction coefficient defined in Section 11.4.1.2; and εfu is the
design rupture strain of CFRP reinforcement.
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The required development was provided by the installation details.
7.8.1
Bond—Bond of the CFRP strips to the concrete was critical to the success of the
repair. Surface preparation included grinding protrusions and undulations on the
concrete surfaces, and all corners to the radius prescribed by the CFRP manufacturer; and sandblasting the concrete surfaces to remove contaminants and laitance.
After the CFRP strips had been installed, bond pulloff testing was performed to
verify the quality of the bond in accordance with ASTM D7522/D7522M.
Acceptance of CFRP repairs by the authorities having jurisdiction
7.8.1
Repair material—CFRP reinforcement in accordance with ACI 440.8 is a
permitted repair material in ACI 562, which in this case has been adopted as a
supplement by the local jurisdiction.
7.9.1, 7.9.3, 7.9.4
Performance under fire and elevated temperatures—The potential for fire and
elevated temperatures at the repair locations was evaluated and reviewed with the
authorities having jurisdiction. It was noted that there were no flammable materials
in the steel tank area and that the treatment process did not generate flammable
materials, so that the probability of fire in this area appeared quite low. A natural
gas pipeline in this area could create a torch effect if the pipe ruptured, but the pipe
included emergency shut-offs to mitigate this occurrence.
5.5.1, 5.5.2, 5.5.2.1, 5.5.3, 7.9.2
Heat shields/deflectors could also be installed at repair areas above this pipeline. The owner and the authorities having jurisdiction found these considerations
persuasive and no supplemental fire protection was required.
Durability of repairs
Aesthetics of repairs
The CFRP repairs were coated with an acrylic coating to blend the repairs with
the adjacent concrete. The coating also provided protection to the epoxy from the
degradation effects of ultraviolet light, which in an interior exposure were minimal.
Contract specifications
1.6.1
The LDP prepared contract documents that specified repair materials that satisfied governing regulatory requirements and that conveyed necessary information
to perform the work.
The LDP used ACI 563 as a source for construction specifications. The specification sections that were referenced included:
Section 1—General requirements
Section 2—Shoring and bracing
Section 9—Crack repair by epoxy injection
Based on the size of the repairs, conventional concrete and proprietary cementitious and polymer repair materials were specified by the LDP in place of a proprietary material or shotcrete.
ACI 563, “Specifications for Repair of Concrete Buildings,” addresses conditions that are@Seismicisolation
unique to the project. The standard has mandatory and nonmandatory
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University of Toronto User.
8.1.1, 8.1.2, 8.1.3, 8.3.1, 8.3.2, 8.4.1, 8.5.1
The durability of the repair materials and the repairs was considered. The service
environment was an interior space with no special exposures, such as to acids
or moisture, or other potentially deleterious conditions. Cracks at the ends of the
double-tee stems would be injected with epoxy to restore the concrete strength and
seal the cracks, and the repairs addressed the causes of the cracking. Corrosion was
not an issue in this environment, so no special corrosion-resistance measures or
surface treatments were necessary.
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182
requirements checklists at the end of the standard to help the specifier submit as
complete a specification as possible. For the adaptive reuse of a historic structure,
the main sections from the mandatory and nonmandatory checklists are extracted
to include as a minimum in the Project Contract Document:
a. Section 1.5.1.1—State the maximum dead and live loads and any temporary
reduction in loads, to be permitted during repair and after completion of repair
program, in concert with the requirements of 2.1.1.1.
b. Section 1.5.2—Designate Owner-approved work areas, and schedule
requirements.
c. Section 1.5.4.1—Show the demarcation line of the project location, specific
Work areas, and adjacent construction.
d. Section 1.8.2.1—Identify work to be performed by certified personnel.
e. Section 1.8.2.2(d)—Point out specific repair procedures that require review and
approval.
f. 1.8.2.2(e)—Specify submittal of component materials, repair material mixture
proportions or batch requirements, and concrete supplier’s or repair material
manufacturer’s QC program.
g. 1.8.3.2(d)—Determine frequency of sampling and whether sampling will be
performed on a random basis. Indicate testing requirements in accordance with
critical design performance requirements.
h. Section 2.3.3.2—State whether specialty engineer inspection is required.
i. Section 9—Repair of cracks by epoxy injection in accordance with ACI 503.7.
Construction
Quality assurance
1.5.1, 10.2.1, 10.2.2, 10.4.1
The repair specifications included quality assurance and control measures for
material approvals and field verification of quality. The specified quality control
measures and construction observations were performed during the construction,
including the following:
a. Review of material submittals
b. Review of sealed calculations submitted by the CFRP manufacturer, confirming
the design details
c. Review of shop drawings of the CFRP layouts
d. Review of contractor qualifications, including previous experience installing
CFRP strips and certified training by CFRP manufacturer
e. Inspection of each stem end for cracks to inject. GPR testing to confirm the
as-built reinforcement and determine the exact extent of CFRP reinforcement
f. Required presence of a representative of the CFRP manufacturer at the site
during the early stages of the installation
g. Visual inspection of the work in progress
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9.1c, 9.2.1a, 9.2.1b, 9.4.1
As discussed in Section 5.4, the LDP evaluated the need for temporary shoring
and bracing and determined that none was required. The as-constructed condition
was sufficient for dead loads. The owner was notified to ensure no live load would
be present. Additionally, repairs were to be completed prior to the winter season
such that snow loads would not be present. The contract documents required the
contractor to monitor the construction for any conditions that were not consistent with the available information or that might affect the short-term or longterm safety of the structure, including the possible need for temporary shoring or
bracing. Enclosures were erected around repair areas to control dust and debris
from construction activities. Disposal of construction debris was specified in
conformance with local ordinances.
The construction is shown in Fig. 16.13 to 16.16. As shown in Fig. 16.15 and
16.16, the contractor elected to install CFRP sheets at the double-tee stem ends,
rather than the CFRP strips envisioned in Repair/replacement Option 4 (6.4) and
shown in Fig. 16.12.
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GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Fig. 16.13—Epoxy-injected cracks on primed double-tee stem.
University of Toronto User.
Fig. 16.14—Laying up CFRP sheet into epoxy saturant.
h. Observation of the crack injection work
i. Observation of the prepared concrete surfaces
j. Observation of the CFRP installation
10.2.3
10.3.1
k. Daily fabrication of CFRP composite coupons for visual examination and testing
of physical properties (ASTM D3039/D3039M)
l. Hammer tapping the installed CFRP strips to verify bond through the absence
of hollow sounds, and pulloff bond strength testing of installed sheets (ASTM
D7522/D7522M) (Fig. 16.17)
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Fig. 16.15—Installed CFRP sheets. Note that contractor elected to install CFRP
sheets rather than CFRP strips shown in Fig. 16.12.
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University of Toronto User.
Fig. 16.16—Completed CFRP installation with acrylic coating.
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Fig. 16.17—Pulloff bond testing of the CFRP sheets.
PROJECT CLOSE-OUT
Periodic maintenance
1.5.1, 10.2.1, 10.2.2, 10.4.1
Periodic maintenance requirements were discussed with the owner. The LDP
recommended annual monitoring of the repairs for visible deterioration and
debonding. The LDP also recommended periodic maintenance or reapplication of
the acrylic coating on the CFRP.
Record documents
1.6.3, 1.5.3d, 1.5.3j
The owner was provided with copies of the project and construction documents
and the recommended monitoring and maintenance program.
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University of Toronto User.
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Description of structure
The structure is a multi-level post-tensioned parking structure, constructed
in the early 1980s (Fig. 17.1), and is located in the northern United States. The
facility provides parking for approximately 500 vehicles, with the majority of
the vehicles entering and exiting the facility daily. The structure was constructed
using a combination of post-tensioned beams and slabs with a typical span of 24 ft
(7.3 m) for the slabs and a beam span of 54 ft (16.5 m). The parking slabs are 6 in.
(152 mm) thick, and post-tensioned with 0.5 in. (12.7 mm) diameter Grade 270 ksi
(1862 MPa) strands.
Project initiation and objectives
During the condition assessment survey, three beams were observed with a nontypical cracking pattern (Fig. 17.2). The cracking typically started approximately
3 ft (0.9 m) from the end of the beam and extended diagonally to approximately
12 ft (4.5 m) from the beam ends. Therefore, the cracks were approximately 9 ft
(2.7 m) long. Two of the affected beams were adjacent to each other, and the third
was located on a different floor. Based on the crack widths observed during the
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Chapter 17: Project Example 6—Concrete Beam Repair by Section Enlargement
University of Toronto User.
Fig. 17.1—Exterior of post-tensioned parking structure.
ACI 562-19 provision numbers applying to each section of text are shown in red at the top right of each paragraph.
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Fig. 17.2—Non-typical cracking of post-tensioned beam.
preliminary evaluation, a detailed investigation of the cracking was performed. The
condition survey of the remaining portions of the garage identified only limited
damage, including corrosion with low cover reinforcing steel, isolated failures of
post-tensioning strands with inadequate cover, and deterioration of a waterproofing
membrane over a retail space. The durability-related repairs were addressed in a
multi-year repair program.
1.7
The non-typical cracking of the girders required a detailed investigation to
determine the cause of the cracking and if required to develop appropriate repair
strategies.
Jurisdiction—Northern U.S. City
Original building code—1983 Municipal Building Code
Original concrete design code—ACI 318-77
Current building code—2019 Municipal Building Code
Existing building code—Not adopted
1.2.3
1.2.2
1.2.1
1.1.2, 1.4.2
Design-basis code—Because the local jurisdiction had not adopted an existing
building code, use of ACI 562-19 as the design-basis code was approved by the
Building Official.
A.2.3, A.2.5
The overall rehabilitation project was limited to repairs to the existing structure,
with no changes in use, occupancy or alterations. Therefore, the structural design
was based upon the original concrete design code, ACI 318-77, using the additional requirements of ACI 562 in the design of the repairs. The use of ACI 562-19
and the original concrete design code was also consistent with the level of damage
present in the
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structure (Chapter 4 of ACI 562-19).
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Governing building code
Based upon discussions with the local building officials, as well as the information available in the original design drawings, the original design code and the
current building codes adopted by the jurisdiction were determined as follows:
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188
Structural assessment
Structural analysis
6.5, 4.3
The structural analysis to review the adequacy of the original design was
completed using the material properties shown in Table 17.1. These values were
obtained from the design drawings and were not confirmed by testing. Therefore,
the load combinations and strength reduction factors shown in Chapter 9 of ACI
318-77 were used in the analysis. The analysis confirmed the original design of the
beams was adequate for a design live load (parking)@Seismicisolation
of
50 psf (2.4 kPa). The analysis
@Seismicisolation
University of Toronto User.
1.7, 6.1, 6.2
The preliminary assessment of the beams by the licensed design professional
(LDP) identified cracking inconsistent with available construction documents.
The unexpected cracking served as a trigger to complete a detailed assessment
of the cracked beams. At the time of the assessment, the structure had been in
service for over 35 years and routinely experienced loading from full vehicle occupancy. Outside of the observed cracking, no signs of durability-related damage or
distress were observed in the three cracked beams. Further, the cracking damage
was limited to the near-end region of the three beams. The remaining beams in the
structure had no apparent damage. Therefore, the goal of the structural assessment
was to determine the likely cause of the cracking and then ensure the affected
beams had adequate ultimate strength.
6.2.1, 6.2.2, 6.2.3, 6.3.1
Given the satisfactory structural performance of the remaining members in the
structure, the investigation focused on the damaged beams. To limit the impact of
the investigation on the operation of the structure, and to limit assessment costs, no
materials testing was performed in the investigation. The material properties used
in the assessment were obtained from original design drawings.
6.2.4, 6.4.1.1, 8.1.2
Based upon their previous experience, the LDP suspected that the observed
cracking was likely caused by misplacement of the post-tensioning tendons during
initial construction. To evaluate the cause of the cracking, ground-penetrating
radar (GPR) was used to determine the location of the post-tensioning tendons and
shear stirrups. As described in ACI 228.2R, GPR is a test method that uses radar to
locate embedded elements in concrete structures. GPR test results showed the tendon
bundle profiles were inconsistent with the design drawing, as shown in Figure 17.3,
with the measured tendon bundles found to have “kinks” along the span.
6.1, 6.2.4, 6.4.1.1
GPR results also showed the stirrup spacing near the beam ends was consistent
with the design drawings. Away from the beam ends, the measured stirrup spacing
in the cracked portion of the beams exceeded the maximum design spacing of
24 in. (610 mm) on center in some locations. Similar GPR results were obtained
from each of the three cracked beams.
1.5.2, 1.5.3, 1.7.2, 6.1.1
The measured post-tensioning tendon bundle profiles indicated the cracking
likely occurred during initial stressing or shortly thereafter. During stressing, the
tendons attempted to straighten and eliminate kinks, resulting in the localized
downward pressure that caused the observed cracking. The large spacing between
the existing stirrups contributed to the cracks extending over an extended length
of the beams.
1.6.2, 1.7.4, 1.7.5, 6.1.1, 6.2.1
The flexural capacity of the cracked sections was not a significant concern as the
highest force on the post-tensioning strands occurred during initial stressing. No
flexural cracking was observed in the beams, indicating the beams were effectively
prestressed. Therefore, at an ultimate load level, the post-tensioning strands were
expected to have sufficient capacity to resist design loads. Further, no damage was
documented at the critical sections for flexure. Due to concerns about the shear
capacity of the affected beams, repairs to address the damage were considered.
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Chapter 17: Project Example 6—Concrete Beam Repair by Section Enlargement189
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Fig. 17.3—Typical results of GPR scanning to locate stirrups and post-tensioning
tendons.
Table 17.1—Material properties used in structural assessment
Material / property
Concrete / compressive strength
Reinforcing steel / yield strength
Post-tensioning strand / yield strength
Value / standard
4000 psi (28 MPa) / ASTM C39
60,000 psi (414 MPa) / ASTM
A615
270 ksi (1862 MPa) / ASTM
A416
Source
Design drawings
Design drawings
Design drawings
results confirmed that the demand-capacity ratio for the cracked beams was less
than 1.5 and was therefore not a potentially dangerous structural condition.
Repair options
University of Toronto User.
6.7.1
The results of the structural assessment indicated the shear strength of the
section was a concern due to uncertainty in the shear capacity of the concrete in
the cracked portion of the beams. Therefore, the primary goal of the repair was to
ensure the shear capacity of the section, and to provide an independent mechanism
to resist shear loads in the cracked area. If the section was unrepaired, spalling of
the cracked concrete section was possible. Therefore, an additional consideration
in the repair design was to provide supplemental confinement for the section.
6.7.2, 6.7.3, 7.8, 7.9
Options considered for the repairs included use of fiber-reinforced polymer
(FRP) materials to provide supplemental shear strength of the section, epoxy injection of the cracks, encasement of the section with concrete, or the addition of steel
plates. The use of either FRP or steel plates was not adopted due to concerns about
anchorage of the FRP reinforcement near the top of the beam, and the need for fire
protection of the FRP or steel components.
7.3.1
Removal of the cracked concrete section of the beams was not considered as a
repair option. If the cracked concrete were removed, it is possible for the beam
post-tensioning force to cause the reinforcing steel in the beams to buckle. Buckling of reinforcing steel can occur when concrete surrounding the steel is removed
when a compression force is present.
7.3.1, 7.3.2, 8.3
After reviewing repair options, a strategy of epoxy injection of the cracks and
concrete encasement was selected. The epoxy injection was intended to restore
the structural integrity of the cracked concrete section. The epoxy injection
was considered a viable strategy as the cracks were relatively narrow in width,
reinforcement
@Seismicisolation
was present that crossed the crack, and the loads were well defined.
@Seismicisolation
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190
Due to concerns about creep deformation of the epoxy, injection may not be a
viable strategy when wide cracks are present without crossing reinforcement. The
encasement of the section was intended to provide supplemental capacity of the
section. The combination of epoxy injection and encasement provided a “belt and
suspenders” approach to restoring the shear capacity of the section.
Design of repairs
University of Toronto User.
7.3, 9.2
At the start of the design process, the LDP considered shoring of the affected beams
prior to completion of the repairs. Rather than install shoring, the LDP selected to
remove the live load and account for the remaining loads due to the self-weight and
post-tensioning forces in the design. The parking area above the damaged beams
was closed during the repair period to remove the live load. Given the post-tensioned
nature of the beams and the need for multiple levels of shoring in an operating
parking structure, installation and engagement of a shoring system to relieve the dead
load was not considered. The added section was conservatively designed to resist all
superimposed live load.
The repair zone was selected to be 12 ft (3.7 m) long starting 1 ft (0.3 m) from the
end of the beam and allowed the repairs to extend beyond the affected area. During
construction, the contractor chose to start the encasement at the face of the column.
7.4
A concrete encasement was designed to supplement the shear capacity of the
affected beams. Figure 17.4 outlines the steps and details used for the repairs,
including preparation and placement procedures. The repair design included injection of the cracks in the affected three beams. The epoxy injection specification
was based upon ACI 563/503.7. Prior to injection, the crack faces were routed and
injection ports installed. The injection was specified to start at the base of the crack
and proceed upwards when epoxy was observed flowing from injection port to
the next injection port. The owner of the structure was not willing to pay for additional testing (coring or non-destructive testing) to confirm the epoxy injection.
Confirmation of epoxy injection is typically recommended. ICRI 210.1R describes
quality assurance methods to verify quality of injection.
7.3.1, 7.6.4
A complete encasement of the affected section of the beams created a repaired
section that behaved as an integral member with the original construction. To fully
encapsulate the original beam, channels were removed from the top of the beam.
The channel spacing was adjusted slightly in the field based upon GPR results to
avoid damage to existing reinforcement and post-tensioning. Removing concrete
to create the channels allowed for the supplemental stirrups to be anchored by
doweled reinforcing bars at the top of the beam, and by the bars at the bottom of
the beam. Consistent with ACI 318-77 Section 12.14.2.3, stirrups are developed
when anchored in this manner. The added encasement concrete provided sufficient
capacity to resist the live load from vehicular traffic. The concrete channels also
provided a means for concrete placement from the top side of the beam.
A uniform encasement thickness of 4 in. (102 mm) was selected to provide sufficient space in the enlarged section to allow for concrete cover, while minimizing
the decrease in parking head room. The new encasement was reinforced with shear
stirrups at 12 in. (305 mm) on center and horizontal skin reinforcement to help
mitigate the potential for shrinkage cracks. One bar on the bottom of the added
section was placed outside of the stirrups in a non-traditional manner. The intent of
the bar placement outside of the stirrups was to have the bar closer to the face of
concrete and therefore be more effective at crack control. The added encasement
concrete provided sufficient capacity to resist applied live load shear.
7.4
To promote bond between the new concrete and the original structure, the
surface of the concrete beam was specified to be sandblasted and wetted prior to
new concrete placement. Although the design of the encasement did not rely upon
bond to transfer load, the complete encasement of
@Seismicisolation
the beam allowed for integral
@Seismicisolation
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Chapter 17: Project Example 6—Concrete Beam Repair by Section Enlargement191
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Fig. 17.4—Detail of concrete encasement installation.
Durability of repairs
8.1.2, 8.1.3, 8.3
The primary concern of the project was the development of a structural repair
to address significant cracks in three concrete beams. The cracked beams were
not directly exposed to chlorides or other deleterious materials, and outside of
the cracking damage, showed no signs of deterioration. Therefore, the durability
requirements were based upon satisfying requirements equivalent to new construction for a similar exposure. Specific durability requirements for the repairs included:
• The concrete was specified to be a 5000 psi (34.5 MPa), air-entrained concrete
with a maximum water-cementitious materials ratio of 0.40;
• Epoxy-coated reinforcing steel was used in the repairs; and
• The perimeters of the slab channels were tooled during concrete placement to allow
for sealant installation after the encasement concrete cured. The sealant was intended
to prevent infiltration of water and other deleterious materials at these locations.
@Seismicisolation
@Seismicisolation
University of Toronto User.
behavior of the repaired beam with the new section. Alternately, the section could
have been doweled to the original beam to provide for load transfer between the
new section and the original beam.
The repaired section was painted a high-visibility yellow due to the decrease in
head space for vehicles.
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192
Contract documents
The design professional prepared contract documents that specified repair materials which satisfied governing regulatory requirements and conveyed necessary
information to perform the work. The contract documents included minimum
requirements for temporary closure of affected portions of the structure.
Construction specifications
The LDP used ACI 563 as a source for construction specifications. The specification sections that were referenced included:
Section 1—General requirements
Section 3—Concrete removal and preparation for repair
Section 4—Formwork
Section 5—Reinforcement and reinforcement support
Section 6—Conventional concrete mixtures
Section 7—Handling and placing of conventional concrete
Section 9—Crack repair by epoxy injection
As discussed previously, the repair design strategy selected by the design professional did not require the use of shoring of the affected beams prior to repairs,
therefore Section 2 was not referenced. Based upon the size of the repairs, a
conventional concrete was specified by the design professional in lieu of a proprietary material or shotcrete.
The ACI 563 specifications are intended to address conditions that are unique to
repair applications. For the section enlargement, these include:
• Section 3.1.1.2—Provide the surface profile and remove laitance, debris, and
bond-inhibiting materials using methods that satisfy the requirements indicated in the contract documents.
• Section 3.1.2.4—Submit documentation of existing conditions, especially
areas of preexisting damage and deterioration unrelated to the work, including
finishes of surfaces, before starting demolition.
• Section 3.2.1.1—Select the means and methods for concrete removal that
will minimize damage to the structure and bruised surfaces on the concrete
substrate that remains within and adjacent to the work areas.
• Section 9—Repair of cracks by epoxy injection in accordance with ACI 503.7
Construction
Quality assurance / construction observations
10.2, 10.3, 10.4
The project specifications included quality assurance and control requirements
for material approvals and field verification of quality. During construction, specific
quality control measures included:
• On-site review during the epoxy injection to confirm filling of the crack and
port to port travel of the epoxy during injection;
• Review of shop drawings for the reinforcing steel;
• Review of the concrete mixture design for conformance with project requirements;
• Review of reinforcing steel placement prior to installation of formwork;
• Observation of concrete placement and curing operations; and
• Testing of the repair concrete for slump, air content, temperature and compressive strength.
After the removal of formwork, the concrete section was hammer sounded to
confirm bond of the new concrete to the substrate.@Seismicisolation
@Seismicisolation
University of Toronto User.
9.1
The contract documents required the contractor to monitor the construction for
any unexpected conditions or conditions that may impact the execution of the
repairs. Specific requirements to the contractor included instructions related to
observation of possible damage to existing post-tension system during the repair
phase. Figure 17.5 shows the repairs in progress, with the completed repair is
shown in Figure 17.6.
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Chapter 17: Project Example 6—Concrete Beam Repair by Section Enlargement193
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Fig. 17.5—Reinforcing steel in place prior to formwork installation.
PROJECT CLOSE-OUT
Periodic maintenance
The beam repairs were completed in one phase of a multi-year repair program. As
a part of the overall repair program, recommendations for routine maintenance of the
structure were provided to the owner. The maintenance recommendations included:
• Annual cleaning of the parking decks to remove deicing salts carried in by
vehicles;
• Use of rubber-bladed plows for snow removal to avoid damage to traffic
bearing coatings; and
• Use of a non-chloride-containing material for deicing of the structure
Record documents
The owner was provided with copies of the construction documents including
results from repair phase concrete testing and the recommended periodic maintenance program.
@Seismicisolation
@Seismicisolation
University of Toronto User.
Fig. 17.6—Completed repair, painted yellow with warning sign of
low clearance.
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194
Description of structure
The structure is a two-story concrete frame constructed of mild-reinforced
perimeter beams and columns supported on pile foundations (Fig. 18.1). The
concrete frame structure was constructed in 1954 and is located in the western
United States. The 30 ft (9.1 m) tall structure is octagonal-shaped in plan, approximately 33.5 ft (10.2 m) wide, and includes two levels of concrete beams: a lower
level approximately 16 ft (4.9 m) above grade and an upper level at the top of the
frame. The lower-level beams are approximately 30 in. (762 mm) tall by 30 in.
(762 mm) wide and the upper-level beams are approximately 54 in. (1372 mm) tall
by 33 in. (838 mm) wide. The frame supports a vertical vessel on the upper level
beams with a design weight of approximately 500 kip (226,800 kg).
Project initiation and objectives
The frame structure is located at an industrial site that is subject to the local
jurisdiction’s Accidental Release and Prevention (ARP) Program. The objective of
the program is to prevent the release of regulated substances with potential consequences to the public and environment. The owner of a facility that contains a regulated substance, as defined by the state, works closely with the authority having
jurisdiction (AHJ) to determine the level of documentation required to develop a
site-specific risk management plan. As part of the risk management plan, the owner
should conduct a hazard analysis to identify, evaluate, and control hazards associated with the regulated substance considering a variety of natural or manmade
events, including earthquakes. The ARP program requires that a licensed design
professional (LDP) perform a seismic evaluation of any structures, distribution
systems, and equipment where failure or displacement could release the regulated
substance and that the hazard analysis, including the seismic evaluation, be revalidated every 5 years.
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Chapter 18: Project Example 7—Concrete Frame Strengthening by Steel Jacket
University of Toronto User.
Fig. 18.1—Overall view of concrete frame structure.
ACI 562-19 provision numbers applying to each section of text are shown in red at the top right of each paragraph.
@Seismicisolation
@Seismicisolation
195
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
The project was initiated to meet the AHJ’s program for accidental release
prevention and to review the risk for release of a regulated substance during a
seismic event. The LDP performed a seismic assessment of the concrete frame to
evaluate the structure’s ability to resist the required seismic forces and to identify
conditions that require maintenance, repair, or both.
Governing building codes
Based on discussions with the local building officials, as well as the information available in the original design drawings, the original design code and current
building codes adopted by the jurisdiction were determined to be as follows:
Jurisdiction—Western U.S. city
Original building code—1943 Uniform Building Code (1943 UBC)
Current building code—2013 State Building Code
Existing building code—2013 State Building Code
1.2.3
1.2.2
1.2.1
The State Building Code was modeled after the 2012 International Building
Code (IBC) and included provisions for the alteration, repair, addition, and
change of occupancy of existing structures. Additionally, the State Building Code
included alternative compliance provisions for work performed on existing buildings in accordance with the 2012 International Existing Building Code (IEBC). In
addition to the adopted codes, the AHJ required the use of ACI 562 for repair of
concrete structures.
Preliminary evaluation
1.2.4.5.1
The seismic evaluation of the concrete frame structure began with a preliminary
evaluation to review the actual condition of the structure and to determine if calculations are needed to complete the evaluation of the structure. The preliminary
evaluation included a visual survey supplemented by a review of related documents.
Document review
1.7.1
The original design drawings, construction documents, and previous ARP
report were available and reviewed by the LDP. The prior ARP report included the
results of the previous seismic evaluation and associated repairs and retrofits that
were made. The original construction documents showed the configuration of the
existing frame structure, the location of embedded reinforcement, and the foundation for the concrete frame. The drawings were used to verify anchorage details
and to identify configurations that were not readily accessible for visual observation (Fig. 18.2 and 18.3).
@Seismicisolation
@Seismicisolation
University of Toronto User.
1.2.4.2
Design-basis code—Because the AHJ adopted an existing building code,
ACI 562 directs the LDP to determine the design-basis code in accordance with
ACI 562-19 Chapter 4.
4.1.1, 4.1.3
Based on a preliminary evaluation of the frame structure, its location in a region
of high seismicity, and discussion with the AHJ, the design-basis code was determined to be the 2013 State Building Code. Additional supplemental requirements
were identified in the guidance document for the ARP Program seismic assessments. The guidance document identifies recommendations for performing a deterministic evaluation of structural systems and components to provide reasonable
assurance for preventing the release of regulated substances.
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Fig. 18.2—Original construction drawing for concrete frame structure (plan view).
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Chapter 18: Project Example 7—Concrete Frame Strengthening by Steel Jacket197
University of Toronto User.
Fig. 18.3—Original construction drawing for concrete@Seismicisolation
frame structure (elevation view).
@Seismicisolation
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Existing site conditions review
1.7.1, 1.7.2, 1.7.5, 6.1, 6.2
A critical part of the preliminary evaluation was the on-site review of the existing
structure by the LDP. This was primarily a visual survey that considered the current
condition of the structure in a systemic manner. The LDP walked throughout the
concrete frame to look for potential seismic vulnerabilities in the primary seismicload-resisting elements and potential areas of weakness due to the following:
a. Original design
b. Construction
c. Previous modifications
d. Deterioration or damage
The on-site review identified localized sections of spalled concrete that exposed
rectangular reinforcing bars. Based on the experience of the LDP, the age of the
structure, and the presence of rectangular reinforcing bars, the LDP determined
that additional analysis was necessary to evaluate the adequacy of the concrete
frame structure. The LDP did not observe any other readily visible signs of distress
within the concrete frame.
Uc = D + L ±
Ehoriz
+ Evert ≤ φRn
Q
and
Uc = D ±
Ehoriz
− Evert ≤ φRn
Q
where Uc is the strength design demand; D is the dead load including
operating loads; L is any sustained live load expected during an earthquake; Ehoriz is
the unreduced elastic earthquake horizontal load; Q is the ductility factor in accordance with the ARP guidance document; Evert is the unreduced elastic earthquake
vertical load; f is the strength reduction factor; and Rn is the nominal strength of
the member.
6.5
Following the previous inspection cycle, the ARP guidance document was
changed to reflect updates to the seismic assessment criteria. The changes resulted
in increased seismic loads compared to previous seismic evaluations. The LDP
performed a structural evaluation of the concrete frame using the increased seismic
loads to assess
@Seismicisolation
the reliability of the concrete frame structure.
@Seismicisolation
University of Toronto User.
Structural assessment
Because the visual survey did not reveal signs of structural distress that would
have indicated overstress of the gravity supporting system, the LDP performed a
lateral analysis to assess the concrete frame. Based on the observed spacing
of the square steel ties in the beams and columns and the LPD’s experience, the
LDP determined that the frame structure could be nonductile. Therefore, the
LDP determined that seismic loading and ductility requirements governed the
structural assessment.
6.3.1, 6.3.2
Based on the age of the structure, the LDP used ACI 562-19 Table 6.3.2a to
determine a concrete compressive strength of 3000 psi (21 MPa) and Table 6.3.2b
to determine a yield strength of 40 ksi (280 MPa) for the reinforcing steel in the
analysis.
4.5.2, 6.5
In accordance with the design basis code and the supplemental ARP guidance
document, the seismic ground motion for evaluation of the concrete frame was
calculated in accordance with ASCE 7 for new design of a nonbuilding structure.
The strength design demands were calculated using the modified load combinations
in accordance with the ARP guidance document.
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198
The concrete frame and foundation were evaluated in accordance with the recommendations of the ARP guidance document. The LDP used structural analysis software to model the existing concrete frame and proposed retrofit strengthening. The
effects of torsion and drift were included in the analysis model. The analysis considered
a uniform acceleration equal to the spectral response acceleration parameter SDS (at
a period of approximately 0.5 seconds) and a ductility factor Q of 1.5 to account
for damage and possible nonductile behavior of the frame structure. Considering
the load combinations from the guidance document identified previously, the LDP
determined that under lateral loading from the design seismic event, the beams and
columns would be overstressed in both shear and flexure. The calculated demandto-capacity ratios were a maximum 4 for columns, 2.3 for the upper beams, and
7.5 for the lower beams. The existing foundation was evaluated for the potential of
overturning and sliding considering the reactions obtained from the analysis model
and found to be adequate to support the increase seismic load.
Strengthening concepts
The results of the structural assessment indicated that the shear and flexural strength
of the beams and columns were inadequate for the design seismic event. Therefore,
the primary goal was to perform a seismic retrofit to strengthen the concrete frame
structure. The concrete frame was located adjacent to other supporting structures
on site and had to remain operational during the repairs. The effect of fire was
not considered as part of the seismic retrofit design as the open frame structure
does not support a flammable material and the facility has dedicated fire suppression systems throughout the site to mitigate the risk of damage due to fire. The
following strengthening concepts were discussed with the owner:
Concept 1
Carbon fiber reinforced polymer (CFRP)—Wrap beams and columns with
CFRP to strengthen the member sections. This strengthening concept was not
considered feasible due to level of overstress in all structural members calculated
in the structural analysis.
Concept 3
Steel jackets and supplemental bracing—Wrap beams and columns with steel
plate jackets to provide additional strength and ductility, and install new steel
cross-bracing between lower-level columns. The LDP determined that steel jackets
could be installed considering clearances to adjacent structures and in conjunction
with bracing would provide sufficient strength increase to the structure to meet the
requirements of the ARP program.
Structural analysis and repair design
7.2.1, 7.2.2
Design loads were calculated based on ASCE 7-10 Chapter 15 for nonbuilding
structures. Because the lower level would be symmetrically braced with supplemental braced frames, but the upper bay would remain unbraced, two different
coefficients were calculated, using the response modification factors (R) of 3.0 and
2.0, respectively. The design of drag strut and seismic connections requires an over
strength factor (Ω) of 2.0. Each element was therefore checked based on the appropriate set of load combinations considering R and, where applicable, Ω.
7.3.1, R7.3.2
The final repair design included steel jackets around the columns and upper
beams. The columns were fully encased by steel jackets
@Seismicisolation
and analyzed as a concrete@Seismicisolation
University of Toronto User.
Concept 2
Section enlargement—Increase the size of beams and columns with reinforced concrete. This strengthening concept was not considered feasible due to
size limitations. The columns and beams could not be sufficiently enlarged due to
the location of the concrete frame relative to other adjacent structures and piping.
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filled rectangular box section in accordance with ANSI/AISC 360. The compactness of the steel jacket section was determined considering a concrete filled tube in
accordance with ANSI/AISC 360. The existing concrete column was not considered to contribute to the column capacity and the built-up tube section (steel jacket)
was designed to independently support the additional seismic loads. Figure 18.4
shows the column jacket detail designed by the LDP for the strengthening.
The upper beams were encased in a U-shaped steel jacket because the supports
for the vertical vessel were attached to the top of the concrete beams and access
was not available to install a continuous top plate. The U-shaped steel jackets were
bolted through the concrete beams as shown in Fig. 18.5 to transfer shear flow
between the concrete beam and the supplemental steel plates, and to brace the
steel plates against buckling. The through bolts were staggered top and bottom and
spaced 14 in. (356 mm) on center. After the through bolts were installed, the holes
were filled with nonshrink grout to ensure bearing between the bolts and concrete.
In addition to the steel jackets, structural strengthening included adding supplemental diagonal braces in alternate bays below the lower beams to increase the
lateral resistance of the frame structure. Steel wide flange beams were added below
all lower-level concrete beams to increase the strength of the lower level beams
and act as a drag strut between the braced bays. New concrete grade beams were
installed on top of the mat foundation between the concrete columns to support
the new diagonal braces (Fig. 18.6). The grade beams were doweled to the mat
foundation and the columns at each end with epoxy-set reinforcing bars to transfer
the brace forces to the existing foundation.
In conjunction with the structural strengthening, traditional concrete repairs were
performed to address localized concrete damage and distress observed during the walkthrough assessment and provide a uniform substrate under the steel jackets. Based on
observations made during the initial walkthrough, the LDP determined that the localized concrete damage was the result of low concrete cover over the reinforcing steel.
Durability
Contract documents
1.5.1, 1.6.1, 9.4.1
The LDP prepared contract documents that specified repair materials that satisfied
governing regulatory requirements and conveyed necessary information to perform
the work. The work shown in the contract documents was considered a voluntary
seismic upgrade of an existing structure to address specific issues identified as part of
the ARP seismic assessment. The contract documents also instructed the contractor
to provide all measures to protect life and property during construction.
Construction specifications
The LDP used AISC 303 and AISC 341 as sources for construction specifications
for fabrication and erection of the supplemental steel strengthening.
The LDP used ACI 563 as a source for construction specifications for all
remaining aspects
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of the project including new concrete construction and concrete
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University of Toronto User.
8.1.1, 8.2.1, 8.4.1, 8.5.1
The durability of the repair materials and steel jackets was considered. The
structure was exposed to the environment and was located at an industrial site
with hazardous materials. During installation, the gap between the steel jackets
and the concrete members was grouted to ensure intimate contact between the
plates and the concrete surface. The new steel members, plates, and jackets were
completely coated with a protective paint during fabrication to protect the exposed
steel. Consideration was given to environmental conditions and exposure to chemicals
when selecting an appropriate coating. The paint was selected by the owner for
chemical resistance, cost, and ease of maintenance. The top surface of the upper
beams was also painted to limit moisture penetration through the concrete. The
transition between the concrete and the steel plate was sealed with a sealant to
prevent water infiltration behind the steel jackets.
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200
Fig. 18.4—Construction drawing for strengthening: section detail for steel jacket around column.
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Chapter 18: Project Example 7—Concrete Frame Strengthening by Steel Jacket201
University of Toronto User.
Fig. 18.5—Construction drawing for strengthening: section detail for upper beam
steel jacket.
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GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
repair of the existing structure. The specification sections that were referenced
included the following:
Section 1—General requirements
Section 3—Concrete removal and preparation for repair
Section 4—Formwork
Section 5—Reinforcement and reinforcement support
Section 6—Conventional concrete mixtures
Section 7—Handling and placing of conventional concrete
Section 8—Proprietary cementitious and polymer repair materials
As discussed previously, the repair design strategy selected by the LDP did not require
the use of shoring of the structure prior to repairs, therefore Section 2 was not referenced.
Appropriate surface preparation was required for the conventional concrete
repairs to the@Seismicisolation
existing concrete structure and for preparation of the existing column
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University of Toronto User.
Fig. 18.6—Construction drawing for strengthening: concrete frame elevation for typical braced bay.
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202
and foundation surfaces for installation of the new concrete grade beams. For the
steel jacket strengthening, surface preparation was required to remove any surface
contaminant prior to installation of the steel plates. The ACI 563 specifications are
intended to address conditions that are unique to concrete repair applications. The
concrete surface preparation was considered in accordance with the following:
Section 3.1.1.2—Provide the surface profile and remove laitance, debris, and
bond-inhibiting materials using methods that satisfy the requirements indicated in
the contract documents.
Construction
9.1, 9.4.1
The structural strengthening did not require removing members from the existing
structure; therefore, the seismic retrofit could be installed without interrupting
day-to-day operation of the facility and supported equipment. The contractor
was required to notify the LDP of any discrepancies between the contract documents and existing construction and to repair any damage caused as a result of the
work. The contractor was also required to maintain a continuous fire watch during
welding or cutting near combustible materials.
During construction, the contractor notified the LDP that the two-sided steel
jacket sections would be difficult to install around the column due to the location
of existing piping and adjacent structures. To address these conflicts with the steel
jacket installation, the contractor proposed modifying the steel jacket detail for
the columns to include separate steel plates on each side of the column that were
fastened together at the column corners. The LDP evaluated the design modification and determined that the proposed alternate steel jacket fabrication and installation procedure was acceptable and provided sufficient capacity for the seismic
retrofit (Fig. 18.7).
Quality assurance
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University of Toronto User.
1.5.1, 10.2.1, 10.2.2, 10.4.1
The repair drawings and specifications included quality assurance and control
measures for material approvals and field verification of quality. The specified
quality control measures and construction observations were performed during
construction, including the following:
a. Visual inspection of the work for conformance with the approved construction
documents
b. Inspection of formwork and bracing to verify that supports, fastenings, wedges,
ties, and items were secure prior to concrete placement
10.2.3
c. Observation of installed reinforcement and reinforcing bar accessories for new
concrete grade beams
d. Observation of the concrete placement and curing operations for new concrete
grade beams
10.3.1
e. Testing of repair concrete, including slump, temperature, compressive strength,
and air content
10.4.1
f. Observation of post-installed dowel preparation and installation
g. Inspection of welded connections to verify conformance with approved welding
performance specifications, including materials, surface preparation, alignment,
weld size, length, and location
h. Inspection of bolted connections to verify preparation and installation
10.2.3
i. Inspection of anchor rods and other items embedded in the concrete which
supported the structural steel to verify diameter, grade, type, length, and depth
of embedment
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Chapter 18: Project Example 7—Concrete Frame Strengthening by Steel Jacket203
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Fig. 18.7—Overall view of completed steel jacket strengthening with protective
paint coating.
PROJECT CLOSE-OUT
R1.5.3
Periodic maintenance requirements were discussed with the owner. The LDP
recommended yearly visual inspection and touch-up painting of the protective
coating.
Record documents
1.6.3
The owner was provided with copies of the project and construction documents
and the recommended monitoring and maintenance schedule.
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Periodic maintenance
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204
Description of structure
The building is a three-story retail structure constructed in 2004 with a footprint
of 120 x 66 ft (36.6 x 20 m). The primary structural frame is composed of reinforced concrete (RC) columns, RC beams, and one-way RC slabs. The typical floor
has 10 spans in the long direction at 12 ft (3.6 m) each and three spans in transverse
direction at 22 ft (6.7 m) each. The span for one-way slab is 12 ft (3.6 m) centerto-center of beams and the span for the beams is 22 ft (6.7 m) center to-center of
the columns. The slabs are 6 in. (150 mm) thick and reinforced with No. 5 (No. 16)
steel bars at 16 in. (400 mm) on center both bottom and top. A typical floor plan
showing the layout of slab, beams, and columns is provided in Fig. 19.1.
The beams are 12 in. (300 mm) wide by 24 in. (600 mm) deep and reinforced
with three No. 7 (No. 22) bottom steel bars, assumed three No. 6 (No. 19) top bars,
and No. 3 (No. 10) stirrups at 8 in. (200 mm) on center. The RC beams have a clear
concrete cover of 1.5 in. (40 mm) and were constructed using 4000 psi (28 MPa)
concrete made up of carbonate aggregate as obtained from the contract document
concrete mixture design data sheet. The floors are supported on 18 x 18 in. (450 x
450 mm) columns. All the steel reinforcement used in the original construction is
ASTM A615/A615M Grade 60 ksi (420 MPa) steel bars. A typical elevation of the
beam is provided in Fig. 19.2 and a typical section is provided in Fig. 19.3.
As the lengths of the top steel bars could not be confirmed, the beams are
analyzed assuming simply supported end conditions with a clear span of 20.5 ft
(6.25 m). The existing retail store floors were originally designed to carry a live
load of 75 lb/ft2 (366 kg/m2) and a superimposed dead load of 25 lb/ft2 (122 kg/m2).
A fire resistance rating of 2 hours was specified on the original design documents
for the building.
In this example, only flexural design will be performed. Shear strength was
found to be adequate and fire load had no effect on shear capacity.
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Chapter 19: Project Example 8—Building Subjected to Fire
University of Toronto User.
Fig. 19.1—Typical floor plan.
ACI 562-19 provision numbers applying to each section of text are shown in red at the top right of each paragraph.
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205
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Fig. 19.2—Typical beam elevation.
Assumed top bars
Fig. 19.3—Typical beam section.
University of Toronto User.
Project initiation, objectives, and remediation summary
Scenario 1 (higher live loads)
After a change in the ownership of the building in 2017, the entire second floor
was repurposed to be a wholesale store. Due to the change in occupancy of the
second floor, the new live load for the second floor was increased from 75 lb/ft2
(366 kg/m2) (original design) to 125 lb/ft2 (610 kg/m2) (wholesale). It was estimated that there would be minimal change in the superimposed dead load, which
remains at 25 lb/ft2 (122 kg/m2).
Structural evaluation of the second floor revealed that the columns and slabs are
adequate to support the new live load and the fire rating requirement of 2 hours.
However, the existing beams were found to be deficient in positive flexural
strength and require strengthening to carry the higher new live load. The licensed
design professional (LDP) for the project was tasked with developing a strengthening solution for the second-floor beams and to evaluate and enhance the fire
resistance of the beams to meet the required 2-hour fire rating.
The LDP determined that strengthening of the beams can be achieved using a
one-ply, 12 in. (300 mm) wide strip of externally bonded carbon fiber-reinforced
polymer (FRP) system on the soffit of the beams. To achieve the required fire rating,
the LDP specified a UL-certified 3/4 in. (20 mm) thick spray-applied cementitious
fire protection system that was tested with the FRP system selected for the project.
A schematic for the beam with FRP and spray applied fire protection is shown in
Fig. 19.4 and 19.5.
The design approach and calculation steps used to determine the fire resistance
rating of an existing and strengthened RC beam are discussed in the following
sections. @Seismicisolation
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206
Fig. 19.4—Typical beams strengthened with FRP and insulated with fire protection system.
University of Toronto User.
Fig. 19.5—Installation of fire protection system.
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GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Scenario 2 (lower concrete cover)
After the change of ownership of the building, the design live load for the second
floor was changed to 125 lb/ft2 (610 kg/m2); however, an area on the second floor
was selected to remain at 75 lb/ft2 (366 kg/m2) live load to house some lightweight
equipment.
During the site investigation of the second-floor slab, it was discovered that the
clear concrete cover thickness for the bottom steel bars at two of the beams in the
75 lb/ft2 (366 kg/m2) area was, on average, 3/4 in. (20 mm), which is less than the
1.5 in. (40 mm) clear cover specified on the original design documents.
These conditions created concerns for the LDP with the fire resistance of the
beams with lower concrete cover. Upon preliminary analysis, the existing beams
were found to provide only 1-hour fire resistance rating with the existing conditions. The LDP was requested to develop a solution to enhance the fire resistance
of the two beams to meet the required 2-hour fire rating.
The fire resistance rating of the beams was enhanced by installing a 1 in. (25 mm)
thick concrete jacket to provide additional cover to the existing reinforcement.
Governing codes
Based on discussions with the building officials, the building codes adopted by
the jurisdiction were determined, as described in the following:
Jurisdiction—Northeastern U.S. city
Original building code—2009 International Building Code (IBC 2009)
Current building code—2015 International Building Code (IBC 2015)
Concrete design code—ACI 318-14
Fire design code—ACI 216.1-14
Design loads—ASCE 7-16
Repair code—ACI 562-19
1.2.3
1.2.2
1.2.1
Muθ,Exist = 1.2MD + 1.6ML,Exist + 0.5MSL
= (1.2)(75) + (1.6)(48) + (0.5)(0) = 166 ft-kip (225 kN·m)
where MD = 75 ft-kip (102 kN·m); ML,Exist = 48 ft-kip (65 kN·m); and MSL = 0
ft-kip.
New higher live loads
Muθ,Exist = 1.2MD + 1.6ML,Exist + 0.5MSL
= (1.2)(75) + (1.6)(78) + (0.5)(0) = 215 ft-kip (292 kN·m)
where MD = 75 kip-ft (102 kN·m); ML = 78 kip-ft (106 kN·m); and MSL = none
(load due to super imposed live load).
Fire loading
Based on the geometrical configuration and tributary width, loadings during fire
conditions are calculated per ACI 562 Eq. (5.5.3).
ϕexR ≥ (0.9 or 1.2)D + 0.5L + 0.2S
5.5.3
Existing loads:
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5.5.3
University of Toronto User.
Fire resistance rating calculations
Ambient condition loading (room temperature)
Based on the geometrical configuration and tributary width, loadings under room
temperature conditions are calculated per ASCE/SEI 7 Section 2.3.1.
Existing loads
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208
Muθ,Exist = 1.2MD + 0.5ML,Exist + 0.2MSL
= (1.2)(75) + (0.5)(48) + (0.2)(0) = 114 ft-kip (155 kN·m)
where MD = 75 ft-kip (102 kN·m); ML,Exist = 48 ft-kip (65 kN·m); and MSL =
0 ft-kip.
New higher loads
Muθ,Exist = 1.2MD + 0.5ML,Exist + 0.2MSL
= (1.2)(75) + (0.5)(78) + (0.2)(0) = 130 ft-kip (176 kN·m)
where MDL = 75 ft-kip (102 kN·m); ML = 78 ft-kip (106 kN·m); and MSL = 0 ft-kip.
Material properties
Once the temperatures of the steel bars at 1 and 2 hours have been established,
the yield strength of the steel at these elevated temperatures can be determined
using the strength versus fire exposure time curve provided in Fig. 19.9 (Fig.
4.4.2.2.1.b of ACI 216.1-14). The reduced yield strength of the steel bars at 1 hour
and 2 hours into fire exposure are listed in the following.
At 1 hour
Reduced yield strength of corner bars, fyθC,1HR = 0.95fy
Reduced yield strength of middle bar, fyθM,1HR = 1.0fy
At 2 hours
Reduced yield strength of corner bars, fyθC,2HR = 0.68fy
Reduced yield strength of middle bar, fyθM,2HR = 0.90fy
For simplicity, in this design example, the member capacity at elevated temperature
will be conservatively calculated using the yield strength of corner steel bars only.
Because temperature in the concrete in compression remain relatively low, there
is minimal or no strength degradation in the concrete compression block.
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Scenario 1 (new 125 lb/ft2 [610 kg/mm2] live loads)
The beams are exposed to fire on the bottom three sides. The existing beam has
three No. 7 (No. 22) bottom steel bars, out of which two are corner bars and one is
in the middle of the section. The distance from the center of the bars to the outside
surface is calculated at 1.5 in. (cover) + 0.375 in. (No. 3 stirrup) + 0.4375 in. (1/2
No. 7 bar) = 2.31 in. (70 mm) on two exterior sides for the corner bars, 2.31 in.
(70 mm) on the bottom side, and 6 in. (150 mm) from the side of the beam for the
middle bar (Fig. 19.3).
ACI 216.1-14 provides isotherms for beam section for 1-, 2-, and 3-hour fire
exposure. These curves can be used to determine the temperature of the steel bars
at various times into the fire exposure. The temperature of the three bottom bars
were determined using Fig. 19.6 and 19.7, respectively (Fig. 4.4.2.3i and 4.4.2.3j
in ACI 216.1-14) and are listed in the following at 1 hour and 2 hours into fire
exposure.
At 1 hour
Temperature of corner bars at 1 hour, TC,1HR = 600°F (320°C)
Temperature of middle bar at 1 hour, TM,1HR = 450°F (230°C)
At 2 hours
Temperature of corner bars at 2 hours, TC,2HR = 900°F (480°C)
Temperature of middle bar at 2 hours, TM,2HR = 700°F (370°C)
Considering the thickness of the beam and slab, fire exposure on the bottom
sides of the beams typically has minimum effect on top steel bars. In addition,
most damage during a fire event occurs on the upper portions of columns and wall
and underside of the slabs. This is mainly due to heat that rises during a fire event,
causing the top of slabs and beams to stay at relatively low temperature (refer to
fire effect on a reinforced concrete building; Fig. 19.8).
For beam geometries that are not covered in ACI 216.1, simplified equations to
calculate sectional and steel bar temperatures can be found in Kodur et al. (2013).
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Fig. 19.6—Temperature distribution in a normalweight concrete rectangle unit at
1 hour of fire exposure.
2.65 

φM n = φAs f y (d − a /2) = (0.9)(3)(0.6)(60)  21.68 −
/12 = 165 ft-kip (224 kN·m)

2 
a=
(3)(0.6)(60)
= 2.65 in. (67 mm)
(0.85)(4)(12)
where fc′ = 4000 psi (28 MPa); fy = 60,000 psi (420 MPa); As = 3(0.6 in.2) = 1.8 in.2
(852 mm2); d = 24 – (1.5 + 3/8 + 7/16) = 21.68 in. (551 mm); b = 12 in. (300 mm);
and ϕ = 0.9.
Per ACI 562-19 Section 5.5.2, the existing member without FRP strengthening
is required to satisfy the following equation.
ϕMn ≥ Mu = 1.1MD + 0.75ML
= (1.1)(75) + (0.75)(78) = 141 ft-kip (191 kN·m)
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Flexural capacity
Using the reduced yield strength of steel bars, the moment capacity of the beam
at midspan under fire exposure can be evaluated using standard sectional analysis.
The strength contribution of external FRP strengthening during fire exposure can
be ignored per ACI 562-19 Section 5.5.3.3. In addition, per ACI 562-19 Section
5.5.3, the strength reduction factor (ϕ) is taken as 1.0 for strength calculations
under fire exposure Buchanan (2009).
Beam capacity at room temperature:
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210
Fig. 19.7—Temperature distribution in a normalweight concrete rectangle unit at
2 hours of fire exposure.
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Chapter 19: Project Example 8—Building Subjected to Fire211
University of Toronto User.
Fig. 19.8—Effect of fire on reinforced concrete structure—notice spalling of
concrete cover of beam and exposure of bottom bars (image courtesy of Sandberg.
co.uk).
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GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Fig. 19.9—Strength of flexural reinforcement steel bar and strand at high
temperature.
ϕMn = 165 ft-kip (224 kN·m) > Mu = 141 ft-kip (191 kN·m)
Based on the calculations, the existing beams exhibit the minimum required
strength indicating that FRP strengthening is feasible for these beams under the
new higher live loads.
Beam capacity after having been exposed to fire for 1 hour:
a 
2.85 


/12
φM nθ,1HR = φAs f yθ,1HR  d − θ  = (1.0)(3)(0.6)(0.95)(60)  21.68 −


2
2 
aθ =
(3)(0.6)(0.95)(60)
= 2.85 in. (72 mm)
(0.85)(4)(12)
where fcT = 4000 psi (28 MPa); fyθ,1H = (0.95)(60 ksi) = 57 ksi (399 MPa); As =
3(0.6 in.2) = 1.8 in.2 (852 mm2); d = 24 – (1.5 + 3/8 + 7/16) = 21.68 in. (551 mm);
b = 12 in. (300 mm); and ϕ = 1.0.
5.5.3.2
Beam capacity after having been exposed to fire for 2 hours
a 
1.82 


/12
φM nθ,2HR = φAs f yθ,2HR  d − θ  = (1.0)(3)(0.6)(0.68)(60)  21.68 −


2
2 
= 127 ft-kip (172 kN.m)
aθ =
(3)(0.6)(0.68)(60)
= 1.82 in. (46 mm)
(0.85)(4)(12)
where fcT = 4000 psi (28 MPa); fyθ,2HR = (0.68)(60 ksi) = 40.8 ksi (281 MPa); As =
3(0.6 in.2) = 1.8 in.2 (852 mm2); d = 24 – (1.5 + 3/8 + 7/16) = 21.68 in. (551 mm);
b = 12 in. (300 mm); and ϕ = 1.0.
5.5.3.2
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= 174 ft-kip (236 kN·m)
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212
Fire resistance rating
The fire resistance rating of the beam is calculated as the duration (in hours)
during which the member is able to support the load combination during a fire
event, as shown by the following equation.
ϕMn,θ ≥ Mu,fire
5.5.3.2
Under the new higher loads, the beams exhibited only 1-hour fire resistance
rating and did not meet the required 2-hour rating for the structure. Therefore, the
FRP strengthened beams are required to be protected with fire protection system.
Table 19.1 summarizes the fire rating calculation for the original condition and the
new condition of higher live loads at 1 hour and 2 hours into fire exposure.
Note that the moment capacity of beams at 1-hour fire rating is greater than the
moment capacity at room temperature. This is because concrete members subjected
to fire have a reduction factor of 1.0, and the reduction in steel strength at 1-hour
is 5 percent only (0.95fy), thus resulting in 5 percent increase in moment capacity.
University of Toronto User.
Scenario 2 (lower concrete cover)
The beams are exposed to fire on the bottom three sides. The existing beam has
three No. 7 (No. 22) bottom steel bars, out of which two are corner bars and one is
in the middle of the section. Because the existing concrete cover for the steel bars
was found to be 3/4 in. (20 mm), the existing distance from the center of the bars
to the outside surface is 1.56 in. (40 mm) on two exterior sides for the corner bars
and 1.56 in. (40 mm) on the bottom side and 6 in. (150 mm) from the side of the
beam for the middle bar.
ACI 216.1 provides isotherms for beam section for 1-, 2-, and 3-hour fire exposure. These curves can be used to determine the temperature of the steel bars at
various times into the fire exposure. The temperature of the three bottom bars were
determined using Fig. 19.10 and 19.11, respectively (Fig. 4.4.2.3i and 4.4.2.3j
in ACI 216.1-14), and are listed in the following at 1 hour and 2 hours into fire
exposure.
Beam capacity after having been exposed to fire for 1 hour:
Temperature of corner bars at 1 hour, TC,1HR = 900°F (480°C)
Temperature of middle bar at 1 hour, TM,1HR = 680°F (360°C)
At 2 hours
Temperature of corner bars at 2 hours, TC,2HR = 1150°F (620°C)
Temperature of middle bar at 2 hours, TM,2HR = 900°F (480°C)
Considering the thickness of the beam and slab, fire exposure on the bottom
sides of the beams typically has minimum effect on top steel bars. In addition, as
discussed previously, as heat rises up during a fire event, the top of slabs and beams
stay at relatively low temperature.
Material properties
Once the temperatures of the steel bars at 1 and 2 hours have been established,
the yield strength of the steel at these elevated temperatures can be determined
using the strength versus fire exposure time curve provided in Fig. 19.12 (Fig.
Table 19.1—Summary of beam capacity with higher live load at room temperature and at fire loading
Condition
Clear
cover, in.
(mm)
MD,
ft-kip
(kN·m)
ML,
MU,
MU,fire,
ft-kip
ft-kip
ft-kip
ϕMn,Room,
ϕMn,fire2HR,
(kN·m)
(kN·m)
(kN·m)
ft-kip (kN·m) ft-kip (kN·m)
SCENARIO #1 (NEW 125 lb/ft2 LIVE LOAD)
ϕMn,fire1HR,
ft-kip (kN·m)
Original
design with
lower cover
1.5 (40)
75 (102)
48 (65)
165 (226)
114 (155)
165 (224)
127 (172)
174 (236)
New design
with higher
load
1.5 (40)
75 (102)
78 (106)
215 (292)
130 (176)
165 (224)
127 (172)
174 (236)
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Chapter 19: Project Example 8—Building Subjected to Fire213
Fire rating
1 hour (enlarge
section to meet
cover to meet
2HR)
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
4.4.2.2.1.b of ACI 216.1-14). The reduced yield strength of the steel bars at 1 hour
and 2 hours into fire exposure are listed in the following.
At 1 hour
Reduced yield strength of corner bars, fyθC,1HR = 0.69fy
Reduced yield strength of middle bar, fyθM,1HR = 0.92fy
At 2 hours
Reduced yield strength of corner bars, fyθC,2HR = 0.38fy
Reduced yield strength of middle bar, fyθM,2HR = 0.69fy
For simplicity, in this design example, the member capacity at elevated
temperature will be conservatively calculated using the yield strength of corner
steel bars only.
Sectional capacity
Using the reduced yield strength of steel bars, the moment capacity of the
beam at midspan
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under fire exposure can be evaluated using standard sectional
@Seismicisolation
University of Toronto User.
Fig. 19.10—Temperature distribution in a normalweight concrete rectangular unit
at 1 hour of fire exposure.
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214
analysis. The strength contribution of external FRP strengthening during fire
exposure can be ignored per ACI 562-19 Section 5.5.3.3. In addition, per ACI
562-19 Section 5.5.3, the strength reduction factor (ϕ) is taken as 1.0 for strength
calculations under fire exposure (Buchanan 2009).
Beam capacity at room temperature:
a
2.65 


φM n = φAs f y  d −  (0.9)(3)(0.6)(60)  22.43 −
/12


2
2 
= 170 ft-kip (230 kN·m)
a=
(3)(0.6)(60)
= 2.65 in. (67 mm)
(0.85)(4)(12)
where fcT = 4000 psi (28 MPa); fy = 60,000 psi (420 MPa); As = (3)(0.6 in.2) =
1.8 in.2 (852 mm2); d = 24 – (1.5 + 3/8 + 7/16) = 22.43 in. (570 mm); b = 12 in.
(300 mm); and ϕ = 0.9.
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Fig. 19.11—Temperature distribution in a normalweight concrete rectangular unit
at 2 hours of fire exposure.
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Chapter 19: Project Example 8—Building Subjected to Fire215
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
Fig. 19.12—Strength of flexural reinforcement steel bar and strand at high
temperatures.
Beam capacity after having been exposed for 1 hour:
a 
1.82 


/12
φM nθ,1HR = φAs f yθ,1HR  d − θ  = (1.0)(3)(0.6)(0.69)(60)  22.43 −


2
2 
= 133 ft-kip (180 kN.m)
aθ =
(3)(0.6)(0.69)(60)
= 1.82 in. (46 mm)
(0.85)(4)(12)
= 75 ft-kip (102 kN.m)
aθ =
(3)(0.6)(0.387)(60)
= 1.0 in. (25 mm)
(0.85)(4)(12)
where fcT = 4000 psi (28 MPa); fyθ,1HR = (0.38)(60) = 22.8 ksi (157 MPa);
As = (3)(0.6 in.2) = 1.8 in.2 (852 mm2); d = 24 – (1.5 + 3/8+ 7/16) = 22.43 in. (570 mm);
b = 12 in. (300 mm); and ϕ = 1.0.
5.5.3.2
Fire resistance rating
With the lower concrete cover, the beams exhibited only 1-hour fire resistance
rating and did not meet the required 2-hour rating for the structure. Therefore, the
beams are required to be strengthened to achieve the minimum concrete cover
thickness and the required fire resistance rating using concrete jacketing. Table 19.2
summarizes the fire rating calculation for the condition of lower concrete cover at
1 hour and 2 hours into fire exposure.
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where fcT = 4000 psi (28 MPa); fyθ,1HR = (0.68)(60) = 40.8 ksi (281 MPa);
As = (3)(0.6 in.2) = 1.8 in.2 (852 mm2); d = 24 – (1.5 + 3/8 + 7/16) = 22.43 in. (570 mm);
b = 12 in. (300 mm); and ϕ = 1.0.
5.5.3.2
Beam capacity after having been exposed for 2 hours:
a 
1.0 


M nθ,2 HR = As f yθ,1HR  d − θ  = (3)(0.6)(0.38)(60)  22.43 −
/12


2
2 
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216
Fire protection system
For Scenario 1, the beams were strengthened with a one-ply, 12 in. (300 mm)
wide FRP system to carry higher design loads. There are certified fire protection
systems that can be used to enhance the fire rating of FRP-strengthened flexural
members. The fire resistance rating of these beams was enhanced by installing
3/4 in. (20 mm) thick fire protection system compatible with the FRP system.
For Scenario 2, the beams were discovered with lower concrete cover. To
address lower fire rating of these beams, additional nonstructural lightweight 1 in.
(25 mm) thick concrete jacket was installed. Concrete screws were installed at 12 in.
(300 mm) on center each way to facilitate proper adherence of the new concrete
material to the existing substrate. This additional concrete cover satisfied the code
required minimum clear cover and enhanced the fire resistance rating of the beam
to meet the required fire rating of 2 hours.
Contract specifications
University of Toronto User.
1.5.1, 1.6.1, 9.4.1, 10.2.2
The LDP prepared contract documents that specified repair materials that satisfied governing regulatory requirements and conveyed necessary information to
perform the work. The contract documents included the minimum requirements for
shoring and bracing for all phases of the repair project, including requirements for
the contractor to submit shoring documents that were signed and sealed by an LDP.
The LDP used ACI 563 as a source for construction specifications. The specification sections that were referenced included:
Section 1—General requirements
Section 3—Concrete removal and preparation for repair
Section 6—Conventional concrete mixtures
Section 7—Handling and placing of conventional concrete
Based on the size of the repairs, conventional concrete material was specified by
the LDP instead of a proprietary material or shotcrete.
ACI 563, “Specifications for Repair of Concrete Buildings,” addresses conditions that are unique to the project. The standard has a mandatory and nonmandatory requirements checklists at the end of the standard to help the specifier submit
as complete a specification as possible. The main sections from the mandatory
and nonmandatory checklists are extracted to include as a minimum in the Project
Contract Document:
a. Section 1.5.1.1—State the maximum dead and live loads and any temporary
reduction in loads, to be permitted during repair and after completion of repair
program, in concert with the requirements of 2.1.1.1.
b. Section 1.5.2—Designate Owner-approved work areas and schedule
requirements.
c. Section 1.5.4.1—Show the demarcation line of the project location, specific
work areas, and adjacent construction.
d. Section 1.8.2.1—Identify work to be performed by certified personnel.
e. Section 1.8.2.2(d)—Point out specific repair procedures that require review and
approval.
f. Section 1.8.2.2(e)—Specify submittal of component materials, repair material
mixture proportions or batch requirements, and concrete supplier’s or repair
Table 19.2—Summary of beam capacity due to low concrete cover at room temperature and at fire loading
Condition
Original
design with
lower cover
Clear cover,
in. (mm)
MD, ft-kip
(kN·m)
0.75
75
(102)
ML, ft-kip MU, ft-kip MU,fire, ft-kip
ϕMn,Room,
(kN·m)
(kN·m)
(kN·m)
ft-kip (kN·m)
SCENARIO #2 (LOW CONCRETE COVER)
48
(65)
165
(225)
114
(154)
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165
(230)
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Chapter 19: Project Example 8—Building Subjected to Fire217
ϕMn,fire2HR,
ft-kip (kN·m)
ϕMn,fire1HR,
ft-kip (kN·m)
75
(102)
133
(180)
Fire rating
1 hour
(enlarge section
to meet cover to
meet 2HR)
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
material manufacturer’s quality control program.
g. Section 2.3.3.2—State whether specialty engineer inspection is required.
h. Section 3.1.1.2—Provide the surface profile and remove laitance, debris, and
bond-inhibiting materials.
i. Section 6.2.2.7—Indicate the specified concrete compressive strength fc′ for the
work.
j. Section 7.1.2.2—List the information in 7.1.2.2(a) to 7.1.2.2(g) that is to be
submitted.
Construction
9.1b, 9.4.1
The contract documents required the contractor to monitor the construction
for any conditions that were not consistent with the available information or that
might affect the short- or long-term safety of the structure, including the possible
need for temporary shoring or bracing.
Requirements for environmental issues, such as allowing water with debris
to flow into floor drains or off the site and disposal of construction debris, were
specified in conformance with local ordinances.
Quality assurance
10.2.1, 10.2.2, 10.4.1
The repair specifications included quality assurance and control measures for
material approvals and field verification of quality. The specified quality control
measures and construction observations were performed during the construction,
including the following:
a. Review of material submittals
10.2.2
b. Visual inspection of the work in progress at critical stages of the repair
c. Observation of the prepared concrete surfaces and comparison with ICRI
concrete surface profiles (ICRI No. 310.2R) to verify that minimum roughness
had been achieved
10.2.3
d. Observation of the concrete placement and curing operations
e. Observation of the surface preparation and installation of the CFRP sheets
f. Bond strength testing of installed CFRP sheets (ASTM D7522/D7522M)
6.8
After the repairs had been installed, a representative portion of the repaired
supported garage slab was evaluated by load testing to demonstrate the strength
of the repaired slab. The test area was selected based on typical repairs in the area
and ease of setting up and running the test.
Test procedure
6.8.2
ACI 562 references ACI 437.2 for load testing. The 2009 IBC references ACI
318-08, which includes Chapter 20, “Strength Evaluation of Existing Structures.”
Based on ACI 562 Sections 1.1.2 and 1.4.1, ACI 562 governs for all matters
pertaining to evaluation and shall govern when in conflict with other referenced
standards. Accordingly, the monotonic load test procedure described in ACI 437.2
was used for the evaluation. The monotonic load test was selected after consultation with the contractor’s available means, methods, and familiarity with the
monotonic test. The test procedure included the following details.
Loading—The test load magnitude (TLM) was calculated per ACI 437.2-13,
Section 4.2.2.
TLM = 1.3(DW + DS)
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Load test
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218
TLM = 1.0DW + 1.1DS + 1.6L + 0.5(Lr or S or R)
TLM = 1.0DW + 1.1DS + 1.6(Lr or S or R) + 1.0L
where Dw is load due to self-weight of the concrete structural system; Ds is superimposed dead load other than self-weight of structural system; L is live load due
to use and occupancy of the building; Lr is roof live load produced during maintenance by workers, equipment, and materials or by moveable objects or people; S
is snow load; and R is rain load.
The test loads were applied by hydraulic jacks that reacted against the soffit
of the plaza slab. Back-up shoring was installed underneath the supported
garage slab. The jack arrangement included two interior panels of the supported
garage slab.
Instrumentation—Instrumentation included load cells to measure the load
applied by the jacks, cable-extension transducers to measure vertical deflections,
strain gauges to measure the strain in individual reinforcing bars, Whittemore
strain gauges to measure strains in the concrete, and linear variable differential
transformers (LVDTs) for measuring crack widths. All the instrumentation was
wired to a data acquisition system.
Test procedure—The test procedure (ACI 437.2-13 Section 5.3) consisted of
applying the load in four equal increments, holding the load after each increment
for deflection measurements, holding the total load for 24 hours, and releasing the
load as quickly as practicable.
Acceptance criteria—The acceptance criteria (ACI 437.2-13 Section 6.3)
included the following items:
Δr ≤ Δ1/4 or Δ1 < 0.05 in. (1.3 mm) or Δ1 ≤ ℓt/2000
and
Δ1 ≤ ℓt /180
where Δ1 is the measured maximum deflection; ℓt is the shorter span under load for
a two-way slab; and Δr is the measured residual deflection.
PROJECT CLOSE-OUT
Periodic maintenance
Record documents
1.6.3, 1.5.3
The owner was provided with copies of the project and construction documents
and the recommended monitoring and maintenance program.
References
Buchanan, A. H., 2009, Structural Design for Fire Safety, John Wiley and Sons,
Ltd., Devon, UK.
Kodur, V. K. R.; Yu, B.; and Dwaikat, M. M. S., 2013, “A Simplified Approach
for Predicting Temperature in Reinforced Concrete Members Exposed to Standard
Fire,” Fire Safety Journal, V. 56, pp. 39-51.
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1.5.3, 8.1.3
The LDP recommended that a visual inspection of the repaired structure be
performed 1 year after the repair installation to verify that no unanticipated
behavior had occurred. The LDP also recommended periodic monitoring and
maintenance of crack repairs, traffic-bearing membranes, and CFP. The northern
climate dictated that these durability maintenance issues be monitored.
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Chapter 19: Project Example 8—Building Subjected to Fire219
University of Toronto User.
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GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
220
Committee documents are listed first by document number
and year of publication followed by authored documents
listed alphabetically.
Because these documents are revised frequently, the reader
is advised to contact the sponsoring group if it is desired to
refer to the latest version.
American Concrete Institute (ACI)
ACI 1910 Standard Building Regulation for the Use of
Reinforced Concrete
ACI 117-10 (Reapproved 2015) Specification for
Tolerances for Concrete Construction and Materials and
Commentary
ACI 201.1R-08 Guide for Conducting a Visual Inspection
of Concrete in Service
ACI 201.2R-16 Guide to Durable Concrete
ACI 214.4R-10 (Reapproved 2016) Guide for Obtaining
Cores and Interpreting Compressive Strength Results
ACI 216.1-14 (Reapproved 2019) Code Requirements
for Determining Fire Resistance of Concrete and Masonry
Construction Assemblies
ACI 222R-19 Protection of Metals in Concrete against
Corrosion
ACI 222.2R-14 Report on Corrosion of Prestressing Steels
ACI 224.1R-07 Causes, Evaluation, and Repair of Cracks
in Concrete Structures
ACI 228.1R-19 In-Place Methods to Estimate Concrete
Strength
ACI 228.2R-13 Report on Nondestructive Test Methods
for Evaluation of Concrete in Structures
ACI 311.1R-07 ACI Manual of Concrete Inspection
(SP-2)
ACI 311.4R-05 Guide for Concrete Inspection
ACI 318-63 Building Code Requirements for Reinforced
Concrete
ACI 318-05 Building Code Requirements for Structural
Concrete and Commentary
ACI 318-08 Building Code Requirements for Structural
Concrete and Commentary
ACI 318-14 Building Code Requirements for Structural
Concrete and Commentary
ACI 347R-14 Guide to Formwork for Concrete
ACI 347.3R-13 Guide to Formed Concrete Surfaces
ACI 355.2-19 Qualification of Post-Installed Mechanical
Anchors in Concrete and Commentary
ACI 355.4-11 Qualification of Post-Installed Adhesive
Anchors in Concrete and Commentary
ACI 362.1R-12 Guide for the Design and Construction of
Durable Concrete Parking Structures
ACI 364.1R-19 Guide for Evaluation of Concrete Structures before Rehabilitation
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University of Toronto User.
ACI 364.3T-15 Treatment of Exposed Epoxy-Coated
Reinforcement in Repair
ACI 365.1R-17 Service-Life Prediction
ACI 369R-11 Guide for Seismic Rehabilitation of Existing
Concrete Frame Buildings and Commentary
ACI 423.4R-14 Corrosion and Repair of Unbonded Single
Strand Tendons
ACI 423.8R-10 Report on Corrosion and Repair of
Grouted Multistrand and Bar Tendon Systems
ACI 437R-19 Load Tests of Existing Concrete Buildings
ACI 437.1R-07 Load Tests of Concrete Structures:
Methods, Magnitude, Protocols, and Acceptance Criteria
ACI 437.2-13 Code Requirements for Load Testing of
Existing Concrete Structures and Commentary
ACI 440.2R-17 Guide for the Design and Construction of
Externally Bonded FRP Systems for Strengthening Concrete
Structures
ACI 440.6-08(Reapproved 2017) Specification for
Carbon and Glass-Fiber Polymer Bar Materials for Concrete
Reinforcement
ACI 440.8-13 Specification for Carbon and Glass FiberReinforced Polymer (FRP) Materials Made by Wet Layup for
External Strengthening of Concrete and Masonry Structures
ACI 503.7-07 Specification for Crack Repair by Epoxy
Injection
ACI 515.3R-20 Guide for Assessment and Surface Preparation for Application of Protection Systems for Concrete
ACI 546R-14 Concrete Repair Guide
ACI 546.3R-14 Guide for the Selection of Materials for
the Repair of Concrete
ACI 562-13 Code Requirements for Evaluation, Repair,
and Rehabilitation of Concrete Buildings and Commentary
ACI 562-16 Code Requirements for Assessment, Repair,
and Rehabilitation of Existing Concrete Structures and
Commentary
ACI 562-19 Code Requirements for Assessment, Repair,
and Rehabilitation of Existing Concrete and Commentary
ACI 563-18 Specifications for Repair of Concrete in
Buildings
ACI C630 Concrete Construction Special Inspector
ACI CT-16 Concrete Terminology
ACI RAP-8(05) Installation of Embedded Galvanic
Anodes
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Referenced Standards and Reports
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
American National Standards Institute (ANSI)
ANSI/AISC 360-10 Specification for Structural Steel
Buildings
American Society of Civil Engineers (ASCE)
ASCE/SEI 7-05 Minimum Design Loads for Buildings
and Other Structures
ASCE/SEI 7-10 Minimum Design Loads for Buildings
and Other Structures
ASCE/SEI 7-16 Minimum Design Loads for Buildings
and Other Structures
ASCE/SEI 11-99 Guideline for Structural Condition
Assessment of Existing Buildings
ASCE/SEI 31-03 Seismic Evaluation of Existing Buildings
ASCE/SEI 37-14 Design Loads on Structures during
Construction
ASCE/SEI 41-17 Seismic Rehabilitation of Existing
Buildings
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ASTM International
ASTM A160 Specification for Axle-Steel Bars for
Concrete Reinforcement (withdrawn 1969)
ASTM A370-17 Standard Test Methods and Definitions
for Mechanical Testing of Steel Products
ASTM A615/A615M-20 Standard Specification for
Deformed and Plain Carbon-Steel Bars for Concrete
Reinforcement
ASTM A617/A617M-96a Standard Specification for AxleSteel Deformed and Plain Bars for Concrete Reinforcement
ASTM A706/A706M-16 Standard Specification for
Low-Alloyed Deformed and Plain Bars for Concrete
Reinforcement
ASTM A1061/A1061M-20a Standard Test Methods for
Testing Multi-Wire Steel Strand
ASTM C42/C42M-20 Standard Test Method for Obtaining
and Testing Drilled Cores and Sawed Beams of Concrete
ASTM C94/C94M-20 Standard Specification for ReadyMixed Concrete
ASTM C309-19 Standard Specification for Liquid
Membrane-Forming Compounds for Curing Concrete
ASTM C496/C496M-17 Standard Test Method for Splitting Tensile Strength of Cylindrical Concrete Specimens
ASTM C597-16 Standard Test Method for Pulse Velocity
through Concrete
ASTM C803/C803M-18 Standard Test Method for
Penetration Resistance of Hardened Concrete
ASTM C805/C805M-18 Standard Test Method for
Rebound Number of Hardened Concrete
ASTM C823/C823M-12(2017) Standard Practice for
Examination and Sampling of Hardened Concrete in
Construction
ASTM C856-20 Standard Practice for Petrographic
Examination of Hardened Concrete
ASTM C873/C873M-15 Standard Test Method for
Compressive Strength of Concrete Cylinders Cast in Place
in Cylindrical Molds
ASTM C876-15 Standard Test Method for Corrosion
Potentials of Uncoated Reinforcing Steel in Concrete
ASTM C882/C882M-20 Standard Test Method for Bond
Strength of Epoxy-Resin Systems Used With Concrete By
Slant Shear
ASTM C900-19 Standard Test Method for Pullout
Strength of Hardened Concrete
ASTM C1074-19 Standard Practice for Estimating
Concrete Strength by the Maturity Method
ASTM C1152/C1152M-20 Standard Test Method for
Acid-Soluble Chloride in Mortar and Concrete
ASTM C1315-19 Standard Specification for Liquid
Membrane-Forming Compounds Having Special Properties
for Curing and Sealing Concrete
ASTM C1383-15, Standard Test Method for Measuring
the P-Wave Speed and the Thickness of Concrete Plates
Using the Impact-Echo Method
ASTM C1399/C1399M-10(2015) Standard Test Method
for Obtaining Average Residual-Strength of FiberReinforced Concrete
ASTM C1550-19 Standard Test Method for Flexural
Toughness of Fiber Reinforced Concrete (Using Centrally
Loaded Round Panel)
ASTM C1581/C1581M-18a Standard Test Method for
Determining Age at Cracking and Induced Tensile Stress
Characteristics of Mortar and Concrete under Restrained
Shrinkage
ASTM C1583/C1583M-20 Standard Test Method for
Tensile Strength of Concrete Surfaces and the Bond Strength
or Tensile Strength of Concrete Repair and Overlay Materials by direct Tension (Pull-off Method)
ASTM C1609/C1609M-19a Standard Test Method for
Flexural Performance of Fiber-Reinforced Concrete (Using
Beam With Third-Point Loading)
ASTM C1740-16 Standard Practice for Evaluating the
Condition of Concrete Plates Using the Impulse-Response
Method
ASTM D3039/D3039M-17 Standard Test Method for
Tensile Properties of Polymer Matrix Composite Materials
ASTM D4580/D4580M-12(2018) Standard Practice for
Measuring Delaminations in Concrete Bridge Decks by
Sounding
ASTM D6432-19 Standard Guide for Using the
Surface Ground Penetrating Radar Method for Subsurface
Investigation
ASTM D6916-18 Standard Test Method for Determining
the Shear Strength Between Segmental Concrete Units
(Modular Concrete Blocks)
ASTM D7522/D7522M-15 Standard Test Method for
Pull-Off Strength for FRP Laminate Systems Bonded to
Concrete Substrate
ASTM E119-20 Standard Test Method for Fire Tests of
Building Construction and Materials
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222
American Welding Society
D1.4/D1.4M:2018
Structural
Reinforcing Steel
Welding
Code—
Applied Technology Council (ATC)
ATC 20 Post Earthquake Evaluation of Buildings
ATC 45 Field Manual: Safety Evaluation of Buildings
after Wind Storms and Floods
ATC 78 Identification and Mitigation of Nonductile
Concrete Buildings
Federal Emergency Management Agency (FEMA)
FEMA P-58—Seismic Performance Assessment of
Buildings
FEMA P-154—Rapid Visual Screening of Buildings for
Potential Seismic Hazards
FEMA 306 and 307—Evaluation of Earthquake Damaged
Concrete and Masonry Wall Buildings
International Code Council (ICC)
2006 IBC 2006 International Building Code
2009 IBC 2009 International Building Code
2012 IBC 2012 International Building Code
2015 IBC 2015 International Building Code
2018 IBC 2018 International Building Code
2012 IEBC 2012 International Existing Building Code
2015 IEBC 2015 International Existing Building Code
2018 IEBC 2018 International Existing Building Code
International Organization for Standardization
(ISO)
Maintenance and Repair of Concrete Structures 163113:2014 (ISO/TC 71/SC 71)
ISO 9000 International Standards for Quality Management
International Council of Building Officials (ICBO)
1961 Uniform Building Code 1961 UBC
National Association of Corrosion Engineers
(NACE)
NACE SP0290-2019 Impressed Current Cathodic Protection of Reinforcing Steel in Atmospherically Exposed
Concrete Structures
NACE SP0187-2017 Design Considerations for Corrosion Control of Reinforcing Steel in Concrete
NACE SP0408-2019 Cathodic Protection of Reinforcing
Steel in Buried or Submerged Concrete Structures
NACE 01101-2018 Electrochemical Chloride Extraction
from Steel-Reinforced Concrete
Occupational Safety & Health Administration
(OSHA)
Construction Industry Regulations & Standards 2020
Edition (Standards-29 CFR 1926). Retrieved from https://
www.osha.gov/laws-regs/regulations/standardnumber/1926
Southern Building Code Congress International
(SBCCI)
Standard Building Code (SBC)
The American Railway Engineering and
Maintenance-of-Way Association (AREMA)
AREMA 2005 Manual for Railway Engineering
The Concrete Society
The Concrete Society TR 50 Guide to Surface Treatments
for Protection and Enhancement of Concrete
The Concrete Society TR 68 Assessment, Design and
Repair of Fire-damaged Concrete Structures
European Committee for Standardization
EN 1504-10: 2003 Products and systems for the protection
and repair of concrete structures. Definitions. Requirements.
Quality control and evaluation of conformity. Site application of products and systems and quality control of the works
The Masonry Society
TMS 402/602-16 Building Code Requirements and Specification for Masonry Structures
Wire Reinforcement Institute
TF 101-R-14 Historical Data on Wire, Triangular Wire
Fabric/ Mesh and Welded Wire Concrete Reinforcement
(WWR)
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International Concrete Repair Institute (ICRI)
ICRI No. 210.3R-2013 Guide for Using In-Situ Tensile
Pulloff Tests to Evaluate Bond of Concrete Surface Materials
ICRI No. 210.4-2009 Guide for Nondestructive Evaluation Methods for Condition Assessment, Repair, and Performance Monitoring of Concrete Structures
ICRI No. 310.1R-2008 Guide for Surface Preparation for
the Repair of Deteriorated Concrete Resulting from Reinforcing Steel Corrosion
ICRI No. 310.2R-2013 Selecting and Specifying Concrete
Surface Preparation for Sealers, Coatings, Polymer Overlays, and Concrete Repair
ICRI No. 320.2R-2018 Guide for Selecting and Specifying Materials for Repair of Concrete Surfaces
ICRI No. 510.1-2013 Guide for Electrochemical Techniques to Mitigate the Corrosion of Steel for Reinforced
Concrete Structures
ICRI Concrete Surface Repair Technician
ICRI Concrete Repair Terminology: http://www.icri.org/
GENERAL/repairterminology
Building Officials and Code Administrators
International (BOCA)
Building Officials Code Administrators National Building
Code (BOCA/NBC)
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Referenced Standards and Reports223
GUIDE TO THE CODE FOR ASSESSMENT, REPAIR, AND REHABILITATION OF EXISTING CONCRETE STRUCTURES
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