Department of Civil Engineering, University of Engineering and Technology Peshawar
Structure Codes and the Design Basis of
RC Structures
By: Prof Dr. Qaisar Ali
Civil Engineering Department
UET Peshawar
drqaisarali.com
drqaisarali@nwfpuet.edu.pk
Department of Civil Engineering, University of Engineering and Technology Peshawar
Topics Addressed
 Building Codes and the ACI Code
 Objectives of Design
 Design Process
 Limit States and the Design of Reinforced Concrete
 Basic Design Relationship
 Structural Safety
Department of Civil Engineering, University of Engineering and Technology Peshawar
Topics Addressed
 Design Procedure Specified in the ACI Code
 Design Loads for Buildings and other Structures
 Customary Dimensions and Construction Tolerances
 Admixtures
 Factors Affecting Strength of Concrete
 High Strength Concrete
Department of Civil Engineering, University of Engineering and Technology Peshawar
Topics Addressed
 Durability of Concrete
 Concrete Subjected to High Temperatures
 Reinforcing Steel
 Chapter 3 : Materials
 Chapter 4 : Durability of Concrete
 Chapter 5 : Concrete Quality, Mixing and Placing
Department of Civil Engineering, University of Engineering and Technology Peshawar
Building Codes and the ACI Code
 General Building Codes

Cover all aspects of building design and construction from
architecture to structural to mechanical and electrical---.
UBC, IBC and Euro-code are general building codes.
 Seismic Codes

Cover only seismic provisions of buildings such as SEAOC
and NEHRP of USA, BCP-SP 07 of Pakistan.
Department of Civil Engineering, University of Engineering and Technology Peshawar
Building Codes and the ACI Code
 Material Specific Codes

Cover design and construction of structures using a specific
material or type of structure such as ACI, AISC, AASHTO
etc.
 Others such as ASCE

Cover minimum design load requirement, Minimum Design
Loads for Buildings and other Structures (ASCE7-02).
Department of Civil Engineering, University of Engineering and Technology Peshawar
Building Codes and the ACI Code
 General Building Codes in USA

The National Building Code (NBC),

The Standard Building Code (SBC),

The Uniform Building Code (UBC),
Department of Civil Engineering, University of Engineering and Technology Peshawar
Building Codes and the ACI Code
 General Building Codes in USA

The International Building Code IBC,

Published by International Code Council ICC for the first time in 2000,
revised every three years.

The IBC has been developed to form a consensus single code for USA.

Currently IBC 2012 is available.

UBC 97 is the last UBC code and is still existing but will not be updated.
Similarly NBC, SBC will also be not updated.

In future only IBC will exist.
Department of Civil Engineering, University of Engineering and Technology Peshawar
Building Codes and the ACI Code
 Seismic Codes in USA

NEHRP
(National
Earthquake
Hazards
Reduction
Program)
Recommended Provisions for the Development of Seismic Regulations for
New Buildings
developed
by FEMA (Federal Emergency Management
Agency).

The NBC, SBC and IBC have adopted NEHRP for seismic design.

SEAOC “Blue Book
Structural Engineers Association of California
(SEAOC), has its seismic provisions based on the Recommended Lateral
Force Requirements and Commentary (the SEAOC “Blue Book”) published
by the Seismology Committee of SEAOC.

The UBC has adopted SEAOC for seismic design.
Department of Civil Engineering, University of Engineering and Technology Peshawar
Building Codes and the ACI Code
 Building Code of Pakistan

Building Code of Pakistan, Seismic Provision BCP SP-07
has adopted the seismic provisions of UBC 97 for seismic
design of buildings.

IBC 2000 could not be adopted because some basic input
data required by IBC for seismic design does not exist in
Pakistan.
Department of Civil Engineering, University of Engineering and Technology Peshawar
Building Codes and the ACI Code
 The ACI MCP

ACI MCP (American Concrete Institute Manual of Concrete
Practice) contains 150 ACI committee reports; revised every
three years.

ACI 318: Building Code Requirements for Structural Concrete.

ACI 315: The ACI Detailing Manual.

ACI 349: Code Requirement for Nuclear Safety Related Concrete
Structures.

Many others.
Department of Civil Engineering, University of Engineering and Technology Peshawar
Building Codes and the ACI Code
 The ACI 318 Code

The
American
Requirements
Concrete
for
Institute
Structural
“Building
Concrete
(ACI
Code
318),”
referred to as the ACI code, provides minimum requirements
for structural concrete design or construction.

The term “structural concrete” is used to refer to all plain or
reinforced concrete used for structural purposes.

Prestressed concrete is included under the definition of reinforced
concrete.
Department of Civil Engineering, University of Engineering and Technology Peshawar
Building Codes and the ACI Code
 The ACI 318 Code

7 parts, 22 chapters and 6 Appendices.
 Brief visit of the code
Department of Civil Engineering, University of Engineering and Technology Peshawar
Building Codes and the ACI Code
 Legal Status of The ACI 318 Code

The ACI 318 code has no legal status unless adopted by a
state or local jurisdiction.

It is also recognized that when the ACI code is made part of
a legally adopted general building code, that general building
code may modify some provisions of ACI 318 to reflect local
conditions and requirements.
Department of Civil Engineering, University of Engineering and Technology Peshawar
Building Codes and the ACI Code
 The Compatibility Issue in BCP SP-2007

Building Code of Pakistan, Seismic Provision BCP SP-07 has
adopted the seismic provisions of UBC 97 for seismic design of
buildings.

As the UBC 97 has reproduced ACI 318-95 in Chapter 19 on
concrete, the load combinations and strength reduction factors of
ACI 318-02 and later codes are not compatible with UBC 97 and
hence BCP SP-07. Therefore ACI 318-02 and later codes cannot
be used directly for design of a system analyzed according to the
seismic provisions of UBC 97.
Department of Civil Engineering, University of Engineering and Technology Peshawar
Building Codes and the ACI Code
 The Compatibility Issue in BCP SP-2007

To resolve this issue, BCP SP-2007 recommends using ACI
318-05 code for design except that load combinations and
strength reduction factors are to be used as per UBC 97.

The IBC adopts the latest ACI code by reference whenever it
is revised and hence are fully compatible.
Department of Civil Engineering, University of Engineering and Technology Peshawar
The Design & Design Team
 General:

The design covers all aspects of structure, not only the
structural design.

The structural engineer is a member of a team whose
members work together to design a building, bridge, or
other structure.
Department of Civil Engineering, University of Engineering and Technology Peshawar
Objectives of Design
 Four Major Objectives of Design
1.
2.
Appropriateness: This include,

Functionality, to suit the requirements.

Aesthetics, to suit the environment.
Economy

The overall cost of the structure should not exceed the client’s budget.
Department of Civil Engineering, University of Engineering and Technology Peshawar
Objectives of Design
 Four Major Objectives of Design
3.
4.
Structural Adequacy (safety)

Strength.

Serviceability.
Maintainability

The structure should be simple so that it is maintained easily.
Department of Civil Engineering, University of Engineering and Technology Peshawar
The Design Process
 Three Major Phases of Design
1.
The client’s needs and priorities.
2.
Development of project concept.
3.
Design of Individual systems.
Department of Civil Engineering, University of Engineering and Technology Peshawar
Basic Design Relationship

Limit State Design approach
Capacity is reduced and demand is increased based on

scientific rationale. In LSD approach, we have

f Mn ≥ Mu (α Ms )

f Vn ≥ Vu (α Vs )

f Pn ≥ Pu (α Ps )

f Tn ≥ Tu (α Ts )

f = strength reduction factor

α = load amplification factor
Department of Civil Engineering, University of Engineering and Technology Peshawar
Structural Safety
 Variability in Resistance

Effects of simplifying
assumptions

The fig shows Comparison of
measured
(Mtest)
computed
(Mn)
and
failure
moments for 112 similar RC
beams
Department of Civil Engineering, University of Engineering and Technology Peshawar
Structural Safety
 Variability in Loads

Fig shows variation of Live loads
in a family of 151sft offices.

The average (for 50 % buildings)
sustained live load was around
13 psf in this sample.

1% of measured loads exceeded
44 psf.

Building code specify 50 psf for
such buildings (ASCE 7-02)
Department of Civil Engineering, University of Engineering and Technology Peshawar
Structural Safety
Conclusion

Due to the variability of resistances and load effects, there is
definite chance that a weaker-than-average structure will be
subjected to a higher- than-average load.

In extreme cases, failure may occur.

The load factors and resistance factors are selected to
reduce the probability of failure to a very small level.
Department of Civil Engineering, University of Engineering and Technology Peshawar
Design Procedures Specified in the
ACI Code

The Design Philosophy of the ACI Code

9.1.1- structures and structural members shall be designed to
have design strengths at all sections at least equal to the
required strength calculated for the factored loads and forces
in such combinations as are stipulated in this code.

9.1.2- members also shall meet all other requirements of this
code to ensure adequate performance at service load levels.
Department of Civil Engineering, University of Engineering and Technology Peshawar
Design Procedures Specified in the
ACI Code

The Design Philosophy of the ACI Code
This process is called strength design in the ACI code.


In the AISC Specifications for steel design, the same design process is
known as LRFD (Load and Resistance Factor Design).

Strength design and LRFD are methods of limit-state design, except that
primary attention is always placed on the ultimate limit states, with the
serviceability limit states being checked after the original design is
completed.
Department of Civil Engineering, University of Engineering and Technology Peshawar
Design Loads for Buildings and Other
Structures

ACI 318-02, Section 8.2-LOADING:

8.2.2: Service loads shall be in accordance with the general
building code of which this code forms a part, with such live
load reductions as are permitted in the general building code.

Section R8.2 :The provisions in the code are for live, wind, and
earthquake loads such as those recommended in “Minimum Design
Loads for Buildings and Other Structures,”(ASCE 7).

If the service loads specified by the general building code (of which
ACI 318 forms a part) differ from those of ASCE 7, the general building
code governs. However, if the nature of the loads contained in a
general building code differs considerably from ASCE 7 loads, some
provisions of this code may need modification to reflect the difference.
Department of Civil Engineering, University of Engineering and Technology Peshawar
Design Loads for Buildings and Other
Structures

ASCE Recommendations on Loads:

ASCE 7-02 sections 1 to 10 are related to design loads for
buildings and other structures.

The sections are named as: general, load combinations,
dead, live, soil, wind, snow, rain, earthquake and ice loads.

Brief visit of ASCE 7-02, Section 1 to 10
Department of Civil Engineering, University of Engineering and Technology Peshawar
Design Loads for Buildings and Other
Structures

Loads on Structure During Construction

During the construction of concrete buildings, the weight of
the fresh concrete is supported by formwork, which
frequently rests on floors lower down in the structure.

ACI section 6.2.2 states the following:

No construction loads exceeding the combination of superimposed dead
load plus specified live load (un-factored) shall be supported on any un-
shored portion of the structure under construction, unless analysis
indicates adequate strength to support such additional loads
Department of Civil Engineering, University of Engineering and Technology Peshawar
Customary Dimensions and
Construction Tolerance
 Difference in Working and As-Built Drawings’
Dimensions

The actual as-built dimensions will differ slightly from those
shown on the drawings, due to construction inaccuracies.

ACI Committee 117 has published a comprehensive list of
tolerance for concrete construction and materials.

As an example, tolerances for footings are +2 inches and –
½ inch on plan dimensions and – 5 percent of the specified
thickness.
Department of Civil Engineering, University of Engineering and Technology Peshawar
Admixtures

A material (usually in liquid form) other than cement, water
and aggregates, that is used as an ingredient of concrete
and is added to the batch immediately before or during
mixing to change properties of fresh or hardened concrete.
Department of Civil Engineering, University of Engineering and Technology Peshawar
Admixtures
 Uses
Admixtures are used to:

achieve certain properties in concrete more effectively than
by other means.

maintain the quality of concrete during the stages of mixing,
transporting, placing, and curing in adverse weather
conditions.

reduce the cost of concrete construction.
Department of Civil Engineering, University of Engineering and Technology Peshawar
Admixtures
 Types

As per ACI Committee 212, admixtures have been
classified into following groups:

Air-entraining Admixtures: causes the development of a
system of microscopic air bubbles in concrete, mortar, or
cement paste during mixing. Air-entrained concrete should
be used wherever water saturated concrete may be
exposed to freezing and thawing. Air entrainment also
improves the workability of concrete.
Department of Civil Engineering, University of Engineering and Technology Peshawar
Admixtures
 Types

Accelerating Admixtures: causes an increase in the rate of
hydration of the hydraulic cement and thus shortens the
time of setting, increases the rate of strength development,
or both.

Water Reducing and Set-Controlling Admixtures: Reduce
the water requirements of a concrete mixture for a given
slump, modify the time of setting, or both.
Department of Civil Engineering, University of Engineering and Technology Peshawar
Admixtures
 Types

Admixtures for Flowing Concrete: Flowing Concrete is
concrete that is characterized as having a slump greater
than 190 mm (7-1/2 in.) while maintaining a cohesive
nature.

Miscellaneous

Freeze Resistant, Pigments, Bonding, Grouting etc. (Refer
ACI 212 for details and more types of miscellaneous
admixtures)
Department of Civil Engineering, University of Engineering and Technology Peshawar
Properties of Concrete
 Factors Affecting Concrete Strength

In addition to mixing, conveying, placing and compaction,
the strength of concrete primarily depends on:

Water Cement Ratio:
Decrease in water cement ratio increases the
strength.

Aggregate Cement Ratio:
Decrease in aggregate cement ratio
increases the strength up to a value of around 2.0. Further decrease may
cause decrease in strength.
Department of Civil Engineering, University of Engineering and Technology Peshawar
Properties of Concrete
 Factors Affecting Concrete Strength

Aggregate:
The concrete strength is affected by the aggregate strength,
its surface texture, its grading and maximum size of the aggregate.

Curing: Prolonged moist curing leads to the highest concrete strength
Department of Civil Engineering, University of Engineering and Technology Peshawar
Properties of Concrete
 Rate of Strength Gain

ACI Committee 209 [3-21] has proposed the following
equation to represent the rate of strength gain for concrete
made from Type 1 cement and moist-cured at 70°F.
f ’c(t) = f ’c(28) {t/(4 + 0.85t)}

Where f ’c(t) = is the compressive strength at age t in days.
Department of Civil Engineering, University of Engineering and Technology Peshawar
Properties of Concrete
 Rate of Strength Gain and Cement Types

Figure shows the effect of type of cement on strength gain of concrete
(moist cured; w/c = 0.49).
I = Normal
II = Modified
III = High early strength
IV = Low heat
V = Sulfate resisting
Department of Civil Engineering, University of Engineering and Technology Peshawar
High Strength Concrete
 Concretes with strengths in excess of 6000 psi are referred to as
high strength concrete.
 The resulting concrete has a low void ratio.
 Only the amount of water needed to hydrate the cement in the
mix is provided.
Department of Civil Engineering, University of Engineering and Technology Peshawar
High Strength Concrete
 UET Lab Results for Producing High Strength
Concrete

Mix design results for 6000 and 8000 psi concrete.
Table-A
Trial Test
Proportion
No. of
cylinders
Date of
preparation
Date of
Testing
Slump
(in)
Avg.
Strength
(psi)
6000 psi
(1:1:2)
w/c (0.36)
6
25/6/2010
22/7/2010
2.5
6100
28/6/2010
25/7/2010
2
8000

Admixture
used: Sikament 520BA
8000
psi
(1:0.8:1.5)
6
w/c (0.31)
Department of Civil Engineering, University of Engineering and Technology Peshawar
Durability of Concrete
 Three most common durability problems in
concrete are:

Corrosion of steel in concrete.

Breakdown of the structure of concrete due to freezing and
thawing.

Breakdown of the structure of concrete due to chemical
action.
Department of Civil Engineering, University of Engineering and Technology Peshawar
Concrete Subjected to High
Temperatures
 Compressive Strength of Concrete
Temperatures
at
High
Department of Civil Engineering, University of Engineering and Technology Peshawar
Deformed Bar Reinforcement

ASTM
A
615,
Specification
for
Deformed and Plain Carbon-Steel
Bars for Concrete Reinforcement.

ASTM A 706, Specification for LowAlloy Steel Deformed and Plain Bars
for Concrete Reinforcement.

ASTM A 996, Specification for RailSteel and Axle-Steel Deformed Bars
for Concrete Reinforcement.
Department of Civil Engineering, University of Engineering and Technology Peshawar
Deformed Bar Reinforcement
 Variation in Yield Strength
 Distribution of mill test yield strength for grade 60 steel.
Department of Civil Engineering, University of Engineering and Technology Peshawar
Deformed Bar Reinforcement
 Strength of Reinforcing Steel at High temperatures
 Deformed reinforcement subjected to high temperatures in
fires tends to lose its strength.
Department of Civil Engineering, University of Engineering and Technology Peshawar
ACI Chapter 3: Materials
 Tests of Materials

A complete record of tests of materials and of concrete shall
be retained by the inspector for 2 years after completion of
the project, and made available for inspection during the
progress of the work.
 Water

Water used in mixing concrete shall be clean and free from
injurious amounts of oils, acids, alkalis, salts, organic
materials, or other substances deleterious to concrete or
reinforcement.
Department of Civil Engineering, University of Engineering and Technology Peshawar
ACI Chapter 3: Materials
 Steel Reinforcement

Reinforcement shall be deformed reinforcement, except that
plain reinforcement shall be permitted for spirals or prestressing steel; and reinforcement consisting of structural
steel, steel pipe, or steel tubing shall be permitted as
specified in this code.
Department of Civil Engineering, University of Engineering and Technology Peshawar
ACI Chapter 4: Durability of Concrete
 Sulfate exposures

Concrete to be exposed to sulfate-containing solutions or
soils shall conform to requirements of Table 4.3.1 or shall
be concrete made with a cement that provides sulfate
resistance and that has a maximum water-cementitious
materials ratio and minimum compressive strength from
Table 4.3.1.
Department of Civil Engineering, University of Engineering and Technology Peshawar
ACI Chapter 5: Concrete Quality, Mixing
and Placing

Average Strength of Concrete Produced in the Field

It is emphasized in this chapter that the average strength of
concrete produced in the filed should always exceed the
specified value of fc′ used in the structural design calculations.

This is based on probabilistic concepts, and is intended to
ensure that adequate concrete strength will be developed in the
structure.
Department of Civil Engineering, University of Engineering and Technology Peshawar
ACI Chapter 5: Concrete Quality,
Mixing and Placing
 Average Strength of Concrete Produced in the Field

Variation in Strength

Variations in the properties or proportions of constituents of
concrete, as well as variations in transporting, placing, and
compaction of the concrete, lead to variations in the strength of
the finished concrete. In addition, discrepancies in the tests will
lead to apparent differences in strength.
Department of Civil Engineering, University of Engineering and Technology Peshawar
ACI Chapter 5: Concrete Quality,
Mixing and Placing
 Average Strength of Concrete Produced in the Field

Variation in Strength

Figure shows the distribution of strengths in a sample of 176 concrete
cylinder tests for the concrete having nominal strength of 3000 psi

Strength less than nominal = 9

Strength more than nominal = 167
Department of Civil Engineering, University of Engineering and Technology Peshawar
ACI Chapter 5: Concrete Quality, Mixing
and Placing
 ACI recommendations
strength in the field

for
achieving
specified
The ACI code recommends that selection of concrete
proportions for achieving a specified concrete strength in the
field shall be based on the required average compressive
strength of concrete f cr′ and not on the specified strength.

ACI table 5.2.2.
Department of Civil Engineering, University of Engineering and Technology Peshawar
ACI Chapter 5: Concrete Quality, Mixing
and Placing
 Selection of Concrete Proportions

Proportions of materials for concrete shall be established to
provide:

Workability and consistency to permit concrete to be worked
readily into forms and around reinforcement under conditions
of placement to be employed, without segregation or
excessive bleeding;

Resistance to special exposures as required by Chapter 4 of
ACI;

Conformance with strength test requirements of ACI 5.6.
Department of Civil Engineering, University of Engineering and Technology Peshawar
ACI Chapter 5: Concrete Quality, Mixing
and Placing
 Selection of Concrete Proportions

Recommendations for selecting
proportions for concrete
are given in detail in “Standard Practice for Selecting
Proportions for Normal, Heavyweight, and Mass Concrete”
(ACI 211.1).
Department of Civil Engineering, University of Engineering and Technology Peshawar
ACI Chapter 5: Concrete Quality, Mixing
and Placing
 Sampling Frequency for Strength Tests

ACI R5.6.2.1: As a measure of quality control, the code
recommends following criteria for collecting samples of
concrete cylinders from a given class of concrete:

Once each day a given class is placed, nor less than

Once for each 150 yd3 of each class placed each day, nor less
than

Once for each 5000 ft2 of slab or wall surface area placed
each day.

In calculating surface area, only one side of the slab or wall should
be considered.
Department of Civil Engineering, University of Engineering and Technology Peshawar
ACI Chapter 5: Concrete Quality, Mixing
and Placing
 Strength Test

A strength test shall be the average of the strengths of two
cylinders made from the same sample of concrete and
tested at 28 days or at test age designated for
determination of fc′.
Department of Civil Engineering, University of Engineering and Technology Peshawar
ACI Chapter 5: Concrete Quality, Mixing
and Placing
 Criterion for Satisfactory Concrete Strength

ACI 5.6.3.3: Strength level of an individual class of concrete
shall be considered satisfactory if both of the following
requirements are met:

(a) Every arithmetic average of any three consecutive strength
tests equals or exceeds fc′;

(b) No individual strength test (average of two cylinders) falls
below fc′ by more than 500 psi when fc′ is 5000 psi or less; or by
more than 0.10fc′ when fc′ is more than 5000 psi.
Department of Civil Engineering, University of Engineering and Technology Peshawar
ACI Chapter 5: Concrete Quality, Mixing
and Placing
 The steps taken to increase the average level of
test results:

It will depend on the particular circumstances, but could include
one or more of the following:

An increase in cementitious materials content

Changes in mixture proportions

Reductions in or better control of levels of slump supplied

Closer control of air content

An improvement in the quality of the testing, including strict
compliance with standard test procedures
Department of Civil Engineering, University of Engineering and Technology Peshawar
ACI Chapter 5: Concrete Quality, Mixing
and Placing
 Investigation of Low Strength Test Results

If any strength test of laboratory-cured cylinders falls below
specified value of fc′ by more than the values given in
5.6.3.3(b), steps shall be taken to assure that load-carrying
capacity of the structure is not jeopardized.
Department of Civil Engineering, University of Engineering and Technology Peshawar
ACI Chapter 5: Concrete Quality, Mixing
and Placing
 Investigation of Low Strength Test Results

If the likelihood of low-strength concrete is confirmed and
calculations
indicate
that
load-carrying
capacity
is
significantly reduced, tests of cores drilled from the area in
question in accordance with “Method of Obtaining and
Testing Drilled Cores and Sawed Beams of Concrete”
(ASTM C 42) shall be permitted.

In such cases, three cores shall be taken for each strength
test that falls below the values given in 5.6.3.3(b).
Department of Civil Engineering, University of Engineering and Technology Peshawar
ACI Chapter 5: Concrete Quality, Mixing
and Placing
 Investigation of Low Strength Test Results

According to ACI 5.6.5.4, concrete in an area represented
by core tests shall be considered structurally adequate if the
average of three cores is equal to at least 85 percent of fc′
and if no single core is less than 75 percent of fc′.
Department of Civil Engineering, University of Engineering and Technology Peshawar
ACI Chapter 5: Concrete Quality, Mixing
and Placing
 Investigation of Low Strength Test Results

If criteria of ACI 5.6.5.4 are not met and if the structural
adequacy remains in doubt, the responsible authority shall
be permitted to order a strength evaluation in accordance
with Chapter 20 for the questionable portion of the structure,
or take other appropriate action.
Department of Civil Engineering, University of Engineering and Technology Peshawar
Some Humble Suggestions
 Regular refresher courses for field staff at least twice a year
 Code implementation in full letter and spirit
 Provision for structural design cost in PC-1
 Field execution check lists to be developed
 Certification courses for contractors, fabricators and masons
 Dissemination of FPM and the like material
 Retrofitting of vulnerable structures
 Strong link with Universities.
Department of Civil Engineering, University of Engineering and Technology Peshawar
The End
contact: drqaisarali.com