ACI 318-19
Changes to the Concrete
Design Standard
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1
American Concrete Institute is a Registered Provider with The American
Institute of Architects Continuing Education Systems (AIA/CES). Credit(s)
earned on completion of this program will be reported to AIA/CES for AIA
members. Certificates of Completion for both AIA members and non-AIA
members will be emailed to you soon after the seminar.
This program is registered with AIA/CES for continuing professional
education. As such, it does not include content that may be deemed or
construed to be an approval or endorsement by the AIA of any material of
construction or any method or manner of handling, using, distributing, or
dealing in any material or product.
Questions related to specific materials, methods, and services will be
addressed at the conclusion of this presentation.
The American Institute of Architects has approved this session for
6.0 AIA/CES LU/HSW Learning Units.
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Learning Objectives
1. Understand where higher grades of
reinforcement are accepted and changes to
the requirements for structural concrete to
allow the higher reinforcement grades,
including development lengths and phifactors.
2. Identify the added requirements to address
shotcrete as a concrete placement method.
3. Explain the expanded scope of deep
foundation provisions, including seismic
requirements.
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Learning Objectives
4. Learn the new requirements for postinstalled screw type anchors and shear lug
design for anchoring to concrete.
5. Describe the changes to shear design
provisions and equations.
6. Identify new tension longitudinal
reinforcement requirements in special
structural walls
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Speakers
Speaker bios are included in your handouts for
the presentation
5
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ACI 318-19
Changes to the Concrete
Design Standard
Introduction
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Today’s Seminar
• Major changes
• Grouped by topic
•
•
•
•
•
•
•
•
Organization
Existing structures
Loads & analysis
Slabs
Post-tensioning
Precast/Prestressed
Circular sections
Walls
• Foundations
• Anchorage to
concrete
• Seismic
7
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Today’s Seminar
• Major changes
• Grouped by topic
• High-strength
reinforcement
• Development length
• Shear modifications
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• Durability and
materials
• Strut-and-tie
method
• Shotcrete
• Appendix A
8
Today’s Seminar
• Changes from ACI 318M-14 to ACI 318-19
318M-14
318-19
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Why Do We Change ACI 318?
• Reflects new research
• Construction practices change
• Sometimes tragic events provide introspect
– Earthquakes or other natural disasters
– Collapses or construction accidents
– Observed in-service performance
• New materials
– Or better ways of making established materials
• More powerful analytical tools
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ACI 318-19
Variety of formats, including:
• Printed copy
– Softcover and hardcover
•
Enhanced PDF
Versions
• English
• Spanish
• In.-lb units
• SI units
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ACI Design Handbook
• 15 chapters
• Explanatory text
• Design aids
• 2019 version
expected early next
year
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ACI Design Handbook
•
•
•
•
•
•
•
•
1: Building Systems
2: Structural Systems
3: Structural Analysis
4: Durability
5: One-Way Slabs
6: Two-Way Slabs
7: Beams
8: Diaphragms
•
•
•
•
•
•
•
9: Columns
10: Walls
11: Foundations
12: Retaining Walls
13: Serviceability
14: Strut-and-Tie
15: Anchorage
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ACI 318 Building Code Portal
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ACI 318-19
Changes to the Concrete
Design Standard
Organization
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Major goals of ACI 318 organization
• Ease of use
• Find the information you need quickly
– Consistent organization
– Organized in the order of design
• Increase certainty that a design fully meets
the Code
– A chapter for each member type
– All member design provisions in one chapter
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Navigation
10 Parts
• General
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Navigation
10 Parts
• General
• Loads & Analysis
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ACI 318 Style
19
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Navigation
10 Parts
• General
• Loads & Analysis
• Members
• Joints/Connections/
Anchors
• Seismic
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• Materials &
Durability
• Strength &
Serviceability
• Reinforcement
• Construction
• Evaluation
20
Part 1: General
• 1: General
• 2: Notation and Terminology
– dagg = nominal maximum size of coarse
aggregate, mm
– aggregate—granular material, such as sand,
gravel, crushed stone, iron blast-furnace slag, or
recycled aggregates including crushed hydraulic
cement concrete, used with a cementing
medium to form concrete or mortar.
21
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Part 1: General
• 3: Referenced Standards
Materials
Inspection
Precast/
Prestressed
• 4: Structural System
Requirements
Design
loads
Load paths
Structural
analysis
Fire
Safety
Structural
integrity
Strength
Serviceability
Sustainability
Durability
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Part 3: Members
• 7: One-Way Slabs
• 11: Walls
• 8: Two-Way Slabs
• 12: Diaphragms
• 9: Beams
• 13: Foundations
• 10: Columns
• 14: Plain Concrete
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Typical member chapter sections
•
•
•
•
•
•
•
•
X.1
X.2
X.3
X.4
X.5
X.6
X.7
X.?
Scope
General
Design Limits
Required Strength
Design Strength
Reinforcement Limits
Reinforcement Detailing
?
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ACI 318-19
Organization
Anchorage, Ch. 9
12
10
Flexure, Ch. 9
Δ
11
Shear, Ch. 9
Deflection, Ch. 9
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Part 4: Joints / Connections / Anchors
• 15: Beam-column and
slab-column joints
• 16: Connections
between members
• 17: Anchoring to
concrete
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Part 5: Seismic
• 18: Earthquake
Resistant Structures
27
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Part 6: Materials & Durability
• 19: Concrete: Design and Durability
Properties
• 20: Steel Reinforcement Properties,
Durability, and Embedments
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(Credit: PCA)
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Part 7: Strength & Serviceability
• 21: Strength Reduction Factors
• 22: Sectional Strength
29
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Organization
Member Chapter
9.5 — Design strength
9.5.2 — Moment
9.5.2.1 — If Pu < 0.10f’cAg,
Mn shall be calculated in
accordance with 22.3.
Toolbox Chapter
9.5.2.2 — If Pu ≥ 0.10f’cAg,
Mn shall be calculated in
accordance with 22.4.
22.4 — Axial strength or
combined flexural and axial
strength…
22.3 —Flexural strength…
22.3.3.4 …
22.4.3.1 …
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Part 7: Strength & Serviceability
• 23: Strut-and-Tie Method
• 24: Serviceability
l
,
31
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Part 8: Reinforcement
• 25: Reinforcement Details
150 mm
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Part 9: Construction
• 26: Construction Documents and Inspection
– 318 is written to the engineer, not the contractor.
– Construction requirements must be
communicated on the construction documents.
– All construction requirements are gathered
together in Chapter 26.
– Design information – job specific
– Compliance requirements – general quality
– Inspection requirements
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Part 10: Evaluation
• 27: Strength Evaluation of Existing Structures
– Applies when strength is in doubt
– Well understood – analytical evaluation
– Not well understood – load test
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Benefits of ACI 318 organization
•
•
•
•
•
•
•
Organized from a designer’s perspective
Easier to find specific requirements
Intuitive location of information
Clarified cross references
Tables improve speed of understanding
Consistent language in text
Single idea for each requirement
35
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ACI 318-19
Changes to the Concrete
Design Standard
Existing Structures
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1.4—Applicability
1.4.1 This Code shall apply to concrete
structures designed and constructed under the
requirements of the general building code.
…
1.4.3 Applicable provisions of this Code shall
be permitted to be used for structures not
governed by the general building code.
37
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Concrete designs governed by other ACI codes
216 - Fire
307 - Chimneys
349 – Nuclear Facilities
369 – Seismic Retrofit
350 – Environmental
376 – RLG Containment
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313 - Silos
332 – Residential
359 – Nuclear Contain.
437 – Strength Evaluation
562 - Repair
38
Design recommendations provided in guides
• Slabs-on-ground (ACI 360R)
• Blast-resistant structures (ACI 370R)
• Wire Wrapped Tanks (ACI 372R)
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1.4.2—Repair
1.4.2 Provisions of this Code shall be permitted
to be used for the assessment, repair, and
rehabilitation of existing structures.
R1.4.2 Specific provisions for assessment,
repair, and rehabilitation of existing concrete
structures are provided in ACI 562-19. Existing
structures in ACI 562 are defined as structures
that are complete and permitted for use.
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Chapter 27 – Strength Evaluation of Existing
Structures
Applies when strength is in doubt
• Well understood – analytical evaluation
• Not well understood – load test
– Monotonic procedure, ACI 318
– Cyclic procedure, ACI 437.2
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27.4.6.2—Total test load, Tt
Greatest of:
(a) Tt = 1.15D + 1.5L + 0.4(Lr or S or R)
→Tt = 1.0Dw + 1.1Ds + 1.6L + 0.5(Lr or S or R)
(b) Tt = 1.15D + 0.9L + 1.5(Lr or S or R)
→ Tt = 1.0Dw + 1.1Ds + 1.0L + 1.6(Lr or S or R)
(c) Tt = 1.3D
→Tt = 1.3(Dw + Ds)
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ACI 318-19
Changes to the Concrete
Design Standard
Loads & Analysis
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Wind Loads (R5.3.5)
• Added commentary
– ASCE 7-05
• Wind = service-level wind
• Use 1.6 load factor
– ASCE 7-10 & ASCE 7-16
• Wind = strength-level wind
• Use 1.0 load factor
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Torsional Stiffness (R6.3.1.1)
• Clarification in commentary
• Two factors
– Torsional vs. flexural stiffnesses
GJ
vs.
EI
– Equilibrium requirements
45
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Torsional Stiffness
Equilibrium torsion
Cantilever
slab
• Torsion in beam
required to maintain
equilibrium
• Torsion and torsional
stiffness of the beam
must be considered
Beam
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Torsional Stiffness
Compatibility torsion
Interior
girder
Beam
• Torsion in girder not
required to maintain
equilibrium
• Torsion and torsional
stiffness of the beam
may be neglected
47
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Torsional Stiffness
Compatibility torsion
• Torsion in girder not
required to maintain
equilibrium
• Torsion and torsional
stiffness of the girder
should be included
Exterior
girder
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Beam
48
Shear Area (6.6.3.1)
Table 6.6.3.1.1(a)— Moments of Inertia and cross-sectional areas permitted for
elastic analysis at factored load level
Member and condition
Moment of
inertia
Columns
0.70Ig
Walls
Uncracked
0.70Ig
Cracked
0.35Ig
Beams
0.35Ig
Flat plates and flat slabs
0.25Ig
Cross-sectional Cross-sectional
area for axial
area for shear
deformations
deformations
1.0Ag
bwh
• No previous guidance
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Floor Vibrations (R24.1)
• Typical floors
– Good performance
• Areas of concern
–
–
–
–
Long/open spans
High-performance (precision machinery)
Rhythmic loading or vibrating machinery
Precast
• Commentary references
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Floor Vibrations
P-T Precast
CIP
• Resources
– ATC Design Guide 1, “Minimizing Floor Vibration,”
– Fanella, D.A., and Mota, M., “Design Guide for
Vibrations of Reinforced Concrete Floor Systems,”
– Wilford, M.R., and Young, P., “A Design Guide for
Footfall Induced Vibration of Structures,”
– PCI Design Handbook
– Mast, R.F., “Vibration of Precast Prestressed
Concrete Floors
– West, J.S.; Innocenzi, M.J.; Ulloa, F.V.; and Poston,
R.W., “Assessing Vibrations”
• No specific requirements
51
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Concerns about deflection calculations
• Service level deflections based on Branson’s
equation underpredicted deflections for ρ
below ≈ 0.8%
𝟑
𝟑
𝑰𝒆 =
𝑴𝒄𝒓
𝑴𝒂
𝑰𝒈 + 𝟏 −
𝑴𝒄𝒓
𝑴𝒂
𝑰𝒄𝒓
• Reports of excessive slab deflections
(Kopczynski, Stivaros)
• High-strength reinforcement may result in
lower reinforcement ratios
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Midspan moment
Heavily reinforced
Experimental
Branson’s Eq.
Bischoff’s Eq.
Midspan deflection
53
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Midspan moment
Lightly reinforced
Experimental
Branson’s Eq.
Bischoff’s Eq.
Midspan deflection
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Ie should be the average of flexibilities
55
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Comparison of Branson’s and Bischoff’s Ie
• Branson
𝐼 =
𝐼 + 1−
=
+ 1−
𝐼
≤𝐼
• Bischoff
≤
Branson combines stiffnesses. Bischoff combines flexibilities.
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Effective Moment of Inertia
•
Table 24.2.3.5 ~ Inverse of Bischoff Eqn.
𝐼
𝑀 > 2⁄3 𝑀 , 𝐼 =
1−
2⁄3 𝑀
𝑀
1−
𝐼
𝐼
𝑀 ≤ 2⁄3 𝑀 , 𝐼 = 𝐼
•
2/3 factor added to account for:
– restraint that reduces effective cracking moment
– reduced concrete tensile strength during
construction
•
Prestressed concrete
57
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ACI 318-19
Changes to the Concrete
Design Standard
One-Way Slabs
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Structural Integrity Reinforcement
Structural integrity provisions have been
added
• To improve structural integrity
– To ensure that failure of a portion of a slab does
not lead to disproportional collapse
• To be similar to that for beams
– bring one-way cast-in-place slab structural
integrity in line with beam structural integrity
provisions
59
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Structural Integrity Reinforcement
• 7.7.7 Structural integrity reinforcement in
cast-in-place one-way slabs
– 7.7.7.1 Longitudinal reinf. consists of at least ¼ of
max. positive moment to be continuous
1/4 M+ continuous
Beam
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Structural Integrity Reinforcement
– 7.7.7.2 Longitudinal reinf. at noncontinuous
supports to be anchored to develop fy at the
face of the support
Beam
61
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Structural Integrity Reinforcement
– 7.7.7.3 Splices
• Splice near supports
• mechanical or welded in accordance with 25.5.2 or
25.5.7
• or Class B tension lap splices in accordance with 25.5.2
Beam
Splice
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Shrinkage and Temperature Reinforcement
7.6.4.1 → 24.4 Shrinkage and temperature reinforcement
24.4.3.2 : Ratio of deformed shrinkage and temperature
reinforcement area to gross concrete area
• 318M-14: as per Table 24.4.3.2
•
318-19: Ratio ≥ 0.0018
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Minimum Flexural Reinforcement in
Nonprestressed Slabs – One way
7.6.1.1:
• 318M-14: As,min as per Table 7.6.1.1
•
318-19: As,min = 0.0018Ag
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ACI 318-19
Changes to the Concrete
Design Standard
Two-Way Slabs
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The Direct Design Method and The Equivalent
Frame Method
– Removed: The direct design method (8.10) and the
equivalent frame method (8.11)
– Provisions in 318M-14
– 8.2.1 … The direct design method or the equivalent
frame method is permitted.
– 6.2.4.1 Two-way slabs shall be permitted to be
analyzed for gravity loads in accordance with (a) or
(b):
(a) Direct design method for nonprestressed slabs
(b) Equivalent frame method for nonprestressed and
prestressed slabs
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Shearheads
• Removed Shearhead
provisions in 318M-14
– 8.4.4.1.3 Slabs
reinforced with
shearheads shall be
evaluated for two-way
shear at critical sections
in accordance with
22.6.9.8.
67
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Opening in Slab Systems
Without Beams
ACI 318M -14: 8.5.4.2(d)
• within a column strip or closer
than 10h from a concentrated
load or reaction area satisfy
– 22.6.4.3 for slabs without shearheads
– or 22.6.9.9 for slabs with shearheads
•
22.6.4.3: Reduced perimeter of
critical section (bo)
– Fig. R22.6.4.3
•
22.6.9.9: Reduction to bo is ½ of
that given in 22.6.4.3
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Fig. R22.6.4.3—Effect of openings
and free edges (effective perimeter
shown with dashed lines)
Note: Openings shown are located
within 10h of the column periphery
68
Opening in Slab Systems
Without Beams
ACI 318 -19: 8.5.4.2(d)
• closer than 4h from the
periphery of a column,
concentrated load or
reaction area satisfying
22.6.4.3
•
22.6.4.3: Reduced perimeter
of critical section (bo)
– Fig. R22.6.4.3
Fig. R22.6.4.3—Effect of openings and
free edges (effective perimeter shown
with dashed lines).
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Minimum Flexural Reinforcement in
Nonprestressed Slabs – Two way
8.6.1.1
• 318M-14 : As,min as per Table 8.6.1.1.
•
318-19: As,min of 0.0018Ag, or as defined in
8.6.1.2 (discussed under two-way shear)
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Reinforcement Extensions for Slabs without
Beams
ACI 318M-14: 8.7.4.1.3 Column strip top bars
• Extend to at least 0.3ℓn
• May not be sufficient
for thick slabs
– may not intercept
critical punching shear
crack
– Reduce punching shear
strength
Punching shear cracks in slabs
with reinforcement extensions
71
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Punching shear failure - Podium Slab
Top Steel (34 #29)
50% to 0.3L (2400 mm)
600 mm
3.5 mm
50% to 0.2L (1600 mm)
300x1100 column
(reinforcement not shown for clarity
• The failure crack did not intercept the top reinforcement.
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Reinforcement Extensions for Two-Way Slabs
without Beams
ACI 318-19: 8.7.4.1.3 Column strip top bars
• Extend to at least
0.3ℓn but, not less
than 5d
d
d
Fig. R8.7.4.1.3 - Punching shear cracks in ordinary
and thick slabs
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Reinforcement Extensions for Two-Way Slabs
without Beams
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ACI 318-19
Changes to the Concrete
Design Standard
Post-tensioning
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Residential P-T Slabs (1.4.6)
• Past confusion about P-T slab foundation
design on expansive soils
– Intent was for residential, but not mentioned with
residential design provisions
• Commentary clarifies use of PTI DC10.5-12
for P-T residential slabs and foundations on
expansive soils
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Residential P-T Slabs (1.4.6)
• Coordinates with 2015 IBC requirements
• Adds reference to ACI 360 if not on
expansive soil
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Max. Spacing of Deformed Reinf. (7.7.2.3)
• Class C (Cracked) and T (Transition) oneway slabs with unbonded tendons rely on
bonded reinforcement for crack control
• Previously no limits for spacing of deformed
reinforcement for Class C and T prestressed
slabs
• Industry feedback provided
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Max. Spacing of Deformed Reinf. (7.7.2.3)
• New limit is s ≤ 3h and 450 mm
• Same as non-prestressed slabs
Deformed
reinforcement
Unbonded P-T
Slab Section
s ≤ 3h and 450 mm
79
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P-T Anchorage Zone Reinforcement
(25.9.4.4.6)
•
•
•
•
Referenced from slab and beam chapters
Applies for groups of 6 or more anchors in thick
slabs
Anchorage zone requires backup bars for
bearing and hairpins for bursting
Hairpins must be anchored at the corners
Hairpins
Backup bars
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Anchor bars
80
81
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P-T Anchorage Zone Reinforcement
(25.9.4.4.6)
• Thin slabs ≤ 200 mm → Anchor bars serve as
backup bars
• Thick slabs > 200 mm → Both backup bars
and anchor bars required
Hairpins
Backup bars
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Anchor bars
82
For slabs with h > 200 mm, provide #13 or
larger straight bars parallel to slab edge,
in contact with or not farther than 100 mm
ahead of bearing face of anchorage device
#10 or larger
hairpins required
if s ≤ 300 mm
h > 200
mm
≥ 150 mm extension
#10 or larger hairpin
with minimum inside
bend diameter
in accordance
with Table 25.3.2
#13 or larger straight bars
parallel to slab edge, in
contact with or not farther
than 100 mm ahead of bearing
face of anchorage device
200 mm
≤ 100 mm
h ≤ 200 mm
#10 or larger hairpin
With minimum inside
Bend diameter in
Accordance with
Table 25.3.2
#13 or larger straight bars
parallel to slab edge,
in contact with or not farther
than 100 mm ahead of bearing
face of anchored device
h ≤ 200 mm
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Design of Formwork for P-T (26.11.1.2 (5) and (6))
• Members may move when P-T strand is
stressed
• Movement may redistribute loads
• Added requirement to allow for movement
during tensioning
• Added requirement to consider
redistribution of loads on formwork from
tensioning of the prestressing reinforcement
85
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ACI 318-19
Changes to the Concrete
Design Standard
Precast/Prestressed
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86
Precast/Prestressed Concrete
• Confinement for
column/pedestal
tops
• Connection forces
• Construction
document
requirement
• φ at ends of precast
members
87
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Confinement
• 10.7.6.1.5: confinement required at tops of
columns/pedestals
• Assists in load transfer
Anchor
• Not a new provision
bolts
125 mm
Two No. 13 or
Three No. 10 ties
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88
Confinement
• 10.7.6.1.6: extends confinement
requirement to precast columns/pedestals
Future precast
member
Mechanical
coupler
125 mm
Two No. 13 or
Three No. 10 ties
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89
Volume Change in Precast Connections
• Volume change
– Creep
– Shrinkage
– Temperature
• May induce connection reactions if restrained
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90
Volume Change in Precast Connections
• Load magnitude?
• Load factor?
• Past guidance for
brackets and corbels
– Use Nuc ≥ 0.2Vu as
restraint force
– Use a 1.6 load factor
• Approach was often
to design around
forces
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91
Volume Change and Connections
318-19 changes (16.2.2.3)
• Nuc = factored restraint force,
shall be (a) or (b)
– (a) restraint force x LL factor (no
bearing pad)
– (b) 1.6 x 0.2(sustained unfactored
vertical load) for connections on
bearing pads
•
•
Nuc,max ≤ connection capacity x
LL factor
Nuc,max ≤ 1.6 x μ x (sustained
unfactored vertical load) if μ is
known, (See 16.2.2.4)
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92
Brackets and Corbels
• 26.6.4.1(a) Details for welding of anchor
bars at the front face of brackets or corbels
designed by the licensed design
professional in accordance with 16.5.6.3(a).
Fig. R16.5.6.3b
Fig. R16.5.1b
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93
Strength Reduction Factor
Near end of
precast member
• Linear
interpolation
of φ
• φ p depends
on state of
stress
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94
Strength Reduction Factor
Near end of
precast member
• Similar for
debonded
strand
95
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ACI 318-19
Changes to the Concrete
Design Standard
Circular Sections
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96
Variable definitions (22.5)
• 22.5 One-way shear
– Interpretation for hollow circular sections
d?
opening
ρw ?
bw ?
97
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Variable definitions (22.5)
• 22.5.2.2 – calculation of Vc and Vs
– d = 0.8 x diameter
– bw = diameter (solid circles)
– bw = 2 x wall thickness (hollow circles)
t
d = 0.8D
opening
ρw = As/bwd
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bw = D
bw = 2t
98
Variable definitions (22.5)
• What about As?
(2/3)D
As
99
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Torsion for circular sections (R22.7.6.1.1)
• Do ACI 318 torsion equations apply to
circular cross sections?
• Code Eqns are based on thin-tube theory
• Examples added to figure
125
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100
Circular Column Joints
• Based on equivalent
square column
– Aj for joint shear strength h = 0.89D
(15.4.2)
– Width of transverse
beams required for joint
to be considered
confined (15.2.8)
– Column width ≥ 20 db for
special moment frames
(18.8.2.3)
101
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ACI 318-19
Changes to the Concrete
Design Standard
Walls
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102
Scope of walls
• Change in scope
11.1.4 - Design of cantilever retaining walls shall be
in accordance with Chapter 13 (Foundations)
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103
11.7.2.3 Bar placement
• If wall thickness h > 250 mm
• Two layers of bars near each face
• Exception, single story basement walls
• 318M-14
• ½ to 2/3 of reinf. placed near exterior face
• Balance of reinf. placed near interior face
• Confusion with exterior and interior
– Face versus wall location
• ½ to 2/3 was arbitrary
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104
14.6 Plain concrete
At windows, door openings, and similarly sized
openings
• At least two No. 16 bars (similar to walls
11.7.5.1)
• Extend 600 mm beyond or to develop fy
2-No. 16 bars
≥ 600 mm
105
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ACI 318-19
Changes to the Concrete
Design Standard
Foundations
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106
Ch. 13 – Foundations – significant changes
•
Added design provisions
– Cantilever retaining walls
– Deep foundation design
•
Other
– Minimum concrete strengths for shallow and deep
foundations
– Cover
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107
Foundations and 318
•
ACI 318M-71 to ACI 318M11 (Ch. 15)
• Shallow footings, pile caps
•
ACI 318M-14 (Ch. 13)
• Shallow footings, pile caps
•
ACI 318-19 (Ch. 13)
• Shallow footings, pile caps,
deep foundations, and walls
of cantilevered retaining
walls
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108
Cantilever retaining walls
It’s a wall
(2014)
It’s a slab
(2019)
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109
13.3.6.1—Cantilever stem walls
•
Design as one-way slab (Ch. 7)
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110
13.3.6.2—Cantilever stem wall with counterfort
• Design as two-way slab (Ch. 8)
111
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Maximum bar spacing in stem wall
Wall
Stem wall
reinforcement
Maximum
bar
spacing
(2014)
Design as
wall
(2014)
Slab
Maximum
bar spacing
(2019)
Design as
one-way
slab
(2019)
Longitudinal
bars
Lesser of:
Long. (Wall) or
Flexural (Slab)
3h, or
450 mm
11.7.2.1
Trans. (Wall) or
S & T (Slab)
3h, or
450 mm
11.7.3.1
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 40,000 
15 
 − 2.5cc
 fs 
 40,000 
12 

 fs 
5h, or
450 mm
7.7.2.2
(24.3)
s
Transverse
bars
7.7.6.2.1
112
Minimum reinforcement in stem wall
ACI 318M-14
ACI 318-19
Minimum
reinforcement, ρ
Design as
wall
Minimum
reinforcement
As,min
Design as
one-way
slab
≤ No. 16
ρℓ = 0.0012
> No. 16
ρℓ = 0.0015
11.6.1
As,min = 0.0018 Ag
7.6.1.1
≤ No. 16
ρt = 0.0020
> No. 16
ρt = 0.0025
11.6.2
AS+T = 0.0018 Ag
7.6.4.1
(24.4)
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113
1.4.7— Scope changes – deep foundations
• Scope: This code does not govern design and
installation of portions of concrete pile, drilled piers,
and caissons embedded in ground, except as
provided in (a) through (c)
• (a) For portions in air or water, or in soil incapable of providing
adequate lateral restraint to prevent buckling throughout
their length
• (b) For precast concrete piles supporting structures assigned
to SDC A and B
• (c) For deep foundation elements supporting structures
assigned to SDC C, D, E, and F (SDC C is added to scope)
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114
Deep Foundations (13.4)
•
•
•
•
•
•
13.4.1 General
13.4.2 Allowable axial strength
13.4.3 Strength design
13.4.4 Cast-in-place deep foundations
13.4.5 Precast concrete piles
13.4.6 Pile caps
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115
Pre- ACI 318-19 – design of deep
foundations
•
ACI 543 - Piles (diam. < 750 mm)
•
ACI 336.3 - Design of drilled
piers (diam. ≥ 750 mm)
Not code language
documents
Also used deep footing provisions
from:
IBC and ASCE/SEI 7
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116
Design of deep foundation memberscompressive axial force (13.4.1)
• Design axial strength of
members in accordance to
two methods:
– Allowable Axial Strength Design
(13.4.2)
– Strength Design (13.4.3)
Photos courtesy Larry Novak
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117
Allowable axial strength method (13.4.2)
13.4.2.1 It shall be permitted to design a deep foundation
member using load combinations for allowable stress
design in ASCE / SEI 7, Section 2.4, and the allowable
strength specified in Table 13.4.2.1 if (a) and (b) are
satisfied
(a)Deep foundation is laterally supported for its entire
height
(b)Applied forces causing bending moments less than
moment due to an accidental eccentricity of 5
percent of the pile diameter or width.
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118
13.4.2 deep foundation design
119
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Confinement of metal casing (13.4.2.3):
Diam ≤ 400 mm
• not used to resist axial load
• sealed tip and mandrel-driven
• seamless or welded seamless
Physical properties
• wall thickness ≥ 14 ga. (1.63 mm)
• fy ≥ 2100 kg/cm2 (210 Mpa)
• fy ≥ 6 f’c , and
• nominal diameter ≤ 400 mm
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Metal
casing
Sealed
tip
120
Deep foundations – strength design (13.4.3)
Pu
• Method may be used any time
•
Mu ≥ 0
Method must be used when pile
does not meet criteria for
allowable axial strength design
– Soils do not provide lateral support
– Moment is not negligible
•
Use Section 10.5 (columns)
– 𝝓 Pn ≥ Pu
– 𝝓 Mn ≥ Mu
– Combined Pn and Mn calculated by
22.4
121
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Strength design (13.4.3) – axial force, no moment
Nominal axial compressive strength; Pn
𝝓 Pn,max ≥ Pu
Maximum axial strength
- For deep foundations members with ties
conforming to Ch. 13 (new in Table
22.4.2.1)
Pn,max = 0.80 Po
Pu
Mu = 0
Where:
Po = nominal axial strength at zero
eccentricity
Po = 0.85f’c(Ag – Ast) + fyAst
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122
Deep foundations
13.4.4.1 CIP deep
foundations that are subject
to (a) uplift or (b) Mu > 0.4Mcr
shall be reinforced, unless
enclosed by a steel pipe or
tube
Confined for ductility
Reinforced for flexure
Reinforced for tension
Unreinforced
123
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Table 19.2.1.1 –
Additional minimum strength, f’c
Shallow foundations
Min. f’c
(MPa)
Foundations in SDC A, B, or C
17
Foundation for Residential and Utility …. 2 stories or less
….stud bearing construction …… SDC D, E, or F
17
Foundation for Residential and Utility …. More than 2
stories….stud bearing construction …… SDC D, E, or F
21
Deep foundations
Drilled shafts or piers
28
Precast nonprestressed driven piles
28
Precast prestressed driven piers
35
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124
Concrete cover – deep foundations
Steel pipe
Table 20.5.1.3.4
75 mm
Cast-in-place against
ground
40 mm
Cast-in-place enclosed
by steel pipe,
permanent casing, or
stable rock socket
125
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Concrete cover – deep foundations
Table 20.5.1.3.4
40 mm precast nonprestressed
and precast prestressed
In contact with ground
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65 mm precast nonprestressed
50 mm precast prestressed
Exposed to seawater
126
ACI 318-19
Changes to the Concrete
Design Standard
Anchorage to
Concrete
127
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Sections
•
•
•
•
•
•
•
•
17.1 Scope (Screws) •
17.2 General
17.3 Design limits
17.4 Required
strength
•
17.5 Design strength
17.6 Tensile strength
17.7 Shear strength •
17.8 Tension and
shear interaction
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17.9 Edge distances,
spacings, and
thicknesses to
preclude splitting
failure
17.10 Earthquakeresistant design
requirements
17.11 Attachments
with shear lugs
128
Ch. 17 – Anchoring to Concrete
Scope
• Headed studs and
headed bolts
• Hooked bolts
• Post-installed
undercut anchors
• Post-installed
expansion anchors
• Post-installed
adhesive anchors
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129
New Content/Design Information
• Post-installed screw anchors
– pre-qualification per ACI 355.2
• Attachments with shear lugs
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130
Screw Anchors (17.3.4)
•
For screw anchors satisfying:
– hef ≥ 40 mm and
– 5da ≤ hef ≤ 10da
•
•
Manufacturer provides hef, Aef,
and pullout strength
Concrete breakout evaluated
similar to other anchors
– 17.6.2 in tension
– 17.7.2 in shear
•
Spacing and Cover (17.9.2a)
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131
17.1.6 – Reinforcement used as anchorage
Check anchorage for bars
developed per Ch. 25
• Check concrete
breakout in tension (and
maybe shear)
• Greater development
length should be
considered
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132
17.1.6 – Reinforcement used as anchorage
• Straight bars behave
like adhesive anchors
• Hooked and headed
bars behave like
headed anchors
• Anchor reinforcement
may be an alternative
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133
Shear Lugs (17.11.1)
Shear lugs are
fabricated from:
• Rectangular plates
or
• Steel shapes
composed of platelike elements,
welded to an
attachment base
plate
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134
Shear Lugs (17.11.1)
• Minimum four
anchors
• Anchors do not
need to resist shear
forces if not welded
• Anchors welded to
steel plate carry
portion of total
shear load
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135
Shear Lug Detailing (17.11.1.1.8)
• Anchors in tension, satisfy both (a) and (b):
(a) hef/hsl ≥ 2.5
(b) hef/csl ≥ 2.5
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136
Shear Lug Detailing (17.11.1.2)
•
•
•
•
Steel plate to have 25 mm dia. (min.) hole
Single plate – one on each side
Cross / cruciform plate - one each quadrant
More vent holes are not detrimental
137
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Bearing Strength (17.11.2)
• Bearing strength:
Vbrg ,sl = 1.7 f c' Aef ,sl ψ brg ,sl
• Aef,sl is the surface perpendicular to the
applied shear:
2tsl2tsl
2tsl
tsl
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138
Bearing Area
Direction of
shear load
Direction of
shear load
139
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Stiffeners
• 17.11.2.3 - If used, the length of shear lug
stiffeners in the direction of the shear load
shall not be less than 0.5hsl
T/Conc
Stiffener
0.5hsl
hsl
Shear lug
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140
17.11.2.2 – Bearing factor
Vbrg ,sl = 1.7 f c' Aef ,sl Ψ brg ,sl
Tension load
• Ψbrg,sl = 1 + Pu/(nNsa) ≤ 1.0
• Pu – negative for tension
• n – number of anchors in tension
• Nsa – Nominal tension strength of a single anchor
Ψbrg,st = 1
No applied axial load:
Compression load: Ψbrg,sl = 1 + 4Pu/(Abpfc’) ≤ 2.0
• Pu – positive for compression
141
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17.11.2.4 – Bearing for Multiple Shear Lugs
• If τ ≤ 0.2 f’c, use bearing from
both lugs
τ = Vu/(A1 + A2)
A1
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A2
142
17.11.3 – Concrete breakout strength of
shear lugs
• Nominal concrete breakout strength of a
shear lug
– Use Anchor provisions of 17.7.2
A
Vcb , sl = Vc ψ ed ,V ψ c ,V ψ h,V Vb
AVco
• Where:
Vb = 3.7λ a
f c' (ca1 )1.5
143
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ACI 318-19
Changes to the Concrete
Design Standard
Seismic Design
Philosophy
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144
Seismic
• Both concrete and
reinforcement are
permitted to
respond in the
inelastic range
• This is consistent
with the strength
design approach
adopted throughout
the Code
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145
Seismic
•
•
Controlled inelastic action is permitted at predetermined locations, called plastic hinges
Typical plastic hinge locations are at the ends
of beams in moment frames, and at the bases
of shear walls
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146
Seismic
•
•
Prescriptive rules for
detailing of
reinforcement are
enforced, creating
robust plastic hinges
Plastic hinging
reduces the stiffness
of the structure,
which lengthens the
period; and plastic
hinges dissipate
earthquake energy
147
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ACI 318-19
Changes to the Concrete
Design Standard
Special Moment
Frames
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148
18.6.3.1 and 18.8.2.3—Special moment frame
beams (and joints)
• Longitudinal Reinforcement
@ interior joints, 𝑑 ≤
hc/20 (Gr 420)
hc/26 (Gr 550)
0.025𝑏 𝑑 (Gr 420)
≥ 𝐴 or 𝐴
𝟎. 𝟎𝟐𝟎𝒃𝒘 𝒅 (Gr 550)
hc
0.25 𝑓 𝑏 𝑑
𝑓
b) 1.4𝑏 𝑑
𝑓
c) min 2 bars continuous
≥ max a)
≥ 2ℎ
𝑀
𝑀
hb
𝑀
≥
𝑀
2
𝑀
𝑀 𝑜𝑟 𝑀
≥
𝑀
2
at any section ≥
max 𝑀 at either joint
4
149
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18.6.4.4—Special moment frame beams
• Transverse reinforcement
hc
≤ 50 𝑚𝑚
s≤
d/4
150 mm
6db (Gr 420), 5db (Gr 550)
𝑠 ≤ 𝑑/2
s≤
d/4
100 mm
hb
Hoops
along 2hb
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Hoops @ lap splice
Stirrups with seismic hooks
150
18.4.3.3—Columns in intermediate moment
frames
• Hoops or spirals required
• First hoop at so/2 from the joint
ℓo
face
ℓo ≥
ℓu /6 clear span
[c1, c2]max
450 mm
so
so ≤
8db (Gr 420) and 200 mm
6db (Gr 550) and 150 mm
1/2[c1, c2]min
oo
ℓ
151
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18.7.2, 18.7.3—Columns of SMF
Strong Column/Weak Beam
• Column dimensional limits,
18.7.2
Mnc
Beam
– Smallest dimension ≥ 300 mm
Mnb
– Short side/long side ≥ 0.4
Mnb
• Flexural strength check,
18.7.3.2
– ∑Mnc ≥ (6/5)∑Mnb,
– Exception, 18.7.3.1
Column
Mnc
• Ignore check at top story where
𝑷𝒖 ≤ 𝟎. 𝟏𝑨𝒈 𝒇𝒄
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152
18.7.4.3—Bond splitting failure in columns
Splitting can be
controlled by
restricting the
longitudinal bar
size to meet
1.25ℓd ≤ ℓu/2
Woodward and Jirsa (1984)
Umehara and Jirsa (1982)
Sokoli and Ghannoum (2016)
153
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18.7.5.3 and 18.7.5.5—Columns in special
moment frames
• First hoop at so/2 from the
joint face
ℓ /6 clear span
u
ℓo ≥
s≤
so ≤
[c1, c2]max
450 mm
6db,min (Gr 420), 5db,min (Gr 550)
150 mm
6db,min (Gr 420), 5db,min (Gr 550)
¼[c1, c2]min
100 +
ℓo
so
s
so
ℓo
, ≤ 150 mm; ≥ 100 mm
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154
18.14.3.2—Nonparticipating columns
Clarification
• Transverse spacing over full
length is the lesser of
ℓo
– 6db of the smallest long. bar
– 150 mm
• Transverse detailing along ℓo
is according to 18.7.5.2 (a)
through (e)
ℓo
– 18.7.5.2(f) is not required
155
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ACI 318-19
Changes to the Concrete
Design Standard
Special Structural
Walls
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156
Ch. 18.10—Special structural wall
• Cutoff of longitudinal
bars in special
boundary elements
• Reinforcement ratios at hw
ends of walls
• Shear demand
• Drift capacity check
• Detailing in special
boundary elements
• Ductile coupled walls
Mu
Pu
Vu
δu
Special
boundary
element
ℓw
Shear wall
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157
18.10.2.3(a)—Longitudinal bars
• Previously,
– tension (vertical boundary) reinforcement in
special structural walls to extend 0.8ℓw beyond
the point at which it is no longer required to resist
flexure
• Overly conservative
– This was an approximation of d
– Similar to beams which extend d, 12db and ℓn/16
– Actual behavior is different
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158
18.10.2.3(a)—Longitudinal bars
(a) Except at the top of ℓd
a wall, longitudinal
reinforcement shall
extend at least 3.6 m
above the point at
which it is no longer Bars “a”
required to resist
flexure but need not
extend more than ℓd
above the next floor
level.
Floor
level
≥ 3.6m
Bars “a”
no longer
required
Floor
level
159
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18.10.2.3(c)—Longitudinal bars
•
Lap splices not
permitted over hsx
above (6 m, max)
and ℓd below
critical sections
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6m
160
18.10.2.4—Longitudinal reinforcement ratio
at ends of walls
hw/ℓw ≥ 2.0
• Failures in Chile and
New Zealand
• 1 or 2 large cracks
• Minor secondary
cracks
Crack patterns for walls with fixed minimum
longitudinal reinforcement content of 0.25% (Lu
et al. 2017)
161
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18.10.2.4—Longitudinal reinforcement ratio
at ends of walls
New ratio
0.5 f c'
ρ=
fy
• Many well
distributed cracks
• Flexure yielding
over length
Crack patterns for walls with ρ according to
equation (Lu et al. 2017)
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162
18.10.2.4—Longitudinal reinforcement ratio
at ends of walls
Bar Cutoff
• Mu/2Vu similar
to wall with full
reinforcement
• Mu/3Vu good
distribution
• Mu/4Vu
significant
strain above
cut off
Mu/2Vu
Mu/3Vu
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Mu/4Vu
163
18.10.2.4—Longitudinal reinforcement ratio
at ends of walls
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164
18.10.2.4—Longitudinal reinforcement ratio
at ends of walls
Walls or wall piers with hw/ℓw ≥ 2.0 must satisfy:
a) Long. reinf. ratio within 0.15 ℓw and minimum
0.5 f c'
ρ=
fy
b) Long. reinf. extends above and below critical
section the greater of ℓw and Mu/3Vu
c) Max. 50% of reinf. terminated at one section
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165
18.10.3—Shear amplification
•
Similar to approach in New Zealand Standard, NZS 3101
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166
18.10.3—Shear amplification
18.10.3.1 The design shear force Ve shall be
calculated by: Ve = Ωv ωvVu ≤ 3Vu
Vu = the shear force obtained from
code lateral load analysis with
factored load combinations
Ωv = overstrength factor equal to the
ratio of Mpr/Mu at the wall critical
section.
ωv = factor to account for dynamic
shear amplification.
-880
-440
0
440
880
Max/Min Shear Force, V (kN)
Gogus and Wallace, 2015
167
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18.10.4.4—Clarification of Acv
Acv = gross area of concrete
section bounded by web
thickness and length of
section in the direction of
shear force considered in the
case of walls, and gross area
of concrete section in the
case of diaphragms. Gross
area is total area of the
defined section minus area of
any openings.
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Acv wall = Acw1+Acw2+Acw3
1
2
3
Acw2
Vertical wall segments
168
18.10.6.2—Displacement based approach
Boundary elements of
special structural walls:
• Walls or wall piers
with hwcs/ℓw ≥ 2.0
• Continuous
– Uniform for full height
• Single critical
(yielding) section
– Plastic hinge
Continuous
Single critical section
169
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18.10.6.2—Displacement based approach
δu
(a) Compression zone with
special boundary elements
required if:
1.5δ u

≥ w
600c
hwcs
•
c = [Pu, φMn]max in direction of
design displacement δu and
•
hwcs
δu/hwcs ≥ 0.005
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Extreme
compression fiber
Single critical section
170
18.10.6.2—Displacement based approach
(b) Boundary elements req’d, then (i) and
either (ii) or (iii)
i. Transv. reinf. extends above and below
critical section [ℓw, Mu/4Vu]max
ii. b ≥ 0.025 wc
iii. δc/hwcs ≥ 1.5 δu / hwcs , where

δc
1 
1    c 
Ve
 4 −  w   −
 ≥ 0.015
=
hwcs 100 
50  b  b  0.66 f c' Acv 


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171
18.10.6.4—Special Boundary Elements
• Single perimeter hoops with 90-135 or 135135 degree crossties, inadequate
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172
18.10.6.4(f)—Special Boundary Elements
Longitudinal bars supported
by a seismic hook or corner of
a hoop
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173
18.10.6.4(h)—Special Boundary Elements
• Concrete within the thickness of the floor
system at the special boundary element
location shall have specified compressive
strength at least 0.7 times f′c of the wall.
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174
18.10.6.4(i)—Special Boundary Elements
• 18.10.6.4(i) – for a distance specified in
18.10.6.2(b) above and below the critical
section, web vertical reinforcement shall
have lateral support
– crossties vertical spacing, sv ≤ 300 mm
175
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18.10.6.5(b)—If the maximum longitudinal ρ at
the wall boundary exceeds 2.8/fy
Table 18.10.6.5b—Maximum vertical spacing of transverse reinforcement at wall boundary
Grade of primary
flexural reinforcing
bar
420
550
690
Transverse reinforcement
required
Vertical spacing of transverse reinforcement1
Within the greater of ℓw and
Mu/4Vu above and below
critical sections2
Lesser of:
Other locations
Lesser of:
Within the greater of ℓw and
Mu/4Vu above and below
critical sections2
Lesser of:
Other locations
Lesser of:
Within the greater of ℓw and
Mu/4Vu above and below
critical sections2
Lesser of:
Other locations
Lesser of:
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6 db
150 mm
8 db
200 mm
5 db
150 mm
6 db
150 mm
4db
150 mm
6db
150 mm
176
18.10.9—Ductile Coupled Walls
Issues preventing ductile behavior
• Inadequate quantity or
distribution of qualifying
coupling beams
• Presence of squat walls causes
the primary mechanism to be
hwcs
shear and/or strut-and-tie
failure in walls
• Coupling beams are
inadequately developed to
provide full energy dissipation
ℓw
ℓn
ℓw
h
177
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18.10.9—Ductile Coupled Walls
• Individual walls satisfy
– hwcs/ℓw ≥ 2
• All coupling beams must
satisfy:
ℓw
ℓn
ℓw
h
– ℓn/h ≥ 2 at all levels
– ℓn/h ≤ 5 at a floor level in at
hwcs
least 90% of the levels of the
building
– Development into adjacent
wall segments, 1.25fy (18.10.2.5)
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178
ACI 318-19
Changes to the Concrete
Design Standard
Foundations
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179
18.13.4—Foundation seismic ties
SDC C through F
• Seismic ties or by other means
SDC D, E, or F, with Site Class E or F
• Seismic ties required
Other means, 18.13.4.3
• Reinforced concrete beams within the slab-onground
• Reinforced concrete slabs-on-ground
• Confinement by competent rock, hard cohesive
soils, or very dense granular soils
• Other means approved by the building official
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180
18.13.4.3—Seismic ties
Column
load
Minimum tensile and
compressive force in tie
• Load from pile cap or
column
– Largest at either end
Tie force
• 0.1SDS x Column factored
dead and factored live
load
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181
18.13.5—Deep foundations
• (a) Uncased CIP concrete drilled or
augered piles
• (b) Metal cased concrete piles
• (c) Concrete filled pipe piles
• (d) Precast concrete piles
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182
18.13.5.2—Deep foundations
SDC C through F
• Resisting tension loads
 Continuous longitudinal
reinforcement over full length to
resist design tension
Source: Ground Developments
183
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18.13.5.3—Deep foundations
SDC C through F
• Transverse and
longitudinal
reinforcement to
extend:
Pile cap
– Over entire unsupported
length in air, water, or
loose soil not laterally
supported
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184
18.13.5.4 and 18.13.5.5—Deep foundations
SDC C through F
• Hoops, spirals or ties
terminate in seismic
hooks
D
SDC D, E, or F, with Site
Class E or F
• Transv. reinf. per column
req. within seven
member diameter
• ASCE 7, soil strata
Soft
strata
7D
7D
Hard
strata
185
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18.13.5.7—Uncased cast-in place piles
SDC C
•ℓbar ≥
Pile cap
1/3 ℓpile
3m
3dpile
Distance to 0.4Mcr > Mu
Closed ties or
spirals ≥ No. 10
• 3 dpile from bottom of pile cap
• s ≤ 150 mm; 8db long. bar
•Extended trans. reinf.
• s ≤ 16db long. bar
ℓbar
•Transverse confinement zone
s
dpile
ρmin ≥ 0.0025
ℓbar = minimum reinforced pile length
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186
18.13.5.7—Uncased cast-in place piles
Pile cap
SDC D, E, and F
ℓbar
Transv
confin
reinf.
A,B,C,D
Closed ties or spirals
≥
No. 10 (≤ 500 mm) or
No. 13 (> 500 mm);
18.7.5.2
Class E,F
• 1/2 ℓpile
Full length
• 3 dpile from bot.
of pile cap
• s of 18.7.5.3
• ρmin ≥ 0.06 fc′/fyt
• 7 dpile from bot.
of pile cap
• s of 18.7.5.3
• ρmin ≥ 0.06 fc′/fyt
•3m
• 3dpile
• Distance to
0.4Mcr > Mu
ℓbar
Class
s
dpile
Extend. • 12db long. Bar
trans. • 0.5dpile
reinf. • 300 mm
ρmin ≥ 0.005
ℓbar = minimum reinforced pile length
187
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18.13.5.8—Metal cased concrete piles
Pile cap
SDC C through F
•Metal casing replaces
transverse reinforcement in
uncased piles
•Extend casing for ℓbar
ℓbar
•Longitudinal same as
uncased piles
dpile
t ≥ 14 gauge
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188
18.13.5.9—Concrete-filled pipe piles
•ℓd,pile ≥ 2ℓpilecap
ℓdt,bar
ℓpile cap
•ρmin ≥ 0.01
Pile cap
2ℓpile cap ≥
ℓd
SDC C through F
dpile
Steel pipe
189
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18.13.5.10—Precast nonprestressed piles
SDC C
Pile cap
Closed ties or spirals
≥
No. 10 (≤ 500 mm) or
No. 13 (> 500 mm);
18.7.5.2
•ℓbar Full length of pile
•Transverse confinement zone
•Extended trans. reinf.
• s ≤ 150 mm
ℓbar
• 3 dpile from bottom of pile cap
• s ≤ 150 mm; 8db long. bar
s
dpile
ρmin ≥ 0.01
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190
18.13.5.10—Precast prestressed piles
SDC C through F
Pile cap
ℓbar
•Satisfy 18.13.5.10.4 through
18.13.5.10.6
•Minimum amount and
spacing of transverse
reinforcement
s
dpile
191
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18.13.6—Anchorage of piles, piers and
caissons
SDC C—F
• Tension loads: load path
to piles, piers, or caissons
• Transfer to longitudinal
reinforcement in deep
foundation
Source: Dailycivil
Source: Stockqueries
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192
18.13.6—Anchorage of piles, piers and
caissons
18.13.6.2 SDC C—F
•
Dowel
ℓd compr.
ℓdt tension
Anchor dowel between piles and
pile cap
18.13.6.3 SDC D—F
•
•
If tension forces and dowel postinstalled in precast pile
Grouting system to develop min.
1.25 fy (shown by test)
1.25fy
Source:
Gayle Johnson
193
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ACI 318-19
Changes to the Concrete
Design Standard
High-Strength
Reinforcement
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194
Ch. 20 – Yield strength determination
•
318-19, 20.2.1.2:
Nonprestressed bar
yield strength
determination:
– The yield point by the
halt-of-force method
– T he offset method, using
0.2 percent offset
•
20.2.1.3
– A615 and A706
additional requirements
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195
Ch. 3 – Update of ASTM A615-18ε1
• Latest ASTM A615 allows:
– Gr. 690
– Bars up to No. 65
• ACI 318-19 allows
– No. 57 and smaller
– Gr. 550 & 690 with
restrictions
• No. 65 not acceptable:
– Development length
– Bar bends
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196
Table 20.2.2.4(a)
550
690
• Main changes
–
–
–
–
690
690
Gr. 550
Gr. 690
Footnotes
Clarifications
690
550
550
690
420
420
420
550
420
550
550
550
420
197
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Ch. 20 – Steel Reinforcement Properties
Usage
Flexural, axial
force, and
shrinkage and
temperature
Application
Special moment
frames
Special
seismic Special
systems structural
walls[1]
Other
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Maximum value of
fy or fyt permitted
for design calc.,
MPa
Applicable ASTM Specification
Deformed bars
550
A706[2]
690
690[3] [4]
A615M, A706M, A955M,
A966M, A1035M
198
Ch. 20 –Seismic Requirements for A615 Gr. 420
• Section 20.2.2.5 specifies
– ASTM A706 Gr. 420 allowed
– Requirements for ASTM A615, Gr. 420
• Section 20.2.2.5(a) permits ASTM A706
–
–
–
–
Grade 420
Grade 550
Grade 690
(as discussed previously)
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199
Ch. 20 – Seismic Requirements for A615
• For seismic design ASTM A615 GR. 550 and
690 are not permitted
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200
Ch. 20 – Steel Reinforcement Properties
Special moment
Special
frames[8]
seismic
systems[7] Special structural
walls[9]
Shear
Spirals
Shear friction
Stirrups, ties, hoops
Torsion
Longitudinal and transverse
WWW.CONCRETE.ORG/ACI318
550
A615M, A706M, A955M, A996M
690
420
A615M, A706M, A955M, A966M
420
A615M, A706M, A955M, A966M
420
A615M, A706M, A955M, A966M
550
Not permitted
420
A615M, A706M, A955M, A966M
201
Design limits
ACI 318M-14ACI 318-19
εt ≥ 0.005
εt ≥ (εty + 0.003)
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202
Design limits
ACI 318-19
ACI 318-19 Provisions 7.3.3.1,
8.3.3.1, and 9.3.3.1 require
slabs and beams be tension
controlled
εt ≥ (εty + 0.003)
ε ty =
fy
Es
203
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Design limits
ε ty =
fy
Es
Reinforcement ratio, ρtcl
GR 420 εt ≥ 0.0051
GR 550 εt ≥ 0.00575
GR 690 εt ≥ 0.0065
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f’c = 28 MPa
f’c = 70 MPa
1.79%
1.24%
0.92%
3.42%
2.37%
1.75%
204
Design limits
GR 420
GR 690
As,tcl = 3866 mm2
As,tcl = 1987 mm2
Mn,tcl = 738 kNm
Mn,tcl = 649 kNm
Approximately 50% of
reinforcement achieved 88% of
nominal moment
400 x 600 mm beam
d = 540 mm
f’c = 28 MPa
Grade
420
550
690
Reinforcement ratio, ρtcl
f’c = 28 MPa f’c = 70 MPa
1.79%
3.42%
1.24%
2.37%
0.92%
1.75%
205
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ACI 318-19
Changes to the Concrete
Design Standard
Development Length
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206
Development Length
• Deformed Bars and Deformed Wires in
Tension
– Simple modification to 318M-14
– Accounts for Grade 550 and 690
• Standard Hooks and Headed Deformed
Bars
– Substantial changes from 318M-14
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207
Development Length
• Deformed Bars and Deformed Wires in
Tension
• Standard Hooks in Tension
• Headed Deformed Bars in Tension
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208
Development Length of Deformed Bars and
Deformed Wires in Tension
0
140
280
420
550
700
830
970
fcalc (MPa)
Unconfined Test Results
1100
1250
0
140
280
420
550
700
830
970
1100
1250
fcalc (MPa)
Confined Test Results
ftest = reinforcement stress at the time of failure
fcalc = calculated stress by solving ACI 318M-14 Equation 25.4.2.3a
209
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Development Length of Deformed Bars and
Deformed Wires in Tension
•
•
•
Modification in
simplified
provisions of
25.4.2.3
Ψg : new
modification
factor based on
grade of
reinforcement
Modification in
Table 25.4.2.3
 f yψt ψeψg 

d
 2.1λ f '  b
c 

 f y ψt ψeψ g

 1.4λ f '
c

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
 db


 f yψt ψeψg 

d
 1.7λ f '  b
c 

 f y ψt ψeψ g

 1.1λ f '
c


 db


210
Development Length of Deformed Bars and
Deformed Wires in Tension
• Modification in general development length
equation 25.4.2.4(a)
Modification factors




fy
ψt ψ eψ s ψ g 
d = 
d
 1.1λ f '  cb + K tr   b
c

 d

b



λ : Lightweight
ψt : Casting position
ψe : Epoxy
ψs : Size
ψg : Reinforcement grade
• Provision 25.4.2.2
Ktr ≥ 0.5db for fy ≥ 550 MPa , if longitudinal bar
spacing < 150 mm
211
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Development Length of Deformed Bars and
Deformed Wires in Tension
Table 25.4.2.5—Modification factors for development of deformed
bars and deformed wires in tension
Modification factor
Lightweight λ
Reinforcement
grade ψg
Epoxy[1]
ψe
Size ψs
Casting position[1] ψt
Condition
Value of
factor
Lightweight concrete
0.75
Normalweight concrete
1.0
Grade 280 or Grade 420
1.0
Grade 550
1.15
Grade 690
1.3
Epoxy-coated or zinc and epoxy dual-coated reinforcement
with clear cover less than 3db or clear spacing less than 6db
1.5
Epoxy-coated or zinc and epoxy dual-coated reinforcement for
all other conditions
1.2
Uncoated or zinc-coated (galvanized) reinforcement
1.0
No. 22 and larger bars
1.0
No. 19 and smaller bars and deformed wires
0.8
More than 300 mm of fresh concrete placed below horizontal
reinforcement
1.3
Other
1.0
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212
Example—Development Length of Deformed
Bars and Deformed Wires in Tension
Check development length of No. 25 longitudinal
bar in a beam. Assume f’c = 28 MPa NWC, Grade 550
reinforcement, 50 mm cover and no epoxy coating.




fy
ψt ψ eψ s ψ g 

d =
d
 1.1λ f '  cb + K tr   b
c
λ = 1.0

 d

ψe = 1.0
b



ψs = 1.0
From Table 25.4.2.5
ψt = 1.0
Grade 280 or Grade 420
1.0
ψtψe = 1.0 < 1.7
Grade 550
1.15
ψg
ψg = 1.15
Grade 690
1.3
confinement term (cb + Ktr)/db = 2.5 (using the upper limit)
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213
Example—Development Length
Substituting in Eq. 25.4.2.4a:
 550 (1)(1)(1)(1.15) 
d = 
 (25) = 910 mm
2.5
 1.1(1) 28

In comparison a similar bar with fy = 420 MPa;
 420 (1)(1)(1)(1) 
d = 
 (25) = 604 mm
2.5
 1.1(1) 28

Increase of ~50 percent in development length for Grade
550
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214
Development Length of Deformed Bars and
Deformed Wires in Tension
• Differences in higher grade steel for 28 MPa
concrete
Grade
ψg
ℓd,Gr#/ℓd,Gr420
420
550
690
1.0
1.15
1.3
1.0
1.5
2.2
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215
Development Length
• Deformed Bars and Deformed Wires in
Tension
• Standard Hooks in Tension
• Headed Deformed Bars in Tension
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216
Development Length of Std. Hooks in Tension
•
Failure Modes
Front Pullout
•
Front Blowout
Side splitting
Side blowout
Tail kickout
Mostly, front and side failures
– Dominant front failure (pullout and blowout)
– Blowouts were more sudden in nature
217
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Development Length of Std. Hooks in Tension
𝐴𝐶𝐼 318M − 14: ℓ
=
0.24𝑓 𝜓 𝝍𝒄 𝝍𝒓
𝜆 𝑓
𝑑
No. 16
No. 19
No. 22
No. 25
No. 29
No. 36
No. 16
No. 19
No. 22
No. 25
No. 29
No. 36
0
35
70
105
140
Concrete Compressive Strength (MPa)
Unconfined Test Results
No. 16
No. 19
No. 25
No. 22
No. 36
No. 16
No. 19
No. 25
No. 22
No. 36
0
35
70
105
140
Concrete Compressive Strength (MPa)
Confined Test Results
fsu = stress at anchorage failure for the hooked bar
fs,ACI = stress predicted by the ACI development length equation
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218
Development Length of Std. Hooks in Tension
- 25.4.3.1—Development length of standard hooks in
tension is the greater of (a) through (c):
(a)
 f y ψ eψ r ψ oψ c 
 db1.5
 dh = 
'
 23λ f

c


(b)
8db
(c)
150 mm
ACI 318M- 14
 0.24 f y ψ eψ c ψ r
 dh = 

λ f c'


 db


- Modification factors
𝝍𝒓 : Confining reinforcement (redefined)
𝝍𝒐 : Location (new)
𝝍𝒄 : Concrete strength (new – used for cover in the past)
219
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Development Length of Std. Hooks in Tension
Table 25.4.3.2: Modification factors for development of hooked bars in
tension
Modification
factor
Condition
For 90-degree hooks of No. 36 and smaller
bars
318M-14
(1) enclosed along ℓdh within ties or stirrups
Confining
reinforcement,
perpendicular to ℓdh at s ≤ 3db, or
(2) enclosed along the bar extension
ψr
beyond hook including the bend within ties
or stirrups perpendicular to ℓext at s ≤ 3db
Other
318-19
For No.36 and smaller bars with
Confining
Ath ≥ 0.4Ahs or s ≥ 6db
reinforcement,
Other
ψr
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Value of
factor
0.8
1.0
1.0
1.6
220
Development Length of Std. Hooks in Tension
•
(1) Confining
reinforcement placed
parallel to the bar (Typical
in beam-column joint)
– Two or more ties or stirrups
parallel to ℓdh enclosing
the hooks
– Evenly distributed with a
center-to-center spacing
≤ 8db
– within 15db of the
centerline of the straight
portion of the hooked bars
Fig. R25.4.3.3a
221
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Development Length of Std. Hooks in Tension
• (2) Confining
reinforcement placed
perpendicular to the
bar
– Two or more ties or stirrups
perpendicular to ℓdh
enclosing the hooks
– Evenly distributed with a
center-to-center spacing
≤ 8db
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Fig. R25.4.3.3b
222
Development Length of Std. Hooks in Tension
Table 25.4.3.2: Modification factors for development of hooked bars in
tension
Modification
factor
318M-14
Cover
ψc
318-19
Location, ψo
Condition
Value of
factor
For No. 36 bar and smaller hooks with side
cover (normal to plane of hook) ≥ 65 mm
and for 90-degree hook with cover on bar
extension beyond hook ≥ 50 mm
0.7
Other
1.0
For No.36 and smaller diameter hooked bars
(1) Terminating inside column core w/ side
cover normal to plane of hook ≥ 65 mm, or
(2) with side cover normal to plane of hook ≥
6db
1.0
Other
1.25
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223
Development Length of Std. Hooks in Tension
Table 25.4.3.2: Modification factors for development of hooked bars in tension
Modification
Condition
Value of factor
factor
For f’c < 40 Mpa f’c/100 +0.6
Concrete
strength, ψc
For f’c ≥ 40 MPa
1.0
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224
Example—Development Length of Std Hook
Check hooked bar anchorage of longitudinal beam
reinforcement, 3-No. 32 bars in a 500 x 500 mm exterior
column. Assume f’c = 28 MPa NWC, Grade 420
reinforcement, 65 mm cover normal to plane of hook, and
no epoxy coating. Steel confinement is provided such that
Ath = 0.4 Ahs and no epoxy coating.
ℓ
𝑓 𝜓 𝝍𝒓 𝝍𝒐 𝝍𝒄
=
23𝜆 𝑓
λ = 1.0
ψe = 1.0
ψr = 1.0
ψo = 1.0
ψc = f’c/100 + 0.6 = 28/100 + 0.6 = 0.88
𝑑 𝟏.𝟓
225
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Example—Development Length of Std Hook
Substituting in the equation:
 (420)(1.0)(1.0)(1.0)(0.88) 
1.5
 dh = 
 (32)
(23)(1.0) 28


ℓdh = 550 mm > 500 mm
NG
In comparison to the equation in 318M-14:
 0.24 f y ψ eψ c ψ r
 dh = 

λ f c'


 db


ψe = 1.0
ψc = 0.7 (65 mm side cover and
50 mm back cover)
ψr = 1.0
ℓdh(318M-14) = 427 mm < 500 mm
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OK
226
Example—Development Length of Std Hook
Standard Hooked Bars; f'c = 28 MPa
700
Development Length, ℓdh (mm)
600
ℓ
500
=
𝑓𝜓 𝜓 𝜓 𝜓
23𝜆 𝑓
400
𝑑
.
300
Standard Hooked Bars; f'c = 40 MPa
200
318-14
700
100
318-19
10
15
20
25
30
35
40
Bar Diameter, mm
ℓ
=
0.24𝑓 𝜓 𝜓 𝜓
𝜆 𝑓
𝑑
Developmet Length, ℓdh (mm)
600
0
500
400
300
200
318-14
100
318-19
0
10
15
20
25
30
35
40
Bar diameter; mm
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227
Development Length
• Deformed Bars and Deformed Wires in
Tension
• Standard Hooks in Tension
• Headed Deformed Bars in Tension
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228
Development Length of Headed Deformed
Bars in Tension
25.4.4.1 Use of a head to develop a deformed bar in
tension shall be permitted if conditions (a) through (f)
are satisfied:
(a)Bar shall conform to 20.2.1.6
(b)Bar fy shall not exceed 420 MPa
(b) Bar size shall not exceed No. 36
(c) Net bearing area of head Abrg shall be at least 4Ab
(d) Concrete shall be normalweight
(e) Clear cover for bar shall be at least 2db
(f) Center-to-center spacing between bars shall be at
least 3db
229
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Development Length of Headed Deformed
Bars in Tension
ACI 318M − 14:
0
35
70
105
140
Concrete Compressive Strength, fcm (Mpa)
Unconfined Test Results
ℓ
=
0.19𝑓 𝜓
𝑓
𝑑
No. 16a
No. 16b
No. 25a
No. 25b
No. 25c
No. 36a
No. 25d
No. 36b
No. 36c
No. 16a
No. 16b
No. 25a
No. 25b
No. 25c
No. 36a
No. 25d
No. 36a
No. 36b
No. 16a
No. 16b
No. 25a
No. 25b
No. 25c
No. 25d
No. 36a
No. 36b
No. 36c
No. 16a
No. 16b
No. 25a
No. 25b
No. 25c
No. 25d
No. 36a
No. 36b
No. 36c
0
35
70
105
140
Concrete Compressive Strength, fcm (Mpa)
Confined Test Results
fsu = stress at anchorage failure for the hooked bar
fs,ACI = stress predicted by the ACI development length equation
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230
Development Length of Headed Deformed
Bars in Tension
- 25.4.4.2: Development length ℓdt for headed
deformed bars in tension shall be the longest of (a)
through (c):
ACI 318M- 14
𝑓𝜓 𝜓 𝜓 𝜓
.
0.19𝑓 𝜓
(a) ℓ =
𝑑
ℓ =
𝑑
31 𝑓
𝑓
(b)
8db
f ’c ≤ 40 MPa
(c)
150 mm
- Modification factors
𝝍𝒑 : Parallel tie reinforcement
𝝍𝒐 : Location
𝝍𝒄 : Concrete strength
231
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Development length of Headed
Deformed Bars in Tension
Table 25.4.4.3—Modification factors for development of headed bars in
tension
Modification
factor
Condition
Value of factor
Parallel tie
reinforcement,
ψp
For No.36 and smaller bars with Att ≥ 0.3Ahs or
s ≥ 6db
1.0
Other
1.6
For headed bars
(1) Terminating inside column core w/ side
cover to bar ≥ 65 mm, or
(2) with side cover to bar ≥ 6db
1.0
Location, ψo
Concrete
strength, ψc
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Others
1.25
For f’c < 40 Mpa
f’c/100+0.6
For f’c ≥ 40 MPa
1.0
232
Development Length of Headed Deformed
Bars in Tension
• Parallel tie reinforcement (Att)
– locate within 8db of the centerline of the headed bar
toward the middle of the joint
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233
Example—Development Length of Headed
Deformed Bars in Tension
Check development length of No. 29 longitudinal bar
in a beam. Assume f’c = 28 MPa NWC, Grade 420
reinforcement, 65 mm cover, and no epoxy coating.
Steel confinement is provided such that Att = 0.3 Ahs.
 f y ψ eψ p ψ oψ c 
ψe = 1.0
 d b1.5
 dt = 
'


ψp = 1.0
 31λ f c 
ψo = 1.0
ψc = f’c/100 + 0.6 = 28/100+0.6 = 0.88
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234
Example—Development Length of Headed
Deformed Bars in Tension
Substituting in the equation :
 (420)(1.0)(1.0)(1.0)(0.88) 
1.5
 dt = 
 (29)
31(1.0) 28


ℓdt = 352 mm
In comparison to the equation in 318M-14:
ℓ
0.19 1.0 420
=
(29)
28
ℓdt(318M-14) = 437 mm
Decrease in development length of headed bars in tension
as per 318-19 in this example
•
– No.36 and smaller bars with Att 0.3Ats
– bars terminating inside column core with side cover to bar ≥ 65 mm
235
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Example—Development Length of Headed
Deformed Bars in Tension
Headed bars, f'c = 28 , Unconfined
Developmet Length, ℓdt (mm)
900
800
ℓ
318-14
700
318-19
600
𝑓𝜓 𝜓 𝜓 𝜓
𝑑
31 𝑓
.
500
400
300
ℓ
200
=
0.19𝑓 𝜓
𝑓
100
0
10
15
20
25
30
35
600
500
400
300
200
318-14
Developmet Length, ℓdt (mm)
Headed Bars, f'c = 28 Mpa, Confined
600
100
𝑑
Headed bars, f'c = 70 MPa, confined
40
Bar diameter; mm
Developmet Length, ℓdt (mm)
=
500
400
300
200
318-14
100
318-19
318-19
0
0
10
15
20
25
Bar diameter; mm
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30
35
40
10
15
20
25
30
35
40
Bar diameter; mm
236
ACI 318-19
Changes to the Concrete
Design Standard
Shear Modifications
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237
Shear equations change
• One-way beam/slab shear – provision 22.5
– Size effect
– Reinforcement ratio
• Two-way slab shear – provision 22.6
– Size effect
– Reinforcement ratio
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238
Why shear equations changed in 318-19
• Reasons for
changes
– Evidence shows
• Size effect
• Low ρw effect
• More prevalent
– Deeper beams
– Deep transfer slabs
239
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ACI 318-19
Changes to the Concrete
Design Standard
One-way Shear
Equations
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240
Why one-way shear eqns. changed in 318-19
d = 250 mm – λs, size effect factor
Vc = 0.17λ f c' bw d
Av ≤ Av ,min
Vtest/Vn = 1
0
500
1000
1500
2000
2500
3000
Depth, d (mm)
Figure: Strength Ratio (Vtest/Vn) that was calculated by 318M-14 Simplified
241
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Why one-way shear eqns. changed in 318-19
d = 250 mm – λs, size effect factor
Vc = 0.17λ f c' bw d

V d
Vc =  0.16λ f c' + 17ρ w u  bw d
Mu 

Av ≤ Av ,min
Vtest/Vn = 1
0
500
1000
1500
2000
2500
3000
Depth, d (mm)
Figure: Strength Ratio (Vtest/Vn) that was calculated by both ACI 318M-14 Simplified and Detailed
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242
Why one-way shear eqns. changed in 318-19
0.0018 – min. slab ρw
0.015 – ρw effect
Vc = 0.17λ s λ f c' bw d
Av ≤ Av ,min
Vtest/Vn = 1
Figure: Strength Ratio (Vtest/Vn) that was calculated by the Simplified Method of ACI318-19 including size effect
243
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Why one-way shear eqns. changed in 318-19
d = 250 mm – λs, size effect factor
Av > Av ,min
Vtest/Vn = 1
0
500
1000
1500
2000
2500
3000
Depth, d (mm)
Figure: Strength Ratio (Vtest/Vn) that was calculated by the Simplified Method of ACI 318M-14
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244
ACI 318-19 New one-way shear equations
Table 22.5.5.1 - Vc for nonprestressed members
Criteria
Av ≥ Av,min
Vc
Either
of:
0.17𝜆 𝑓′ +
0.66𝜆 𝜌𝑤
0.66𝜆 𝜆 𝜌𝑤
Av < Av,min
⁄
⁄
𝑁
6𝐴
𝑓′ +
𝑓′ +
𝑏 𝑑
𝑁
6𝐴
𝑁
6𝐴
𝑏 𝑑
𝑏 𝑑
(a)
(b)
(c)
Notes:
1. Axial load, Nu, is positive for compression and negative for tension
2. Vc shall not be taken less than zero.
245
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Effect of ρw
ACI 318-19 Shear Equation
Vn / sqrt(f’c)
2.5
0.211
2
0.17
1.5
0.124
1
0.083
0.66𝜆 𝜌𝑤
⁄
00
0.3%
0.4%
0.5%
0.6%
0.7%
0.8%
0.9%
1.0%
1.1%
1.2%
1.3%
1.4%
1.5%
1.6%
1.7%
1.8%
1.9%
2.0%
2.1%
2.2%
2.3%
2.4%
2.5%
0.5
0.041
Longitudinal Reinforcement Ratio (As/bd)
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246
18.13.5.7—Uncased cast-in place piles
Pile cap
SDC D, E, and F
ℓbar
Transv
confin
reinf.
A,B,C,D
Closed ties or spirals
≥
No. 10 (≤ 500 mm) or
No. 13 (> 500 mm);
18.7.5.2
Class E,F
• 1/2 ℓpile
Full length
• 3 dpile from bot.
of pile cap
• s of 18.7.5.3
• ρmin ≥ 0.06 fc′/fyt
• 7 dpile from bot.
of pile cap
• s of 18.7.5.3
• ρmin ≥ 0.06 fc′/fyt
•3m
• 3dpile
• Distance to
0.4Mcr > Mu
ℓbar
Class
Extend. • 12db long. Bar
trans. • 0.5dpile
reinf. • 300 mm
s
dpile
ρmin ≥ 0.005
ℓbar = minimum reinforced pile length
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247
Other limitations for Table 22.5.5.1
• Provision 22.5.5.1.1:
– Limits the maximum value of Vc
Vc ≤ 0.42λ f c' bw d
• Provision 22.5.5.1.2:
– Limits the maximum value of the Nu/6Ag term
Nu
≤ 0.05 f c'
6 Ag
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248
9.6.3.1 - Minimum shear reinforcement
• ACI 318M-14
– Av,min required if Vu > 0.5 φVc
• ACI 318-19
– Av,min required if Vu > φ0.083λ√f’c bwd
• Exceptions in Table 9.6.3.1
249
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22.5.6.2.3—Prestressed members:
Vu d p

'
 0.05λ f c + 4.8
Mu


 bw d

( 0.05λ
)
f c' + 4.8 bw d
0.42λ f c' bw d
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250
Examples: SP-17(14) 5.7 One-way slab Example 1
•
•
•
•
•
•
•
•
•
•
Span = 4.3 m
Live load = 490 kg/m2
Slab = 175 mm thick
f’c = 35 MPa
No. 16 bars at 300 mm
d~150 mm
b = 300 mm
Av = 0 mm2
As = 653 mm2/m
Vu= 35 kN/m
251
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Examples: SP-17(14) 5.7 One-way slab Example 1
• SP-17(14) One-way shear calc ACI 318M-14
φVc = φ0.17λ f c' bd
φVc = (0.75)(0.17)(1) 28 MPa (1000 mm)(150 mm)
φVc = 101.2 kN > 35.0 kN
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∴ OK
252
Examples: SP-17(14) 5.7 One-way slab Example 1
• SP-17(14) One-way shear calc ACI 318-19
• Av ≤ Av,min, therefore use Eq. 22.5.5.1(c)
φVc = φ0.66λ s λ (ρ w )
ρw =
1
3
f c' bd
653
= 0.0044 ← low ρw
(1000)(150)
φVc = (0.75)(0.66)(1)(1) ( 0.0044 )
1
3
28(1000)(150)
φVc = 64.4 kN > 35 kN ∴ OK
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253
Examples: SP-17(14) 5.7 One-way slab Example 1
• φVc ACI 318-19 < φVc ACI 318M-14
– 318-19 for the example given is ~2/3 of ACI 318M-14
– Effect of low ρw
• Design impact
– Thicker slabs if depth was controlled by shear in
318M-14.
– No change if one-way slab thickness was controlled
by flexure or deflections
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254
ACI 318-19
Changes to the Concrete
Design Standard
Two-way Shear
Equations
255
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Why two-way shear provisions changed in 318-19
• Eqn. developed in 1963 for slabs with
t < 125 mm and ρ > 1%
• Two issues similar to one-way shear
– Size effect
– Low ρ
Table 22.6.5.2 – Calculation of vc for two-way shear
vc
0.33λ f c'
Least of (a), (b),
and (c):

2
0.17  1 +  λ f c'
 β

αd
0.083  2 + s  λ f c'
bo 

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(a)
(b)
(c)
256
Two-way shear size effect
• Table 22.6.5.2—vc for two-way members
without shear reinforcement
where
vc
0.33λ s λ f c'
Least of (a), (b),
and (c):

2
0.17  1 +  λ s λ f c'
 β

αd
0.083  2 + s  λ s λ f c'
bo 

(a)
(b)
λs =
2
≤1
1 + 0.004d
(c)
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257
Two-way shear low ρ effect
• D, L only, cracking ~𝟎. 𝟏𝟕 𝒇𝒄 ; punching 𝟎. 𝟑𝟑 𝒇𝒄
• Aggregate interlock
• Low ρ  bar yielding, ↑ rotation, ↑crack size,
allows sliding of reinforcement
• Punching loads < 𝟎. 𝟑𝟑 𝒇𝒄
Source: Performance and design of punching –
shear reinforcing system, Ruiz et al, fib 2010
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258
Why two-way shear provisions changed in 31819:
New two-way slab reinforcement limits
8.6.1—Reinforcement limits
• As,min ≥ 0.0018Ag
• If vuv > φ0.17λ s λ
• Then As ,min ≥
WWW.CONCRETE.ORG/ACI318
f c'on the critical section
0.42vuvbslabbo
φα s f y
259
Why two-way shear provisions changed in 318-19:
8.4.2.2.3
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260
Table 8.4.2.2.3
bslab is the lesser of:
h
h
Slab
edge
1.5h
Slab
edge
1.5h
1.5h
bslab
bslab
261
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Table 8.4.2.2.3
bslab is the lesser of:
1.5 hdrop
Slab
edge
1.5hcap
h
h
hdrop
1.5h
Span/6
t ≥ h/4
1.5h
Depth ≤ Proj.
bslab
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bslab
262
ACI 318-19
Changes to the Concrete
Design Standard
Wall Shear Equations
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263
Coordination of Chap. 11 and 18 Wall Shear Eqs.
• ACI 318M-83 introduced seismic equation
– Two wall shear equation forms
• Equation forms gave similar results
• Committee 318 wanted consistency in form
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264
Coordination of Chap. 11 and 18 Wall Shear Eqs.
• Chapter 11: all changes
• Chapter 18: no change
• 318M-14 simplified compression
eq. (Table 11.5.4.6)
Vn = 0.17λ f hd +
'
c
Av f yt d
s
265
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Coordination of Chap. 11 and 18 Wall Shear Eqs.
• 318-19 Eq. 11.5.4.3
(
)
Vn = α c λ f c' + ρt f yt Acv
• 318-19 Eq. 18.10.4.1 (same as -14)
Vn = α c λ f c' + ρt f yt Acv
(
• αc
)
0.25
0.17
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266
Coordination of Chap. 11 and 18 Wall Shear Eqs.
• Impact minor
• Similar results 318-14 to 19
• Note use of ℓw in 318-19 vs d in 318M-14
– d in 318M-14 assumed 0.8 ℓw
– Results in a “lower” max Vn:
𝑉 = 0.83 𝑓 ℎ𝑑 (318M − 14)
𝑉 = 0.67 𝑓 ℎℓ
= 0.67 𝑓 𝐴
(318 − 19)
267
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ACI 318-19
Changes to the Concrete
Design Standard
Spacing of Shear
Reinforcement
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268
Maximum spacing of legs of shear reinforcement
Source: Lubell et. al, “Shear Reinforcement Spacing in Wide Members, ACI Structural Journal 2009
269
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Table 9.7.6.2.2—Maximum spacing of legs of
shear reinforcement
Maximum s, mm
Nonprestressed beam
Required Vs
≤ 0.33 f c' bw d
> 0.33 f c' bw d
Lesser of:
Lesser of
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Prestressed beam
Along length
Across
width
Along
length
Across
width
d/2
d
3h/4
3h/2
d/4
d/2
3h/8
3h/4
600 mm
300 mm
270
Maximum spacing of legs of shear reinforcement
Beam stirrup configuration with three
closed stirrups distributed across the beam
width
s maximum = d or d/2 nonprestressed, 3h/2 or 3h/4 prestressed
Single U-stirrup (with 135-degree hooks)
across the net width of the beam, two
identical U-stirrups (each with 135-degree
hooks) distributed across the beam interior,
and a stirrup cap
s maximum = d or d/2 nonprestressed, 3h/2 or 3h/4 prestressed
Single U-stirrup across the net width of the
beam, two smaller-width U-stirrups nested in
the beam interior, and a stirrup cap
s maximum = d or d/2 nonprestressed, 3h/2 or 3h/4 prestressed
271
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ACI 318-19
Changes to the Concrete
Design Standard
Bi-directional Shear
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272
Interaction of shear forces
• Biaxial shear
• Symmetrical RC circular sections
– φVc equal about any axis
– Vu on 2 centroidal axes, Vu = resultant
2
vu = (vu , x ) + (vu , y )
2
vu,y
vu,x
273
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Interaction of shear forces
• Biaxial shear
• Rectangular RC sections
– φVc differs between axes
– Vu on 2 axes, φVc≠ resultant
vu,y
vu,x
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vu
274
Interaction of shear forces
• Biaxial shear on non-circular cross section
• φVc = Elliptical interaction diagram
2.5
Interaction Curve
N>0
N=0
N<0
Vexp(y)/Vpre(y)
2
1.5
1
0.5
0
0
0.5
1
1.5
Vexp(x)/Vpre(x)
2
2.5
275
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• 22.5.1.10 Neglect
interaction of shear
forces
If vu,x/φvn,x ≤ 0.5, or vu,y/φvn,y ≤ 0.5
• 22.5.1.11 requires
interaction consideration
If vu,x/φvn,x > 0.5, and vu,y/φvn,y > 0.5,
then
Vexp(y)/Vpre(y)
Interaction of shear forces
1.5
1
0.5
0
0
ν u, x
φν n , x
+
νu, y
νn, y
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0.5
1
1.5
Vexp(x)/Vpre(x)
≤ 1 .5
276
ACI 318-19
Changes to the Concrete
Design Standard
Hanger
Reinforcement
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277
Monolithic beam-to-beam joints: Hanger steel
• Commentary added: R9.7.6.2
• Hanger reinforcement
– Suggested where both the following are true:
– Beam depth ≥ 0.5 girder depth
– Stress transmitted from beam to girder ≥ 0.25√f’c of
the beam
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278
Monolithic beam-to-beam joints: Hanger steel
279
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ACI 318-19
Changes to the Concrete
Design Standard
Concrete Durability and
Materials
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280
Changes in durability and materials
•
•
Changes in material properties (19.2)
– Additional minimum f’c requirements
– Ec requirements
Changes in durability (19.3)
–
–
–
–
•
Calculating chloride ion content
Sulfate exposure class S3
Water exposure class W
Corrosion exposure class C0
Changes in material (26.4.1)
– Alternative cements
– New aggregates
• Recycled aggregates
• Mineral fillers
•
Inspection (26.13)
281
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Table 19.2.1.1 –
Additional minimum strength, f’c
Structural walls in SDC D, E, and F
Special structural walls with Grade 690 reinforcement
Min. f’c
(MPa)
35
Higher strength concrete used with higher strength steel
• Enhances bar anchorage
• Reduces neutral axis depth for improved
performance
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282
19.2.2.1R Modulus of Elasticity
• Ec from Code equations is appropriate for
most applications
• Large differences for HSC (f′c > 55 MPa),
LWC, and mixtures with low coarse of
aggregate volume
283
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19.2.2.2 Modulus of Elasticity
Ec can be specified based on testing
of concrete mixtures:
a) Use of specified EC for proportioning
concrete mixture
b) Test for specified EC
c) Test for EC at 28 days or as
indicated in construction
documents
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Source: Engineering discoveries
284
Contract Document Information
• Members for which Ec testing of concrete
mixtures is required (26.3.1(c))
• Proportioning (26.4.3.1(c))
– Ec is average of 3 cylinders
– Cylinders made and cured in the lab
– Ec ≥ specified value
Source: Engineering Discoveries
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285
Changes in durability and materials
•
Changes in durability (19.3)
–
–
–
–
Calculating chloride ion content
Sulfate exposure class S3
Water exposure class W
Corrosion exposure class C0
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286
Table 19.3.2.1 – Allowable chloride limits
• Percent mass
of total
cementitious
materials
rather than
percent
weight of
cement
Class
Max
w/cm
Min.
f’c,
MPa
Maximum water-soluble
chloride ion (Cl–) content
in concrete, by percent
mass of cementitious
materials
Nonprestressed
concrete
Prestressed
concrete
C0
N/A
17
1.00
0.06
C1
N/A
17
0.30
0.06
C2
0.40
35
0.15
0.06
Additional
provisions
None
Cover
per 20.5
For calculation, cementitious
materials ≤ cement
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Determining chloride ion content
• 26.4.2.2(e) - 2 methods to calculate total
chloride ion content
(1) Calculated from chloride ion content from
concrete materials and concrete mixture
proportions
(2) Measured on hardened concrete in accordance
with ASTM C1218 at age between 28 and 42 days
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288
Sulfate Attack – Change in S3
Credit: PCA
289
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Table 19.3.2.1 –
Exposure Category S – ‘S3’ Options 1 and 2
Class
Max.
w/cm
Min. f’c
(MPa)
Cementitious Materials, Type
SO
N/A
17
S1
0.50
28
II
IP, IS, or IT
Types with
(MS)
MS
No restriction
S2
0.45
31
V
IP, IS, or IT
Types with
(HS)
HS
Not permitted
IP, IS, or IT
Types with
(HS) + Pozz
or slag
HS +
Pozz or
Slag
Not permitted
Types with
(HS)
HS
Not permitted
C150
C1157
Calcium chloride
admixture
No restriction
S3
Option 1
0.45
31
V + Pozz
or slag
S3
Option 2
0.40
35
V
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C595
290
Added advantage of sulfate exposure S3 –
Option 2
• Option 1: 18 month test results
• Option 2: 6 and 12 month test results
291
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Table 19.3.2.1 – Water Exposure Category W
Two Categories – concrete in contact with water: W1 and W2
Class Condition
Example
WO
Concrete dry in service
Interior concrete
W1
Concrete in contact with water where low
permeability is not required
Foundation member
below water table
W2
Concrete in contact with water where low
permeability is required
Pavement parking deck
surface
Class
Max. w/cm
Min. f’c
(MPa)
Additional
requirements
WO
N/A
17
none
W1
N/A
17
26.4.2.2(d)
W2
0.50
35
26.4.2.2(d)
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292
Exposure W1 and W2 check for reactive
aggregates
•
26.4.2.2(d) – Concrete
exposed to W1 and W2,
concrete mixture to comply
with
• ASR susceptible
aggregates not permitted
unless mitigated
• ACR susceptible
aggregates not permitted
293
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26.4.2 Concrete Mixture Requirements
26.4.2.2(g) Concrete placed on or against
stay-in-place galvanized steel forms, max.
chloride ion content shall be 0.30 percent by
mass of cementitious materials unless a
more stringent limit for the member is
specified
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Source: DIY Stack Exchange
294
Changes in durability and materials
•
Changes in material (26.4.1)
– Alternative cements
– New aggregates
• Recycled aggregates
• Mineral fillers
295
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New materials allowed
• Alternative cements (26.4.1.1)
Courtesy: PCA
– Inorganic cements used as 100% replacement of
PC
– Recycled glass and others in ITG-10
• Alternative aggregates and mineral fillers
(26.4.1.2 and 3)
– Recycled aggregated from crushed concrete
– Mineral fillers – finely ground recycled glass or
others
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296
New materials allowed
Courtesy: PCA
Permitted if:
• Documented test data confirms
mechanical properties are met for design of
structural concrete (strength, durability, fire)
• Approved by LDP and Building official
• Ongoing testing program and QC program
(alternative recycled aggregates) to
achieve consistency of properties of
concrete
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297
Changes in durability and materials
•
Inspection (26.13)
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298
26.13—Inspection
26.13.1.1 Concrete construction inspection per:
• General building code (GBC)
• ACI 318 in absence of GBC
Source: Galvanizeit
299
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26.13—Inspection
Inspector must be certified when inspecting:
• Formwork,
• Concrete placement,
• Reinforcement,
• Embedments
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Photo courtesy Larry Novak
300
Seismic Inspections (26.13.1.3)
Inspection performed by:
• LDP responsible for the design
• An individual under the supervision of LDP
• Certified inspector
Elements to be inspected:
• Placement and reinforcement for SMF
• Boundary elements of SSW,
• Coupling beams, and
• Precast concrete diaphragms in SDC C, D,
E, or F using moderate or highdeformability connections
• Tolerances of precast concrete
diaphragm connections per ACI 550.5
Source: NIST page
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301
Other Inspections (26.13.1)
• Reinforcement welding → qualified welding
inspector
• Expansion, screw, and undercut anchors →
inspector certified or approved by LDP and
building official
• Adhesive anchors → certified inspector
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302
26.13.3.2 Items requiring continuous inspection
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303
26.13.3.3 Items requiring periodic inspection
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304
26.13.3.3 Items requiring periodic inspection
305
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ACI 318-19
Changes to the Concrete
Design Standard
Strut-and-Tie Method
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306
Why strut-and-tie method?
• Valuable tool where plane-sections
assumption of beam theory does not apply
• Truss analogy used to analyze concrete
structures
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307
Strut and Tie Method
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308
Deletion of bottle-shaped strut
Bottle-shaped strut
• Spreads out at a slope of 2:1
• Reinforcement is at an angle orthogonal to
grid (Not used)
• Requirement deleted
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309
Code Changes—Strut-and-tie method
• Minimum angle between strut and tie
• Effect of prestressing
• Development of tie forces
• Strut strength and maximum shear stress
• Minimum reinforcement in D-region
• Curved nodes
• STM part of seismic force resisting system
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310
R23.2.7 Angle between strut and tie
25° ≤ θ ≤ 65°
• Mitigate cracking
• Compatibility
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311
Code Changes—Strut-and-tie method
• Minimum angle between strut and tie
• Effect of prestressing
• Development of tie forces
• Strut strength and maximum shear stress
• Minimum reinforcement in D-region
• Curved nodes
• STM part of seismic force resisting system
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312
23.2.8 Effect of Prestressing
1600
1140
12-13 Strand
1187 mm2
110
1233 kN
1600
800
800
800
800
800
1600
910
800
800
800
910
910
910
910
313
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23.2.8 Effect of Prestressing
1600
1140
12-13 Strand
1187 mm2
110
1233 kN
1820
1820
1600
800
800
800
800
430
369
430
1233 kN
1233 kN
800
800
910
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910
910
910
314
23.2.8 Effect of Prestressing in STM
• Use as an external load
• Prestress force applied at end of strand
transfer length
• Load factors per 5.3.13
– LF of 1.2 if PT effects increase net force in struts or
ties
– LF of 0.9 if PT reduce net force in struts or ties
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315
23.7 Strength of ties
Tensile strength:
– Simple tension element
– Fnt = Atsfy +AtpΔfp
– φ = 0.75 for all ties
• Atp = 0 (nonprestressed)
• Δfp = 420 MPa for bonded prestressed reinf. and
70 MPa for unbonded prestressed reinf.
• T Δfp,max
= fpy - fse
Note: tie centroid coincides with reinforcement centroid
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316
Code Changes—Strut-and-tie method
• Minimum angle between strut and tie
• Effect of prestressing
• Development of tie forces
• Strut strength and maximum shear stress
• Minimum reinforcement in D-region
• Curved nodes
• STM part of seismic force resisting system
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317
23.8.2 Strength of ties
Anchorage of tie reinforcement is accomplished
by:
•
Mechanical devices
•
Post-tensioning anchorage devices
•
Standard hooks
•
Straight bar development
•
Except ties extending from curved-bar nodes
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318
23.8.2 Strength of ties
319
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23.8.3 Development of Tie Forces
• Tie force is developed in
each direction at the point
where the centroid of the
reinforcement in the tie
leaves the extended nodal
zone.
• Removed requirement to
develop difference in tie
force within the extended
nodal zone.
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320
Code Changes—Strut-and-tie method
• Minimum angle between strut and tie
• Effect of prestressing
• Development of tie forces
• Strut strength and maximum shear stress
• Minimum reinforcement in D-region
• Curved nodes
• STM part of seismic force resisting system
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321
23.4 Strength of struts
• 3 components
– Struts
– Ties
– Nodal zones
Strut strength:
Fns = fce Acs + A’s f’s
and
fce = 0.85βcβsf’c
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322
23.4 Strength of struts
Strut coefficient, βs → Table 23.4.3
Strut location
βs
Strut type Criteria
Tension members or
tension zones of
members
All other cases
Any
All cases
0.4
(a)
Boundary
strut
All cases
1.0
(b)
Reinforcement satisfying (a) or
(b) of Table 23.5.1
0.75
(c)
𝑽𝒖 ≤ 𝝓𝟎. 𝟒𝟐𝝀𝝀𝒔 𝒇𝒄 𝒃𝒘 𝒅 𝐭𝐚𝐧 𝜽
0.75
(d)
Beam-column joints
0.75
(e)
All other cases
0.4
(f)
Interior
struts
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323
23.4 Strength of struts
𝑽𝒖 ≤ φ0.42𝝀𝝀𝒔 𝒇𝒄 𝒃𝒘 𝒅 𝐭𝐚𝐧𝜃
With λs:
1- λs = 1 if distributed reinforcement is provided
2- λ s =
2
≤1
1 + 0.004d
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324
23.4 Strength of struts
𝑽𝒖 ≤ φ𝟎. 𝟒𝟐𝐭𝐚𝐧𝜃𝝀𝝀𝒔 𝒇𝒄 𝒃𝒘 𝒅
Assume 𝝀 = 1, 𝝀𝒔 = 1, and 25° ≤ θ ≤ 65°
tan 65° = 2.14
 𝑽𝒖 ≤ φ𝟎. 𝟒𝟐 𝟐. 𝟏𝟒 𝟏 𝟏
𝒇𝒄 𝒃𝒘 𝒅
θ
≤ φ𝟎. 𝟗 𝒇𝒄 𝒃𝒘 𝒅
Limit to 0.83
𝒇𝒄 consistent with deep beam
provision 9.9.2.1
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325
Code Changes—Strut-and-tie method
• Minimum angle between strut and tie
• Effect of prestressing
• Development of tie forces
• Strut strength and maximum shear stress
• Minimum reinforcement in D-region
• Curved nodes
• STM part of seismic force resisting system
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326
23.5 Minimum distributed reinforcement
ACI 318-19 – minimum distributed reinforcement
requirements in deep beams and walls
Member
Distributed reinforcement, ρmin
Deep beams
Min. [d/5 and 300
mm]
≥ 0.0025 in each direction
(9.9.3.1 & 9.9.4.3)
Vu ≤ φVc/2
Wall
Spacing, s
(11.6.1)
Longitudinal
Transverse
CIP 0.0012 to 0.0015
0.002 to 0.0025
Precast 0.001
0.001
0.0025
≥ 0.0025
Vu > φVc/2
(11.6.2)
Min. [3h, 450 mm]
(11.7.2 & 11.7.3)
327
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Minimum Reinforcement of D Regions
Strength Ratio (Vtest/Vstm)
3.5
3
2.5
2
1.5
1
0.5
0.25%
0
0
0.002
0.004
0.006
0.008
0.01
Minimum (Vert. & Hor.) Distributed Reinforcement Ratio
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328
23.5 Minimum distributed reinforcement
Table 23.5.1—Minimum distributed reinforcement
Lateral restraint of
strut
Not restrained
Restrained
Reinforcement
configuration
Minimum distributed
reinforcement ratio
Orthogonal grid
0.0025 in each
direction
Reinforcement in one
direction crossing strut
at angle αi
0.0025/(sin2αi)
Distributed reinforcement not required
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329
23.5 Minimum distributed reinforcement
Distributed reinforcement
must satisfy:
(a) Spacing not greater than
300 mm
(b) α1 not less than 40
degrees
Note: smaller α1 controls
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330
23.5 Minimum distributed reinforcement
Struts are considered laterally restrained if:
(a)Discontinuity region is continuous ┴ to plane of
STM
Discontinuity Region
331
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23.5 Minimum distributed reinforcement
Struts are considered laterally restrained if:
b) Concrete restraining strut
extends beyond each side
face of strut a dist. ≥ 1/2 ws
Source: Yun et al. 2016
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332
23.5 Minimum distributed reinforcement
Struts are considered laterally restrained if:
c) Strut in a joint restrained on all 4 faces (15.2.5 & 15.2.6)
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333
Code Changes—Strut-and-tie method
• Minimum angle between strut and tie
• Effect of prestressing
• Development of tie forces
• Strut strength and maximum shear stress
• Minimum reinforcement in D-region and
deletion of bottle-shaped strut
• Curved nodes
• STM part of seismic force resisting system
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334
Curved Nodes
Definition
Node, curved-bar – The bend region of a
continuous reinforcing bar (or bars) that
defines a node in a strut-and-tie model
Dapped-end T-beam
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Column Corbel
335
23.10 Curved-bar Nodes
Why curved nodes?
Nodal zones are
generally too small to
allow development
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336
23.10 Curved-bar Nodes
T1
Two issues that need to
be addressed:
Circumferential
stress
1. Slipping of bar
Radial stress
2. Concrete crushing
T2
337
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23.10 Curved-bar Nodes
T
What is the bend radius?
C
How long is the arc
length of the bar bend
along centerline of bar?
T
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C
338
23.10 Curved-bar Nodes
C-T-T
θ < 180 degree bend
T
• T1 = T2 = Asfy
• Radial compression
stresses are uniform
C
• Bond stresses = 0
rb ≥
2 Ats f y
T
'
s c
C
b f
but not less than half bend diameter of
Table 25.3
339
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23.10 Curved-bar Nodes
θ = 180 degree bend
rb ≥
1 .5 Ats f y
w t fc'
C-C-T
But not less than half bend
diameter of Table 25.3
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340
23.10 Curved-bar Nodes
Curved-bar nodes with
more than one layer of
reinforcement
rb ≥
2 Ats f y
bs f c'
Ats - total area of tie
rb - radius of innermost
layer
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341
23.10 Curved-bar Nodes
23.10.2 Cover ≥ 2db
23.10.3 cover < 2db
 rb x (2db /cc)
23.10.5 At frame corners, joint and bars are
proportioned such that center of bar curvature
is located within the joint
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342
23.10 Curved-bar Nodes
2nd Condition
Tie forces are not equal:
• Compressive stress on the
inside radius of bar varies
• Circumferential bond stress
develops along bar
θc is the smaller of the two
angles
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C3 =
Ats f y
cos θ c
343
23.10 Curved-bar Nodes
23.10.6 The curve must be
sufficient to develop
difference in force
ℓcb > ℓd(1 – tan θc)
In terms of rb
rb >
2 d (1 − tan θc ) d b
−
π
2
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344
ACI 318-19
Changes to the Concrete
Design Standard
Shotcrete
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345
Shotcrete
• Shotcrete equals
regular concrete
• Placement
method
• Additional
information in
ACI 506R and
ACI 506.2
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346
Shotcrete - Minimum Spacing of
Reinforcement
• 25.2.7: Parallel
nonprestressed
reinforcement
– (a) at least the
greater of 6db
and 65 mm
12db
– (b) If two curtains
of reinforcement
are provided,
• At least 12db in
the curtain nearer
the nozzle
• remaining curtain
confirm to (a)
Max (6db, 65 mm)
Max (6db, 65 mm)
12db
347
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Shotcrete - Minimum Spacing of
Reinforcement
• 25.2.10
– For ties, hoops, and spiral reinforcement in
columns to be placed with shotcrete, minimum
clear spacing shall be 75 mm.
≥ 75 mm
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348
Shotcrete –Splices
•
25.5.1.6 Non-contact lap
splices
– Clear spacing - No. 19 and
smaller bars, at least greater of
6db and 65 mm
– Clear spacing - No. 22 and larger
bars, use mockup panel
•
25.5.1.7 Contact lap splices
– Plane of the spliced bars be
perpendicular to the surface
of the shotcrete
– Need approval of the LDP
based on a mockup panel
Reinforcement laps
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349
Shotcrete
Mockup panels
• To demonstrate proper encasement of the
reinforcement
• Represent most complex reinforcement
configurations
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350
Shotcrete
• Mockup panels
Mockup panel
Crew shooting
mockup panel
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351
Shotcrete
Construction Documents and Inspection
• 26.3.1-26.3.2: Where shotcrete is required
– Identify the members to be constructed using
shotcrete
• 26.4.1.2 – 26.4.1.7: Materials
– Aggregate gradation - ASTM C1436.
– Admixtures – ASTM C1141.
– Packaged, preblended, dry, combined materials
for shotcrete – ASTM 1480
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352
Shotcrete
• 26.4.2 - Concrete mixture requirements
– Maximum coarse aggregate size ≤ 13 mm
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353
Shotcrete
•
26.5.2.1: Placement and consolidation
– Remove rebound and overspray prior to placement
of a new layer
– Cuttings and rebound shall not be incorporated into
the Work
– Roughen existing surface to 6 mm amplitude before
placing subsequent shotcrete
– Before placing additional material onto hardened
shotcrete,
• Remove laitance
• clean joints
• dampen surface
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354
Shotcrete
• 26.5.2.1: Placement and consolidation
– Remove and replace in-place fresh shotcrete
that exhibits sags, sloughs, segregation,
honeycombing, and sand pockets
– Shotcrete nozzle operator
• must be certified
• able to shoot an approved
mockup panel
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355
Shotcrete
26.5.3: Curing Satisfying (1) – (3)
(1) Initial curing : for first 24 hours
(i) Ponding, fogging, or continuous sprinkling
(ii) Absorptive mat, fabric, or other protective
covering kept continuously moist
(iii) Application of a membrane-forming curing
compound
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356
Shotcrete
26.5.3: Curing Satisfying (1) – (3)
• (2) Final curing: After 24 hours
(i) Same method used in the initial curing process
(ii) Sheet materials
(iii) Other moisture-retaining covers kept continuously
moist
•
(3) Maintain final curing
for a minimum duration of:
– 7 days
– 3 days if either a high-early-strength cement or an
accelerating admixture is used
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Shotcrete
26.5.6: Construction, contraction, and isolation
joints
• cut at a 45° unless a square joint is
designated
• Submit locations to LDP for approval
– For joints not shown on the construction
documents
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Shotcrete
150 mm
26.12—Evaluation and
acceptance
• Strength test
– Average strength of
minimum three 75 mm
diameter cores from a
test panel
– Tested at 28 days or at
test age designated for
fc′
300 mm
75 mm
450 mm
13 mm
Material test panel sketch showing
where to cut five cores
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Shotcrete
26.12.2 Frequency of testing
• Prepare a test panel
– For each mixture
– For each nozzle operator
– at least once per day or for every 38 m3
• whichever results in the greater number of panels
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Shotcrete
26.12.4 Acceptance criteria for shotcrete
• 26.12.4.1(a): Test specimens to satisfy (1)
and (2):
(1) Test panels shall be prepared
• in the same orientation
• by same nozzle operator
(2) Cores as per ASTM C1604
361
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Shotcrete
26.12.4 Acceptance criteria
• 26.12.4.1(b): Strength to
satisfy (1) and (2):
(1) average strengths from three
consecutive test panels ≥ fc′
(2) average compressive
strength of three cores from a
single test panel ≥ 0.85fc′ and
no single core strength < 0.75fc′
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Take steps to
increase strength
if not satisfied
Investigate
if not satisfied
362
ACI 318-19
Changes to the Concrete
Design Standard
Design Verification
Using Nonlinear
Dynamic Analysis
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363
Appendix A – Design Verification Using Nonlinear
Dynamic Analysis
What is Design Verification Using Nonlinear
Dynamic Analysis?
• Design basis
• Initial design per ACI 318 (Ch. 18)
• Nonlinear software
• Behaviors in model based on
– Testing
– Estimated properties
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Appendix A – Design Verification Using Nonlinear
Dynamic Analysis
• Analysis results vs Design basis
• Peer review
• Agreement that structure meets IBC 2018
req.
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Appendix A – Design Verification Using Nonlinear
Dynamic Analysis
Why would an engineer use Design Verification
Using Nonlinear Dynamic Analysis?
• Tall buildings (over 73 m)
– IBC 2018 ≠ special concrete shear walls
– Forces dual system
• Nonlinear Dynamic Analysis
– Allows concrete shear walls over 73 m
– Exception per IBC 2018 104.11
• NOT JUST FOR SEISMIC
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ACI 318-19
Changes to the Concrete
Design Standard
Closing Remarks
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367
Certificates
• emailed to you within 1-2 weeks
• Check email and name on sign-in sheet
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368
Feedback
• Survey in the
email with your
certificate
• Brief, 11-question
survey
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369
An Invitation to Join – ACI Membership
30,000 members form the premier community
dedicated to the best use of concrete
– Free access to ACI’s 200+ guides reports
– Concrete International, Structural Journal, Materials Journal
– ACI University, discounts, Q+A opportunities, and more
Learn more and join: concrete.org/membership
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371
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Shear Lug Example
• Reinforced Concrete Design Manual
• Anchorage example 20
• See handout
800 mm
DV = 267 kN
LV = 334 kN
WV = ±756 kN
DH = ± 35.6 kN
LH = ± 40 kN
WH = ±53.4 kN
800 mm
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Shear Lug Example
• Can we replace upper ties with shear lug?
– Remove shear from anchor rod design
– May reduce bolt size/length
400
– Simplify design
115
50 Typ
38 x 530 x 530 mm
#13 ties
W360
(8) #25
400
190
75 mm
75 mm
800
310
= 647 mm
381
800
373
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Size Shear Lug
• Size shear lug so entire lug is effective
– tsl = 38 mm
– Width = 38 mmm + 4(38 mm)
= 190 mm
T/Conc
V
75 mmm
– Depth = 75 mm + 75 mm
= 150 mm
38 mmm
– Stiffeners at least 0.5 hsl or 38 mm wide
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374
Shear Lug Example
• Check anchor rod depth (only required if
attachment has tension)
– hef/hsl ≥ 2.5 → hef = 2.5 (75 mm) = 188 mm
– hef/csl ≥ 2.5 → hef = 2.5 (200 mm) = 500 mm <= controls
– Increase rod embedment
from 450 mm to 500 mm
hsl = 75 mm
hef
csl = 200 mm
400 mm
375
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Strength Checks
• Vua,g ≤ φ Vbrg,sl (bearing)
≤ φ Vcb,sl (concrete breakout)
• φ = 0.65
38 x 530 x 530 mm
W360
75 mm
75 mm
647 mm
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Bearing Strength Check
V
• Vua,g ≤ φ Vbrg,sl (bearing)
– Vua,g = 133 kN
– Vbrg,sl = 1.7 f’c Aef,sl Ψbrg,sl
1.7 f’c
• For tension on attachment, bearing is reduced
– Ψbrg,sl = 1+Pu/(nNsa)
–
= 1+(-516 kN)/(4 rods(323 kN/rod))= 0.601
– Vbrg,sl = 1.7 (31 MPa)(190 mm)(75 mm)(0.601)
= 451 kN
• φ Vbrg,sl = 0.65 (451 kN) = 293 kN > 133 kN
OK
377
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Concrete Breakout Strength Check
• Vua,g ≤ φ Vcb,sl (concrete breakout)
• Vcb,sl = (AVc/AVc0) Ψed,V Ψc,V Ψh,V Vb
– AVc = [75 + 1.5 (800 - 38)/2](800)-(75)(190)
= 502,950 mm2
V
ca1 = 381 mm
75 mm
572 mm
800 mm
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800 mm
378
Concrete Breakout Strength Check
• Vcb,sl = (AVc/AVc0) Ψed,V Ψc,V Ψh,V Vb
– AVc0 = 4.5 ca12 = 4.5(381)2 = 653,225 mm2
ca1 = 381
mm
1.5 ca1
1.5 ca1
800 mm
379
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Concrete Breakout Strength Check
• Vcb,sl = (AVc/AVc0) Ψed,V Ψc,V Ψh,V Vb
– Ψed,V = edge effect modification factor
= 0.7 + 0.3ca2/(1.5ca1)
= 0.7+0.3(305)/(1.5(381))=0.860
ca1 =
381 mm
ca2 = 305 mm
800 mm
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Concrete Breakout Strength Check
• Vcb,sl = (AVc/AVc0) Ψed,V Ψc,V Ψh,V Vb
– Ψc,V = concrete cracking modification factor
– Assume cracking and No. 4 ties between lug and
edge (see Table 17.7.2.5.1)
– Ψc,V = 1.2
– Ψh,V = member thickness modification factor
=1.0 (depth > 1.5 ca1)
– Vb = 3.7λa√f’c(ca1)1.5
= 3.7(1)(√31 MPa)(381)1.5 = 153.2 kN
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Concrete Breakout Strength Check
• Vcb,sl = (AVc/AVc0) Ψed,V Ψc,V Ψh,V Vb
= (502,950 mm2/653,225 mm2)(0.860)(1.2)
(1.0)(153.2 kN)
= 121.7 kN
• φ Vcb,sl = 0.65(121.7 kN) = 79 kN < 133 kN ←NG
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Shear parallel to an edge or at a corner
• Shear parallel to an edge
– 17.11.3.2 → 17.7.2.1(c)
• Shear at a corner
– 17.11.3.3 → 17.7.2.1(d)
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Summary
• φ Vcb,sl = 79 kN < 133 kN ← anchor
reinforcement required
• From example:
– all 4 rods resisting and supplementary
reinforcement → φ Vcbg = 131 kN
– back 2 rods resisting and supplementary
reinforcement → φ Vcb,sl = 96.5 kN
• Shear lugs not helpful for breakout
• Helpful when shear in rods is controlling
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900 mm
Examples: SP-17(14) 11.6 Foundation Example 1
• ℓ = 3.6 m
• h = 750 mm
500 mm x 500 mm
• d~650 mm
150 mm basement slab
• f’c = 28 MPa
• 13-No. 25 bars
• b = 3.6 m
• Av = 0 mm2
• As = 6630 mm2
• Analysis Vu = 1028 kN
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Examples: SP-17(14) 11.6 Foundation Example 1
• SP-17(14) One-way shear calc ACI 318M-14
φVc = φ0.17λ f c' bd
φVc = (0.75)(0.17)(1) 28 MPa (3600 mm)(650 mm)
φVc = 1579 kN > 1028 kN ∴ OK
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Examples: SP-17(14) 11.6 Foundation Example 1
• SP-17(14) One-way shear calc ACI 318-19
• Av ≤ Av,min, Eq. 22.5.5.1(c)
• Per ACI 318-19 (13.2.6.2), neglect size effect
for:
– One-way shallow foundations
– Two-way isolated footings
– Two-way combined and mat foundations
φVc = φ0.66λ (ρ w )
1
3
f c' bd
387
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Examples: SP-17(14) 11.6 Foundation Example 1
• SP-17(14) One-way shear calc ACI 318-19
• Av ≤ Av,min, Eq. 22.5.5.1(c)
φVc = φ0.66λ (ρ w )
ρw =
1
3
f c' bd
6630 mm 2
= 0.0028
(3600 mm)(650 mm)
φVc = (0.75)(0.66)(1) ( 0.0028 )
1
3
28 MPa (3600 mm)(650 mm)
φVc = 864 kN < 1028 kN ∴ NG
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Examples: SP-17(14) 11.6 Foundation Example 1
SP-17(14) One-way shear using ACI 318-19
Av ≤ Av,min, Eq. 22.5.5.1(c)
Per ACI 318-19, 13.2.6.2, neglect size effect
Add 200 mm thickness
•
•
•
•
φVc = φ0.66λ (ρ w )
ρw =
1
3
f c' bd
6630 mm 2
= 0.0022
(3600 mm)(830 mm)
φVc = (0.75)(0.66)(1) ( 0.0022 )
1
3
28 MPa (3600 mm)(830 mm)
φVc = 1018 kN < 1028 kN ∴ Say OK ?
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Examples: SP-17(14) 11.6 Foundation Example 1
• Foundation φVc ACI 318-19 < φVc ACI 318M-14
– 318-19 for this example given is ~1/2 of ACI 318M-14
– Effect of low ρw
• Design impact
–
–
–
–
Increased thickness; or
Increase flexural reinforcement; or
Increase concrete strength; or
Combination
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Examples: Grade beam
• Infill wall
– Vu~14.6 kN/m
– Vu~37 kN ea. end
• Grade beam
– bw =300 mm
– d = 500 mm
(h = 600 mm)
– f’c = 28 MPa
– ℓ=6m
– ρw = 0.0033
Infill Wall
Ftg.
Grade Beam
Ftg.
391
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Examples: Grade beam
• Infill wall
– Vu~14.6 kN/m
– Vu~37 kN ea. end
• Grade beam
– bw =300 mm
– d = 500 mm
(h = 600 mm)
– f’c = 28 MPa
– ℓ=6m
– ρw = 0.0033
• ACI 318M-14
φVc = φ0.17λ f 'c bw d
φVc = 0.75(0.17)(1) 28(300)(500)
φVc = 101 kN ∴ OK
Vu < (1/ 2)φVc ∴ Av ,min not required
• ACI 318-19
φVc = φ0.66λ s λ(ρ w )
λs =
1
3
f 'c bw d
2
= 0.82
1 + 0.004d
φVc = 0.75(0.66)(0.82)(1)(0.0033)
1
3
28(300)(500)
φVc = 48 kN ∴ OK
Vu < φ0.083λ f 'c bw d = 49 kN ∴ Av ,min not required
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