Module 13 Wight
Transcript of Module 13 Wight
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Chapter 23 - Strut-and-Tie Models
ACI 318-14:
Reorganized for Design
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Ch. 23 Strut-and-Tie Models
23.1 Scope
23.2 General
23.3 Design strength
23.4 Strength of struts
23.5 Reinforcement crossing bottle-shaped struts
23.6 Strut reinforcing detailing
23.7 Strength of ties 23.8 Tie reinforcement detailing
23.9 Strength of nodal zones
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Why strut-and-tie models?
Valuable tool where plane-sections
assumption of beam theory does not apply
Truss analogy used to analyze concretestructures
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Strut and tie models
3 components
Struts
Ties
Nodal zones
P P
RR
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Struts
Compression elements
2 types
Prismatic
Bottle-shaped
P P
RR
Prismaticstrut
Bottleshapedstrut
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23.4 Strength of struts
Strut strength Without longitudinal reinforcement,
Fns = fceAcs
With longitudinal reinforcement, Fns = fceAcs + Asfs
= 0.75 for all struts
Where:
Acs = bwws ws based on width at node
fce = 0.85 sfcsTable 23.4.3
ws bw
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23.4 Strength of struts
Strut coefficient, sTable 23.4.3
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Struts in a flexural tension zone
T
C
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23.5 Reinf. crossing bottle-shaped struts
Distributed transverse reinforcement
(Asi / bssi)sin i0.003
for fc6000 psi
Only required if using s = 0.75
Not practical in all situations
Also meet deep beam minimumreinforcement in Section 9.9
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Strut and tie models
3 components
Struts
Ties
Nodal zones
P P
RR
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23.7 Strength of ties
Tensile strength:
Simple tension element
Fnt = Atsfy (nonprestressed)
= 0.75 for all ties
Tie centroid coincides with reinforcement
centroid
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23.8 Tie reinforcement detailing
Develop bars at the centroid within the
extended nodal zone
Develop difference between force on one
side and the other within the nodal zone
T
C
NodalzoneExtendednodal
zoneRd, min
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Strut and tie models
3 components
Struts
Ties
Nodal zones
P P
RR
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23.9 Strength of nodal zones
Node strength
Depends on node type
CCC CCT CTT
T
C
R
C
C
P
T
C
T
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23.9 Strength of nodal zones
Node strength
Fnn = fceAnz fce = 0.85 nfcnTable 23.9.2
= 0.75 for all nodal zones
CCC
CCT
CTT
Typeofnode
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Examples
Deep beam from SP-17(14)
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Examples
Deep beam from SP-17(14)
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Examples
Deep beam from SP-17(14)
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Examples
Deep beam from SP-17(14)
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Examples
Corbel from SP-17(14)
Strut
Tie
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Examples
Pile cap from SP-17(14)
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Resources
SP-208: Examples for the Design of Structural
Concrete with Strut-and-Tie Models
SP-273 Further Examples for the Design of
Structural Concrete with Strut-and-Tie
Models