Design of a T-beam - Reinforced Concrete with FRP Bars: Mechanics and Design - page 299

• Compatibility torsion—ACI 318-11, Section 11.6.2:

⋅

2

A
p

cp

T: = φ⋅ ⋅ 4fpsi ′ ⋅ =66kip ft ⋅ ⋅

cr v c

cp

• Threshold torsion—ACI 318-11, Section 11.6.1:

⋅

2

A
p

cp

T: = φ⋅ fpsi ′ ⋅ =17kip ft ⋅ ⋅ tr v c

cp

• FRP reinforcement contribution to torsional strength—following ACI
318-11, Equation (11-21):
The angle of the torsional cracks is taken equal to 45°:

θ := 45° = 0.785

The cross-sectional area resisting to torsion can be computed as

A o := 0.85·A oh = 219·in. 2

The area of the FRP reinforcement resisting to torsion is

A t := A f _ stirrup = 0.196·in. 2

The spacing of the FRP torsional reinforcement is

s st := s sv3 = 3·in.

Provided that closed FRP stirrups are used, the FRP contribution to resist
torsion could be computed as follows:

2A ⋅ Af ⋅

o t fv

T: = cot( )=54 kipft θ ⋅ ⋅

n

s

st

• Limitation on cross section: ACI 318-11, Section 11.6.3.1:
The following ACI 318-11 limitation to the cross-section geometry
should be satisfied:

2

2

V
bd

Tp
1.7A

⋅
⋅

V
bd +8

u1 u h c1

max + ≤φ⋅ max ⋅ fpsi ′ ⋅

c

2

⋅ ⋅

w1 1 oh w1 1