Structural Concrete - Hassoun

15.8 Torsion in Reinforced Concrete Members (ACI Code Procedure) 537
Figure 15.12 Example 15.2.
Assuming that a torque less than or equal to T cr /4 will not cause a significant reduction in the
flexural or shear strength in a structural member, the ACI Code, Section 22.7.4, permits neglect of
torsion effects in reinforced concrete members when the factored torsional moment T u ≤ φT cr /4, or
T u ≤ φλ √ ( )
A
2
f c
′ cp
(15.20)
P cp
When T u exceeds the value in Eq. 15.20, all T u must be resisted by closed-stirrup and longitudinal
bars. The torque, T u , is calculated at a section located at distance d from the face of the support and
T u = φT n ,whereφ = 0.75.
Example 15.2
For the three sections shown in Fig. 15.12, and based on the ACI Code limitations, it is required to
compute the following:
a. The cracking moment φT cr
b. The maximum factored torque φT n that can be applied to each section without using torsional
web reinforcement
Assume f c ′ = 4ksi,f y = 60 ksi, a 1.5-in. concrete cover, and no. 4 stirrups.