Structural Concrete - Hassoun

666 Chapter 17 Design of Two-Way Slabs
10 no. 4
top bars
Figure 17.29
strip.
Example 17.9: Concentration of reinforcement within exterior column
2 no. 6 2 no. 6 2 no. 6
no. 4 @ 4″
Figure 17.30
Example 17.9: Reinforcement in edge of slab to resist torque.
Check: a = A s f y 1.93 × 60
0.85f c ′ = = 0.73 in.
b 0.85 × 4 × 47
Use 10 no. 4 bars within a width 47 in. divided equally at both sides from the center of the column
(Fig. 17.29). Additional reinforcement of four no. 4 bars, as indicated before, provides a better
solution.
5. Torque on slab: The torque from both sides of the exterior column is equal to 40% of the column
strip moment.
T u = 0.4(107) =42.8K⋅ ft
42.8
Torque on each side: = 21.4K⋅ ft = 257 K ⋅ in.
2
A slab section of width equal to the column width will be assumed to resist the torsional stresses:
T u = 1 3 v tu
∑
x 3 y
where x is 9 in. and y is 20 in. The critical section is at a distance d from the face of the column
(Fig. 17.30). Assuming that the torque varies in a parabolic curve to the center of the slab, then
the torque at a distance d is
( ) 140 − 7.9 2
T u = 257
= 229 K ⋅ in.
140