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Structural Concrete - Hassoun

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20.5 Special Requirements in Design of Structures Subjected to Earthquake Loads 831<br />

Therefore, use 10 no. 3 hoops at each end of the beam at 5 in. center to center with the first<br />

hoop located at 2 in. from the face of the support.<br />

At the distance 48 in. from the face of the support, shear strength is<br />

V u = 77.66 − 2.78 × 48<br />

12 = 66.48 K<br />

The shear strength contributed by the concrete is<br />

√<br />

V c = 2 × 1 × 4000 × 20 × 21.5 = 54.4K<br />

V s = 66.54<br />

0.75<br />

− 54.4 = 34.2K<br />

S = A v f y d 4 × 0.11 × 60,000 × 21.5<br />

= = 16.3in.<br />

V s 34.2<br />

Spacing of the stirrups should not be taken greater than<br />

s = d 2 = 21.5 = 10.75 in.<br />

4<br />

or<br />

s = A s f y (2 × 0.11)×60,000<br />

= = 26.4in.<br />

50b 50 × 20<br />

Therefore, use stirrups with seismic hoops spaced 5 in. center to center starting at 48 in. from<br />

the face of the support. Figure 20.18 shows reinforcement detailing.<br />

24"<br />

7 no. 8<br />

A<br />

2 no. 8<br />

7 no. 8<br />

h = 24"<br />

2"<br />

50"<br />

6 no. 7<br />

A<br />

No. 3 stirrups @ 8"<br />

50"<br />

11 no. 3 hoops @ 5"<br />

11 no. 3 hoops @ 5"<br />

28 ft<br />

A – A<br />

30 ft<br />

7 no. 8<br />

24"<br />

No. 3 hoops<br />

6 no. 7<br />

20"<br />

Figure 20.18<br />

Example 20.6: Reinforcement detailing.

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