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Structural Concrete - Hassoun

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670 Chapter 17 Design of Two-Way Slabs<br />

(c)<br />

Figure 17.32<br />

(continued)<br />

2. Calculate factored loads:<br />

Slabload = 24 + 8(150)<br />

12<br />

= 124 psf<br />

q u = 1.2(124)+1.6(80) =277 psf<br />

Drop panel load = 24 + 10(150)<br />

12<br />

= 149 psf<br />

q u = 1.2(149)+1.6(80) =307 psf<br />

Because the drop panel length is L/3 in each direction, the average q u<br />

( )<br />

1<br />

(307) =287 psf.<br />

3<br />

3. Check two-way shear (at distance d/2 from the face of column):<br />

a. In the drop panel: d = 10 − 0.75 − 0.5 = 8.75 in.<br />

[ ( ) 28.75 2<br />

]<br />

V u = 0.287 24 × 20 −<br />

= 136.1K<br />

12<br />

b 0 = 4(20 + 8.75) =115 in.<br />

(<br />

φV c = φ 2 + 4 ) √f<br />

′<br />

β c b 0 d<br />

β = 24<br />

20 = 1.2<br />

φV c = 0.75 ×<br />

= 254.38 K<br />

(<br />

2 + 4 ) √ 4000<br />

× 115 × 8.75<br />

1.2 1000<br />

is<br />

(<br />

2<br />

3<br />

)<br />

(277)+

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