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Structural Concrete - Hassoun

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524 Chapter 15 Design for Torsion<br />

Figure 15.1<br />

Torque applied to a cantilever beam.<br />

Section N (K) M x<br />

(K ⋅ ft) M y<br />

(K⋅ft) V x<br />

(K) V y<br />

(K) T(K⋅ft)<br />

1 0 –135 +108 +12 +15 0<br />

(15 × 9) (12 × 9)<br />

2 –12 0 +108 +20 +15 135<br />

Compression (15 × 9)<br />

3 –12 –180 +348 +20 +15 135<br />

Compression (15 × 9)<br />

If P 1 , P 2 ,andP 3 are factored loads (P u = 1.2 P D + 1.6 P L ), then the values in the table will be the factored<br />

design forces.<br />

15.2 TORSIONAL MOMENTS IN BEAMS<br />

It was shown in Example 15.1 that forces can act on building frames, causing torsional moments.<br />

If a concentrated load P is acting at point C in the frame ABC showninFig.15.3a, it develops a<br />

torsional moment in beam AB of T = PZ acting at D. When D is at midspan of AB, then the torsional<br />

design moment in AD equals that in DB, or 1 T. If a cantilever slab is supported by the beam AB in<br />

2<br />

Fig. 15.3b, the slab causes a uniform torsional moment m t along AB. This uniform torsional moment<br />

is due to the load on a unit width strip of the slab. If S is the width of the cantilever slab and w is

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