Page 213 - Handbook of Civil Engineering Calculations, Second Edition

1.196 STRUCTURAL STEEL ENGINEERING AND DESIGN

3. Compute the allowable unit live
load if flexure is the sole criterion
Thus M f c S x 19,340(3.54)/12 5700 ft·lb
2
2
(7729.2 N·m); w 8M/L 8(5700)/16 178
lb/lin ft (2.6 kN/m); w LL 178 – 50 128 lb/lin
ft (1.87 kN/m).
4. Investigate the deflection under
the computed live load
Using E 29,500,000 lb/sq.in. (203,373 MPa) as
given in the AISC Manual, we have LL
4
4
3
5w LL L /(384EI x ) 5(l28)(16) (12) /[384(29.5)
(10) 12.4] 0.516 in. (13.1 mm); LL,allow
6
16(12)/360 0.533 in. (13.5 mm), which is
satisfactory.
5. Investigate the shearing stress
under the computed total load
FIGURE 23 Refer to the AISC Specification. For the individ-
ual channel, h D – 2t 6.79 in. (172.5 mm); h/t
2 2
64.7; 64,000,000/64.7 > /3f b ; therefore, v allow
13,330 lb/sq.in. (91.9 MPa); the web area
2
0.105(6.79) 0.713 sq.in. (4.6 cm ); V
1 /4(178)16 712 lb (3.2 kN); v 712/0.713 < v allow , which is satisfactory. The allowable
unit live load is therefore 128 lb/lin ft (1.87 kN/m).

LIGHT-GAGE STEEL BEAM WITH STIFFENED
COMPRESSION FLANGE

A beam of light-gage cold-formed steel has a hat cross section 8 12 in. (203.2 304.8
mm) of no. 12 gage, as shown in Fig. 24. The beam is simply supported on a span of 13 ft

FIGURE 24