Page 164 - Handbook of Civil Engineering Calculations, Second Edition

STRUCTURAL STEEL DESIGN 1.147

FINDING THE LIGHTEST SECTION
TO SUPPORT A SPECIFIED LOAD

Find the lightest W8 in A36 steel to support a factored load of 100 kips (444.8 kN) in ten-
sion with an eccentricity of 6 in. (15.2 cm). The member is 6 ft (1.8 m) long and is lateral-
ly braced only at the supports; C b 1.0. Try the orientations (a) to (c) shown in Fig. 41.

Calculation Procedure:

1. Try the first orientation, (a), Fig. 41
Given
100 kips × 6 in.
P u 100 kips (44.8 kN); M u P u e 50 kip-ft (67.8 kNm)
12 in./ft
For orientation (a) in Fig. 41
P u 100 kips, M ux 50 kip-ft, M uy 0

Try a W8 28: the design tensile strength (for a cross section with no holes)
t P n t F y A g 0.90 36 ksi 8.25 sq.in. 267 kips (1188 kN)

For (L b 6.0 ft) < (L p 6.8 ft), the design flexural strength for x-axis bending

FIGURE 41