sm7 16

________________________________________________________________________
PROBLEM (7.16) An unsymmetrical W beam is acted upon by a bending moment Mz ,as
shown in Fig. P7.16. For the ratio of bending stresses of 5/8, at the top and bottom of the beam,
determine the width b of the bottom flange.
SOLUTION
58
tb
σ
σ
=
5(240) 92.3
13
b
cm==m
8(240) 147.7
13
t
cm==m
120 27.7
b
y
cmm
=
−+=−
Thus, ii
i
Ay
y=A
∑
∑
ii
i
Ay
yA =∑
∑
150 20 110 (20)110 27.7
150 20 200 15 (20)
bb ×× −
==
×+ ×+ −
m
Solving,
301.5bm=
z’
y
15 0 mm
y
z
15 m
C
20 mm
m
b
20 mm
100 m
m
c
t
100 mm
cb
Excerpts from this work may be reproduced by instructors for distribution on a not-for-profit basis for testing or
instructional purposes only to students enrolled in courses for which the textbook has been adopted. Any other
reproduction or translation of this work beyond that permitted by Sections 107 or 108 of the 1976 United States
Copyright Act without the permission of the copyright owner is unlawful.