sm7 33

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PROBLEM (7.33) A simply supported beam L = 15 ft long is constructed of two C 10 x 20 steel
channels (see Table B.10) bolted back to back. Using an allowable bending stress of 22 ksi, determine
the central concentrated load P that can be applied for two cases:
(a) The webs are horizontal (Fig. P7.33a).
(b) The webs are vertical (Fig. P7.33b).
SOLUTION
max (7.5 12) 45
2
P
M
P=×=
P
Refer to Table B.10
for properties of
a
10 20C
×
section.
4
2(78.4) 157.8 .
z
I
in==
2
2[2.81 5.88(0.606) ]
z
I=+ 4 9.94 .in=
(a) 345 (2.739)
;2210 9.94
all z
Mc P
I
σ =×= , 1.77Pkips
=
(b) 345 (5)
;2210 157.8
all z
Mc P
I
σ =×=, 15.4Pkips
=
7.
C
7.5 f
t
5 ft
2
P
2
P
y
y
C 2.739 in.
z
C
5 in.
z
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