sm7 69

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PROBLEM (7.69) As shown in Fig. P7.69, a rectangular beam 6 in. wide and 12 in. deep
supports a total distributed load of W pounds and a concentrated load of 2W pounds. If all
σ
= 1800
psi and all
τ
= 120 psi, determine the maximum value of W.
SOLUTION
WRWWRM BBA 2,0)6()9(12)12(:0 ==−−=
∑
WRF Ay ==
∑:0
W
2W
2W
-2
W
9 ft
A
B
C
W
x
-0.25W
V
W (total)
x
M
-1.75W
3 ft
5.625W lb
⋅
ft
=67.5W lb
⋅
in.
12 in.
y
6 in.
z
34
1(6)(12) 864 .
12
I
in==
67.5 (6) 1800, 3840
864
all Mc W Wl
I
σ == = = b
332120, 1920
2268
all VW Wl
A
τ == = =
×b
all 1920=
Thus,
W lb
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