ch01-03 stress & strain & properties
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01 Solutions 46060 5/6/10 2:43 PM Page 24<br />
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*1–36. The bars of the truss each have a cross-sectional<br />
area of 1.25 in 2 . If the maximum average normal <strong>stress</strong> in<br />
any bar is not to exceed 20 ksi, determine the maximum<br />
magnitude P of the loads that can be applied to the truss.<br />
3 ft<br />
B<br />
C<br />
A<br />
E<br />
4 ft 4 ft<br />
D<br />
Joint A:<br />
P<br />
0.75 P<br />
+ c ©F y = 0; -P + a 3 5 bF AB = 0<br />
F AB = (1.667)P<br />
: + ©F x = 0; -F AE + (1.667)Pa 4 5 b = 0<br />
F AE = (1.333)P<br />
Joint E:<br />
+ c ©F y = 0; F EB - (0.75)P = 0<br />
F EB = (0.75)P<br />
: + ©F x = 0; (1.333)P - F ED = 0<br />
F ED = (1.333)P<br />
Joint B:<br />
+ c ©F y = 0; a 3 5 bF BD - (0.75)P - (1.667)Pa 3 5 b = 0<br />
F BD = (2.9167)P<br />
: + ©F x = 0; F BC - (2.9167)Pa 4 5 b - (1.667)Pa 4 5 b = 0<br />
F BC = (3.67)P<br />
The highest <strong>stress</strong>ed member is BC:<br />
s BC = (3.67)P = 20<br />
1.25<br />
P = 6.82 kip<br />
Ans.<br />
24