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ch01-03 stress & strain & properties

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01 Solutions 46060 5/6/10 2:43 PM Page 24<br />

© 2010 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently<br />

exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher.<br />

*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

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