Example

Example 12-3: Design Example

A 20 ft long, uniformly loaded, beam is simply supported at one end, and rigidly connected at the other. The beam is composed of a steel tube with thickness t = 0.25 in. Select the radius such that Vmax < 18 ksi, and Amax < L/360.

A

20'

Solution:

1. Steel has E = 29, 000 ksi, and from above Mmax = Wf-, Amax = wEi , and I = nr3t.

2. The maximum moment will be wL2 (1) k/ft (20)2 ft2

3. We next seek a relation between maximum deflection and radius

185Enr3t

(1) k/ft(20)4 ft4(12)3 in3/ ft3 (185)(29,000) ksi(3.14)r3(0.25) in

4. Similarly for the stress a =

5. We now set those two values equal to their respective maximum

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