Practice Question: Maximum Tension on the Bottom Chord of a Truss

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Solution

Answer: D) 500 kip

A truss functions to resist load by developing axial forces in its members. Given the truss shown in the problem statement and associated loading, we can deduce that the top chord is in compression and the bottom chord is in tension as shown in the following image. We can think of truss action analogous to that of a deep beam where the top flange is in compression and the bottom flange is in tension. 

Calculate the maximum moment on the truss based on uniform load over the length:
$$ M_u = \frac{w_u \ast \ L^2}{8} = \frac{(10 \ kip / ft) \ (40 \ ft)^2}{8} $$

$$ M_u = 2000 \ kip-ft $$

Calculate the tension based on depth of the truss:

$$ d = 4 \ ft $$

$$ T = \frac{M_u}{d} = \frac{2000 \ kip-ft}{4 \ ft} = 500 \ kip $$
 

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