Multiple choice

A strut in a steel truss is composed of two equal angles ISA 150 mm x 150 mm of thickness 100 mm connected back-to-back to the same side of a gusset plate. The cross sectional area of each angle is 2921 mm2 and moment of inertia (Ixx = Iyy) is 6335000 mm4. The distance of the centroid of the angle from its surface (Cx = Cy) is 40.8 mm. The minimum radius of gyration of the strut is

  1. 93.2 mm

  2. 62.7 mm

  3. 46.6 mm

  4. 29.8 mm
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C Correct answer
Explanation

The radius of gyration is sqrt(I/A). For a built-up section, calculate the combined moment of inertia about the axis of interest using the parallel axis theorem and divide by the total area.

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