Question

When one sag rod is used, the moment about web axis

(a) reduces by 50%

(b) increases  by 50%

(c) increases by 75%

(d) reduces by 75%

This question was addressed to me in examination.

My query is from Purlins in division Design of Beams of Design of Steel Structures

Answer 1

Right option is (d) reduces by 75%

To elaborate: If sag rods are not used, the maximum moment about web axis would be wl2/8. When one sag rod is used, the moments are reduced by 75% and when two sag rods are used at one-third points, the moments are reduced by 91%.