Question

The required section modulus of the channel/I-section purlin can be determined by

(a) Zpz = Myγm0/fy + (b/d)(Mzγm0/fy)

(b) Zpz = Mzγm0/fy + (b/d)(Myγm0/fy)

(c) Zpz = Mzγm0/fy + 2.5(b/d)(Myγm0/fy)

(d) Zpz = Myγm0/fy + 2.5(b/d)(Mzγm0/fy)

This question was posed to me in semester exam.

The above asked question is from Purlins topic in chapter Design of Beams of Design of Steel Structures

Answer 1

Right answer is (c) Zpz = Mzγm0/fy + 2.5(b/d)(Myγm0/fy)

The explanation: The required section modulus of the purlin section can be determined by Zpz = Mzγm0/fy + 2.5(b/d)(Myγm0/fy ), where γm0 is partial safety factor for material = 1.1, d is depth of trial section, b is the breadth of the trial section, Mz and My are factored bending moments about Z and Y axes, respectively, and fy is yield stress of steel. Since the above equation involves b and d of a section, trial section must be used and from the above equation , it is checked whether chosen section is adequate or not.