Question

Which of the following relation is correct for design of channel/I-section purlin?

(a) (Mz/Mdz) + (My/Mdy) ≥ 1

(b) (Mz/Mdz) + (My/Mdy) ≤ 1

(c) (Mdz/Mz) + (My/Mdy) ≤ 1

(d) (Mdz/Mz) + (Mdy/My) ≥ 1

The question was posed to me during a job interview.

The question is from Purlins topic in portion Design of Beams of Design of Steel Structures

Answer 1

Correct option is (b) (Mz/Mdz) + (My/Mdy) ≤ 1

To explain I would say: The local capacity of the section is checked by interaction equation. It is given by (Mz/Mdz) + (My/Mdy) ≤ 1 , where Mdz and Mdy are design moment capacity about Z and Y axes, respectively, and Mz and My are factored bending moments about Z and Y axes, respectively.