Question

The optimum depth of web of plate girder is given by

(a) (k/fy)^0.33

(b) (Mzk/fy)

(c) (Mzk/fy)^0.33

(d) (Mzk/fy)^2

I got this question during an interview.

The doubt is from Proportioning of Web & Flanges topic in section Gantry Girders, Design of Plate Girders & Industrial Buildings of Design of Steel Structures

Answer 1

Correct choice is (c) (Mzk/fy)^0.33

Explanation: The depth of plate girder for which area of steel used is minimum and will have minimum weight is called optimum depth. It is given by (Mzk/fy)0.33, Mz is moment resisted entirely by flanges, k = d/tw, d is depth of web, tw is thickness of web, fy = design strength of flanges.