Question

The second moment of area of torsional stiffeners about center line of the web is given as

(a) Is ≤ αssD^3

(b) Is ≤ 0.34αsD^3Tcf

(c) Is ≥ 0.34αsD^3Tcf

(d) Is ≥ αsD^3

I had been asked this question at a job interview.

My doubt stems from Stiffeners topic in division Gantry Girders, Design of Plate Girders & Industrial Buildings of Design of Steel Structures

Answer 1

Correct answer is (c) Is ≥ 0.34αsD^3Tcf

Explanation: When bearing stiffeners are required to provide torsional restraint at the support of the beams, the second moment of area of the stiffener section about center line of the web should be such that Is ≥ 0.34αsD^3Tcf , where αs = 0.006 for LLT/ry ≤50, 0.3/( LLT/ry) for 50< LLT/ry≤100, 30/( LLT/ry)^2 for LLT/ry ≥100, D = overall depth of beam at the support, Tcf = maximum thickness of compression flange in the span under consideration, KL = laterally unsupported effective length of compression flange of beam, ry = radius of gyration of the beam about minor axis.