Lintel Beam Design

[Escobales]

Hello Fellow Engineers:

I am interested in studying homogeneous non-symmetrical sections subjected to torsion. For example, built-up sections, (I-beams), having the bottom flange extended to carry brick. So far, I have studied the modified flexure analogy presented by Salmon & Johnson, 4th Edition, (Steel Structures) but I seem not be able to find anything related to torsional rotation other than the AISC Steel Design Guide Series 9 or any mechanics of materials book. What about calculating deflections? Are the standard procedures still applicable for this non-symmetrical sections? I think not! Should I use the principal moments of inertia Iu & Iv to calculate the deflection? Any suggestions?

 

[Gourile]

I think there are not many experiences on the torsion of nonsymetrical sections. Salmon & Jhonson, as you mentioned, developed the theory in a simple form as well as a more complex form for symetrical torsion. They have also made some comments on sections like channels. The idea would be so complex if the section has no axis of symetry. You have to see if it worth to study the problem in depth, as in most cases the effect of torsion is minor. Even in design of crane girders or roof purlins with a "Z" shape cold formed section, it is good enough to just consider half the bending modulus in weak direction to account for the torsion.