Beam Sizing

[bwilcox]

I am sizing some steel beams and I have calculated maximum deflections, maximum bending stresses, and maximum shear stresses in all of them. Can I use these stresses in one of the failure theories? If so, which one is most appropriate. Or is there a general rule of maximum bending and shear stresses? All my reference books tell how to calculate these values but not on how much deflection will be too much. I thought I might be able to use the bending stress as the normal stress but, like in the Distortion Energy Theory, two principal stresses are needed and I am not sure if there is another one. Thanks for any help you can give me.

 

[boo1]

The common biaxial and triaxial stress theories are:

Brittle Materials- Maximium-stress criterion and Mohr's theory

Ductile Materials- Maxinium-shear therory and von Mises criterion

For steel beam design the softare package I have uses the von Mises criterion.

Beam deflection for floor beams (with plaster clg) is limited by UBC and SBC as 1/360 of the span length for LL and 1/240 for DL+LL. Beams W/O plaster clg L/240 for DL and L/180 DL+LL