Shear stress in AISC ASD code 2

[tnteng]

Can anyone tell me why the AISC ASD code specifies the use of the average shear stress formula as opposed to the tranverse shear formula VQ/IT when computing shear stress on a beam.

Thanks in advance for any help.

Tony Billeaud
Mechanical Engineer

 

[swearingen]

Quite simply because it is easier to do. The forumla takes into account the fact that the average shear stress is less than the maximum shear stress that is actually in the beam. It is consistent in thin, open shapes such as wide flanged beams and was specifically done to ease computation.



If you "heard" it on the internet, it's guilty until proven innocent. - DCS

 

[UcfSE]

Note that it is the average stress of the web, not the entire section. Using this gives about the same result as using the effective shear area for a wide flange. Alternatively, you can think of it as though the area of the web is about the same as the effective area for the section. As swearingen states, it is easier that way.