Eccentric load on a wide flange beam. 1

[graybeach]

Hello all,

I have been asked if it would be ok to hang a load of about 1.5 kips per foot (unfactored) along the tip of one of the flanges of a W8x31. The beam is a 16' simple span and only the web and the unloaded flange are supported at the ends. The load is parallel to the web. See attached for a sketch of the configuration.

The beam can handle the strong axis bending (it has cover plates), but I am worried about torsion. Checking the torsion using the AISC guide seems pretty daunting especially since I do not know how to handle the unsupported flange. As a simple check (that seems to show that this is not a good idea) could I just check if the web of the W8 can carry 1.5 kips/ft * 4"?

Doing this I get a moment of 0.5 k.in/in. Dividing by S = .285^2/6 = 0.0135, I get a bending stress of 37 ksi. Not good since our fy is only 33 ksi (it's from the '50s).

Am I oversimplifying here?

Thanks!

 

[graybeach]

Thanks BA. Your method makes sense. None of the info I have found, including the examples in DG9, go into how the web support is designed for torsionally pinned conditions. After spending whole day Friday pondering this, I decided to have the RE to at least prepare a detailed explanation of why torsion should be neglected.