Uniform load on bottom flange of composite beam with small ecc.

[anchorengineer]

I'm checking a beam for a uniform load hanging from the bottom flange of a composite w18x30 beam with a 1.5" eccentricity. See sketch. My instincts say this load is not too much but I want to have calcs backing it up. The span is 38 feet and the beam is simply supported. I thought about adding stiffeners to the opposite side of the ecc. and check the bottom flange like it was a cantilevered beam. Any thoughts?

Clarke Engineering Services, PC
Jobsite Engineering and Consulting

http://www.anchorengineer.com

 

[anchorengineer]

BTW, I can eliminate the load of 1,352plf which is 5.25' long. This load could be moved along the beam. Adding kickers to account for torsion is not prefered. I might just do this but now I'm just curious. I'm confident the 163plf load would be fine with a 1.5" ecc.

Clarke Engineering Services, PC
Jobsite Engineering and Consulting

http://www.anchorengineer.com

 

[BAretired]

I don't have W18x30 in my handbook. Lightest is W18x35. Your sketch shows W18x40 and I assume that is what you meant to say.

I doubt that you will need stiffeners for the 163#/' load because the web is likely adequate for that small moment. If you do use stiffeners, why on the opposite side? Put them on the same side as the eccentric load.

As far as calculations are concerned, M = 163*1.5 = 244"#. S = 12*t^2/6. f = M/S.

Same calc. for beam web but add tension of 163#/'.

Don't forget to check the effect on the composite studs as you will be adding a little tension to each one.

For the larger load over the 5' span, it might be a good idea to add stiffeners and possibly studs over a 5' or 6' length offset to the side of the load.

BA

 

[anchorengineer]

Thanks BA. That 30 was a type-o. I meant 40. I was thinking a stiffener on the opposite side, full height, would prevent rotation of the bottom flange. Then just check the flange as you siggested for bending. This is an LRFD job also. I considered checking the local flange bending formula in chapter K of AISC LRFD (I'm using an old version) but I believe this is for loading the top flange. I also considered looking at the the beam as if the top flange was fixed and the bottom is cantilevered and then checking for bending of the web due to the eccentricity.

Clarke Engineering Services, PC
Jobsite Engineering and Consulting

http://www.anchorengineer.com