w shape loading?
i have a large w shape as my beam with 6x14 timbers (rafters) every 2' on both sides of the beam, each timber has a 6k reaction. the owners want to place these rafters on the bottom flange of the beam. i've never done that, all i've ever seen is the rafters or joists bearing on top of the beam (top of the top flange). are w shapes designed such that one can load it an any shape or form or do i need to do some other kind of check. the loading will be equal on both sides so the torsion will be small. any advice would be great. thanks
find a job or post a job opening
check the bottom flange for localized bending (as a short cantilever fixed at the web). also, check the bearing on the joists since you will likely have less bearing distance now.
this may also interfere with your bracing assumptions. look into these carefully.
actually your beam may be able to handle a larger load if loading is via the bottom flange. that is if localized flange bending does not control and the ltb bracing is the same.
tonyes- check out section j10.1 (this is what structuraleit was referring to)
dwha- how do you figure that?
dwha, how do you figure?
dang, beat me by a second.
funny
aisc 13th ed commentary f2.1 pg 16.1-271.
in any new design i ignor it. but if there is an existing structure that has bott flange loading, i will utilize it if needed.
people like simpson and ups make special hangers for these types of applications. they stradle over the top of the beam and provide a hanger for the beam...
you might want to check them out
dwha-
this only applies if ltb controls. for a section adequately braced to develop phi mn, it makes no difference where the load is. additionally, you are ignoring that fact that by moving the joists and, consequently, the bracing to the bottom flange, you now have an unbraced compression flange (assuming a simply supported beam)