C Channel Beam
C Channel Beam
(OP)
I have a client who wants to weld two c channels together to form a rectangular tube/beam. Apparently this is cheaper than having to purchase the equivalent sized HSS rectangular tube.
I kind of want to model this up in RISA3D to check a number of things but the built up beam from two C channels has me scratching my head. Has anyone ever run across this or a similar situation? Modeling the C channels as separate members is probably the conservative route, but maybe too conservative. I really don't want to have to generate a custom section.
I kind of want to model this up in RISA3D to check a number of things but the built up beam from two C channels has me scratching my head. Has anyone ever run across this or a similar situation? Modeling the C channels as separate members is probably the conservative route, but maybe too conservative. I really don't want to have to generate a custom section.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com






RE: C Channel Beam
RE: C Channel Beam
1) If load will be applied to both channels, the only demand on the weld is the ability to develop the shear strength / stiffness required to use the combined section for lateral torsional buckling. And that demand would be very small and easily satisfied by any practical weld.
2) If load will be applied from one side, I would design the welds for #1 longitudinally and also ensure that they could transfer at least 1/2 the applied load across the flanges such that you could plausibly claim to have both channels participating in load resistance.
3) The weld quality has always been a concern for me in this situation. I don't see how one would get a reliable weld connecting the channel flanges unless they were prepped for partial penetration welding which would be costly. I'd prefer to weld the two members together with stitch plates if those plates wouldn't interfere with other elements.
Re-reading the original post, I see that you're interested in the modelling rather than the weld design. Oh well, no sense deleting good information. I would model it as a custom tube section with the side walls matching the channel web thickness and the top and bottom walls matching the average channel flange thickness. Easy.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: C Channel Beam
The "beam" will be loaded from the top onto both channels which in my estimation will be acting as a single member provided the welded connection is sufficient. There will be two steel HHS 3.5x3.5x0.25 posts supporting it. The intended configuration is 4'left overhang, 12' middle span, 4' right overhang -> 20' total beam length.
I had not even got to thinking about the welding of the seam between the two channels. I was thinking probably a skip weld for both top and bottom seams. The composite beam will be fully braced at 4' intervals along its top (compression) face, bottom will be unbraced except at the supports.
Pretty much as I expected a custom tube section, I guess I need to dive a little deeper into RISA3D.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: C Channel Beam
RE: C Channel Beam
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RE: C Channel Beam
I'm not even going to place the sill plate bolts through the seam, they will be offset into the solid C channel flange.
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: C Channel Beam
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: C Channel Beam
RE: C Channel Beam
RE: C Channel Beam
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com
RE: C Channel Beam
RE: C Channel Beam
I think Koot's bolted idea might not be too bad cost wise.
RE: C Channel Beam
another day in paradise, or is paradise one day closer ?
RE: C Channel Beam
Remember NOT to assume you have only one web with twice the thickness of the two separate skinny channel webs. A weld at top and bottom -even a "big" weld - means both of the two webs reacts and bends and twists independently from its neighbor.
RE: C Channel Beam
A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com