Back to Back Channels
Back to Back Channels
(OP)
Is there a standard procedure for analyzing a beam made of back to back channels with a non-continuous spacer plate between? I'm working backwards, I know the I-beam size for what I need, but want complete out of channels so I can place a tension rod between the channels. I have looked at the shear flow, but since the plates are not continuous I am unsure if I can do this. Also, would I have to look at the bolts for tension capacity? Any help would be appreciated.






RE: Back to Back Channels
Shear flow is not an issue because of symmetry.
BA
RE: Back to Back Channels
Two unconnected channels back to back have very different buckling characteristics (for strong axis bending) than when they are connected together.
Granted, the shear required to avoid LTB is small, but it does exist.
RE: Back to Back Channels
My earlier comments apply to double channels connected together. It was my understanding that the OP intends to connect them with non-continuous spacer plates.
I agree that shear flow exists, just as it does in an I-beam, but shear flow in the flanges of one channel counteracts shear flow in the flanges of the other so that the shear center and the centroid of the combined shape are in the same place.
I hadn't thought about lateral torsional buckling, but if the unbraced length is substantial, that would be a consideration.
BA
RE: Back to Back Channels
RE: Back to Back Channels
Perhaps, instead of 1 1/2" spacer plates, you could use 1 1/2 x 1 1/2 HSS spacers.
BA
RE: Back to Back Channels
RE: Back to Back Channels
RE: Back to Back Channels
RE: Back to Back Channels
RE: Back to Back Channels
If you provide bolts each side of the tension rod, then:
T = P*e/d
where T is the tension in the upper bolts each side of the tension rod (T/2 each).
P is the applied load in the tension rod.
e is the eccentricity
d is the vertical distance between bolts (perhaps a bit conservative)
In calculating e, the point of application of gravity load may be taken as the center of channel web.
Tension in the bolts is expected to be very small.
BA
RE: Back to Back Channels
BA
RE: Back to Back Channels