unbraced length
unbraced length
(OP)
I design equipment with plate and C channel stiffeners welded to the plate to resist internal pressure loads, ductwork for power plants, to be specific.
If the free flange, away from the plate, is in compression, what is the maximum length for the channel to run without cross bracing if it is designed to a maximum stress of .6Fy in the composite shape? What is the relationship of allowable stress to unbraced length when length is greater than the first case?
If the free flange, away from the plate, is in compression, what is the maximum length for the channel to run without cross bracing if it is designed to a maximum stress of .6Fy in the composite shape? What is the relationship of allowable stress to unbraced length when length is greater than the first case?





RE: unbraced length
The spec can be downloaded for free at http://www.aisc.org/2010spec
RE: unbraced length
Did I read it incorrectly?
RE: unbraced length
If you insist on using a channel, chapter F12 is applicable. I will summarize for you: Determine buckling stress by analysis. In the commentary, it is recommended to use Galambos Guide to Stability Design to calculate the buckling stress (6th edition free if you are an AISC member) or to use one of the many choices given in the previous parts of Chapter F.
RE: unbraced length
RE: unbraced length
If the shape is built up from plate or hot rolled, the stability equations are the same provided that the two members are adequately connected. If they are not adequately connected, they act independently, and a previous section of Chapter F applies.
If there is some way that I am not understanding to connect a shell and a plate, please provide a sketch.
RE: unbraced length
RE: unbraced length
"I have a member that is built from a channel and plate (see attached picture). The tension flange is braced by welding to the plate, but the compression flange is free. Since the plate welded to the tension flange produces some resistance to rotation of the cross section, how would I determine the maximum unbraced length of the combined section? AISC only shows the unbraced or fully braced condition and this is one of intermediate fixity."
If you are using the properties of the combined section, you should not consider the plate as stability bracing. It is either part of the section or part of the bracing, but not both. If you are using only the properties of the channel, there may be some resistance to buckling due to the plate, but the conservative approach is to neglect this effect and add bracing as necessary since the bracing is connected to the tension not the compression flange.
RE: unbraced length
RE: unbraced length