Eccentrically Loaded Steel Columns

[carson116]

thread507-225735

After reading this thread I still didn't see anything stating that a minimum eccentricity needs to be included in the calculation. Does anyone know of a code reference with regards to a minimum eccentricity requirement for a concentrically loaded column? I always assumed the column tables accounted for eccentricity (for concentrically loaded columns) by the unbraced length.

 

[JoshPlumSE]

FWIW Column tables (or rather the column capacity curves) include an assumed out-of-straightness of the column. They consider nothing about connection eccentricity, which is what that previous thread appears to be addressing.

This is a bit of a tangent, but the direct analysis method requires that you consider some assumed out-of-plumbness of your column. That's a code requirement for stability. You could interpret that requirement to mean that you should use that out-of-plumbness as a minimum eccentricity for your connection forces even when the loading is nominally concentric.

 

[a2mfk]

I read through that last thread, and the only straightforward statement offered from AISC was:

In the 13th Edition of the AISC manual there is a statement on page 10-103 (bottom paragraph)"The design procedure for extended single-plate shear connections permits the column to be designed for an axial force without eccentricity."


I have done it both ways. When using tables I usually ignored it, but if using a program, especially with larger HSS, I have put some eccentricity on the column. Especially if the loads are not very balanced due to irregular spans, or one sided connections. I think rarely it leads to an increase in column size unless you are really close on your axial capacity. Which is another way to handle it if you are using tables, just under-design your column a little for axial to leave some reserve for any possible eccentricity. Also, unless you are reducing your live loads for tributary area, a lot of columns probably are mostly over-designed for the actual loading scenario. I guess that could be said about almost all properly designed structures. And that is a good thing.