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Re: Simple connection eccentricity on columns

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I'll be honest - I usually don't. The amount of eccentricity in an unbalanced column is usually very small compared to the allowable moment capacity, and tends to make a very small difference in the design. I usually leave a bit of headroom on any column picked out of a table, because hand calcs are just not that accurate. Leaving 10-15% capacity "on the table" also puts in a little future capacity should the usage change. It rarely increases the weight of the column appreciably, and I'd rather have the stability. Also, the amount of time to hand calc the full solution on a small job rarely justifies the potential savings in steel.

This is, of course, subject to engineering judgment. My background is such that I feel I should be able to calc most common things in my head, on the fly, to within 20-25%. It comes from reviewing presentations in meetings. Knowing simple mass properties, CTEs, common emissivities, etc. can quickly identify if someone has slipped a decimal place, goofed an in-ft dimension (factor of 3.5 or 2.3 off) or fouled up their units completely (frequencies are often off by 386.4^0.5, or about a factor of 20 by young engineers). If I get out of a tight range of shear offsets, I'll check it just to make sure, though it might just be a scribble in the margin of a calc sheet or a number run in the memory of my HP48. Oh, and I'm not an "old guy" - not even 40 yet - though my hair is a bit grayer than I'd like. I've just done a lot of calcs by hand, and have gotten to work with some pretty darned smart folks over the years and was able to pick up some of their tricks.

Jordan



Will Haynes wrote:

How many of you (that do not use RAM or other software that calculates it automatically) actually figure the eccentricity of a simple beam to column connection and add that moment to the column design? I know when I first started, the older guys would always pick a column out of the AISC concentric load tables without regard to the moment from the actual connection eccentricity. Will Haynes


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