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RE: steel retro fits

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Title: steel retro fits

>I would like to get opinion on how best to approach adding
>
area to a steel column without unloading it. My thinking was
>to use small welds and stitch
maybe 3 @ 12 and go up the
>column. Then go with another 3 @ 12 adjacent to original
>and fill in
with the 3rd and 4th passes of 3 welds. As far as
>evaluating how safe the column is during welding I am
>wondering if
I can justify the column by neglecting the heat
>effected zone (how big is that) and checking the column. It’s
>a
fully braced frame in both directions.

Your approach may work depending upon the load in the column during welding. There are two good papers in the AISC Engineering Journal that give sound guidance on reinforcing members under load.

    David T. Ricker, Field Welding to Existing Steel Structures, 1qtr88
    Raymond H.R. Tide, Reinforcing Steel Members and the Effects of Welding, 4qtr90

Each of these is available to AISC members for free download at http://www.aisc.org If you are not a member, you can still download then for a nominal charge.

>I will use strain compatibility to look at existing area vs.
>new area and how much each will carry. My thinking is
>I will not be able to add much strain so new plate will be
>at low allowable stress while column is high. Any insight
>on the weld effects usi
ng this approach would be appreciated.

I do not think it is necessary to superimpose the stresses as you describe. The loads redistribute prior to failure. The load distribution in the reinforced column under load would not be any worse than the pattern of residual stresses in the crolled ross-section, the variations in which are already accounted for in the design equations for columns. Thus, I would use the full cross-section, assuming the reinforcement is adequately interconnected.

Charlie