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Re: ??Reinforcing DL's in compression??[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: Re: ??Reinforcing DL's in compression??
- From: "Bill Sherman" <SHERMANWC(--nospam--at)cdm.com>
- Date: 09 Oct 98 10:11:55 -0400
>I have a consultant who proposes to reinforce an underdesigned DL truss diagonal by welding additional plate to their projecting legs. The area of steel required is based on the required additional capacity needed. For welding design, the consultant is using the full axial load in the combined section in order to determine the length of weld. While this may produce conservative results, I feel like the approach is not logical. I think the plate should be attached to the hosting DL's in such a manner to be stable in compression and to be able to contribute the lacking strength. If the plate should provide 10 kips of additional capacity, then its weld spacing should be determined based on stability of the plate in compression, and allowable compressive stresses associated to that. < Starting with the assumption that the truss diagonals are not under load when welded, the weld length required at each end should be equal to the compressive stress times the area of the added plate. The spacing of the welds between the ends should be based on maintaining the allowable compressive stress as determined by the KL/r ratio of each element. (I would probably use the same weld length as at the ends, although the intermediate welds could be based on 2 percent of the compression load.) If the member is under load during welding, consideration must be given to the weakening effect of welding while under load. And then the added plates will only carry stress due to any added loads.
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