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Re: ??Reinforcing DL's in compression??

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>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.