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Reinforce Existing WF Column 1

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spats

Structural
Joined
Aug 2, 2002
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I have a situation where I need to reinforce an existing 18' long column to increase it's axial capacity, which of course is controlled by minor axis buckling. One side of the column is partially embedded in a block wall, so I have access from one side only... the edge of the flanges and the web. I'm thinking of taking maybe two eight foot long plates (1' shy top and bottom), and stitch welding them to the edges of the exposed flanges. The plate width would be slightly narrower than the depth of the column to allow welding.

I have several questions:
1. Is stitch welding sufficient to enhance ry?
2. How do you size the welds, other than making sure the reinforcing plate does not buckle between welds?
3. Do the two stacked plates need to be full pen welded at the splice?
4. Can you count on the area of the added plate to reduce the P/A (for added loads only), as well as enhance the Fa because of KL/ry is less?

I thought about adding a kicker down from the roof beam that frames into the web at the top, but installing a brace would be difficult in the restricted space available.
 
Lil busy at the moment but here are some related articles:





I will revisit this later but I'd say your're on the right track. Basically check for b/t limits for local buckling and also check the plate element for flexural (column) buckling.

Also you can use the reduced KL/r given in AISC 13th Ed section E6 which will also specify a maximum spacing between fasteners.

EIT
 
Don't forget the you are moving the center of gravity over by using unsymmetrical reinforcing and thereby inducing bending into the column. You should account for this additional bending load.
 
Specify your welding technique and metho: DON'T allow stresses to buildup at both ends of the welded new flange reinforcement - if you decide to go that method. Weld in the middle towards both ends, or at one end with the other clamped "loosely" to allow expansion. If you stitch weld, do both sides at the same time (alternating sides) but NOT all-one-side-then-the-other.

If you do both sides of the web, do them at the same time from the top down (going from the bottom up would be a bit tricky) - allowing lots of room for expansion as the base metal and both side plates heat up. If you weld one side, then the other, you will warp the existing beam substantially.
 
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