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Reinforcement Strategies for Steel Joists with Cold Formed Chords

Reinforcement Strategies for Steel Joists with Cold Formed Chords

Reinforcement Strategies for Steel Joists with Cold Formed Chords

(OP)
I need to reinforce a bunch of steel joists having cold formed hat sections as chords. The vertical walls of the hats are not quite vertical which is causing me some serious detailing headaches. I have a wealth of information on reinforcing joists when they're made of double angle chords but not so much for cold formed hat sections.

Does anyone know of a good resources for reinforcing steel joists with cold formed hat section chords? I'm particularly concerned about the joist seats. Rod reinforcing for the chords and angle reinforcing for the crimped tube webs is pretty straight forward. The seats elude me though.

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RE: Reinforcement Strategies for Steel Joists with Cold Formed Chords

Never heard of such a beast. I would build my joist from scratch using the cold formed code.

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RE: Reinforcement Strategies for Steel Joists with Cold Formed Chords

KootK:
It would probably help if you showed some photos or catalog pages of the jsts. you are dealing with. What are the loads, stresses, dimensions, weak spots that you are dealing with? I don’t have a magic answer or formula, and I’m not sure that there is a nice clean book showing all the right details. Show us your details and calcs. and lets discuss them. We just don’t know where to start. You claim to have a bunch of details for jsts. with double angle chords, how do and don’t these work in your case, lets discuss these. Maybe someone will see something you don’t, but we can’t see it from here. Do you have the book “Designing with Steel Joists, Joist Girders, Steel Deck,” by James M. Fisher, Michael A. West & Julius P. Van De Pas, Copyrighted by Nucor Corp, 1991?

For starters you have to shore, unload, de-stress, even over camber a bit, each jst. as you work on it for the reinforcements to pick up their share of the loads/stresses. For the seat and end diags., could you bend two slightly smaller dia. rods, same shape as existing diag. Then, on both sides of the existing diag., weld one horiz. leg of the new rod to the seat, and nest the other horiz. leg along side the existing diag. and against the bot. of the hat section, and weld it to the hat sect.

RE: Reinforcement Strategies for Steel Joists with Cold Formed Chords

A lot depends on how widespread you need the reinforcement. Is this a localized spot to accommodate some roof top units or other point loads, or is the whole joist simply overstressed for whatever reason? Chord reinforcement between the joints is probably most easily accomplished by either adding a second hat (or other) shape to the inner side of the chord or adding a vertical from the center of the panel segment down to the opposing joint in the other chord. Web sections can have an angle or other piece welded to the tube to reinforce the section (effective for compression, but probably not going to do much for tension diagonals which typically aren't the problem anyway). Joints are probably the most problematic, although in many cases it may be possible to add flare bevel welds to the joint to beef up the shear capacity. A word of caution, light gauge welding can be a bit of an art, particularly if your welder is working on the tubes. It is very easy to burn clear through the tube wall which then makes an extremely messy repair to get the strength back.
As noted, a couple of pictures showing the joist would be very helpful to everyone.

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