Reinforcing Joist Floor
Reinforcing Joist Floor
(OP)
I have a steel joist floor that I did not design but discovered was underdesigned while analyzing for additional loads. 14k3 spanning 27.5' at 2' c/c. 4-1/2 slab on 1/2 deck. First Floor Retail Load. The entire floor needs to be reinforced.
It is a strip mall so adding joists/beams or reinforcing each joist would be extremely difficult and expensive.
I am proposing adding a vertical strut at midspan of the joists and a new dropped girder to cut the span in half, along with new columns and footings. I realize that the bearing/strut needs to be designed and the entire joist needs to be analyzed for stress reversal issues and each member checked.
Does anybody have any experience on this type of project? Any better ideas? Any thought on my proposed plan?
It is a strip mall so adding joists/beams or reinforcing each joist would be extremely difficult and expensive.
I am proposing adding a vertical strut at midspan of the joists and a new dropped girder to cut the span in half, along with new columns and footings. I realize that the bearing/strut needs to be designed and the entire joist needs to be analyzed for stress reversal issues and each member checked.
Does anybody have any experience on this type of project? Any better ideas? Any thought on my proposed plan?






RE: Reinforcing Joist Floor
Consider adding a cover plate to the bottom chord which can be secured to the chord member using intermittent fillet welds. It will push the neutral axis toward the bottom chord, but you can live with that.
the amount of reinforcing required is influenced by the error in the initial design. Depending on the increase in the floor capacity required, other options may have to be considered.
Best regards - Al
RE: Reinforcing Joist Floor
RE: Reinforcing Joist Floor
RE: Reinforcing Joist Floor
By "1/2 deck", do you mean form deck, or is the decking covering only 1/2 of the joist?
If it is form deck, there is no composite action, and very little, if any, if the deck covers only half of the joist.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Reinforcing Joist Floor
RE: Reinforcing Joist Floor
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Reinforcing Joist Floor
RE: Reinforcing Joist Floor
RE: Reinforcing Joist Floor
If the owner is okay with all the extra columns (unlikely if rental space?), your plan is about as cost effective as possible. With joists at 24" o/c you end up with far too many local members to fix if the joists are more than say 15% under. All the site welding, inspections, access, finishes, and mech/elec costs make this a costly problem to fix.
If the joists are under, are the beams too?
This all smells like a lawsuit and seems to be a problem for either the EOR or Vulcraft to fix. I would stay far far away from this unless you are being hired as the expert witness. I have had too many problems getting paid in a timely manner when working for developers in this situation.
Brad
RE: Reinforcing Joist Floor
They are good for 98 psf +-. The live load is 100psf. Then there is the pesky weight of the slab. So its not even close. The beams are OK. There is one shorter span bay and I think they designed the joists for that bay and coipied over and didnt realize.
I am going to call Vulcraft and I am going to require payment in full before I release anything.
Thanks for the advice.
RE: Reinforcing Joist Floor
Brad
RE: Reinforcing Joist Floor
TECHNICAL DIGEST No 12 - EVALUATION AND MODIFICATION OF OPEN WEB STEEL JOISTS AND JOIST GIRDERS 2007 (February 2007)