Open Web Steel Joist vs the Derecho

[BubbaJ]

Hello from wind ravaged Iowa,

I am starting to get calls to review wind damage in our area. The building I looked at today had some interesting damage. The bottom chord of the open web steel joists was kinked between the rows of bridging. Bottom chords braced at 1/3 points do not like being in compression when the roof is sucked up by 110mph winds and force reversal occurs. Derecho - 1, Steel Joist - 0

I've designed joist reinforcement for added loads before. Due to the kink, using rods in the leg of the angles doesn't really work. There were also a few locations where at least one side of a web weld had broken loose from the bottom chord angle. For this situation, I have 2 options that immediately come to mind:
(1) shore the joist, remove the damaged bottom chord, install new bottom chord (time consuming considering there are about 36 joists that need repaired.)
(2) shore the joist, plate the bottom side of the deformed chord creating a splice to span the damaged area

Does anyone else have a better idea? I know I would also have the option of contacting the manufacturer for a repair, if I could determine who that was.

TIA!

 

[jayrod12]

How did the roofing material fare? If they're re roofing anyway, might be easier to just pull the deck and joists as well and replace with new?

 

[phamENG]

I'd be concerned with more than just the obvious plastic buckling in the bottom chord. There's some significant rotation in the web members. What has that done to the web to top chord connections, top chord to deck connections, and the deck itself. Perhaps there was enough flexibility in each of those to allow that to shift and everything but the bottom chord has remained elastic, but I'd be concerned about those welded connections. All of that material is pretty thin, and the welds are pretty thin, so that may have been enough to crack a few of them.

It may be easier and more structurally effective/efficient to replace the joists. Of course that's not going to be a popular approach given the likely presence of Mechanical units, electrical conduits, roof drains, and sprinkler systems.

 

[BubbaJ]

The roofing will be replaced, the deck seems to be in good shape. They weren't planning to replace the deck.

 

[BubbaJ]

I wasn't able to get up close and personal with the connections (no lift that day.) The bolted connections to the PEMB frames didn't appear to have moved.

Broken welds is definitely a possibility on the web to chord connections.

Mechanical units won't be a problem, those all blew off their curbs. They still would not like to hear "replace the joists" as they already asked if they could reopen. Uh, no.

I will get in touch with the contractor and proceed with a more in-depth investigation.

If the welds are good. Any thoughts on a repair option?

 

[jayrod12]

I'm still fairly partial to a remove and replace.

If there's a contractor on board it might be good to sit and have a meeting with the client and the contractor and discuss what would be the most cost effective and schedule effective. Because repair work is time consuming. One joist fixed per day times how many affected joists? It adds up quick.

 

[phamENG]

I haven't had to deal with anything quite that bad. Most of my joist modifications have been increasing local strength for new mech units or splicing chords that were cut "accidentally." If I come up with something I'll come back and let you know.

How old is the building? Can you identify a manufacturer for the joists? If so, you can reach out to them and request assistance.

 

[JedClampett]

I'd remove and replace. Once you touch these, you own them. You can't really quantify the yielding, necking or other hidden damage. If you fix them locally and something else goes wrong (like when they reinstall the mechanical units), it's on you. And good luck contacting the PEMB supplier and joist manufacturer. If they're still in business and they can find their records, these guys can smell a liability issue a thousand miles away.
You can have them temporarily shore the existing joists and get back to work, but a half baked permanent fix is not responsible. Hopefully they have insurance.