There was a large fire in town a couple of years ago, and it destroyed a grocery store and a couple of other stores with it. They’ve finally started building something in the hole. It’s about 125 feet square and three stories high. First they erected a steel frame–all smallish-looking webs, and only one moment frame about 20 feet wide in the middle of one wall. Then they stuck on steel studs over the entire exterior–not within the opening in the structural steel, but pasted onto the face of it. Now they’re skinning that with plywood.
The steel frame looks much too flimsy to me. This is a seismic 3 zone and there’s just nothing I can see that’s giving the frame any stiffness, except for the one moment frame. The plywood looks good but it doesn’t seem like it’s going to stiffen the frame much.
Does this sound like the way they do it in your town?
Replies
They're probably relying on the concrete decks for lateral bracing, and maybe the elevator and/or stair shafts for shear. The LRFD design spec for steel allows some pretty spindly looking members, and creates some REALLY bouncy floors- but the steel tonnage stays low, which saves $$- which is all most developers care about.
It's doubtful that the plywood is intended to impart any strength to anything, especially if the metal stud framing was hung in a curtainwall fashion as you described. I'm actually suprised they used plywood- most of the commercial buildings here are clad in Densglass, and then covered in that lovely EIFS.
Got any pictures?
Bob
Here are a couple. Shoulda done it a few days earlier when it was easier to see the whole damn spindly thing.
2nd try...
You have snow loads there to be concerned about?
David-
The frame definitely looks light, but given what looks to be a fairly tight column spacing, and the intermediate beams (which cut the effective length of the columns in half), it looks OK. The end bays also appear to have diagonal cross bracing to help with the shear loads.
I'd be curious to find out what type of building this ends up being- those intermediate beams look pretty low.
Bob
To quote Miles Davis, "waz wrong wi' dat?"
Look OK to me. Certainly an engineer was involved. Why don't you find out who it was, and ask him or her.
How familiar are you with the design of steel structures in seismic regions?
i agree with micro, it looks fine to me and i'd be willing to bet it would do fine in a zone 4 seismic situation. those steel stud curtain walls are hell for stout, and will flex but not fail. looks like most modern light commercial construction i have seen in california, and will probably do better in earthquakes than anything else around.