HSS Seismic Connections
HSS Seismic Connections
(OP)
We've got a project that is a small roof (open building) - six columns holding up a perimeter beam that supports light gage steel trusses. No walls at all. Way out in western US with high seismic.
The AISC Seismic provisions for Ordinary Moment Frames do not allow fillet welds for tensile forces and don't seem to deal with HSS shapes at all....only WF shapes.
The governing code is IBC 2000 which references the AISC Seismic provisions with Suppl. No. 1. FEMA 350 doesn't deal with HSS either it seems.
We want to use HSS simply because this is an exterior condition and want to minimize irregular surfaces and avoid bird nests.
So is there a prescribed or pre-qualified tube column to tube beam moment connection that can be used? Or do we have to use WF's?
The AISC Seismic provisions for Ordinary Moment Frames do not allow fillet welds for tensile forces and don't seem to deal with HSS shapes at all....only WF shapes.
The governing code is IBC 2000 which references the AISC Seismic provisions with Suppl. No. 1. FEMA 350 doesn't deal with HSS either it seems.
We want to use HSS simply because this is an exterior condition and want to minimize irregular surfaces and avoid bird nests.
So is there a prescribed or pre-qualified tube column to tube beam moment connection that can be used? Or do we have to use WF's?






RE: HSS Seismic Connections
I do not know of ANY source as of yet that allows the use of HSS moment connections. Personally, I think it should be allowed as long as the connection can take the stresses and be within drift limits and that appropriate testing has been performed.
This is a link to a discussion for whatever its worth...
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RE: HSS Seismic Connections
The discussion will make sense if you read UP from the first posting way at the bottom.
RE: HSS Seismic Connections
The narrative you referenced seems to imply that a lower R (=3) might be used and allow skipping the AISC provisions. However, the IBC 2000 only specifically allows that for SDC A, B and C and not for the higher areas.
It seems like I've seen all sorts of tube-type frames in the magazines and such - just can't believe that they dont' use them out west at all.
RE: HSS Seismic Connections
RE: HSS Seismic Connections
Similarly, if you cut a long slot on all 4 faces, centered on the HSS width, fillet welds to an inner fitted HSS would be in shear, not tension.
RE: HSS Seismic Connections
The long slots are a good idea, but doesn't this still beg the question as to whether the connections must be tested?
The cantilever option seems like a possibility as that then makes the beam to column connections NOT part of the lateral seismic resisting system and therefore we can just connect them as we wish as long as we meet deflection compatibility requirements. With this in mind, we would analyze the system as cantilevered columns with pinned beams. Then after designing the columns and footings based on this, we could then fix the beams, deflect the frame by and amount of Δ (derived from the pinned condition) and design the beam to column connection to simply resist the shears and moments that result from this specified frame deflection. Does this make sense?
RE: HSS Seismic Connections
RE: HSS Seismic Connections
Assuming wide flange beams, I would rest the beams on a column cap plate (bolted to the bottom flange of WF beams). This way, you don't even have to consider secondary moment in the beam to column joint...
RE: HSS Seismic Connections
SareBleu - that's a great idea - I really like it. But this project just isn't that big for that application and we're also trying to keep the top flange surface flat throughout to allow simple bearings for the metal roof trusses - just a covering for a fuel delivery pipe system. ...also...you've got one great handle.
RE: HSS Seismic Connections
I've used the cantilever design successfully in the past (interior stand alone mezzanines, for example). The lateral loads are generally light for small structures like that, and you may find that your typical base plate, anchor rods, piers and footings are still OK for the moments.