Gusset Plate at HSS Column

[Gumpmaster]

I am refreshing a building design that has both SCBF and OCBF braced frames. The original design (using the 2000 IBC) used Square HSS columns, wide flange beams, and Square HSS braces.

The brace gussets are welded onto the wall of the HSS Columns. The AISC seminar "Seismic Braced Frames Design Concepts and Connections" recommends against this type of connection. The forces on the wall of the HSS column can distort the wall. How can I design the wall thickness of the HSS column or detail the connection to make this acceptable? Would there be any differences in the detailing for the OCBF vs. SCBF connection? Is it acceptable in both types of braced frames, or only OCBF?

 

[csd72]

blodgetts "design of weldments" has a formula for this.

Alternatively just weld a plate across the face to spread the loads.

 

[jike]

You are not going to get much capacity out of the wall thickness of the tube. I suggest you provide a reinforcement plate on the face of the tube.

 

[nutte]

The 13th edition of the AISC Manual of Steel Construction has equations to check for plates welded to HSS walls.

 

[Gumpmaster]

Yeah, the AISC Manual gives capacities (I haven't checked them yet), but I don't really think I'm going to get the required SCBF loads (RyFy). I've considered a plate or a WT or something like that to distribute the load to the HSS web, but the reinforcing member will still be subject to flat plate bending. I'm also not certain if I can develop the post-elastic ductility required.

Does anyone have any direct experience with this type of lateral force resisting system?

Thanks

 

[Grizzman]

Why not run the brace completely into the adjoining horizontal member (beam or footing) and avoid the problem all together.

 

[nutte]

Can you even use HSS columns in a SCBF? I know there are particular requirements for these special seismic framing systems.

 

[hokie66]

Why not slot the gussets through the hollow section? That is typically the way we do it in Australia. The doubler plate across the face as others have suggested works also.

 

[Grizzman]

a slot only doubles the capacity as you now check plastification of two faces instead of just one.
If you're in an situation where you have to use SCBF, it's likely the loads are way to large to be carried through even both flange walls.

 

[JAE]

I think the concept that hokie66 was indicating was that by slotting the column, the gusset connection would be better concentrically welded to the supporting base plate and would not depend upon tube wall bending.

 

[Gumpmaster]

I think attaching the gusset eccentricly to the beam only is problematic (especially in an SCBF) because all of that tension load gets shoved into your beam and you get 600K of concentrated shear load on the beam.

I think I've talked the Architect into using wide flange columns on the SCBF portion of the building.

My lesson learned is to not use HSS columns in braced frames.