HSS Connections (Black Book Specifications Chapter K)

[SteBer]

The specification differentiates the various geometries of HSS truss connections into "T", "Y", "Cross", "Gapped K", and "Overlapped K" connections.

See page 16.1-133: Section K2 3c (4) specifies that the "gap" in the Gapped K connection must be greater than or equal to the sum of the branch wall thicknesses.

I get that - once you apply the fillet welds, the connections will likely be touching with less than the gap specified.

See page 16.1-134: Section K2 3d provides capacities for Overlapped K connections, but has a minimum Ov of 25% (see page 16.1-366 for a good illustration of Ov).

All my connections fall between Gapped K and Overlapped K connections. My geometries do not meet the criteria for any case. Anyone else experience this? Thoughts?

Thanks,

SB

 

[nutte]

If I had a gap that was less than the minimum, but still greater than zero (meaning there is no overlap), it would depend on if the weld on the face at the gap could be made or not. If the gap was enough for the welds to be made, perhaps you can use the same capacity. If the welds can't be made, you could modify the equations and neglect the contribution of these welds (and their corresponding HSS walls).

The case with overlap greater than zero but less than 25% is tougher. The equations are not intuitive, so I'd have to dig deeper into how the equations were developed, with the hopes of finding something that addresses this condition.

Can you change the members and/or geometry to make the connection fit into the specification examples? If you can, that's what I'd do. If you can't (like you're the connection engineer, and these are the EOR's trusses), I'd point it back to the EOR. These connections can't be designed separately from the members, so if the geometry doesn't fit into these cases, how did he design the members in the first place?

 

[BAretired]

If the overlap is less than 25%, you could modify the connection by adding a plate normal to the chord, trimming the diagonals to fit the plate and welding them to it.

BA

 

[connectegr]

More information and details are available in Design Guide 24.

http://www.FerrellEngineering.com