extended shear tabs 1

Louis Hub · May 12, 2022

Good afternoon,

I have a project where my connection engineer has specified extended shear tabs. He has used 3/4" thick shear tabs with 1/2" stiffener plates on the top side and the bottom side of the tab. The tab is connecting to the wideflange column web. The AISC manual says that the weld size should be 5/8 x thickness of plate which would be close to a 1/2" weld for a 3/4" shear tab. However, my connection engineering is making the case that the limit state is buckling of the shear tab and the weld therefor doesn't need to be sized to meet the full strength of the plate.

My connection engineer says that the weld from shear tab to the column web will only have shear applied to it. Does this sound reasonable or should we be following the 5/8 x thickness of plate rule that AISC recommends?

structSU10 · May 12, 2022

As I understand that provision it is to ensure the plate yields prior to weld fracture to allow for proper redistribution of the load so only a shear is delivered at the plate to support interface. The 3/4" shear tab also may be too thick to meet the ductility requirements (tmax = 6*M/Fy*d^2) depending on the bolt arrangement.

DrZoidberWoop · May 12, 2022

The connection engineer's logic is reasonable, but I'd make them develop the shear plate anyway. You're going from perhaps 1 weld pass to handle the actual loads (presumably 5/16" fillets) to 3 weld passes (1/2" fillets) to develop the plate. It's not the end of the world, unless you're doing hundreds of these connections.

The workflow for our calc sheets goes 1) complete analysis to size shear tab. Welds typically selected to develop shear tab. Redo if required weld for loads exceeds that required to develop plate. 2) check support limit states (column web yield line is probably your culprit here), 3) add stiffeners if the axial force needs to be diverted to the flanges because the web is too flimsy. Conservatively, we don't loop back and resize the shear tab welds for shear only.

KootK · May 12, 2022

I'm with the steel fabricator on the welds when the stiffeners are included. In my mind, the 5/8 business is predominantly about developing the flexural strength of the tab when the amount of moment that tab will see at the support is high or difficult to ascertain. With the stiffeners in play, any moment or axial load on the tab will be drawn to the welds shown in blue below. Thus, they don't need to be considered at the weld between the shear tab and the column.

Here's a good, recent article on this connection that includes the blurb shown below: Link

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extended shear tabs 1

Louis Hub

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