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re: shear lug

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Myself and other SEs I know use shear lugs all of the time for beam bearing connections in tie columns, tie beams and tilt panels. Gets you past the Appendix D headaches where headed studs used to work, though we use headed studs to resist the tension from eccentricity which causes a moment in the connection.

In a column application such as in a PEMB where you may have high uplift and shear forces at the base, we have used them also like you are suggesting. I think HSS8x8 may be a bit overkill for that force, but you just design the steel portion as a mini cantilever column, which the welds may in some instances be critical. The concrete you design as bearing just like a seated beam connection, which you can usually find design examples in concrete text books if not straight out of ACI. For cheap backup we would detail rebar or hairpins perp. at each side of the shear lug in the potential shear failure plane.

The kicker is that they will have to cast the base plate with the shear lug into the footing, which is unusual, then they would have to field weld the column to the base plate which I don't think with erection scheduling they will like. But perhaps you could do some type of field bolt connection from the BP to the column?

I would also think you could have them form a block-out in the top of the footing slightly larger than your base plate size, maybe 6" deep or so into the top of the footing (or whatever you need per your concrete design), and use the same type of design method for the concrete and thus eliminate the shear lug. Have them place non-shrink, high strength grout around the column after the column is set. Same deal as before, I would detail an extra bar in the potential shear plane.

Just some suggestions, others ideas seem like they would work too. Recessing the base plate may work well in conjuntion with the idea of welding horizontal rebar to the base plate and then just developing the bars into the top of the footing. That will take some coordination and precision on the part of the bar setting, which in a typical foundation has some slop so detail extra carefully if you go that route!

HTH,
Andrew Kester, PE

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