Beam Cover Plate Moment Splice Check 3

[bookowski]

See attached. This is from a shop drawing, the detailer's proposed moment splice in a beam. He is doing bolted at the top flange and a welded cover plate at the bottom (due to clearance/height issues). The plate is wider than the beam, I'm guessing that this is to avoid overhead welding. He is not welding the end, only the sides.

When checking this I feel like there should be some kind of double shear lag check to get the force up to the connection plane and then out to the corners. Am I imagining this? Any special checks for this beyond the usual? Something about this rubs me the wrong way. I'd like to weld the end but that would force him to weld overhead or flip the beam once spliced.

 

[KootK]

Thanks for the interesting detail Bookowski. You're good like that.

My feeling is that this will put more stress on the weld, though I don't know exactly how.

I think this is how:

I suppose that you might get some flexure in the lower plate prior to bolt engagement.

That plate moment would imply weld tension forces perpendicular to the beam axis. The effect would be localized near the connection centreline I think.

I once asked a super, super, super senior engineer about bolt slop in a bracing connection. He said that any connection with six or more bolts would effectively have no slip. At least one bolt would be engaged from the start. No science behind that that I'm aware of however. Just an intuitive sense of random variable probability distribution.


I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[hokie66]

Like KootK, I wouldn't get too excited about this connection. Steel is a wonderful material, and adapts to a lot of strange things we do to it.

But I do wonder about why one would splice the beam in that way. Like the bottom picture of SRE's post, the top plate and bolts make installation of the deck messy.

But one for SRE...surely it doesn't take that many bolts to splice a W16x26 flange?

 

[Teguci]

1. Any shear transfer at the splice will allow a vertical shift between beam ends due to bolt slop. This would put an unzipping force on the welds. Not too concerned though. If unzipping starts, it will stop when the lower plate can flex enough to cover the minor amount of vertical shift.
2. If the contractor is set up to field weld, he might as well finish the job. I'd detail a skinny plate on top for a top down weld and do an all weld splice. To me, bolts only make sense when you can prevent field welding or can allow the crane to move to the next pick. This detail works, but doesn't make sense to me.

 

[dhengr]

Did anyone else notice that the WF flange area is (5.81 x .51") = 2.96sq.in. and the flg. splice pl. is (.375 x 6.5") = 2.44sq.in., what’s with that? No full moment cap’y there. From the fabricator’s standpoint, I would use a single web splice pl. and weld it and both flg. pls. to the left beam. This happens on both ends of the left beam if needed. Then punch/drill web and flg. holes in the right hand beam. I would make the flg. splice pls. 6" x .50" x 20.5" long. I would send the left hand beam down my welding fit-up line and the right hand beam down my punch/drilling line. This would save some material handling in the shop and avoid the field welding, all good things from the productivity standpoint.