Beam Splice Connection 1

[iv63]

The contractor has already installed top flange splice plate and web plate but he is asking to weld bottom splice plate because drilling those holes is a little difficult. I did not want to mix bolting and welding in connection so I recommended welding all splice plates and removing already installed bolts and sealing bolt holes with with 1” dia round bar about 1/2” long (see attached sketch). However the contractor is asking if he can leave top and web plates bolted and weld just bottom splice plate. Or weld all plates but leave bolts in place without sealing holes.
I appreciate your comments.
iv

 

[BridgeSmith]

A similar situation is currently under discussion in another thread Here. You may find applicable information there.

I think the consensus there was that it would not be good to have the tension flange welded with bolts elsewhere, and even for a welded compression flange, the bolted connections need to fully tensioned and adequate to prevent slip at the design loading.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[JLNJ]

I take the AISC requirement about not mixing bolts and welds to mean that they shouldn't be used to share force on the same line into or out of a member. I don't think this precludes bolts on the tension side and welds on the compression side or, for example, welding the tension splice plate to one side and bolting the tension splice plate to the other side. SC bolts for sure and I would avoid a 7/16 weld at all costs.

 

[iv63]

Thank you bridgesmith and jlnj for your valuable comments. This is 7ft cantilevered beam with about 70ft-kip unfactored (ASD) bending moment so top flange is in tension and bottom in compression. I have also interpreted AISC that mixing bolts and welds in connections is not recommended but after reading all these threads I have “changed” my mind. Bolts are bearing type and not SC. Does this matter?
Regards,
iv

 

[dhengr]

Iv63:
Yes, it matters that the bolts are SC or bearing, and then mixed with welding. The whole idea of mixing bolts and welds in a connection (as a bad idea) is that the welds are very rigid and inflexible, while in the bearing connection, the bolts and pieces must move a bit before the bolts actually start picking up their respective loads. Until this small movement, bolt bearing, bending and minor yielding, and the bearing yielding of the plates and bolt holes has taken place, the bolts are not carrying their (any) loads. The welds and top pl. are carrying all of the load, and you have not designed for that. The welds and pl. will have to yield and strain enough for the bolts to move enough, or the bolts will not pick up their share of the loads. Our normal design approach assumes that some bolts will come into play before others, hole tolerances and all, and more yielding will take place at these to make all share the load. In the SC bolted joint, the connected pieces do not need the joint movement (we assume none for SC) for the loads to start to be transmitted immediately along the whole joint, so this is acting much more in unison with the welded part of the connection. Now, consider essentially the same problem, but rather than your welded top splice pl., make that weld a CJP weld of the top flgs., and consider how this reacts, yields, stretches, rotates, carries all the load, can it do this without failing.

In your case, you have to make an engineering judgement about the strength of the top splice pl. Right at the splice line, it will have to shear (move vertically) to allow the web splice pl. and its bolts to start acting. It will have to bend, stretch and rotate to allow the compression splice pl. and its bolts to come into play; at the very least the space in the comp. joint will have to close so the bot. flgs. are bearing on each other, end to end. Is that top pl. strong enough for this to happen, with the top pl. taking most of the joint loads until this movement does happen?

 

[BridgeSmith]

I agree with dhengr. If you're going to have welds and bolts in the same connection, the plates cannot be allowed to slip at the bolted connections. Some of the bolts and the welded connection will experience unintended and unpredictable loads.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[iv63]

Dhengr, I understand that mixing bolts and welds on the same splice plate is not allowed/ recommended but I agree with jlnj that bolts on tension flange and welds on compression flange should be acceptable.
BTW The contractor has already welded all splice plates, removed all bolts, and sealed bolt holes with 1” dia round bars as I asked for.
Regards,
iv