Coped beam ends and increasing block shear strength of existing members?

[jbuening]

I have a project that involves an existing structure that the client wants to add more loads to (industrial application). It is essentially a steel support structure with 6 columns (2 per side) a continuous beam atop the three columns, and coped beams connecting the two continuous beams (at each column and midspans for a total of 5). Existing loads are applied directly to the coped beams and transferred to the main beams. These beams are relatively smallish (W12x26 and W10x22). I'm having issues with shear at the coped ends, as they are coped top and bottom and cannot satisfy the block shear failure....assuming I'm doing the block shear check correctly by only accounting for the web thickness and not the double angle clip thicknesses. Is anyone aware of a way to increase block shear capacity short of replacing the beam (which is not possible in this situation)? Its a function of net web area and Fu, so I can't think of any way of increasing the capacity.

Just tossing out ideas, but would welding around the clip angles to the web increase the capacity by making the clip angles integral with the web? Would welding another WF with a top plate to the existing column to act as a "seat" help? There are already residual stresses in the connection so I don't think that would work. I'm trying to think outside the box in order to make this work.

 

[JoshPlumSE]

What code are you using? The reason I ask is because the new CSA code (S16-09) uses a new formula based on recent research. Instead of basing the value on shear yield, they base the block shear strength on the average of yield and rupture strengths of the material. I don't know if this is going to make its way into the next AISC code, but I know its being discussed as a possibility. You might look at the latest AISC draft (if it is available for public review yet).

I only mention this because if your connection is close to working, then you may be able to justify it based on a newer version of the code.

 

[jbuening]

I'm using AISC 9th Ed - ASD. I'm quite a bit over in block shear, thus my question about welding the clip angles to over triple the total thickness. The commentary in the LRFD 3rd Ed mentions checking block shear around the periphery of welded connections, so I'm thinking if the block shear capacity of the clip welded around the perimeter works and is greater than the bolted block shear, then this may be a possible modification to the structure. Thoughts?

 

[a2mfk]

Careful when welding a bolted shear connection. Shear values from AISC tables for bolted shear connections depend on the rotation of the connection and end of the beam to transfer negligible moment into the connection (via elastic and inelastic deformations), and remain "simple shear" connections. Once you weld the angle clips, you are now putting moment into the connection.

I don't have AISC handy, so I don't remember if there are tables or formulas for shear connections that are welded to the beam, and bolted to the supporting member.

I believe you can add a doubler plate to your web, though it may foul your angle connection assuming they are double angles.

If you have to redo the entire connection then I think you could weld a shear tab plate to the web of the beam, then extend it to the girder web and bolt via a standard bolted connection (extended shear tab, but bolts and welds are in reverse of how it is more usually done).