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Cutting Existing Beam In Place

Cutting Existing Beam In Place

(OP)
I have an existing crane runway beam (W18x86) resting on a column via bolted connection through the bottom flange. The existing column has a plate welded to the top, on which the beam rests. The beam currently covers the entire plate, extending past the columns center line.

The building is having an additional built and the crane runway beam needs to be extended with it. My question is, how can I cut the beam in place, so that it is 1/4" shy of the column center line so there is a 1/2" joint between the existing beam and the new beam? I was thinking possibly plasma cutting to within 4" of the final dimension and using a bandsaw for the final cut. Would 4" be an acceptable distance to help shield the final cut section from the heat generated during plasma cutting?

Any suggestions would be much appreciated.

RE: Cutting Existing Beam In Place

Why do you need to construct it as described? Why can't you just shear splice the web of the existing beam with the new beam as is?

RE: Cutting Existing Beam In Place

I wouldn't want a shear splice as structSU10 suggested. Why do it in two steps, when you have the ability to sawcut the beam? If the piece to be cut off is just on the cap plate, not much of a problem. If it cantilevers, then you will have to shore it.

RE: Cutting Existing Beam In Place

What about stability? That would be my main concern, and two discontinuous beam on a column would need some stiffeners and some tie plate or something I would think, especially being a crane beam. I guess shear splice may not be fantastic, but modification to that idea may be more economical since it may reduce field work. And would the new beam just be welded to the cap plate? How would it be modified for the new condition? I guess it all depends on how much cap plate there is, how big the beams are, and the amount of room there is to do the work.

RE: Cutting Existing Beam In Place

structSU10,
Continuous beams are only used for light cranes, and a W18X86 indicates that this is not a light crane. Shear splices are not used, as they also develop moment and result in tearing of the webs. The beam would be bolted to the cap plate, and both beams would be braced to the building column for stability.

RE: Cutting Existing Beam In Place

What class of crane is running on these crane girders? Fatigue may be a consideration. Heating part of the section may introduce residual stresses. If they cut it I would make sure the cut surface was ground smooth afterward to eliminate places where stress concentrations could occur.

If the crane runway beams are simple span you could just replace the beam. I know it's a little more expensive, but it eliminates the fatigue concern. I don't see how they could cut the beam without pulling it out anyway.

You definitely do not want to use a shear splice on a crane girder. The two beams on either side of the splice would rotate opposite to each other as the crane passed over them, causing the shear plate or beam webs to tear. The new beam will need to bear on the column cap plate.

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