Structural Steel Beam Retrofit

[TomWaggoner]

I have a two span W8x10 in which my client would like to remove the center support. They are trying to keep the costs down for the retrofit and I am planning on using a W12x22 to support the overlaying roof structure. I am planning on leaving the W8x10 in place and putting the W12x22 directly underneath it. Using the W12x22 vs. a WTx and welding it to the underside would save on a lot of welding in the field. It wouldn’t be the end of the world but I am afraid the small beam will all the wood connected to it might have deeper complications with fire and possible warping from all the heat. The question I have is that I have detailed bearing pads on top of the new beam to avoid any underside beam attachments from the adjacent ceiling and drags at either end. The problem I currently see is that as the beams deflect with a different radius of curvature the planned welding of the bearing pads to the underside of the existing beam could possible shear through as I am only placing them at 7’-0”o/c. Whether or not I have them fully unshore the beam above before welding still would present a problem when live load is introduced. At least in my mind. I woke up this morning picturing people in a restaurant eating dinner then a big pop as one of the welds failed. Any thoughts or feelings on my situation? Maybe I’m right maybe I’m wrong. I haven’t submitted yet and if it only meant me changing my detailing a little that would be great. Possible single pad at center for a point load on new beam? Thank you in advance for all that share and add to this thread!

-Tom

 

[ztengguy]

I would use a staggered weld, and monitor the temperature the beam gets to. Might take a few hours of weld a bit, cool, weld a bit, cool. etc. Dont see how you have the beams unshored and remove the post to get the new beam in. perhaps I am missing something.

 

[TomWaggoner]

No,. I was suggesting shoring,. placing new beam,. then unshoring,. then weld,. I was just saying. Not a real solution,. just throwing ideas out there. Also its 23'-0" long,. so yeah its going to be alot of welding.

 

[TDIengineer]

What do the W8x10's connect to? another column beyond? Are you only partially lapping the new W12x22 to the underside of the pair of beams?

What about just running the beam from (e) far column to column and only connecting it there. Then provide a shim at the end of the W8 where the column was removed. A small plan in the area would also help.

This way you're not considerd with VQ/I of the two shapes together, and also you can jack the roof up slightly before inserting the shims to essential pre-load the W12x22.

And now you just have a simple tack weld to hold the shim in place.

 

[TomWaggoner]

The existing column is bearing on CMU walls at either end. I am planning on putting in HSS columns to bear on at the ends.