Cribbing Layers Required to Spread Load Effectively

[AndBre44]

So I have a situation where I'm attempting to shore an existing steel beam taking on about 760lb/ft across a 53ft length, as the client is removing the bearing wall that's currently supporting one end of the beam. The primary issue here is that there is a cellar below the floor this is being done on, and so I'm attempting to use multiple temporary columns with cribbing below to adequately spread out the load, since wood joists rated to 100psf are not going to be able to handle a 22kip load from a single shoring column.

I've already worked out that by using 4 different shoring columns, I can get each point load down to about 10kips and apply some cribbing below it to spread out the load, but I want to see if I can make it as practical as possible in terms of how much wood should be used. I already know that the overall dimensions would need to be 10' x 10' to spread out the load properly (10kips / (10' * 10') = 100psf) and it would be 6"x6" members, but I wasn't sure of how many layers of wood would be required to adequately spread the load across the base layer of wood. While I know the Maximum height-width ratio would be 3-1 per FEMA's cribbing guidelines, is there any minimum height requirement? Perhaps that is based on how the intermediate layers transfer the load to each other? Any insight/advice on the matter would be greatly appreciated.

As an EIT, I'm open to being wrong now if it means being right when it counts.

 

[phamENG]

How deep is the cellar?

You can get into some detailed relative stiffness calcs to figure out just how the load will spread across the floor (look at cribbing as a beam supported on a bunch of springs, where the springs are the wood joists with a spring stiffness equal to the joist's flexural stiffness), but it may be easier to put shoring posts down in the cellar to shore up the floor, and use squash blocks or something similar to prevent crushing the joists between your multilevel shoring.

 

[XR250]

Is 760 plf the current dead load or dead in addition to code mandated live loads?
It sounds easier to bring the load into the cellar rather than mess with huge piles of cribbing.

 

[johnie134]

do a fem model and run it, you're an engineer not a butcher.

 

[dhengr]

AndBre44:
Why not move inboard of the wall to be removed by 4 or 5’, on the 53’ beam. This gives you working room around the wall to be removed and the beam bearing. This beam reaction will be about 20-25kips (.76)(53/2), plus a little for the 5’ cantilever. You figure that out by where you actually put this reaction. Put a support column under the beam, down to the 1st floor, or alternatively, a short beam perpendicular to the main beam, with columns under each end and down to the 1st fl. Pay attention to bracing at these connections. You pick these col. locations so that all you have immediately below the col. base pls. is the 1st fl . sheathing. Then you build cribbing or cols. in the basement to pick these upper cols. up. Jack the 1st fl. up a bit, so you can shim tightly btwn. the sheathing and the top of the cribbing or lower cols. Let the jacks down, and now you know you have a real load path to the found. Of course, you must have some firm handle on what your found. conditions are. Don’t try to support that temp. beam reaction on the 1st fl.