Appropriate protection underneath the shoring

[SKJ25POL]

I appreciate if somebody can help me out with direction on this,
I am involved in a project that the owner temporary wants to remove one leg/column of a mezzanine and I proposed the best is shoring it temporary at the location close to the leg is to be removed temporary.

I was expecting the shoring contractor to take care of the floor slab with providing proper cribbing or mud matt. Which I don't know which is better cribbing or mud mad?

Seems the contractor is not component. Can some body help me out to determine the correct protection of the concrete floor slab?

Some information are as following
1- The load that shoring is supposed to handle is 6000 lbs vertical load.
2- The contractor came up with "This shoring will consist of two post shores and a steel beam pushing against the point in which the two
structural horizontal beams connect to the outer W8x12 beam that is running perpendicular" Please See attached - 2 attachments
3- Floor slab is 12" two way slab #5 @12 Top and bottom

Now mud matt or cribbing? what size? how many layers of cribbing if we go by cribbing?

Thank you for your great help.

 

[CANPRO]

Your slab is fairly hefty compared to the post load, I'd be surprised if you need anything beyond just a nominal base sill. You could check the slab for the applied point load(s) and see if the slab can handle it. I would build up cribbing before I poured a mud slab.

If temporary shoring is the contractors responsibility then he should hire an engineer to evaluate the slab and shoring arrangement. If you are responsible, you need to find some good references for slab on grade design. There is a lot good info for these types of checks on this site, use google and you'll find what you need.

 

[SKJ25POL]

I couldn't find a forum listing the checks for the case like this 6000 lbs on the slab on grade.
If there is handbook or website or forum that outlines the checks, I appreciate sharing with me.
The slab on grade is two-way slab 12" thick #5 top and bottom @ 12 and concrete is 4000 psi.
Dont know about the soil beneath.

Thank you

 

[SKJ25POL]

Can somebody tell me what are the steps to check the slab for the stationary point load of 6 kips?
I have to submit calcs as client requested

Thank you

 

[CANPRO]

This would be a valuable reference to have:

https://www.amazon.ca/Designing-Floor-Slabs-Grade-Step/dp/0924659750

 

[jayrod12]

You said 2 way slab, then you're talking about slab on grade. Which is it, a suspended slab, or slab-on-grade. There's a large difference in the check's you need to do.

 

[SKJ25POL]

jayrod12 (Structural),
Thank you for your point. I called it slab on grade since compare to elevated floor slabs is on the ground but the drawing shows with symbol of a two way slab (to perpendicular arrows) for the reinforcement.

Can't slabs on grade be a two way slabs? Maybe right term is mat fnd.?
Will the method of check be different than a slab on grade?

Thank you

 

[atrizzy]

SK, forget about 2 way or 1 way. Is your slab supported by the ground or by walls/columns/beams?

 

[SKJ25POL]

atrizzy (Structural),
Thank you for your response. The slab is the ground level sitting on soil. I would say supported by ground.

 

[jayrod12]

Ok that is ground-supported (slab-on-grade)

At 12" thick I cannot see even the remotest problem putting a prop right down on it. But you could double check and submit calculations for a point load on a slab-on-ground. There are a few publications on this and the appropriate one would likely depend on your local code to an extent.

 

[Agent666]

Many dedicated foundations for that level of load would be of lesser thickness than you have. So I can't really see any issues given temporary nature of the propping.

For a simplified check assume load spreads 45 degrees though the slab, check bearing on virtual footing of this size using provided reinforcement.

 

[SKJ25POL]

Thank you jayrod12 (Structural), thank you Agent666 (Structural.