Existing Mat Slab Strengthening 1

[RM87]

Hello folks,

Does anyone have any suggestions/experience with strengthening an as-built existing mat slab?

I have a larger point load coming down on the edge of a 15" mat slab (#5 @ 16" O.C. E.W. T&B) and it seems to need some strengthening.

Thank you,
R

 

[AUCE98]

Consider extending the foundation if the load is near a corner. Do you have a geotechnical report that is valid? You may have the geotechnical engineer revisit the previous results to see if they would recommend a higher bearing capacity.

 

[KootK]

What's your governing failure mode? Punching shear?

If space permits, perhaps you could drop a pile beside the load and bracket connected to the raft.

There's also this kind of thing: Link

You could demo some of the slab edge and install a beam to better distribute the point load.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[SlideRuleEra]

Use a "bonded concrete overlay". Here is a typical reference for highway pavement, but it works for foundations, too:

http://onlinemanuals.txdot.gov/txdotmanuals/pdm/bonded_and_unbonded_concrete_overlays.htm

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[RM87]

Thanks for the help. Any suggestions on how I can increase the allowable bearing stress in the soil as well? I was thinking of suggesting a cementitious grout product - do you have any recommendations? The soil is expansive, but I think additives like bentonite could address that issue?

 

[RM87]

The existing slab is a 15" thick, 2500 psi mat slab with #5 @ 16" O.C. T&B E.W. (15'X30' pad)
I have a projected 30k point load coming down on the extreme edge of the slab. I ran some preliminary calculations and I'm not convinced that the slab can take the punching shear or the localized soil bearing stress. That's my current issue.

 

[thaidavid40]

Do you have room to install a grillage beam type base under the column to widely distribute the column point load?

Thaidavid

 

[KootK]

I pitched three alternatives for dealing with punching shear above. The options pitched by SRE, thaiDavid, and AUCE98 would improve punching shear as well. And all of those options would serve to improve load spread and potentially reduce local soil bearing stresses. Is none of them suitable?

Geotechnical soil bearing stress numbers are usually about settlement, not true failure in the collapse sense. Might it be possible to exceed the allowable bearing stress and tolerate some extra settlement locally? What is the source of the 30k load and over what area is it applied?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.