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Re: Fire Damaged Slab on Grade

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Jonathan Smith wrote:

What recommendations do you have for collecting information for a condition
survey of a residential single family dwelling garage slab-on-grade
(presumably a turned down slab at perimeter) that has been subjected to a
fire? I plan to visit the site this weekend. I realize that the extent of
potential damage is a function of the fire duration and burn temperature and
possibly the type of aggregate. 

Expensive petrographic analysis does not appear warranted as a new wood
framed gable roof and light framed walls will be the only structural loads
applied at the perimeter other than vehicle loads within the garage area.
The Client appears reluctant to pay for coring as well. Schmidt hammer
testing should provide some relative idea of compressive strength. What are
your thoughts? 

Jonathan D. Smith, P.E., Owner
Summit Engineering & Inspection
236 Lorraine Drive
Travelers Rest, SC 29690
Phone: (864) 834-3385
Fax: (864) 834-3261

It may be different in South Carolina but here in Southern California a garage slab is rarely constructed with turn down edges. Instead it is considered flatwork and is placed separately from the foundation bearing walls. This allows the slab to also be sloped for drainage to the front of the garage. We would call it flatwork here.

Inasmuch as heat rises, I have rarely found that much damage to a slab on grade, however, unless you are dealing with unusual soil condition like expansive soils then I would probably take a couple of cores and do a shear and compression test to verify the minimum strength. I assume you are not dealing with a post-tensioned slab on grade.

Take a  look at the edges of the slab to verify if it monolithic or dual-pour with the slab itself acting only as flatwork. If damaged, it can be removed and replaced. If you have any expansive soil conditions, I would probably thicken the edge of the slab and dowel it into the perimeter foundation.



Dennis S. Wish, PE
California Professional Engineer
Structural Engineering Consultant


760.564.0884 (office - fax)

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