Determining Construction of Existing Slab 3

[engbeer]

What are the options for determining the construction of an existing slab on grade and its adequacy to support a new steel vessel? In particular, how can one best determine the thickness, compressive strength, and presence of reinforcement?

Some background: I am coordinating the installation of a new steel tank (7.5 foot diameter) on an existing slab on grade, which has historically been home to all sorts of vessels with seemingly greater resultant applied stress (e.g., steel vessels on beam supports or much larger poly vessels with flat bottom on slab surface. Instead of moving forward with the installation based solely on the fact that previous equipment has not been a problem, I want to "do it right" and see what the slab is truly (safely) capable of. The site is in San Diego, CA.

Thanks All.

 

[GeoPaveTraffic]

The thickness can be determined by coring through the slab. Resulting core could then be tested for strength. As for reinforcing, a metal detector can be used to find the bars, but addtional cores would be required to determine the size.

There are some non-destructive mehtods to determine slab thickness and strength, but a core would provide much better data.

The core also allows the subgrade conditions, which also effect slab capacity, to be determined.

 

[apsix]

Knowing that the slab has a history of successfully supporting heavier loads would give me more comfort than calculating a theoretical capacity based on estimated subgrade parameters.

 

[civilperson]

"Doing it right" would include a statement, The previous loads were greater than the proposed loading, therefore OK.

 

[engbeer]

Thanks to the tips so far. I also did some further research and see that ground penetrating radar could yield some valuable information.

The only thing that worries me about basing my comfort on the previous loading is that those scenarios only took into account static dead loads. Is this slab adequate for any additional loading (e.g., seismic)?

Currently looking for a structural engineer to speak with...

 

[civilperson]

Why would you say the previous design ignored seismic/wind loads? Do you have copies of the calcs or detailed as-builts to analyze? My analysis of designs made in the 1940-1950 era show sufficient strength using modern LRFD or USD techniques. The proof is in the lasting structure as inspected after loading applied.

 

[msquared48]

What apsix says is true here, but not all jurisdictions will buy this line of reasoning. To some plan reviewers, all that matters is the numbers, not the history.

Mike McCann
MMC Engineering

 

[engbeer]

civilperson - I don't have the as-builts, which is why I want to determine the actual construction. I agree that history can tell us a lot about the statid dead load capacity. But history can't tell me if the design accounted for seismic loads.

Again - I am just trying to develop an understanding of what the theoretical capacity is so that I (and my client) can feel comfortable that this construction is sound.