Determining if an Existing Concrete Foundation Wall is Reinforced

[woodman1967]

Hello All,

I am working on a project that is a little unusual. It is a small commercial/residential building (30'x70') that will go onto an existing foundation (10" thick concrete walls, 8' high). The foundation was poured a few years ago by another contractor then the project was abandoned. I am working with the new owner and have been tasked to determine if the original foundation is reinforced and if so, to what extent.

There are no original structural drawings or specs. A local engineering firm (A father and son firm) was tasked with reviewing the foundation. The son reviewed the foundation (visual only) and he concluded that the foundation was unreinforced and stated so in his report. The father later said to the contractor that there was no way that the foundation wasn't reinforced (no engineering report here, just a conversation).

Thing is, according to the report we can not use the foundation for the purpose our client wants to.

So, I was wondering if there are tests or scans that can be used to determine whether a foundation wall is reinforced or not? Just would like a bit of background before we go to another engineering firm with this question.

Thanks

 

[phamENG]

woodman - your local testing agency will probably have a GPR (ground penetrating radar) unit for this purpose. It's done frequently to locate strands in prestressed slabs that need to be cored. They can scan the wall and determine if rebar is present, and at what spacing. Size may be a little tough. Once you establish that it is there, you can core through it in a low stress region and measure the bars the core saw cuts through.

I did this for an 80 year old half buried tank I had to analyze for a contractor that wanted to drive equipment around on (really big tank).

 

[JAE]

A testing lab could possibly scan it - depends on what equipment they have.
Or you could carefully chip into the wall to "find" the rebar if it is there - might be a challenge since it is 10" thick and could be rebar centered in the wall (deep chipping).

 

[Teguci]

If the wall is cantilevered, you might want to assure yourself that the bottom bars are properly hooked. It might seem like a silly detail that no one would get wrong, but I remember a job where the drawing clearly called out the main reinforcing bars with 90 degree hooks and, when I was called to the site for a pre-pour review, had the contractor replace the little piece of horizontal bar and long piece of vertical bar stuck into the soil with the proper hooked bars.

Here's a site noting the difference between x-ray and GPR I thought was informative -

https://www.penhall.com/blog/gpr-x-ray-proscons/

Sorry for tagging on, but does anyone have good experience with the different detecting systems out there?

 

[bones206]

You could also try contacting the original foundation contractor. They may still have records/invoices that could clarify whether or not rebar was ordered and if so, how much and what size/shape.

Edit: their records should also show what concrete mix was ordered.

 

[phamENG]

To follow on what bones said, the AHJ or original designer may also have records. You said it was poured a few years ago. Not sure about the requirements up there, but here in the states special inspections likely would have been required for that. At the very least, the building department should have the permit and you may be able to do some sleuthing and find the original designer.

 

[r13]

From the wall height and thickness, I highly suspect it was designed as a structural wall, however the intent was unknown. I guess the upper wall is now exposed to view, why not just hammer out a notch to see if it was reinforced or not, and the reinforcing details, if reinforced. It is a small price to pay, isn't it?

 

[Tomfh]

Scan it, or chip away some concrete and have a look.

 

[msquared48]

Scanning and chipping will work - chipping at a scanned crossing of the steel layers to see the sizes. Grade is another problem that may or may not be discoverable depending on the luck of the chipping location. If there are two layers of steel, you might be able to locate the steel crossing with a small hand held scanner from Ace Hardware. Otherwise, more sophisticated will be needed.

Mike McCann, PE, SE (WA, HI)

 

[Ron]

Ground penetrating radar can be used to determine location of reinforcement. Couple that with magnetic detection methods and you'll get a reasonable idea of the rebar location and size....drill in with a hole saw (coring bit) to verify.