Determing Reinforced Concrete

[Maticuno]

After purchasing my home, I have realized that the previous owner liked to do things his way, which may or may not mean they were done properly. I've observed numerous instances of things he built or "fixed" that were done on the cheap. The detached shop building is, as far as I'm aware, unpermitted and shows numerous things that weren't built to code (namely the electrical).

What I'm mostly curious about is the concrete foundation the 20X36 steel shop sits on. In the near future I'd like to add a 2-post lift, but all manufacturers require a minimum of 4" of reinforced concrete. The depth of the concrete is easy enough to test with a small masonry bit. The reinforcement, however, I'm not so sure of how to test. Would a standard hobbyist metal detector let me know if there is WWM or rebar imbedded in the foundation?

 

[Leaflessshadetree]

Metal detector should give an indication if there is steel. A good one (or a magnetic stud finder) may allow you to determine spacing.
If you get lucky you might see some indication along the edge of the slab. Maybe the end of a piece of bar.

 

[Beemer533]

I use the Milwaukee sub scanner for stuff like this, but it isn't exactly cheap...

http://www.milwaukeetool.com/instruments/inspection-and-detection/2291-20

honestly, if it were me and I was that suspect about all the other work, i would probably just rent a concrete saw, cut out the area and pour a new footer... There are a couple threads around here from folks who have done this previously.

 

[Cyberbear]

I, too, have found that often construction was performed in areas that are not up to present code, but were done before an area was codified and so is "grand fathered" in.
You may wish to check to see if your slab has any footings at all, as in my area it is not uncommon to discover they were never incorporated into the original.
I suggest after determining the thickness of the original slab you decide what must be done. If it comes to replacing the old with new, you use good concrete w/ lots of steel (not wire mesh) and add footings or piers where needed. Doweling where you can is also a good idea. I live on a mountain of DG and solid rock and movement is a real concern, especially with heavy loads high in the air. If lucky, you may only need to install large piers for your lift.

 

[David C]

I have seen contractors use stud finders to determine the location of concrete reinforcing. This test will not tell you the size of the reinforcing or reinforcing steel strength(40ksi or 60ksi it is unlikely that this fellow used higher strength reinforcing).

None of these tests will tell you the concrete strength.

I suggest that you do what was recommended above. Saw cut and re-pour a pad footing for your new lift. Use 12" min thickness and a large sized pad, in plan.

A few years ago I did a design for new pads for a number of lifts at a high school shop. I got the calculations for the pad and reinforcing from the mfg and there were several mistakes. Additionally the mfg's engineer did not consider earthquake forces imposed on the footing from an elevated automobile.

Current codes and mfg's testing for concrete anchor bolts do not even provide design strength values for post installed anchor bolts in 4" concrete. I do not what basis the lift mfgs use to make their recommendations.

I see you are in CA and while you are not likely in the areas most susceptible to strong seismic shaking an earthquake is still a possibility. I guess you can plan on not being under your car when there is an earthquake.

 

[wssix99]

but all manufacturers require a minimum of 4" of reinforced concrete.

Where did you get this information? The only time, I've seen reinforcement called for is in retrofit applications where you have to cut out part of the slab and re-pour.

You don't need reinforcement for a slab-on-grade. Reinforcement in those types of slabs (in residential and light commercial situations) is for shrinkage crack control only. If your current slab doesn't have any cracks, then you are good in that department.

The one thing you need is depth. Depth (and a quality, compacted base) gives you strength in a slab-on-grade and also gives you enough depth for the anchor bolts to hold in to.

For a lift, you'll want to confirm the thickness of your slab and then what is underneath. If you don't have what you need, then you'll have to (at a minimum) cut out the slab and re-pour a proper pad that is either keyed or pinned in to the original slab.

 

[VictorBravo]

Where did you get this information? The only time, I've seen reinforcement called for is in retrofit applications where you have to cut out part of the slab and re-pour.

You don't need reinforcement for a slab-on-grade. Reinforcement in those types of slabs (in residential and light commercial situations) is for shrinkage crack control only. If your current slab doesn't have any cracks, then you are good in that department.

The one thing you need is depth. Depth (and a quality, compacted base) gives you strength in a slab-on-grade and also gives you enough depth for the anchor bolts to hold in to.

For a lift, you'll want to confirm the thickness of your slab and then what is underneath. If you don't have what you need, then you'll have to (at a minimum) cut out the slab and re-pour a proper pad that is either keyed or pinned in to the original slab.

Challenger's manual calls for reinforced concrete:

"Minimum requirements for concrete are 4 inches minimum depth, with steel reinforcement, 3500 psi, cured for 28 days per local commercial practice." (page 3 of the pdf below).

http://www.bestbuyautoequipment.com/v/vspfiles/Challenger/InstructionManuals/e10-manual.pdf

But Bendpak doesn't seem to require it. (specs on page 7 of the pdf below):

http://www.bestbuyautoequipment.com/v/vspfiles/BendPak/InstructionManuals/XPR-7A-10-10A-168-Manual.pdf

 

[Maticuno]

It's possible that pouring of the slab was the only thing done right since it's not something he could have done himself. It definitely has footings, probably 12" or more. I'll post a picture of the most exposed edge once I get home. You can also see the impressions on the floor from where plastic was laid over the concrete while it was curing to help retain moisture content. Not a crack to be found anywhere. Best I can figure was that the shop was built between 2008 and 2012 based on historic Google Earth images and the history of a refinance somewhere around 2008.

 

[Maticuno]

Don't know if this will help, but here is a picture of the most exposed portion of the foundation due to the soil grade. Don't mind the shorter pad to the left, I just poured that as the start of my compressor shed.

 

[wssix99]

Challenger's manual calls for reinforced concrete:

"Minimum requirements for concrete are 4 inches minimum depth, with steel reinforcement, 3500 psi, cured for 28 days per local commercial practice." (page 3 of the pdf below).

Wire mesh would meet this "reinforcement" requirement. They are not talking specifically talking about rebar.

 

[chops101]

I found the wire mesh layout in my garage with a studfinder, prior to my lift install.
Marked the wire locations in chalk and adjusted my column footprint accordingly to miss the wire when drilling.

Oh yeah, I also found the property pins on the backside of my lot, buried 5" below grade, with the same studfinder.

 

[gnpenning]

Looks like you have a quonset hut style building. Most people do not form the footings themselves for these as the need a channel or key for the steel. (Not hard to make yourself). Hopefully he had someone else do all the concrete work.

Is the floor inside the same level as the top of the footer or does it step down?

What is your base soil?

Can you ask the PO? Would you believe him?

 

[Maticuno]

Floor level is the same height as the top of the outside footer. It appears that the concrete was poured in two phases as the lower half seems to be a slightly different color/texture as the upper part that makes the actual floor and the steel "key". This upper part is about 5". Base soil is a gravelly loam that is concrete hard when dry but easily worked when wet.

Never met the PO, and from what I understand from the real estate agent is they moved to Idaho and didn't leave any contact information for me.

I suppose I could give my stud finder a try, but it's a cheapo Stanley that I've never found to be accurate.

 

[wssix99]

I suppose I could give my stud finder a try, but it's a cheapo Stanley that I've never found to be accurate.

At this point, you have what you have. The reinforcing is only there to control shrinkage cracking. (In the majority of applications, there won't be enough steel in there in order to really make it "stronger.") If you have several seasons on the slab and no cracking, then you are good-to-go. If there is steel in there, it's doing its job. If there is no steel there and you don't have any cracks - you don't need it, anyway.

If its still worrisome, then you can always get a BendPak or other lift that doesn't even mention "reinforcement."