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Sat Apr 06, 2019 8:31 am

Garage built some time mid last century. Its an elevated concrete slab in a two story building, held up by railroad steel on concrete blocks with lally columns in the center. Structural engineer says the slab looks in good shape and structure is solid, but won't recommend parking on it, because he can't possibly know if it was made with rebar reinforcement, etc. without more extensive investigation.

Anyone familiar with construction standards of the mid twentieth century? Can the block be X-rayed, ultrasounded, etc. to determine the presence of proper reinforcement?

Sat Apr 06, 2019 8:33 am

Most utility locators have ground penetrating radar (GPR) that will pick up steel in a slab.

Sat Apr 06, 2019 9:01 am

I'd like to see pics of that.

Also, post your question at the forum at GarageJournal.com and you'll get dozens of responses.
https://www.garagejournal.com/

Sat Apr 06, 2019 9:37 am

just an idea...

would sweeping the floor with a metal detector will give you some clue of the presence of the rebars?

Sat Apr 06, 2019 11:29 am

In my part of the world, (Greater Vancouver), the building permit process, even back to the early 1970's (and maybe earlier) required lodging of blueprints with the building inspector's office. For my previous house, I got the 1970 blueprints (shrunken photocopies, but readable) from city hall to allow me to renovate.

Having said that, there were numerous instances on that house in which the builder departed significantly from the blueprints. YMMV.

Sat Apr 06, 2019 1:17 pm

Getting an engineer to certify 50 year old concrete is going to be tough

The creep aging process was actually only identified about 10 years ago at MIT using some our stuff

Sat Apr 06, 2019 3:39 pm

I would think that a common metal detector would identify sreel in your concrete.

And I agree...... photos! We need photis!

Dave

Sat Apr 06, 2019 3:41 pm

Any answer to this poses a serious liability.

Did you look around the edges for signs of steel? Not that that would make it ok to pile 5k lbs on there.

Sat Apr 06, 2019 4:04 pm

I can tell you how to do this all cowboy for cheap but all the other engineers out there trying to make a living will be mad at me.

Your worries will be gone, wallet still heavy, sleep well at night, but you won’t have any paperwork (if what you need is an engineer stamp).

A few photos will help to ensure my method is sound.

Sat Apr 06, 2019 4:22 pm

Really?
How strong is railroad rail?

It has been bent around curves, confirms to the ups and downs of the railroad bed.

It has been hardened, but can it support a lot of weight on a free span?

Railroad ties are what? A foot, maybe sixteen inches apart?

Dave

Sat Apr 06, 2019 5:57 pm

djkeev wrote: Railroad ties are what? A foot, maybe sixteen inches apart?

A railroad car weighs what? Sixty, maybe 75 Vanagons?
A locomotive weighs what? Eighty, maybe 100 Vanagons? :wink:

Haiku:

You know steel is real
Rail section is an I-beam
steel is frickin’ strong

But you’re right it does depend how much is there and how its used.

Sat Apr 06, 2019 7:20 pm

Thanks for the response. Pics will be incoming, once I get back out there. Garage is in need of a general rehab, so they won't be pretty. :oops:

Sat Apr 06, 2019 7:30 pm

Our 1936 house has two steel I-beams spanning the foundation in the basement. I suspect the OP may just have regular I-beams, rather than RR hardware. Can't say as I've ever seen an elevated concrete garage floor. It's seems hard to imagine someone building such a structure without including rebar in the pour.

Sat Apr 06, 2019 8:49 pm

Zeitgeist 13 wrote: Our 1936 house has two steel I-beams spanning the foundation in the basement. I suspect the OP may just have regular I-beams, rather than RR hardware. Can't say as I've ever seen an elevated concrete garage floor. It's seems hard to imagine someone building such a structure without including rebar in the pour.

And with no rebar in the pour it would NOT be standing 50 years later, even if it was a slab on the ground it would be pretty cracked up at 50 years old with no bar.

You know what they say, some concrete cracks, and so will the rest of it :wink:

Sun Apr 07, 2019 6:57 am

Agreed that it likely has some level of reinforcing to be able to be still there 50 years later. Concrete does not hold up well suspended without something to keep it together. It is really good in compression but lousy in tension. As a slab sags the bottom portion will be in tension and that is where it will start to crack, propagate to the top, and then parts fall off.

The problem will be to do some minimally destructive testing in an area to see what is there. If you work with a decent structural guy, likely an old timer who's seen a lot, they could help with what area to pick away at until you expose the reinforcing. Then you have to assume that the whole slab is that way. Then you have to get a Professional Engineer (PE) willing to stake his license on that assumption. (This assumes that your local gov't requires a PE seal)

It will be very difficult and likely expensive to get that old slab sealed as meeting some standard by a PE.

Good luck and let me know how it goes.

(It may be cheaper to look at pouring a new slab on top of the old one and add whatever supports are needed in the basement to support it.)

Dave O (PE in real life)

Sun Apr 07, 2019 7:10 am

X2 with Dave. I'd whack some holes here and there and pour a pad down underneath and then some support. Another advantage of at least one hole is with a light and mirror you can see if the underside looks OK and get an idea of reinforcing as well as how thick she be.

Sun Apr 07, 2019 7:35 am

There are non-destructive tools that can be used to view the rebar in the slab.
Poking holes in it is not the approach I would take. Vanagon forum on the Samba also isn't the place I would expect to find the best answers about suspended slabs and how best to determine their structural soundness.

Sun Apr 07, 2019 7:57 am

Agree with the above. As stated in post #2 GPR is common and is routinely used in this application. The machine is kinda like a lawn mower in size. To have a locator do this might cost $300 or so.

Sun Apr 07, 2019 9:20 am

Might be worth getting a Walabot. According to this video, it will see steel pipe in concrete so I suppose it would see rebar.
https://www.youtube.com/watch?v=iS1BrBnaIfU

Sun Apr 07, 2019 9:28 am

What was this garage used for over the last 70 years? What shape is the crete in? Common sense can tell you a lot. I would have no issues using a garage for what its intended for regardless of what an engineer will or will not certify. A SE is all about liability. Will this garage calc with current building codes, most likely not. Has it had housed a Cadillac since 1950 and is still level and intact?

Another useless tidbit of information.. I have seen light gauge rail used as reinforcing steel in concrete lintels in San Francisco buildings. I love forensic contracting.

J