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Gauche1968
Samba Member
Joined: April 13, 2006
Posts: 1518
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 Posted: Sat Apr 06, 2019 8:31 am Post subject: Elevated Concrete Slab Garage? |
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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?
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Igeo
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Joined: September 25, 2018
Posts: 888
Location: Oakland, CA
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| Posted: Sat Apr 06, 2019 8:33 am Post subject: Re: Elevated Concrete Slab Garage? |
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Most utility locators have ground penetrating radar (GPR) that will pick up steel in a slab.
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jimf909 
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Joined: April 03, 2014
Posts: 7482
Location: WA/ID
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| Posted: Sat Apr 06, 2019 9:01 am Post subject: Re: Elevated Concrete Slab Garage? |
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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/
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0to60in6min
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Joined: November 27, 2006
Posts: 3417
Location: OR & CA (Oregon/California)
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| Posted: Sat Apr 06, 2019 9:37 am Post subject: Re: Elevated Concrete Slab Garage? |
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just an idea...
would sweeping the floor with a metal detector will give you some clue of the presence of the rebars? |
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Howesight
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Location: Vancouver, B.C.
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| Posted: Sat Apr 06, 2019 11:29 am Post subject: Re: Elevated Concrete Slab Garage? |
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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.
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Abscate
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| Posted: Sat Apr 06, 2019 1:17 pm Post subject: Re: Elevated Concrete Slab Garage? |
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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
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djkeev
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AZ Landshaper
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| Posted: Sat Apr 06, 2019 3:41 pm Post subject: Re: Elevated Concrete Slab Garage? |
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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.
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Sodo
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Joined: July 06, 2007
Posts: 9623
Location: Western WA
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| Posted: Sat Apr 06, 2019 4:04 pm Post subject: Re: Elevated Concrete Slab Garage? |
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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.
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Last edited by Sodo on Sat Apr 06, 2019 5:52 pm; edited 2 times in total |
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djkeev
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Sodo
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Location: Western WA
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| Posted: Sat Apr 06, 2019 5:57 pm Post subject: Re: Elevated Concrete Slab Garage? |
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| 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? 
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.
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Last edited by Sodo on Sat Apr 06, 2019 7:33 pm; edited 1 time in total |
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Gauche1968
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Joined: April 13, 2006
Posts: 1518
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| Posted: Sat Apr 06, 2019 7:20 pm Post subject: Re: Elevated Concrete Slab Garage? |
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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. 
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Zeitgeist 13
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| Posted: Sat Apr 06, 2019 7:30 pm Post subject: Re: Elevated Concrete Slab Garage? |
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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.
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jackbombay
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Joined: October 19, 2007
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Location: Eastern Idaho
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| Posted: Sat Apr 06, 2019 8:49 pm Post subject: Re: Elevated Concrete Slab Garage? |
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| 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
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dobryan
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| Posted: Sun Apr 07, 2019 6:57 am Post subject: Re: Elevated Concrete Slab Garage? |
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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)
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DuncanS
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Location: New Hampshire
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| Posted: Sun Apr 07, 2019 7:10 am Post subject: Re: Elevated Concrete Slab Garage? |
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| 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. |
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?Waldo?
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| Posted: Sun Apr 07, 2019 7:35 am Post subject: Re: Elevated Concrete Slab Garage? |
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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. |
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Igeo
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Joined: September 25, 2018
Posts: 888
Location: Oakland, CA
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| Posted: Sun Apr 07, 2019 7:57 am Post subject: Re: Elevated Concrete Slab Garage? |
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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.
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Gizmoman
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Posts: 1554
Location: Nevada
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| Posted: Sun Apr 07, 2019 9:20 am Post subject: Re: Elevated Concrete Slab Garage? |
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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
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jberger
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Posts: 2476
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| Posted: Sun Apr 07, 2019 9:28 am Post subject: Re: Elevated Concrete Slab Garage? |
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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.
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