Suspended Concrete Floor

2 car garage over unfinished basement.

Pic 1:
2 6" steel beams running 21ft
1 screw column in the middle of each beam…neither column is anchored on either end.
ends of beams rest on foundation wall.
is there a problem with the bottom chords of the beams not being continuous???

Pic 2:
Between the top of the beam and the ceiling looked to be a fiberboard material.
It’s only installed directly above the beams…rest of ceiling is concrete.
Possibly acting as a cushion???

Pic 3:
ceiling in corner of basement under garage…no, the pic is not playing with your eyes.
garage floor is bowing in this area.

Garage floor definately flexes and vibrates when you jump on it.

What’s odd is that there was a hump all the way down the garage floor, but it was perpendicular to the beams.

Never ran into a suspended concrete garage floor like this.
Because of this and the factors listed above, I believe a Strucural Engineer is in order.

Any objections?..please share any input.


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By removing the bottom flange of the I-beams, they have greatly reduced their load-bearing capacity.

That and the temporary supports are enough for me to say this needs some serious attention.

That IS one I would HIGHLY recommend an IN GA NEER look at.

Engineering review is warranted.


double yikes

Would it be possible that this slab is constructed with precast cored planks.
That would explain the camber in the middle typical of precast planks with a topping.
Hard to tell from the pictures.
Those temporary post might have been installed because of the bounce and springy action of this system.
Mention of steel beam, but I can’t see them.

Typical bearing for precast plank is 2 & 1/2" secured on the ends with re-bar in the cores and topping.

Marcel :slight_smile: :slight_smile:

Don’t tell me, let me guess…somebody designed and built this thing all by himself, and got a great deal on a couple of pieces of steel, and then decided he wanted to use his trampoline for a garage and added the jacking posts.

How many things can you find right in those pictures?

were precasts around in the late 60’s when this was built?
it all seemed original to me.

the beams are directly above the temporary posts.
painted white like the ceiling.
notice how the bottom flange is only intermittent.

Also, in the garage itself, there was an 18" high plywood “skirting” all the way around the perimiter where the floor meets the wall…drywall above that on walls and ceiling.

Thinking it was due to there obviously being no floor drain.
Snow and rain from cars has no where to go.
Drywall likely soaked it up.

There were some water stains on the floor throughout.

The “skirting” wouldn’t likely be part of the retrofit of the precast panels Marcel was talking about, would it?

Precast panels would have been a rarity in the 60’s, and very unlikely in residential construction.

The bottom flange is not intermittant, it’s gone. What you see is not part of the flange, but plates welded on, perhaps where supports once were considered.

It looks like they cut the I-beam in half, to use it in two locations.

The I-beam and support posts make it clear that this was not designed this way. Not knowing what’s inside the concrete, you should certainly defer this.

Must be the picture quality, that whole thing on my end looks like the edge of a concrete plank, but I will take your word Jeff on this one.

What puzzles me is why would anyone would use a T-beam for support when they cost more than a regular beam then turn around and re-weld some support plates.

Assuming as you said, that a bigger I- beam would have been torched down the middle is not logical due to what happens when torching a piece of steel of that size. The beam would have distorted so much from the heat it would have been unusable.

I agree that a structural Engineer needs to look at this, but considering that this design has been in place since the 60’s, that I was not made aware of, it might only proof that obviously it was able to sustain the load all these years and is far from meeting todays structural standards and this is what I would recommend $5000 later.

I guess the structural engineer could determine as to whether or not these temporary jack post are necessary.

Feel free to make me understand the logic behind this one.

Marcel :slight_smile: :slight_smile:

I based that assumption on the jagged edge of the beam (indicative of a torch cut). I’ve personally cut many I-beams, columns and soldier-piles this way for various reasons on projects, but never to use as a permanent means of support.

It would have made more sense if the flange was on the bottom rather than the top.

My guess is that this was an “after-thought” and possibly installed to eliminate some of the deflection that may have occurred from parking the truck in the garage. But again, this is all speculation on my part.

I have torch many pieces of steel myself, since I started being taught how to weld at 14 years old, but I agree with the highlighted above.

Something in the pictures of the previous post just dose not look right.

Further evaluation would be an understatement on my part at this time.

Thanks for sharing Jeff. Learn something new every day, and been in Construction for over 40 years. ha. ha.

Never to old to learn are we. ???

Marcel :slight_smile: :slight_smile: :wink:

Ain’t that the truth. . .

If the flanges were at the bottom, that would mean that whatever the floor is made of would be supported only on the thin edge of the web. Usually when tees are used as beams, they are used with the flange on top. They are just not used a beams that often…occasionally as lintels.

A beam that depth with no bottom flange spanning 20 feet with a concrete floor above it had best have a couple of posts. Someone took a wild guess at this one and missed the mark.

The flange, if placed at the bottom, would be in tension (as the web is now).

The tension is being placed on (we’ll say) 3/8" of steel (the thickness of the web. Turned over, the tension would be on (we’ll say) 6" of steel (the width of the flange).

The wide flange would offer much greater resistance than the thin web. I don’t have a diagram, but maybe someone else can explain it better.

If you look at the beam, you will notice unused additional flanges for additional columns.

I don’t care how long it’s been there. This is a disaster waiting to happen, so stop jumping on it and don’t walk under it.

I recently built a concrete roof/deck over my kitchen. 14’ x !8’ x 7" @ the thinnest point. 5000concrete. Cantilevered 48" past building. 1" & 3/4" coated rebar @6" o.c. 1" coated rebar @3" o.c. @ cantilever.

Ahhh but the top of the tee would be in compression, and aside from bearing area issues, with the absence of a flange, the top of the inverted tee would be subject to buckling. When you see a concrete double-tee structure, which way are the tees? Tees, when used as beams (which is rare), are used with the flange on top, for a couple of reasons. And if those bottom plates were intended for columns, that would have been one heck of a thicket of columns down there. My guess is still that somebody got a “deal” on some used steel beams, and hoped they would work.

probably got a used beam, then cut it in half. there is no need for that filler piece above the beam but maybe when they formed it, they went right over the top flange and later cut it out - who knows.
those adjustable columns are scary!
a properly designed slab could span that 10 or 12’, but it doesn’t look like an engineer was consulted on this.
the hump might have been installed to shed water. plywood skirt is a good design for a garage, esp if it is kept up off the floor so that water doesn’t wick up into it.

(i would refer to this as an elevated, not suspended, slab, but that doesn’t mean my term is correct.)

defer to structural engineer.

Looks to me like they ripped a big I-beam down the center with a torch, used the two halves in two different parts of the ceiling, then welded some plates on the bottom which were meant to bear on framed walls which never got installed or were removed at some point. Can’t imagine an engineer putting his stamp on this one.

Recommend an SE