Concrete ceiling over basement 3

[JAG-E]

EDIT - I want to reply to the individuals that replied to my original post. How is that done??

I am not sure how to research this floor construction. Single Family Home with basement, built about 1954, by local college professor. No plans, no one knows construction of floor. The walls are cinder block. The exposed basement ceiling is a layer of concrete over cinder block, 21"L, 7.5" tall, 6" thick. The the blocks are on side, with holes horizontal to provide passages for in-floor heating pipes. There is no sign of rebar. There are no beams or joists. According to owner when carpets were replaced the floor is a concrete slab viewed from first floor. The rebar in the photo is just loose in the hole of the cinder block, and may have been forgotten during construction. So other portions of concrete may have rebar. The reason I was asked to look at this, the owners, older couple, intends to remove an old cast iron tub for a shower pan for easy access. The shower company plans to wreck the tub, remove piecemeal, to minimize cosmetic damage around the tub and easier removal. But they are afraid they will weaken this concrete floor. There is one access point where the construction is visible and that is under the subject tub. Can anyone shed light on this type of construction? The only thing I can think of would be to build the walls, create a temporary floor at the same height of the top of the walls, place the cinder blocks on the temporary wall, extending over the top of the basement inner walls, run the piping through the blocks, and then pour the cement. When cement is cured, remove temporary floor. If this method has a name it would provide a start. I am not sure how to up loads more than one photo. Maybe I can comment to my own post and add photos. Thanks Joe.

 

[JAG-E]

Here is a photo showing the ceiling. I have others.

 

[JAG-E]

Another photo different basement room.

 

[lexpatrie]

I'm not sure about the time frame and it's not a nationwide product, but what about Dox Planks?

I always thought these had a diamond shaped void in them, but the article below seems to show a variant that was more like a traditional masonry core.

CONDITION SURVEY OF ASSEMBLED CONCRETE BLOCKS (DOX PLANK), Dolhan, 3rd Residential Building Design & Construction Conference, 2016.

There are other articles, too. I've never had to vouch for these. If you get into that zone, some sort of video exam would be appropriate.

 

[LittleInch]

You can't load more than one attachment, but you can attach a bunch of photos although they loose a bit of definition and it's much more likely to get attention this way.

There does appear to be some rather weedy re-bar - (mesh?) visible in the close up photo.

Kind of hard to figure put what is holding the blocks to the concrete slab?? Any ideas?

Is that rebar under tension? i.e. it's holding all the blocks together?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[XR250]

The reason I was asked to look at this, the owners, older couple, intends to remove an old cast iron tub for a shower pan for easy access. The shower company plans to wreck the tub, remove piecemeal, to minimize cosmetic damage around the tub and easier removal. But they are afraid they will weaken this concrete floor.

It is unlikely you'll ever be able to confirm the capacity of the slab so I would work this from a different angle.
Why do they think they would weaken the concrete slab?

 

[LittleInch]

Actually I just saw that the OP said the rebar you can see is "loose in the hole.

If this is, as it would appear to be, a beam made up of blocks held together by that re-bar, the fact that it is loose is not looking good.

It does all remind me a bit of a domestic version of the Hammersmith flyover in London built in the 1960's using similar techniques. All fine until the tension tendons all started to rust.... The bits you can see are the repair cables they had to install to stop it falling to bits. They seem to like doing things like that in the 1960's...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[lexpatrie]

Ok, what's in the pictures is masonry, not concrete, strictly. Just saying. From what I recall these were a sort of post-tensioned system, anchored at the ends only... not that I'm convinced they are Dox planks, but they are a similar system if nothing else. The exposed rebar sounds pretty consistent as well.

I would imagine the company doing the work is hinky since they've never seen it before. Makes sense to me, it looks like a masonry wall laid on end with rebar thrown in with no obvious connection.

Little inch I gave you a gold star for putting the images in line. Cheers. I'd like it a lot if we started getting the original posters trained that they should be attaching images in line (the photo icon), versus this being the first request in every question in the forum.

 

[LittleInch]

There looks to be some pretty solid framing at the end wall of the middle photo.

You might need something similar all over the basement.

The floor has done 70 years - isn't that good enough?

This might be useful?

https://ascelibrary.org/doi/abs/10.1061/41002(328)48

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[LittleInch]

So Jag-E? Has the ceiling collapsed on top of you?

It's always good to hear back from people.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[JAG-E]

How do I address/reply to specific replies to my original post. I have clicked on many links to see if that was how, and also sent a message to the "contact us" link. Until then thanks to all. The info about Dox Plank a huge help.
Joe

 

[LittleInch]

You just reply in the box using @Littleinch or use the quotes button (little man with a speech bubble above his head).

SO e.g.
@Lexpatrie - thanks for the information.....

@xr250 - Great.....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[JAG-E]

@LittleInch
Like this?

 

[LittleInch]

Yup, that works.

You can do it in separate posts or all one - its up to you.

This site works by just having a single linear thread and not multiple subthreads which make it hard to follow the action.

Back to your original query - The weight of a cast iron bath tub with water must be many time what a shower tray would impose so whilst the whole thing looks very "shaky", it has stood the test of time and if there is no apparent failure marks then it would appear to be sufficiently strong. Somehow. I wouldn't cut any more holes in it though....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bookowski]

Maybe this is a diy/variant of terra cotta flat arch floor systems? Those systems were common in steel framed buildings, maybe a contractor decided that he could do his own version. It would require that there is some type of tie (or other mechanism) to resist thrust. Check out the photos of the terracotta systems in the link below, easy to see how someone would attempt this in cmu.

https://www.structuremag.org/wp-content/uploads/2014/09/C-EngineersNotebook-Stuart-Dec071.pdf

 

[lexpatrie]

I'd be really surprised if this was some sort of improvised system. The loose rebar in an ungrouted cell suggests there's an effective anchorage at the ends of the span. I'm not saying it's "safe" because it's not documented and there's no in-situ load test. But I'd be surprised if this was some sort of improvisation by somebody at random. The flat arch systems work differently, more-or-less compression arch action only and lateral loads on the beams (that somewhat cancel out), this system seems to have tension reinforcement, it's just unbonded except at the ends.

I want to respond....

(This is NOT a literal quote, just so everybody knows).

You mean like that? There's a little speech bubble icon to the right of the ,code/ and gift buttons below signature, but it's a bit clunky. This is my first time using it.

Be prepared to manually type in the name of the person you're quoting and copy/paste whatever you want to quote from them, like I said, it's a bit clunky.

 

[JAG-E]

Now that I know how to reply to replies...thanks
@lexpatrie The Dox Plank puts me on the correct track. Never heard of this type of construction. I am not sure what version of that concept was installed. Not knowing what I was looking at, I did not know what to look for. The owner did mention he had the ceiling plastered for cosmetics. Maybe that is why the rebar grout lines are not apparent. Maybe a powerful magnet can confirm there is rebar. As far as how to use this site, I searched high and low for "How To" FAQ was just FAQ technical questions, not about the site use. So any instruction would help

@XR250 The worry about the floor is due to the very large hammer the contractor uses to demolish the tub to remove in pieces. The contractor has done a number of installs in the area but never saw this type of floor.

@LittleInch it may have been there for 70 years, but I need to put my stamp and signature on the OK or suggest a kinder and gentler way of removing the tub. If they do pound down with a sledge hammer there will be shock loads that floor likely never experienced. The subsequent dead load will be less and live loads likely the same with a shower pan vs tub. But wood joist can likely take that type of impact better than concrete. Will the usual removal method be ok, on an "unusual", never tried on floor construction?

@bookowski In a nut shell you hit on my dilemma. What am I dealing with and is it a proven system or someone's interpretation? Among the various links sent in response to my original post, one addresses clay title used similarly. Even a bigger surprise to me than concrete.

All
That piece of rebar is just as loose as possible. No obvious place is came from. No concrete stuck to it indicating it was grouted at one time. Much longer than the opening, yet, maybe, short enough to remove. The articles say the rebar is grouted into grooves and the pretension claims are over stated. Later designs may have had threaded ended to apply tension to the rebar and compression to the block.

 

[LittleInch]

I think this is a variant on the Dox plank and that re bar is supposed to holding it all together.

For this exercise I would strongly recommend they support the under side with 4 or 5 scaffold boards plus a bunch of acrow props.

Maybe also see if there is any way to look at the end of the floor where it meets the walls to see if the is any plate there to hold the floor together.

Maybe the slab holds it all together?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[XR250]

@XR250 The worry about the floor is due to the very large hammer the contractor uses to demolish the tub to remove in pieces. The contractor has done a number of installs in the area but never saw this type of floor.

Interesting discussion, but this is a lose-lose job. Suggest they use a torch instead (if that would work) or another method if the hammer is a concern.
No way to verify the capacity of something like this. It could fail regardless if they did a remodel or not.
Can't imagine there is enough fee in this job to make it worthwhile.

 

[Eng16080]

If it was me, I wouldn't do anything until you understand how the floor actually works, not how it's supposed to work based on some literature you found. There's the chance it was originally constructed wrong and what you're left with is an unreinforced concrete/masonry floor that somehow hasn't failed yet. Using a "very large hammer" on this floor is almost comically bad. That could be the straw that breaks the camel's back.