Damaged PT Slab 1

[msquared48]

Had a reference from an old client email me yesterday asking if I would inspect a PT slab that had settled about 2" (vertical crack from what he said) in a hallway. Don't know the extent or structural location yet.

This has me real concerned for several reasons, but mainly shear. In that the building was constructed around 1989, does anyone know if stud rails were used back then, or were the high shear loads in the vicinity of the columns just handled with drop caps? I am also concerned if any tendons were damaged, but time will tell that I guess. My guts are screaming shear problem, hopefully not due to local settlement.

I have not signed a contract yet nor visited the site, but this could be a doozie as they want a report and a fix too for whatever the problem is. I guess it's a multi-story apartment over one story of PT.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Ron]

Mike..I believe stud rails were available then, but I don't think they were used much. Your gut is probably right.

 

[southard2]

Unless your a PT expert you might just want to pass the customer on to a specialty company. This is the kind of thing that I've learned to avoid. I would visit the site free of charge and get an idea of what your up against and if its scary explain why its complicated for you to do this one. I find that my customers are usually happy with the fact that I'm more open about my constraints. You can't know everything and those who try to usually end up in trouble.

John Southard, M.S., P.E.

http://www.pdhlibrary.com

 

[lkjh345]

Good advice there southard2!

 

[rapt]

Mike,

That would be at the very early stages of studrail use at best so I would not expect them to have been used in it.

It will be interesting to hear more once you have looked into it, though I casnnot imagine why you would want to pass it on to a "PT expert" company. Better to have a real consultant like yourself look at it!

 

[msquared48]

The owner sent me a few photos, but the one below is the most telling. I will be doing a personal review and inspection next week.

Looks like it slipped vertically at a cold joint. Also has a lot of plumbing leak issues with corrosion.

I am wondering if there was no provision for vertical shear transfer at this location, with uneven PS parallel to the joint on either side of the joint... When the joint deteriorated to the point of losing any bond, this could happen.



Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[rapt]

Mike,

The joint concrete surface looks smooth like it has never been bonded so it was never a proper construction joint. If it is a cold joint you would still expect to see evidence of bond on the surface, but there does not appear to be any from the photo.

Looks to me like it has been built as an expansion joint with no shear connection (as you suggested). I doubt that there was ever any steel across the joint at all from what we can see. There was definitely no bottom steel in the bottom 3-4" of the slab at the joint by the look of it! Maybe there was suposed to be a concrete shear key (corbel/having joint) that was overlooked in the construction!

The epoxy they have used to waterproof the joint does not appear to have been strong enough to provide the necessary shear transfer!!!!

 

[BAretired]

No shear connection at the joint and possibly failed tendons parallel to and to the right of the joint. Otherwise, why would the right side deflect so much more than the left side?

BA

 

[rowingengineer]

I don't like guessing, but if you were concerned about your knowledge of PT, rather than send your client to the local PT engineer, I would take on the job and refer to the PT expert for technical advice, I would arrange a hrly rate with the PT expert. We do this often for projects were the client has large brief and we can only cover 50% of the brief.

A clear conscience is usually the sign of a bad memory

 

[msquared48]

FYI all:

I have a structural engineer friend that I work with occasionally who has much more knowledge of, and experience with PT than I do, and have involved him in this one too.

Here is another photo that kinda has me baffled as to what is going on. I will know more on Monday when I visit the site.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[BAretired]

It looks like an exposed rebar which is cracking away from the concrete, but it's a little hard to say.

BA

 

[rapt]

Or is it a steel pipe?. Bit hard to get a bar to that position outside the concrete in a slab pour. Looks like it has been added afterwards. Maybe to plug a gap while they filled it with some form of joint sealant!

Looks like another long soffit repair several feet to the right of the rusted bar.

Any chance that it is an infill strip poured after stressing is completed in both directions.

We will have to wait for more information.

 

[B16A2]

this website is frightening

 

[msquared48]

It turned out to be just a rusted electrical conduit in that pic.

The drop is on the edge of a 3' wide pour strip between two halves of the PT slab. There is water intrusion all over the place in several locations, and cable runs.

This will be a mess to fix if it is anything but unbonded cables. I will look at the drawings tomorrow.


Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask