Bond between Concrete and Steel column

[DickHallorann]

Hello,

I have a situation in a house basement where the concrete floor slab was poured around the steel HSS teleposts (which are on piles). The floor slab is heaving slightly, and it is lifting the telepost column with it due to the bond between the slab and steel. I'm trying to find a way to quantify the force of this bond but am having trouble. It is not really a "friction" force as there is no force normal to the column. Thanks ahead for any advice.

 

[ishvaaag]

I would also consider if the piles themselves are not coming along, either accompanying the movement or forced by the traction. As you state the question it would seem the connection is becoming either broken at the bolts or plastified at the plate, to just surmise the piles don't move and the steel column does.

Anyway, to the matter of adhesion between structural steel and concrete...

https://bibliotecadigital.ipb.pt/bitstream/10198/1637/1/ref 5.pdf

Since we are seeking upper values, not warranted ones, 15 to 20 MPa?

For hollow void shapes should be lower than solid, out of the feasibility of local detachment starting the failure at lower average stresses.

 

[structSU10]

Yes, I am surprised this would occur unless the pile itself is also moving upward. Are there expansive soils in the area? What do you think may be the cause for the floor slab to heave?water, ground freezing? How deep are the piles? Also is the post loaded? In order to uplift at all without the foundation moving, the uplift force has to exceed the post gravity load, and I would be surprised if a slab heaving could do that on its own.

There seems to be something else at work in this situation.

 

[ToadJones]

Which way was the post installed?
If the screw portion is at the bottom, there is more than just friction there.

 

[DickHallorann]

@ishvaag, thank you for that link. I'm using those values as "worst case" scenarios just to get a base value.

@ToadJones, I'm not sure how the post was actually installed under the slab, can you clarify if that is what you mean?

 

[ToadJones]

If it is an adjustable post with a screw jack built into the end, some contractors place this portion on the bottom and it is then buried in the 'crete. Some place the adjustable portion on top.

 

[ToadJones]

see link...

http://www.google.com/imgres?um=1&h...nw=77&start=0&ndsp=20&ved=1t:429,r:6,s:0,i:94

 

[DickHallorann]

In my case it must be buried under or within the concrete. There is an adjustable portion on the top, is there usually one on both sides? I'm not too familiar with house construction. If it was somehow buried within the concrete when it was poured, this could be an important thing to know.

 

[ToadJones]

I have never seen/used one that had adjustment on both ends.
If you see one at the top, it is probably save to assume that the buried end is just a thin base plate.

 

[shobroco]

Can you use development length formulae to find a force? There are no deformations on the column, and the development length is very short (100mm/4"?) but there seems to be some substantial force greater than say pile friction, for example. I think you might be seeing a case of real-life effects being different than our frequently conservative assumptions, which are fine if we are deciding what the slab will contribute when we are calculating the column's capacity in bearing but confound us when acting in reverse.