×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Bond between Concrete and Steel column

Bond between Concrete and Steel column

Bond between Concrete and Steel column

(OP)
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.

RE: Bond between Concrete and Steel column

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/10198/1...

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.


RE: Bond between Concrete and Steel column

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.

RE: Bond between Concrete and Steel column

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

RE: Bond between Concrete and Steel column

(OP)
@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?

RE: Bond between Concrete and Steel column

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.

RE: Bond between Concrete and Steel column

(OP)
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.

RE: Bond between Concrete and Steel column

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.

RE: Bond between Concrete and Steel column

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.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources