Friction Force of Pipe embedded into concrete ?
Friction Force of Pipe embedded into concrete ?
(OP)
Hello all,
I'm designing a 12ft tall sign. The sign company says the steel Pipe column of the sign actually embeds into the concrete pier all the way down to the bottom of the pier (3" clear from bottom). I'm concerned about the Bond between the steel pipe and the concrete since this would feel like it would be almost the same as putting smooth rebar and having no friction.
But, I just "feel" the skin friction between the steel pipe and the concrete pier is OK to hold gravity and uplift loads if I'm going down 10ft, I just don't know how to prove it and now the sign company is getting impatient because they've been doing it like this for 30 yrs.... I just can't prove them right or wrong.
Any thoughts?
Thank you in advance!
I'm designing a 12ft tall sign. The sign company says the steel Pipe column of the sign actually embeds into the concrete pier all the way down to the bottom of the pier (3" clear from bottom). I'm concerned about the Bond between the steel pipe and the concrete since this would feel like it would be almost the same as putting smooth rebar and having no friction.
But, I just "feel" the skin friction between the steel pipe and the concrete pier is OK to hold gravity and uplift loads if I'm going down 10ft, I just don't know how to prove it and now the sign company is getting impatient because they've been doing it like this for 30 yrs.... I just can't prove them right or wrong.
Any thoughts?
Thank you in advance!






RE: Friction Force of Pipe embedded into concrete ?
BA
RE: Friction Force of Pipe embedded into concrete ?
RE: Friction Force of Pipe embedded into concrete ?
I'm not concerned with the moments. The real problem is the weight of the sign. It has masonry on both sides. It's pretty heavy. I don't want the weight to shear through the bottom of the pipe because there's no base plate (the bottom of the pipe is hollow so that concrete flows inside and around the pipe). So, I'm relying on the friction between the steel and the concrete (if you want to be exact about it, then there is some bearing of the pipe wall thickness in the concrete, but it would shear through without a base plate or without relying of some bonding between the walls of the pipe and the surrounding concrete).
The Pipe is 12" dia. Schedule 40, while the pier is 30" dia.
RE: Friction Force of Pipe embedded into concrete ?
Considering that, I usually assume about 25 psi bond strength between the concrete and the steel. You have a lot of bond area, so that is likely sufficient.
RE: Friction Force of Pipe embedded into concrete ?
RE: Friction Force of Pipe embedded into concrete ?
RE: Friction Force of Pipe embedded into concrete ?
For deformed tension bars, the allowable bond stress was 4.8√f'c/D. For f'c = 2500 and D = 12, this would be 20 psi. Half of that would be 10 psi which is a bit more conservative than Ron's value.
A sudden cooling down in temperature would tend to shrink the pipe faster than the concrete, so it would seem to be good practice to provide a few studs welded to the pipe to ensure mechanical bond.
BA
RE: Friction Force of Pipe embedded into concrete ?
RE: Friction Force of Pipe embedded into concrete ?
RE: Friction Force of Pipe embedded into concrete ?
http://www.isope.org/publications/proceedings/ISOP...