Thrust Block Design
Thrust Block Design
(OP)
I will try to keep this short and sweet. I recently, and for the first time, designed a rectangular stress block for a 54" DIP pipe operating at a peak 250psi thrust. This resulted in a roughly 900kip factored thrust.
As, the structural engineer, I had no idea what thickness DIP was being used and decided that it was rational to provide 'hoop' steel around the pipe, in the thrust block, to tie the longitudinal bars (resisting soil pressure) at the penetration for continuity. The second reason was to resist the hoop stress that I presumed would be transferred from the DIP.
I was told that this was overkill. I thought my approach was rational and the hoops steel would be needed, especially close to the interface of the concrete and pipe.
Has anyone have thoughts about this? FYI, I used the Lame equations for a Thick-walled member, assuming a ring of concrete engaged around the pipe would behave as such. I do understand that if the strain in the very outside fibers of the pipe is near zero, strain compatibility requires the concrete adjacent to be the same.
Should I have assumed a maximum allowable strain in the DIP and checked the concrete from that assumption?
As, the structural engineer, I had no idea what thickness DIP was being used and decided that it was rational to provide 'hoop' steel around the pipe, in the thrust block, to tie the longitudinal bars (resisting soil pressure) at the penetration for continuity. The second reason was to resist the hoop stress that I presumed would be transferred from the DIP.
I was told that this was overkill. I thought my approach was rational and the hoops steel would be needed, especially close to the interface of the concrete and pipe.
Has anyone have thoughts about this? FYI, I used the Lame equations for a Thick-walled member, assuming a ring of concrete engaged around the pipe would behave as such. I do understand that if the strain in the very outside fibers of the pipe is near zero, strain compatibility requires the concrete adjacent to be the same.
Should I have assumed a maximum allowable strain in the DIP and checked the concrete from that assumption?





RE: Thrust Block Design
Nobody I know actually cares if any amount of reinforcement in an anchor block is overkill or not. As long as the aggregate will get through the grid.
From "BigInch's Extremely simple theory of everything."
RE: Thrust Block Design
If this is however e.g. a simple block or wall Pipe penetration, I think both USA manufacturers of this size pipe can supply a factory/welded-on "thrust collar", with about a ¾" plate thickness and that extends outside the pipe and into the wall concrete. [As BigInch notes, it is also not unusual for such wall penetrations to be reinforced with a steel reinforcement lattice tied around same due to the high and localized shear loads at such penetrations.]
RE: Thrust Block Design
IMHO, You are nearing the limits of what can be done with UG thrust blocks.
Perhaps some other method of axial pipe restraint could be considered ?
http://www.ebaa.com/PDF/Brochure.1100.pdf
-MJC
RE: Thrust Block Design
rconner, It was a factored value given to us from our civil guys. It is a straight pipe at a push-on style retrofitted joint, hence just a rectangular block. There was a thrust collar and that was easy to handle just as you would punching shear of a column. Again, this project was a first for me. My concern, and where my ignorance resided, was such a large pipe and high hoop pressure splitting the block. My assumption was that it (the pipe & some amount of concrete) were to behave like an old-fashioned wood barrel with iron straps binding the barrel together. Also, no shear bars, just lots of concrete thickness!
MJCronin: We were delegated the structural design work only. I had no choice but to design as such. I think the issue was the push-on joint was to existing precast pipe? Because I am not in that field , I do not know the particulars. Your attachment only went up to 48"
Thanks Guys
RE: Thrust Block Design