Thrust Block design
Thrust Block design
(OP)
I know....Civil form has topics on thrust blocks, they still don't answer my question. Actually, this is more of a statics question.
I'm reading that to design a thurst block both static pressure and flow velocity must be account for.
Flow velocity I get, but I can't envision how static pressure inside a pipe would transmit any force to an object outside the pipe. The static pressure is the same at any point in a pipe (assuming same elevation). What's the difference if this pressue is along the straight portion of the pipe run or an elbow. Doesn't the pipe have the same chance of rupturing at any point along the pipe run? So, why all of a sudden does the force from static pressure factor into play at bends as opposed to anywhere else outside the pipe? I though the pipe wall thickness accounted for static pressure.
Thanks for any help!
I'm reading that to design a thurst block both static pressure and flow velocity must be account for.
Flow velocity I get, but I can't envision how static pressure inside a pipe would transmit any force to an object outside the pipe. The static pressure is the same at any point in a pipe (assuming same elevation). What's the difference if this pressue is along the straight portion of the pipe run or an elbow. Doesn't the pipe have the same chance of rupturing at any point along the pipe run? So, why all of a sudden does the force from static pressure factor into play at bends as opposed to anywhere else outside the pipe? I though the pipe wall thickness accounted for static pressure.
Thanks for any help!






RE: Thrust Block design
Otherwise, reread that to mean dynamic forces due to the flow and flow direction changes, etc., which you claim to understand. And, static forces such as expansion/ contraction, length changes over long pipe lengths or at shorter lengths btwn. two direction changes, friction btwn. pipe and soil, and how the thrust blocks interact or restrain these actions. What happens beyond flow induced forces if a pipe runs horiz. and then at some point turns up or down hill at 45° for a long run? I think these are the kinds of static forces they are talking about. Obviously, you must design the pipe for internal forces and stresses from pressure and the like, and these might end up being added to some of what is induced by the thrust blocks and reaction hardware above.
RE: Thrust Block design
Just to take it a bit further...
This is for a 30" horizontal pipe which makes a 90 degree bend to exit a pumping station, with 70 psi.
According to 2 different sources (DIPRA and ht
I agree with expansion/contraction and other conditions which may add a static force to a pipe per your explaination. But, the above number of 74,235 is what I was getting at in my original post.
RE: Thrust Block design
Think about a champagne bottle with a cork. let it get warm and shake it a bit, then release the restraint which is the wire. The static pressure will blow the cork out. There is no dynamic force involved.
RE: Thrust Block design
The dynamic effects will quite often be neglible in comparison to the pressure forces.
RE: Thrust Block design
F = p*A
i think the 1.5 factor is a safety factor.
alternatively, 'cause the pipe is bent 90deg, the same force is reacted in both directions, so the total force on the bend is 1.414*(p*A).
RE: Thrust Block design
@ JStephen: The bid drawing shows 2 flange supports at the elbow in each direction. I'm not sure of the restraint capability of them. I'm looking into that also. I attached a jpg of this.
@rb: Yes, 1.5 is just the safety factor. 1.5 * P * A is actually called out for a dead end, I though this would most nearly resemble the 90 degree bend in a conservative manner. Sorry, where is the 1.414 coming from?
Thanks guys.
RE: Thrust Block design
RE: Thrust Block design
RE: Thrust Block design
RE: Thrust Block design
When you look at a pressure diagram of a pipe there is the pressure on the walls that is resisted by the pipe ring pressure and cancels itself out. There is also the pressure along the pipe which is only resisted by the pressure of the other liquid or gas along the pipe.
As others have said this pressure along the pipe causes a force component that acts along the axis of the pipe and at bends this causes an out of plane force that needs to be resisted.
This is why even gas mains need thrust blocks even though the flow momentum is negligible.
As others have said, thermal forces also should be considered.
A useful tool is to apply method of sections to this cutting the pipe at the end of the curve on each side and looking at the resultant force components on the whole bend.