Valve pit Thrust restrained wall design

[Gradstructengineer]

Hi all,

I have to design the walls of a valve pit to restrain thrust from the pipes going in, could you please advise me on how to calculate the thrust force from a pipe that's passing through the valve pit walls (with puddle flanges), no bends or change in size of the pipe as it is passing through. In the middle of the valve pit, there is a tee junction, for this tee junction where can I provide the thrust block, do I need to provide one? Is the thrust force from the tee junction going to be equally divided to the two side walls?

thanks in advance

 

[LittleInch]

This looks like a water pipe with push fit pipes?

Your max thrust is basically end cap thrust assuming the valves are closed.

Thermal effects look very small and the pipe is aisling not stiff so design pressure x surface area of the internal area of the pipe, then add 50% for any shock loading and you will be fine.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Settingsun]

Nice of the pipe designer to nominate your wall thickness. Are they taking responsibility for punching shear? Of course not. Get them to take the thicknesses off their drawing so you're in control of the structural design.

For tee junctions and inline dead ends, the force is just pressure * cross section area. The outside diameter is used to calculate the area for some reason in most guides IIRC. Dynamic force is negligible compared with static. It was 1.25*test pressure or 1.5*operating pressure back when I did these.

The tee force could be resisted by the wall where that branch enters the pit (might need a big wall), or you could cantilever a blade restraint from the floor slab. You'd usually try to avoid putting the pipe in bending when there are joints in the span.

Don't forget to check buoyancy if the water table is anywhere nearby.

 

[JedClampett]

If the joints are harnessed in the vault and restrained outside, there's no thrust in the walls.

 

[LittleInch]

Also in terms of the tee I think you'll also have a sideways force on the main pie equivalent to pressure x area of the pipe.

Could do with a plan view, but again if push fit pipe is used it makes a big difference.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ATSE]

It appears like you have dresser couplers, which do not transmit axial stress.
So if the pipe valve is closed, would you not have simply F = pressure * area?
You need to draw a free body diagram in 3D space that extends to the next expansion or non-tension joint. It is unlikely you have fully restrained joints forever in the entire system.
These pressure forces can be huge. What is your test load? 150 psi? 250 psi?
There is commonly a disconnnect between the mechanical and civil engineers for these situations, and neither ask enough questions about joint behavior, relative movement, and permissible displacements.

 

[XR250]

At my old firm, I ran into this on a wooden pedestrian bridge with an 8" water main hung from below. They used push joints on the pipe. When it was pressurized, it turned into a sine wave - along with the bridge. Ended up de-pressurizing and straightening everything and adding Victaulic type joints.

 

[Gradstructengineer]

Hi All,

Thank you so much for your responses. I have attached the plan view and a snapshot of the parts list, how do I tell if these are push pipe fittings (sorry if this is a dumb question).
I have to design the end walls for punching shear for a thrust force = 1.5*P*A for the three walls and for the thrust force in the tee junction, can a steel support be used to resist it (shown in the plan view)?

thanks in advance

 

[Gradstructengineer]

Parts list attached

 

[ATSE]

Not sure what your pressure is. If you have a common scenario for municipal: 36" pipe, 150 psi service, 225 psi test, then your forces are 225 * 1018 = 229 kips. This is a game changer for your valve box geometry and support system.
Your mechanical piping engineer must define each and every joint on our figure as full restrained, partially restrained, or slip.
One other challenge is dealing with the high service axial loads, but still accommodating expected differential movement from settlement and seismic, but also thermal expansion and contraction strains.
AWWA std practice uses slip on joints (bell-spigot) and then uses long lengths to develop thrust forces at corners. It gives most structural engineers heartburn (me included).
BTW, do you already mention if this pipe is ductile iron or steel?

 

[LittleInch]

They look like push fit - they seem to call them SOC - Slip on or SOCket?, but FL is clearly flange.

the pipe is DICL - Ductile Iron Cement lined so can't be welded.

As the tee is flanged and then connected to your puddle flange it will transmit the forces to the puddle flange. But the support is not good for thrust forces.

But yes - design pressure of the system is needed and you could be looking at some substantial forces.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.