Soil Bearing, Overturning & Sliding check for Vertically Suspended Can Pump Foundation

When checking a Vertically Suspended Can Pump Foundation, is it necessary to use the Thrust forces as horizontal shear loads/forces to check Soil Bearing, Overturning & Sliding?

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I would. But what kind of unbalanced forces are we talking here?

Could this be interpreted to mean that as long as the foundation is sized for at least 3 times the weight of the pump, the Thrust forces do not need to be considered as acting on the foundation? If so, then would it not be necessary to consider the thrust forces for the soil bearing, overturning & sliding checks?

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Redundant with the above. I've seen some vertical pumps generate some pretty substantial loads at nearby piping joints.

You/we need more info from the manufacturer.

EDIT: By the way, your links didn't work for me.

WARose said:

EDIT: By the way, your links didn't work for me.

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Here is the image:

WARose said:

I would. But what kind of unbalanced forces are we talking here?

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The data sheet called the forces "Hyd Thrust" of 1,015 lbs & "Driver Max Thrust" of 5,700 lbs. Since these values were shown on a vendor dwg for a vertical pump I am assuming that they are horizontal forces.

Should these forces be used to check soil bearing, overturning, & sliding? They seem very large. The total weight of the vertical pump is already 1,550 lbs.

The data sheet called the forces "Hyd Thrust" of 1,015 lbs & "Driver Max Thrust" of 5,700 lbs. Since these values were shown on a vendor dwg for a vertical pump I am assuming that they are horizontal forces.

Should these forces be used to check soil bearing, overturning, & sliding? They seem very large. The total weight of the vertical pump is already 1,550 lbs.

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The answer to that question isn't just "yes"....it's "hell yes".

And I'd check to be sure that those are static loads (as they most likely are).

You should ask for clarifications from the vendor, for the nature of the thrusts, and how and where they apply. Usually the vendor drawing will indicate the location and direction of the loads, and distance from the reference point/datum. Sometimes the vendor will address load/safety factors included in the given loads, or anticipated multipliers.

Unbalanced force from pipe pressures can be approximated by
(discharge pipe area x discharge pressure ) - (suction pipe area x suction pressure)

There may also be short circuit loads to consider.



Reality used to affect the way we thought. Now we somehow believe that what we think affects reality.

You are expected to use "Hyd Thrust" of 1,015 lbs for designing the foundation. This force is applied in horizontal direction , at center of outlet.

PIP states that, in the absence of dynamic analysis, for 500 HP or less centrifugal machinery , the foundation weight shall be at least 3 times the weight of the pump.
This is an exemption for dynamic analysis of foundation.

Still you are expected to check for OT, sliding, bearing stress, anchors....

First the foundation needs to be designed for all non-dynamic effects. Thrust loads, short circuit loads and "driver thrust" included. If that resulting fdtn mass is 3x pump mass and the pump's motor is < 500HP, a formal dynamic analysis that ensures that vibration frequencies and amplitudes caused by only the combined cyclic loads of both the pump and motor (i.e. not thrust, pipe pressures, or short circuit load, wind, seismic, etc.) acting on the combined pump and foundation masses are within operating limits, is not necessary.

Reality used to affect the way we thought. Now we somehow believe that what we think affects reality.

HTURKAK said:

PIP states that, in the absence of dynamic analysis, for 500 HP or less centrifugal machinery , the foundation weight shall be at least 3 times the weight of the pump.
This is an exemption for dynamic analysis of foundation.

Still you are expected to check for OT, sliding, bearing stress, anchors....

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I am checking for OT, sliding, bearing stress, anchors already, but I am wondering if it is possible to neglect the Thrust force in either of those checks.

-twentytwo said:

If that resulting fdtn mass is 3x pump mass and the pump's motor is < 500HP, a formal dynamic analysis that ensures that vibration frequencies and amplitudes caused by only the combined cyclic loads of both the pump and motor (i.e. not thrust, pipe pressures, or short circuit load, wind, seismic, etc.) acting on the combined pump and foundation masses are within operating limits, is not necessary.

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It sounds like you're saying that the Thrust force should not be considered if the foundation is 3x the weight of the pump & the pump's HP is less than 500 HP. Would my interpretation of your statement be correct?

r13 said:

You should ask for clarifications from the vendor, for the nature of the thrusts, and how and where they apply.

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I have just reached out to the vendor to get clarification on the Thrusts that they show in the cut sheets.

oengineer,

Glad that you decided to reach out to the vendor. Only one thing to remind you about - thrust is usually considered a force, though dynamic in nature, it is not affecting the foundation the same way as the dynamic effect (vibration) from operation of the pump, which (dynamic effect) is to be offset by adjusting the mass of equipment support/foundation.

"Driver Max Thrust" of 5,700 lbs is valid for internal pump stuff , that is for the pump itself ( thrust bearings, casing ..) .An axial hydraulic thrust develops by the pressure and flow of liquid inside it going up on an impeller and is the sum of the unbalanced forces acting in the axial direction.

The loading on the support plate are weight of the pump, some rotational forces , and the horizontal force :Hyd Thrust of 1,015 lbs at outlet .

If you are in doubt , best call the the manufacturer and ask the design forces on supporting plate.

Thrust force (for me) is not a vibratory load. It can be caused by motor and pump torque, pressure imbalance and pressure build up when starting the pump, as discharge pressure goes from near zero to operating pressure very quickly and then becomes more or less constant until the pump is shut off, when it reverses.

Vibratory loads used in the typical "dynamic" analysis are due to pistons reversing direction in a reciprocating engine, or recip pump, or unbalanced weights of rotary components such as axles and shafts of centrifugal pumps and their motors that spin with operating frequency, thereby causing rotating forces and cyclic loadings on frames, skids and foundations.

Sometimes pump vendors don't give detailed information and combine loads into one "thrust" load, etc. Figuring that it will result in a conservative design, so when it is not obvious, it is always best to clarify where exactly their loads come from.

Reality used to affect the way we thought. Now we somehow believe that what we think affects reality.

Also, discuss with your inhouse owner (the specifier) how the piping is to be supported - will there be a rigid connection, or thrust block.

The vendor has replied back to my questions. He has informed me that the thrust for the pumps are vertical.

With that being said, it appears that the Thrust Force will not effect the sliding & overturning ( actually, if anything it should help in those regards).

Would it make sense to include the Thrust in the 3x the weight calculation to determine the size of the foundation? I would think that to be too conservative.

Suggestions/comments are appreciated.

I would consider pump weight only, somebody might do differently though. You need to take the thrust into consideration for sizing the footing though.

It is true that Thrust Force will not effect the sliding & overturning . The thrust (both axial and radial ) resisted by thrust bearings and pump casing. The vertical load on the base plate will not change for static and operation condition.


You can not include the thrust in the 3x the weight calculation to determine the size of the foundation. Weight of pump includes only the (pump, driver and base plate ..)

I will suggest again ; best call the the manufacturer and ask the design forces on supporting plate.