Pump Footing design

[sdz]

I am still trying to come to terms with whether it is worthwhile trying to do a dynamic analysis of pump footings, especially large slurry pumps.

The critical part is how well we can estimate the dynamic loads in service. Loads calculated from the initial impeller eccentricity are likely to be an order of magnitude less than loads due to hydraulic forces, wear during service, and mechanical failure. Even for a condition that could exist for only a few minutes could result in several thousand load cycles.

There are various graphs showing vibration limits versus frequency but these give vastly different limits and may not be applicable to calculating actual design forces. Limits for a turbine could be different to a slurry pump.

As I see it the problem is in two parts

a) For a pump mounted on a rigid base what are the design loads generated in service during the life of the pump.
b) For a footing designed for those loads what are the design limits; bearing pressures, deflections, etc.

Can anyone help?

 

[BigInch]

Forces that cause vibration are not large enough to worry about from the typical structural perspective and do not fail the footing or overbear the soil in the usual manner. But they should not be thought about only in that context. Although the forces may be small, they may still cause very large vibrations and can thus be very important in creating an acceptable overall design for the machine-foundation system.

In addition to the unbalanced forces, you will probably also need to check start-up, shut-down and short circuit loads.

To prevent differential settlement from long term vibratory loads to the soil it is very important to design the foundation such that the center of gravity of the machine coincides with the center of pressure of the static loads.

Soil bearing allowables, as always, depend on the underlaying strata. A competent soil consultant should be secured to perform a dynamic analysis on the in place soils to determine the appropriate spring constants to use in the dynamic analysis of the machine-foundation.

Both of these will be helpful,

Principles of Foundation Design for Engines and Compressors
W.K. Newcomb - Ingersol Rand

US Army COE (Technical Manual) TM5-818-1 Chapter 7 Machine Foundations


BigInch-born in the trenches.

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