Dynamic Foundation Analysis 1

[sadas91]

Hai all,

I am structural engineer and currently involve in some of dynamic foundation design. Is anyone know what is the minimum load for an equipment to be analyse as a dynamic foundation as I did not see any reference in any codes discussing about it. Your ideas are much appreciated. Thanks

 

[JoelTXCive]

I have always been told that 200 horsepower is a threshold level for dynamic design. Unfortunately, I do not know a source.

Regardless, I think it also depends on the environment that the machine will be placed in. Is this a machine that will be running continuously with workers around? Or, is it a machine isolated from people?

 

[Mohanlal0488]

Hi Sadas91

What type of equipment are you dealing with?

 

[1503-44]

Might even increase that to 500Hp, but depends on type of equipment, operating frequency (ies) and how sensitive it is to vibration. Rotary, reciprocating, electric drive, internal combustion, high speed turbines? Usually the lower range of op frequencies are more prone to upset, 500 to 1200 Hz, as that band often resonates with block foundations on soil, but high frequency devices can be very sensitive to vibrations.

Contact the mfgr for the machine's unbalanced dynamic and short circuit loads.

 

[HTURKAK]

These are excerpts from ACI 351.3R-04 Foundations for Dynamic Equipment:


Rule of thumb =Most engineers consider the rule-of-thumb procedure
satisfactory for a preliminary foundation sizing. Sometimes
engineers use this method to design block-type foundations
supporting relatively small machinery, up to 5000 lbf (22 kN)
in weight and having small unbalanced forces. For reciprocating
machinery and sensitive machinery, rule-of-thumb
procedures by themselves may not be sufficient.



Equivalent static method = 4.1.2.2 Equivalent static loading method—The equivalent
static loading method is a simplified and approximate way of
applying pseudodynamic forces to the machine-supporting
structure to check the strength and stability of the foundation.
This method is used mainly for the design of foundations for
machines weighing 10,000 lbf (45 kN) or less.

 

[sadas91]

The equipment is pump located in petchem plant. The pump just weighing total 1tonnes only and clients need me to provide a dynamic foundation analysis. If there are any references stated the minimum load for centrifugal pump need to be considered for dynamic analysis, it will help me a lot. Before, I just designed much greater pump weight ranging from 2tonnes to 5tonnes without any problem. Just check the foundation weight to equipment weight > 3 is enough.

 

[Mohanlal0488]

The centrifugal forces should be balanced, however with uneven wearing of the components cause small amounts of dynamic effects may come into play. Personally I think this would be an accidental load. For my dewatering pontoon designs I normally checked a load case with the break down torque of the motor. In my experience pumps are generally maintained well and thus the large dynamic loads never really occur, however to be fair we also stipulate the rules and requirements in our IOM, any deviance from that falls under the clients responsibility.

I some cases I have even managed to attain an estimated force Vs time graph for the expected break down torque so that I can perform a transient analysis

 

[1503-44]

Sadas91, you got lucky... at least so far. I dont recommend that 3x "rule" as a one size fits all design method, as it is for small centrifugal pumps < 250H Hp.