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Combining FEA and Field Measurement Techniques for Dynamic Machinery Foundation Design


 Proper foundation design is an essential component in the design process of many types of rotating machinery. Most foundations are designed for static loading, however dynamic foundation design is often overlooked or considered a secondary check. Failing to consider the dynamics of the foundation during the design phase can result in excessive machinery vibrations resulting in failures, forced shutdowns, and expensive in-situ repairs. Foundation dynamics are commonly assessed using finite element analysis (FEA) during the design phase with modal and forced response analyses; however the interactions of machinery, piping, foundation, and soil create a potentially nonlinear system with many degrees-of-freedom. In many applications, it is necessary to design the mechanical natural frequencies of the foundation to avoid excitation mechanisms of the machinery. With modern variable speed machines, accurate prediction of the mechanical natural frequencies is often required to place them in narrow frequency bands between operating orders. These systems are inherently difficult to accurately model, however combining FEA modeling with field measurement techniques allows the possibility of field “tunable” foundation designs. For example, pile foundations can be designed with alternative pile configurations to be connected during commissioning based on the results of modal testing. Modal and vibration data collected on-site can also be used to calibrate the frequencies and mode shapes predicted by the model. This calibrated model is then used to evaluate the effects of proposed changes to the skid and suggest modifications to fix or reduce the problems in existing machinery foundations.