Foundation Analysis for a Rotary Machine Using Coupled Model

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Title: Foundation Analysis for a Rotary Machine Using Coupled Model

Author(s): Raymond A. Schmidt

Publication: Special Publication

Volume: 78

Issue:

Appears on pages(s): 225-242

Keywords: amplitude; caps (supports) ; concrete piles; damping; dynamic structural analysis; foundations; machine bases; models; oils; reinforced concrete; vibration.

Date: 1/1/1982

Abstract:
A dynamic analysis of an Induced Draft Fan and Foundation, subjected to unbalanced rotor loadings, is described and discussed. The installation selected for analysis is supported on piles, and consists of a reinforced concrete foundation and bearing pedestals, fan motor, fan, housing, and exhaust duct (evase’). The modeling techniques presented by the author in this case study will illustrate a method for the Design Engineer to completely analyze complex coupled systems involving both oil film and pile/soil stiffness and damping. The techniques presented do not require that the structural analysis computer program have discrete element damping (dashpot) capabilities. The model is all inclusive and can be used for both static and dynamic analysis. Dynamic responses, particularly modal frequencies and peak-to-peak journal bearing amplitudes of motion are compared with those calculated from relatively simplified lumped mass stick models of the same installation. Insight is gained into the dynamic behavior of the coupled system and the comparison study points out the limitations of the stick model responses. This paper presents a case study of an Induced Draft Pan and Foundation with special emphasis on the computer modeling techniques utilized. The model illustrated idealizes the COMPLETE system installation, and as such, is capable of directly predicting static deflections and internal forces, as well as coupled dynamic responses to earthquake and unbalanced rotor loads. The modeling techniques described are readily adaptable to commercially available structural analysis programs with finite element capabilities (i.e., Nastran, Strudl, Stardyne, Ansys).