Combined experimental and analytical method for a realistic seismic qualification of equipment

The seismic qualification of equipment/structures are, in general, carried out either exclusively by analysis or exclusively by testing using a shake table. The analytical methods have the risk of the model not being a true r eflection of the structure unless very elaborate modelling techniques are u sed. Even with an elaborate model there are many idealisations made which m ay not actually be realised in practice. The shake-table testing, avoids th e modelling deviations to a large extent, but is also not without drawbacks . The important ones are the cost and the availability of a shake table of the required size and capacity. The shake-table testing is also carried out on the isolated equipment without the piping/structural connections from o ther components. The present paper suggests a combined experimental and ana lytical method on the 'as installed' equipment as an attractive alternative which overcomes the above drawbacks. In contrast to the existing practice of using the experimental results just to validate the analytical model, th e suggested method uses the experimentally obtained dynamic characteristics of the 'as installed' equipment to obtain the response to the design seism ic load. The paper brings out through an example of a simple storage tank w hich is too heavy for a shake table, the large deviations in its actual beh aviour vis-g-vis an idealised analytical model. (C) 2000 Elsevier Science S .A. All rights reserved.