During a modal test, a structure must be supported in some manner to the surrounding environment. If a model of the structure is to be reconciled with modal test data, then the support conditions must either be included in the model or assumed to have negligible effects. For example, supports can be ignored in a simulated free test if they do not affect the structure significantly. Frequently, a precise determination of the actual support conditions is not performed. Consequently, there is uncertainty in the conditions and how they affect both the measured modal frequencies and modal dampings. This study examines the effects of support conditions on the measured modal parameters, and discusses the proper design of support conditions for modal testing.
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