Abstract
In a recent letter to the U.S. Department of Energy (DNFSB, 2011), the Defense Nuclear Facilities Safety Board (DNFSB) raised some concerns regarding the technical accuracy and proper validation of the Subtraction Model implemented in different versions of the SASSI program. The DNFSB reported that the response transfer functions calculated using the Subtraction Model for frequencies above 10 Hz exhibited peaks and valleys, while those generated by the Direct Model were smooth and more reasonable. The DNFSB stated that the in-structure response spectra (ISRS) calculated using the Subtraction Model might become in some instances un-conservative for certain frequency ranges. The purpose of this paper is to provide a brief background on several impedance modeling schemes used in SASSI, to examine the accuracy of three such schemes (the Direct, Subtraction, and Modified Subtraction Models) and to provide additional guidance in applying these models to large-scale SSI problems. The conclusions presented in this paper are based on the results of two test problems analyzed in this study.
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