Acceleration amplifications in nif structures subjected to earthquake base motions

NIF technical staff have questioned the possibility of obtaining acceleration amplifications (i.e. amplification of the ground acceleration values) in a structure which are significantly higher than the acceleration amplification exhibited across the period range in the input response spectrum. This note utilizes a simple example to illustrate that the acceleration amplification resulting from the dynamic response of a structural system can indeed be significantly higher than the amplifications indicated in the response spectrum, and that the GEMINI program is computing the appropriate acceleration levels for a simple MDOF system.