Due to its simplicity, shock response spectrum has become widely used as a means of describing the shock responses and fragilities of structures and equipment. This study focuses on the drawbacks of using shock excitation response spectrum for defining equipment shock tolerance. A cantilever beam with a tip mass was used to model a hypothetical equipment, subjected to strong ground motion such as that due to an explosion or a sudden excitation. The exact solution from a detailed modal analysis shows that multiple modes of response were excited. Contributions from higher modes can be more predominant than that from the fundamental mode. Assuming that the total response of the equipment is predominantly in the first mode is erroneous. Current procedures for equipment fragility tests are inadequate, not only due to physical limitations of shake table tests, but also due to the lack of a reliable analytical model.
Journal of Applied Science and Engineering 16(2), pp.117-126