Aseismic Design by Way of Critical Excitation

The critical excitation of a structure is the ground motion which produces the most severe response when compared with all other excitations of the same or lesser intensity. It is a concept which can be used in principle to assess the earthquake resistance of the structure. The paper presents evidence that it holds promise also for use in practice. A measure of intensity of excitation, and one of severity of response, are first selected from a range of possibilities. The critical excitation is then defined accordingly, and is shown to produce responses which are only twice as severe as those to some already recorded ground motions, when applied to a variety of simple elastic structures. If one admits for comparison not only recorded ground motions but also their linear superpositions, the response to the critical excitation is only 1.3 times as severe as some of these. These factors seem to be consistent with structural engineering practice and suggest potential utility for the concept of critical excitation.