Formulation of elastic earthquake input energy spectra

Abstract

SUMMARY The object of this paper is to introduce a procedure for the determination of elastic design earthquake input energy spectra taking into account the influence of magnitude, soil type and distance from the surface projection of the fault. Firstly, an accurate selection of a large set of representative records has been realized. Secondly, the construction of the design input energy spectra has required determining the spectral shapes and a normalization factor which measures seismic hazard in terms of energy. This factor, denoted as the seismic hazard energy factor, has been defined as the area under the earthquake input energy spectrum in the period interval between 0)05 and 4)0 s. Finally, due to the importance of the source-to-site distance in the evaluation of the input energy, an investigation into the attenuation of the seismic hazard energy factor has been carried out. ( 1998 John Wiley & Sons, Ltd. The fundamental need to improve the reliability of the current procedures of earthquake-resistant design of structures has led to the recognition of methodologies based on energy criteria as e⁄ective tools for a comprehensive interpretation of the behaviour observed during recent destructive events. Energy-based design involves considering two essential aspects: the first is related to the establishment of Design Earthquakes, while the second concerns the evaluation of the actual energy absorption and energy dissipation capacities of structures. The aim of this work is to introduce a proposal which could contribute to the resolution of the first of the above-mentioned aspects, namely the definition of a design seismic action as a function of appropriate parameters providing a measure of the energy actually transferred from soil to structures during seismic shaking. The commonly adopted design approach in terms of forces, based on both elastic and inelastic response spectra, as results from the analysis and interpretation of the observed structural behaviour is open to criticism. The most controversial and uncertain aspect of the conventional design procedures specified by the di⁄erent codes is represented by the interpretation of the elastic design spectrum as a measure of destructiveness and, by the definition of the elastic response reduction factor as a function of a presumed inelastic behaviour. This factor, also known as the behaviour factor, although it is based on the comparison between elastic and inelastic response spectra and non-linear structural analysis, is still substantially assigned by the codes according to empirical criteria. Furthermore, uncertainty often arises in various steps of these