Optimum Seismic Load Distribution for Performance-Based Design of Multi-Storey Structures on Different Soil Profiles

Abstract eng:
Structural configuration plays an important role on the seismic behaviour of structures. In recent earthquakes, structures with inappropriate distributions of strength and stiffness had inadequate performance due to configuration problems or wrong conceptual design. In the conventional seismic design methods, height-wise distribution of equivalent seismic loads seems to be related implicitly on the elastic vibration modes. Therefore, the employment of such a load pattern does not guarantee the optimum use of materials in the nonlinear range of response. In this study, a new optimisation method is used to find optimum lateral force distribution for seismic design of regular and irregular shear-buildings to achieve minimum structural damage. The proposed approach is based on the concept of uniform distribution of damage where the structural properties are modified so that inefficient material is gradually shifted from strong to weak areas of a structure. It is shown that the seismic performance of such a structure is better than those designed conventionally. By conducting the optimisation algorithm on shear-building models with various dynamic characteristics subjected to 75 synthetic spectrumcompatible earthquakes, the effects of target ductility demand, fundamental period, seismic excitation, number of storeys, damping ratio, ground motion intensity and soil profiles are investigated on the optimum distribution pattern. Based on the results of this study, a general load pattern is proposed for seismic design of regular and irregular building structures that is a function of soil type, fundamental period of the structure and the target ductility demand. It is shown that using the proposed load pattern leads to a more efficient use of structural materials and better seismic performance.

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