Variations in Optimum Seismic Design Parameters of Important Structures

Abstract eng:
The paper studies how the seismic design coefficient increment for important structures vary according to different concepts such as peak ground saturation, initial costs, structural capacity, and uncertainties in different variables. Optimum values are obtained on the frame of the total cost design criterion. Sites in the near-field and away from the source are under study to determine the variation of the optimum coefficients. We consider that the design is such that it minimizes the expected present value of the total cost, including initial and maintenance costs as well as losses due to damage and failure. As a first approach we assume that the incremental factor in the design parameter of important structures, at one of the sites, is optimum; after that we compute the corresponding factor for the other site. The earthquake generation process used here is composed of background activity as well as characteristic earthquakes, with both constant and time dependent magnitudes. For the site located in the near-field a saturation phenomenon is considered in the peak ground acceleration as the magnitude of the earthquake increases. This phenomenon, together with the initial costs of structures as well as uncertainties in some parameters are taken into account in order to see their influence on the optimal design values, and on the incremental factor at the different sites studied. The influence is measured by comparing the variations in the total costs. Variations in the optimum seismic design values and on the incremental factor for important structures are studied for sites with different seismicity. Preliminary results show that these factors can vary according to the site seismicity, and that their increment when uncertainties in some variables are taken into account, is appreciable.

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