08-10-2014, 04:40 PM
Design force ratio (DFR) spectra give the ratio by which the design force level of a single-degree-of-freedom structure has to be increased such that the damage caused by a number of earthquake events expected to occur during its lifetime is limited to a specified level. In this study, the DFR spectra are compared for three different seismicity models. In the first model, the return periods of earthquakes are assumed to follow exponential distribution over the entire range of magnitudes. In the second and third models, the numbers of large earthquakes are estimated by time-dependent hazard function based on lognormal and Weibull distributions of return period. Different values of seismic gap length, i.e. time elapsed since the last large event, are considered for these two models. The expected magnitudes of earthquake events expected to occur during the lifetime of the structure are estimated by applying the order statistics approach. It has been found from the numerical study on a hypothetical seismic region that the seismicity model may significantly influence the DFR