Occupancy importance factor in earthquake engineering

Seismic codes require that important structures be designed by increasing the seismic design coefficients of the ordinary structures by a factor called the importance factor. At the present time, shear base coefficients are established such that the probability that their value may be exceeded over a period of time does not exceed a small number. On the other hand, at sites near seismic sources, there is a saturation of maximum ground accelerations, as the magnitude of the earthquake increases. Therefore, it would seem that the importance factors at these sites should be smaller than at sites away from the source. To study this, values of the importance factor are calculated for a site in the near-field. We consider that the design is such that it minimizes the present value of the total cost including initial cost as well as losses due to damage and failure. The study considers Poisson and non-Poisson interarrival times for earthquake occurrence. The results show that the importance factor for a site in the near-field is smaller than that of a site away from the source.