RESPONSE MODIFICATION FACTOR FOR SHORT PERIODS OBTAINED FROM A SET OF PERUVIAN SEISMIC ACCELERATION RECORDS

Most earthquake-resistant design codes include a response modification factor that simplifies the calculation of equivalent inelastic lateral seismic force and that are used in the seismic design of the structures. In this paper, the evaluation of resistance reduction factors is presented with the purpose of estimating the demand of inelastic resistance from the elastic resistance demand and for different ductility values. The processing was done from twelve records of seismic accelerations measured in several places of the Peruvian coast. From a model of a degree of freedom that has elastic and elastic-perfectly plastic behaviors, the spectral responses of the selected records were obtained for different critical damping ratios and ductility demands. The elastic and inelastic responses were processed, in order to obtain the resistance modification values for each selected record. For each of the acceleration records it was observed that the resistance modification factor is strongly influenced by the displacement ductility demand and by the vibration period of the system. A simple expression of the response modification factor has been proposed to estimate a reasonable response spectrum of inelastic design for this type of records. Finally, the results obtained were compared with the pseudo-acceleration design spectrum from Peruvian seismic code (E.030) and from Chilean seismic code (NCh433). This comparison provided satisfactory results.