Effects of soft soil and hysteresis model on seismic demands

The main objective of this research is to develop procedures that will permit an explicit incorporation of the effects of deterioration of structural properties and site surface geology on the seismic demands imposed on structures by strong ground motions.; During severe earthquakes the performance of structures depends upon the characteristics of ground motions (frequency content, duration etc.) and the restoring force (hysteretic) characteristics of the structural system. The effects of negative strain hardening (P-delta) and stiffness and strength deterioration on the demand imposed by ground motions on the strength of inelastic SDOF systems are investigated. The required strength (strength demand) for target ductility ratios from 2 to 8 is evaluated statistically for bilinear and stiffness degrading model with +10% to {dollar}-{dollar}20% strain hardening for SDOF systems with a period ranging from 0.10 to 4.0 seconds. A deterioration model is developed that is based on cumulative energy dissipation. The hysteretic energy dissipation in each excursion is used to update a deterioration parameter. This parameter is utilized to incorporate the effect of deterioration into the bilinear hysteresis model.; The research related to the study of soft soil effects on seismic demands is carried out in two parts. In the first part advantage is taken of the extensive set of ground motions recorded during the Loma Prieta earthquake and the availability of data on local soil conditions at recording stations. In the second part of the study simplified models of soil columns are employed for an extensive parameter study on the effects of site soil conditions on seismic demands. A comprehensive set of recorded and generated soft soil ground motions are utilized to obtain phenomenological as well as statistical information on the effects of site soil conditions on PGA, PGD, and elastic and inelastic displacement and strength demands spectra. The study has shown that the soft soil effects can be related to the strength demand of the motion in the underlying rock by a modification function which is a function of soil period and the target ductility ratio of the system. (Abstract shortened by UMI.)...