Performance of base-isolated reinforced concrete buildings under bidirectional seismic excitation considering pounding with retaining walls including friction effects



Seismic pounding of base-isolated buildings has been mostly studied in the past assuming unidirectional excitation. Therefore, in this study, the effects of seismic pounding on the response of base-isolated reinforced concrete buildings under bidirectional excitation are investigated. For this purpose, a three-dimensional finite element model of a code-compliant four-story building is considered, where a newly developed contact element that accounts for friction and is capable of simulating pounding with retaining walls at the base, is used. Nonlinear behavior of the superstructure as well as the isolation system is considered. The performance of the building is evaluated separately for far-fault non-pulse-like ground motions and near-fault pulse-like ground motions, which are weighted scaled to represent two levels of shaking viz. the design earthquake (DE) level and the risk-targeted maximum considered earthquake (MCER) level. Nonlinear time-history analyses are carried out considering lower bound as well as upper bound properties of isolators. The influence of separation distance between the building and the retaining walls at the base is also investigated. It is found that if pounding is avoided, the performance of the building is satisfactory in terms of limiting structural and nonstructural damage, under DE-level motions and MCER-level far-fault motions, whereas unacceptably large demands are imposed by MCER-level near-fault motions. In the case of seismic pounding, MCER-level near-fault motions are found to be detrimental, where the effect of pounding is mostly concentrated at the first story. In addition, it is determined that considering unidirectional excitation instead of bidirectional excitation for MCER-level near-fault motions provides highly unconservative estimates of superstructure demands. Copyright © 2014 John Wiley & Sons, Ltd.