SUMMARY The effects of seismic pounding on the structural performance of a base‐isolated reinforced concrete (RC) building are investigated, with a view to evaluate the influence of adjacent structures and separation between structures on the pounding response. In particular, seismic pounding of a typical four‐story base‐isolated RC building with retaining walls at the base and with a four‐story fixed‐base RC building is studied. Three‐dimensional finite element analyses are carried out considering material and geometric nonlinearities. The structural performance of the base‐isolated building is evaluated considering various earthquake excitations. It is found that the performance of the base‐isolated building is substantially influenced by the pounding. The investigated base‐isolated building shows good resistance against shear failure and the predominant mode of failure due to pounding is flexural. Copyright © 2012 John Wiley & Sons, Ltd.

SUMMARY There is no consensus at the present time regarding an appropriate approach to model viscous damping in nonlinear time‐history analysis of base‐isolated buildings because of uncertainties associated with quantification of energy dissipation. Therefore, in this study, the effects of modeling viscous damping on the response of base‐isolated reinforced concrete buildings subjected to earthquake ground motions are investigated. The test results of a reduced‐scale three‐story building previously tested on a shaking table are compared with three‐dimensional finite element simulation results. The study is primarily focused on nonlinear direct‐integration time‐history analysis, where many different approaches of modeling viscous damping, developed within the framework of Rayleigh damping are considered. Nonlinear direct‐integration time‐history analysis results reveal that the damping ratio as well as the approach used to model damping has significant effects on the response, and quite importantly, a damping ratio of 1% is more appropriate in simulating the response than a damping ratio of 5%. It is shown that stiffness‐proportional damping, where the coefficient multiplying the stiffness matrix is calculated from the frequency of the base‐isolated building with the post‐elastic stiffness of the isolation system, provides reasonable estimates of the peak response indicators, in addition to being able to capture the frequency content of the response very well. Furthermore, nonlinear modal time‐history analyses using constant as well as frequency‐dependent modal damping are also performed for comparison purposes. It was found that for nonlinear modal time‐history analysis, frequency‐dependent damping, where zero damping is assigned to the frequencies below the fundamental frequency of the superstructure for a fixed‐base condition and 5% damping is assigned to all other frequencies, is more appropriate, than 5% constant damping. Copyright © 2013 John Wiley & Sons, Ltd.

SUMMARY 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.

In this paper an analysis of seismic pounding of reinforced concrete buildings with non-equal story heights including soil-structure interaction is presented. Two building configurations, configuration A: 10-story and 9-story buildings and configuration B: two 5-story buildings, are considered. The discrete model is used to incorporate foundation-soil interaction and pounding between buildings is incorporated through impact elements that consist of a gap element and a Kelvin-Voigt element. The responses of the buildings are compared in terms of impact forces, interstory displacements and normalized story shear for two near-field and two far-field earthquakes. The buildings under consideration experience the maximum impact forces and interstory displacements due to the near-field earthquakes for both fixed foundation and flexible (soil) foundation cases. Significant reduction in impact forces are observed when the underlying soil effect is considered. The maximum interstory displacements occurred when there is no pounding. In most of the cases, the consideration of soil results in lower normalized story shear.

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