Keywords: Earthquakes, base isolation, FEMA P695, collapse studies, ASCE7-05, moat walls, pounding
Abstract: This study investigates the pounding phenomenon in base isolated buildings by conducting shake table pounding experiments, developing analytical models for impact to moat walls, and evaluating the adequacy of code specifications for the gap distance of moat walls. The experiments indicated that the contact forces generated during pounding can induce yielding in the superstructure and amplify the response acceleration at all stories of the building. The response amplification and damage depends on the gap distance, moat wall properties, and impact velocity. A detailed finite element model of the test setup was developed in OpenSees and an analytical study on the dynamic behavior of the moat walls resulted in proposing a new impact element. The numerical simulation showed good agreement with the experimental results. Finally, a series of collapse studies using the FEMA P695 methodology was conducted to determine the collapse probability of the base isolated models and the effect of moat wall gap distance on the probability of collapse. These studies verified that pounding to moat walls at the gap distance required by ASCE7-05 results in an acceptable probability of collapse for flexible and ductile moment frame models. However, the braced frame showed a notable drop in collapse margin ratio because of pounding to the moat wall at the required gap distance and requires increasing the gap distance by 17%.to achieve an acceptable collapse probability.