Safety margin ratio-based design of retaining wall clearance for base-isolated structures

Abstract

The risk of pounding against the surrounding structures, usually against the retaining walls, has become a major concern about theseismic performance of base-isolated buildings subjected to unexpectedly large earthquakes. The required retaining wall clearance toensure the superstructure of a base-isolated building not to yield is evaluated through incremental dynamic analysis and the requiredclearance-to-seismic intensity relationship is established. From this relationship, two characteristic clearances, namely the mini-mum required clearance, δ1, and the maximum clearance, δ2, may be identified. Given a base-isolated building and a seismic intensity,e.g., the energy-equivalent velocity in this paper, a retaining wall clearance greater than δ1 would ensure a 50% possibility that thesuperstructure would not yield. On the other hand, the retaining wall clearance would impose no influence on the performance ofthe isolated building if the clearance is greater than δ2. Especially, the minimum required clearance, δ1, is of essential importance forthe performance design of base-isolated buildings. A simple equation of estimating δ1 for buildings with various parameters isproposed through data regression. In addition, a procedure of determining the required strength for the superstructure, given aseismic intensity, is also proposed.