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 the seismic performance of base-isolated buildings subjected to unexpectedly large earthquakes. The required retaining wall clearance to ensure the superstructure of a base-isolated building not to yield is evaluated through incremental dynamic analysis and the required clearance-to-seismic intensity relationship is established. From this relationship, two characteristic clearances, namely the minimum 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 the superstructure would not yield. On the other hand, the retaining wall clearance would impose no influence on the performance of the isolated building if the clearance is greater than δ₂. Especially, the minimum required clearance, δ₁, is of essential importance for the performance design of base-isolated buildings. A simple equation of estimating δ₁ for buildings with various parameters is proposed through data regression. In addition, a procedure of determining the required strength for the superstructure, given a seismic intensity, is also proposed.