Limit height-to-width aspect ratios for slender base isolated objects of heritage architecture

Abstract

Seismic isolation has become a realistic alternative for decreasing the seismic vulnerability of heritage architecture. This article deals with a special technical aspect of base isolation design of slender rigid objects on elastomeric isolators, by considering the condition that the isolators cannot bear any tensile forces under simultaneous horizontal and vertical ground excitations. The main parameters that govern the response in this case are a) mass, mass position and height-to-width aspect ratios of the superstructure, b) stiffness, damping and plan arrangement of the isolators and c) expected horizontal as well as vertical earthquake acceleration components and their interconnections. The limit height-to-width aspect ratios were obtained for horizontal and vertical accelerations from the Eurocode 8 response spectra, as well as from dynamic analyses of seven near-fault ground motion records. The results are presented as maximum allowable aspect ratios for different vibration periods, ground conditions and design ground accelerations. The inclusion of vertical accelerations in governing equations is extremely important because different horizontal and vertical seismic loading combinations might significantly influence the maximum allowable height-to-width aspect ratios. The article concludes that the results from the response spectrum analysis are conservative. Although, in some ground motion records, the critical combination of horizontal and vertical response accelerations can also produce smaller limit height-towidth aspect ratios.