Displacement-based design approach to earthquake-induced torsion in ductile buildings

Abstract

An unconventional, yet very simple, seismic design strategy for asymmetric-plan reinforced concrete ductile building systems is postulated. The proposal considers the need to address primarily inelastic displacement demands and available capacities, particularly those of lateral force-resisting elements remote from the centre of twist, rather than torsional strength. A brief review of existing and widely codified design procedures, applicable to elastic systems, is presented in order to demonstrate their irrelevance to needs arising during ductile seismic response. The emphasis of the proposed design approach is on the determination of a reduction of the anticipated seismic displacement demand on the system, necessary to ensure that the available inelastic displacement capacity of appropriately detailed critical elements is not exceeded. The concept of torsional restraint is used as a basis for a response classification. A few examples illustrate applications. Definitive design recommendations, which are very simple to use, are offered.