Seismic Torsional Effects on Ductile Structural Wall Systems

With a distinct design rather than analysis-oriented approach, some torsional phenomena, arising during the elasto-plastic seismic response of building structures, are addressed. It is postulated that existing code recommendations, expressed only in terms of the properties of elastic structures, are largely irrelevant when the design needs to be based on ductile system behaviour. Torsional restraint provided by elastic elements of a system, is claimed to be the desirable property controlling the amplification of inelastic translatory deformations of critical elements by storey twist. With the identification of the sources of inelastic element deformations, a simple behaviour-based design strategy is proposed. This should ensure that the displacement ductility demand, expected to be imposed on the system, does not result in deformations that, as a consequence of storey twist, may exceed the displacement ductility capacity of critical elements.