Are Existing Seismic Torsion Provisions Achieving the Design Aims?

A simple approach to the consideration of torsional effects on the ductile seismic response of buildings is suggested. Instead of increasing torsional strength, the control of twist, which may amplify local inelastic translational deformations, is emphasised. This may be achieved when assuring in the design that some residual stiffness in ductile systems is available. To this end a classification in terms of torsional restraint is suggested. It is postulated that traditional codified techniques, based on the evaluation of torsional effects on elastic systems, are largely irrelevant to ductile structural response. The primary consideration of inelastic deformation demands rather than strength is advocated. The presentation addresses foremost concepts of torsional behaviour and their relevance to routine seismic design, rather than advancement in analytical techniques.