Predicting torsional response via an effective stiffness-based seismic assessment procedure

Architectural layouts often require buildings to be structurally asymmetric in plan. During earthquake excitation the asymmetry induces a torsional component of response, which can negatively impact performance and render simplified seismic assessment procedures less effective at estimating demands. This paper investigates the seismic response of single-storey asymmetric-plan systems subjected to unidirectional earthquake excitation. A new procedure is developed that leverages off existing displacement-based assessment principles and has a strong focus on the mechanics of the problem at hand. The procedure relies on the assumption that the centre-of-mass displacement can be accurately determined using an equivalent single degree-of-freedom system. The rotation of the system is then determined using a novel approach that assigns effective stiffness properties to the structural elements. Comparison with benchmark results from nonlinear response history analysis shows that the procedure can provide good estimates of displacement demands on structural elements. It is therefore concluded that the procedure may serve as a robust starting point for further development to include the consideration of torsion within multi-storey buildings subject to bidirectional excitation.