Simple seismic design and assessment of buildings incorporating the displacement controlled phenomenon

Seismic design, or assessment, of buildings based on conventional force-based principles typically involves trading-off strength with ductility to provide sufficient capacity of the building to absorb energy in a controlled manner when excited into motions by an earthquake. In conditions of moderate ground shaking which is generated by a small or medium magnitude earthquake the energy demand on the building could subside with increasing effective natural periods. Consequently, the amount of drift imposed on the building could be limited irrespective of the degradation in strength or stiffness of the lateral resisting elements. Seismic response behavior of this nature can be explained by what is known as the displacement-controlled phenomenon. The assumption of a peak displacement demand limit (which is function of the properties of the ground shaking) can potentially simplify the seismic design or assessment of a structure which is flexible or has the capacity to undergo large displacement without collapsing. A generalised response spectrum model which features displacement-controlled phenomenon was first developed to provide seismic response predictions assuming linear elastic behaviour. The model has since been further developed from results generated by parametric studies involving extensive non-linear time history analyses to incorporate the effects of inelastic behavior and torsional actions. The maximum drift demand on a building, of symmetrical or asymmetrical construction, can be conveniently estimated using the developed model thus circumventing the need to undertake time consuming modelling and computations.