Numerical investigation for the nonlinear dynamic response of self-centring rocking frames

Conventional seismic design standards are rooted in the notion of collapse-prevention to ensure life-safety during major seismic events. To this end, modern code-conforming buildings are designed to accept a certain level of damage during earthquakes. Nevertheless, this design philosophy does not explicitly address damage mitigation, which leads to substantial post-earthquake economic losses. Rocking post-tensioned frames are a highly sustainable seismic design solution which remains operational after an earthquake event. They capitalise on the use of: (i) unbonded post-tensioned strands to provide overturning resistance and self-centring action, and (ii) rocking (opening) joints at the column-foundation and beam-column connections. Preceding research has proposed modelling strategies to capture the highly nonlinear behaviour of rocking structures. Nevertheless, numerical modelling techniques generating frequency response functions for the study of the non-linear dynamic properties of post-tensioned rocking moment frames without any sacrificial elements or external damping, are currently limited. Thus, it is imperative to develop modelling procedures which enable an accurate representation of the fundamental non-linear dynamic behaviour of rocking frames over a range of ground-motion excitations. The physical model of a steel post-tensioned rocking frame, which has been formerly tested under static and dynamic conditions, is employed in this paper in order to validate a new advanced finite element framework. A numerical study is presented, which incorporates a one-storey model, and includes static and dynamic responses. The results are compared with experimental and discrete-element models, and generalizable modelling considerations are presented. It is shown that the proposed method encompasses a simplified modelling approach and effectively represents the complete non-linear response of rocking moment-resisting frames.