Performance-based seismic response of frame structures including residual deformations. Part I: Single-degree of freedom systems

The development of performance-based approaches for the design of structures to withstand earthquakes requires the capability to assess performance under different levels of seismic excitation. Although a great deal of work has been completed towards this goal, most of the efforts have focused on the maximum transient response or the cumulative energy dissipation characteristics as the main response indices. Considering the inevitable reality of residual deformations for systems responding in the material nonlinear range and the importance of these permanent deformations to performance characterisation, an alternative approach to quantifying performance is explored in this contribution. In this first of two companion papers, after discussion of the limitations of current performance assessment techniques to fully describe the post-earthquake state of a structure, the framework of a performance evaluation based on residual deformations including both structural and non-structural elements is first presented. A first insight into the parameters that influence residual deformations is presented through time-history analyses of hysteretic single degree-of-freedom systems. Hysteretic characteristics, post-yielding stiffness as affected by P-Δ effects, as well as maximum ductility are found to greatly influence residual deformations. It is also shown that without considering residual deformations, the performance of systems that are inherently self-centring cannot realistically be compared to other systems that sustain residual deformations.