Effect of serviceability limit state and over-strength mechanism on seismic performance of self-centring low damage structures with friction connections

Abstract

Low damage design is an alternative to conventional seismic design, where earthquake-induced damage in the building is controlled and minimised. The most common approach to implement this concept is to design the structural system in a way that damage occurs in a series of specified components. This makes the designer able to predict the performance of the building under earthquakes by deliberately designing these components weaker than the other parts of the structure. These components can be replaced, repaired, or even designed to remain functional after earthquakes. Therefore, the performance of such components (e.g. weak links) is critical for evaluting the performance of the building as a whole.The New Zealand standard defines two extra limit states in addition to the design level earthquake (Ultimate Limit State (ULS)). First is the Serviceability Limit State (SLS), where the system is expected to remain linear and elastic, and the second is the collapse limit state (also known as MCE limit state), where damage is accepted, but the building should not collapse. For a low damage system, the weak links should be designed to remain linear and elastic under SLS actions. Also, they should have adequate reserve capacity to not completely fail under MCE actions. The latter is also called the over-strength mechanism (or the upper bound design level) for designing the low damage components. This study investigates the effect of the over-strength and serviceability limit state on the overall seismic performance of low damage systems. Two types of generic structural responses are considered for the study, self-centring braced frames and self-centring rocking wall systems. Numerical models for both concepts are developed and subjected to nonlinear dynamic time-history analysis with different intensities up to large, rare events (MCE). The results showed that braced frames' appropriate over-strength capacity is relatively smaller than rocking walls. The findings of this study help designers and engineers to perform more efficient and optimised designs for low damage systems. Also, this research helps them to have a better understating of the performance of such systems under large, rare earthquake events.