Quantifying the seismic resilience of bridges: A pathway towards a resilience-based design

The loss of functionality of road networks during the past Canterbury (2010-2011) and Kaikōura (2016) earthquakes has questioned New Zealand's established seismic resilience. In both events, overall bridge performance was satisfactory from a life-safety perspective. However, based on the observed undesirable sub-system performance of the damaged bridges and on the direct and indirect costs due to downtime and non-structural damage, an investigation into possible improvements of the current design philosophy was warranted. Resilience can be considered as a performance indicator that quantifies the residual functionality along with the effort in responding to the seismic event. Resilience is not being considered in the seismic codes, as traditionally their main objective has been to prevent collapse and ensure life-safety. Performance-based design, as a supplement to code objectives, does not include explicit verification of the expected functionality of the structure after the earthquake. On the other hand, resilience-based design appears as a holistic design process, which identifies and mitigates earthquake-induced risks to enable rapid recovery in the aftermath of major earthquakes. This paper presents an overview of the recovery process of the Inland Route in the aftermath of the Kaikōura earthquake. The most severely damaged bridges in the route are introduced as case studies, and the main performance and functionality issues are highlighted. Based on this, a framework to incorporate resilience concepts and measures, as key design criteria and indicators, into the structural design process is also introduced and conceptually exemplified. Applying the proposed framework during the design phase will allow the estimation of final recovery times and preliminary recovery costs of the bridge after an earthquake.