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 Kaikoura (2016) earthquakes has questioned New Zealand’s established seismic resilience. The excessive direct and indirect costs due to downtime and non-structural damage highlighted the need to move towards new performance indicators. Resilience holds the key to describe the performance of modern structures by requiring low failure probabilities, reduced consequences from failures, and less recovery time. Combining the concepts of resilience directly with the structural design process can increase the confidence in implementing damage-resistant technologies to reduce the damage of bridges in an earthquake. Furthermore, translating resilience measures with concise and meaningful terms to decision makers will lead to a better understanding of the benefits of mitigation. 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 (PBD) is a supplement to code objectives and intends to demonstrate that pre-identified earthquake performance objectives for the structure are satisfied. Yet, it does not include explicit verification of the expected functionality of the structure after the earthquake. On the other hand, resilience-based design (RBD) 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 structural performance of road bridges during the Kaikoura Earthquake and introduces the severely damaged ones as case studies. For each of the analyzed bridges, a seismic resilience curve has been developed based on the observations made during site inspections and data obtained on the functionality of the bridges over the time following the earthquake. A framework to incorporate the resilience concepts and measures, as key design criteria and indicators, into the structural design process is also introduced and exemplified using the case studies. Applying the proposed framework during the design phase will allow the estimation, by defining different recovery strategies, of final recovery times and preliminary recovery costs of the bridge after an earthquake.