Seismic robustness and resilience of structures in the framework of the JCSS

The awareness of the significance of robustness and resilience of structural systems has gradually intensified over the years. However, robustness and resilience of structures under strong earthquakes have not been paid much attention to in the earthquake engineering community. The great Wenchuan earthquake occurred on May 12, 2008, which caused severe damage and collapse of many structures and huge society costs, have highlighted the importance of robustness and resilience as desirable seismic performance of structures. In this paper, a new framework for engineering risk assessment is applied to evaluate seismic risk of structures, which extends the concept of direct and indirect consequences and associated risks in probabilistic systems modeling formulated by the Joint Committee on Structural Safety (JCSS) to facilitate modeling and analysis of seismic resilience in addition to robustness. The seismic robustness of structures is assessed by a consequence-based index, defined as the ratio between the direct consequences and the total consequences. Moreover, based on recent insights into the modeling of robustness, the quantification of resilience is formulated utilizing a scenario based systems benefit modeling in which resilience failure is associated with exhaustion of the capital accumulated by the system of time. Numerical studies of a simple structural system are performed using the framework and the two new indicators. The relationships of seismic robustness with some other system properties, including over-strength, and redundancy, are investigated, the correlation between robustness and resilience are also shown. The approaches to increasing seismic robustness and resilience of structures are finally suggested.