Improving the resilience of highway systems to major earthquakes

Today life-safety is no longer the sole requirement for the successful design of a highway system for a major earthquake. Resilience has been added as an essential component of any design strategy to ensure rapid recovery and minimal impact on the socio-economic fabric of modern society. This realization has led to the concept of performance-based seismic design which is a relatively new development in the design and construction of civil infrastructure. Nevertheless substantial progress has already been made in this arena, particularly with respect to the performance of individual components of the built environment, such as buildings and bridges. But the real potential for performance-based design comes when these concepts are applied to systems and subsystems of the infrastructure, such as transportation networks, subject to both service load conditions and extreme events. This paper describes current efforts to apply performance-based design to the earthquake performance of highway networks in the United States. In recent years, a risk-based methodology has been developed for assessing the performance of these systems taking into account the seismic fragility of bridges and their interconnectivity, and estimating congestion and delay times. These efforts have opened the door to performance-based seismic design of highway systems, in which system-level performance criteria, such as maximum permissible traffic delay times and minimum restoration times, are targeted for highway systems immediately following earthquakes of different sizes. This methodology allows the resilience of highway systems to be defined and measured in quantitative terms (such as the time it takes to restore 80% of the system's pre-earthquake capacity). In doing so, financial and societal incentives can be developed that will improve resilience and at the same time reduce risk to life and property. The methodology can be extended to other critical infrastructure systems, such as mass transit, water supply, and telecommunications, and to other extreme events, natural or manmade.