Reliability-based indicator for post-earthquake traffic flow capacity of a highway bridge

Abstract

Bridges are one of the most critical but vulnerable components in a transportation network during an earthquake event. Due to structural damage, the post-earthquake safety of bridges can be reduced significantly, and in order to maintain their safety, the allowable traffic flows of bridges are often controlled or regulated. Since the post-earthquake traffic flow capacities of bridges play an integral role in assessing the flow capacity of a transportation network and subsequently evaluating the resulting disruptions to supply chain systems as well as the movement of people and vehicles, it is imperative to understand the expected post-earthquake functionalities of bridges as part of the transportation network. This paper proposes a reliability-based indicator for assessing the expected post-earthquake traffic flow capacity of a highway bridge. In this paper, the structural safety of a bridge before and after an earthquake event is expressed by its reliability index. In order to simplify the process of computing the post-earthquake reliability indices of a bridge associated with a wide range of earthquake intensities, a bridge-specific reliability-intensity surface is introduced to represent the reliability indices given a set of earthquake intensities and the associated uncertainties. Then, the post-earthquake reliability index of a bridge is linked to the resulting traffic flow capacity by adjusting the nominal values of the live load based on the post-earthquake remaining traffic flow capacity. Using the reliability-intensity surface and the relationship between reliability index and traffic flow capacity, the allowable traffic flow capacity of a bridge subjected to a given earthquake intensity is computed, and by considering a range of earthquake intensities to which a bridge is potentially exposed, the proposed indicator represents the average allowable traffic flow that can be carried by a bridge in the event of an earthquake.