Exploring reliability based bridge design framework against accidental loads - ship collision

As today's urban environments and civil infrastructures are highly complex and interconnected, accidental events such as fire, explosion, dropped objects, and collision of vehicles or vessels are more frequent than in the past and are causing critical structural damage and socioeconomic costs. Therefore, in order to achieve structures that are robust against such hazards, accidental loads should be appropriately considered during the design process. To this end, this paper explores a reliability-based structural design framework for accidental loads based on recent research experience in bridge design against ship collision. The proposed design framework employs a scenario-based simulation in which the occurrence of an accidental event and the resulting structural loads are modeled in a probabilistic manner. The probability distribution of accidental loads is then determined based on the occurrence probabilities of identified scenarios and the conditional probability of structural loads given each scenario. In order to estimate the structural responses caused by accidental loads, an appropriate type of structural analysis is carried out for the prescribed limit states representing collapse or other types of structural failures. As an illustrative example, this paper presents reliability analysis of a cable-stayed bridge whose piers are subject to ship collision hazard. The probability distribution of ship collision load is determined by the scenario-based approach, and the limit state of structural resistance is defined by the P-M diagram after identifying critical sections in the structure. To consider the dynamic amplification of bridge response by ship-bridge collision, time history analysis is performed for the configuration of equivalent static ship collision loads. This paper also summarizes the research needs and challenges identified while exploring the proposed design framework.