System loss assessment of bridge networks accounting for multi-hazard interactions

This paper details an integrated method for the multi-hazard risk assessment of road infrastructure systems exposed to potential earthquake and flood events. A harmonisation effort is required to reconcile bridge fragility models and damage scales from different hazard types: this is achieved by the derivation of probabilistic functionality curves, which express the probability of reaching or exceeding a loss level given the seismic intensity measure. Such probabilistic tools are essential for the loss assessment of infrastructure systems, since they directly provide the functionality losses instead of the physical damage states. Multi-hazard interactions at the vulnerability level are ensured by the functionality loss curves, which result from the assembly of hazard-specific fragility curves for local damage mechanisms. At the hazard level, the potential overlap between earthquake and flood events is represented by a time window during which the effects of one hazard type on the infrastructure may still be present: the value of this temporal parameter is based on the repair duration estimates provided by the functionality loss curves. The proposed framework is implemented through Bayesian Networks, thus enabling the propagation of uncertainties and the computation of joint probabilities. The procedure is demonstrated on a bridge example and a hypothetical road network.

本论文详细阐述了面向潜在地震与洪水灾害的道路基础设施系统多灾害风险评估整合方法。需开展统一协调工作，以统一不同灾害类型下的桥梁易损性模型（bridge fragility models）与破坏等级（damage scales）：本研究通过推导概率功能曲线（probabilistic functionality curves）实现了该目标，该曲线可表征给定地震动强度指标（seismic intensity measure）下，系统达到或超过某一损失水平的概率。此类概率工具是基础设施系统损失评估的核心支撑手段，因其可直接输出功能损失结果，而非仅提供物理破坏状态。易损性层面的多灾害交互效应可通过功能损失曲线实现表征，该曲线由针对局部破坏机制的单灾害易损性曲线（hazard-specific fragility curves）整合得到。在灾害层面，地震与洪水灾害间的潜在重叠影响通过时间窗口（time window）表征：该窗口内某一灾害类型对基础设施的影响仍可能存续，该时间参数的取值基于功能损失曲线给出的修复时长估算结果。所提出的评估框架依托贝叶斯网络（Bayesian Networks）实现，可完成不确定性传播与联合概率（joint probabilities）的计算。本研究以一座桥梁示例与一条假想道路网络为例，演示验证了该评估流程。