In performance-based seismic assessment, structural response is characterised using fragility functions based on a seismic intensity measure (IM). IMs are typically related to the characteristics of ground shaking and structural dynamic properties, with the spectral acceleration at the first and dominant mode of vibration, Sa(T₁), being a popular choice for buildings. In bridge structures, where no single dominant mode typically exists for bridges with some degree of irregularity, the use of Sa(T₁) may be inefficient (i.e. large dispersion) due to multi-modal transverse response. To avoid having to choose a single bridge mode when using Sa(T₁) and to appease the needs of bridge portfolio assessment, peak ground acceleration (PGA) can often be the IM used for bridge fragility functions in some countries. This study examines the efficient assessment of simple bridge structures characteristic of the European context by exploring different IMs based on Sa(T), peak ground velocity (PGV) or a recent candidate average spectral acceleration, AvgSa. Several case study bridges are evaluated via multiple stripe analysis with hazard-consistent ground motion records. The results indicate that PGA and PGV are indeed inefficient IMs compared to other IMs of similar complexity, especially at serviceability limit states, for the bridge structures examined. Also, a relatively casual record selection strategy is seen to not be suitable for risk assessment of bridges and can result in notable differences in risk. In contrast, AvgSa, which is an IM based on a simple combination of Sa(T) values across a range of periods, showed very good predictive power and robustness in terms of its risk estimates across all ranges of structural response. This was observed for the structure-specific IMs in addition to the group IMs used for assessing multiple structures with the same ground motion records. This study has thus shown these AvgSa-based IMs to be an appealing choice to consider for further examination in future fragility function and risk model development for bridge structures.

在基于性能的地震评估中，使用基于地震烈度测度（IM）的脆弱性函数来表征结构响应。IM通常与地震动的特性和结构动力特性有关，在第一振动和主导振动模式Sa（T ₁）处的频谱加速度是建筑物的流行选择。在桥梁结构中，对于具有一定程度的不规则性的桥梁，通常不存在单一主导模式，由于多模态横向响应，使用Sa（T ₁）可能效率低下（即，较大的离散度）。为了避免在使用Sa（T ₁时必须选择单桥模式），为了满足桥梁资产评估的需要，在某些国家/地区，峰值地面加速度（PGA）通常可以用作桥梁易损性功能的IM。这项研究通过基于Sa（T），峰值地面速度（PGV）或最近的候选平均频谱加速度AvgSa探索不同的IM，从而检验了欧洲背景下简单桥梁结构特征的有效评估。通过多条带危险一致的地面运动记录的条带分析来评估几个案例研究桥梁。结果表明，与其他具有类似复杂性的IM相比，PGA和PGV确实是效率低下的IM，尤其对于处于检查状态的桥梁结构而言，尤其是在使用性极限状态下。同样，相对随意的记录选择策略也被认为不适合桥梁风险评估，并且可能导致明显的风险差异。相反，AvgSa是基于Sa（T（）范围内的值，就其在所有结构响应范围内的风险估计而言，都显示出很好的预测能力和稳健性。除了用于评估具有相同地面运动记录的多个结构的IM组外，还针对特定于结构的IM进行了观察。因此，这项研究表明，这些基于AvgSa的IM是一个值得考虑的选择，可以考虑在桥梁结构的未来脆弱性功能和风险模型开发中进行进一步检查。