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This study aims to assess, in a probabilistic manner, the effect of seismic excitation direction on the performance of a 638 m‐long, 12 span prestressed concrete bridge with significant curvature in plan on the basis of overall monetary repair loss. By means of a large number of nonlinear dynamic analyses, the optimum intensity measure (IM) was selected from a pool of twenty candidates considering the impact of seismic excitation direction. Next, the variability of bridge loss with respect to the seismic incidence angle under different groups of earthquake intensities was obtained. Finally, the applicability of combination rules for the seismic performance of curved bridges was evaluated based on the multidirectional loss assessment results. Meanwhile, the effects of seismic excitation direction and earthquake intensity on the evaluation of combination rules were also revealed. Results indicate that velocity‐related or/and structural‐dependent IMs are more appropriate for the probabilistic seismic demand analysis of curved bridges. It is also notable that the total bridge loss gradually turns out to be independent of the seismic excitation direction as the seismic intensity increases and the damage develops throughout the structure. Additionally, the widely used 100/30 and 100/40 rules may lead to an unconservative estimation for the loss of the curved bridge. The above findings highlight the necessity of addressing the issue of ground motion directionality in a rigorous probabilistic manner and pave the way for further research on qualifying the influences of geometric configuration, material parameters, soil type and the consequent soil‐structure interaction effect.

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The effects of ground-motion spatial variability on the seismic vulnerability of a floating cable-stayed bridge with 420-m long main span are investigated using component and system-level fragility analysis methods. Four combinations of the spatial variability components are considered including (a) the incoherence effect; (b) the incoherence and wave-passage effects; (c) the incoherence and site-response effects; and (d) general excitation case including the incoherence, wave-passage, and site-response effects. Parametric study was carried out to assess the sensitivity of seismic fragility to the variation of spatial variability components. The results indicate that the bridge becomes more vulnerable under spatially varying excitations than uniform excitations. The fragile components and the bridge system become more vulnerable with an increase in incoherence level. The component and system-level vulnerabilities are not sensitive to the variation of apparent wave velocities in most cases. However, the site-response effect is more complex than incoherence and wave-passage effects. There is no general trend about its effect on different components, whereas the system fragility increases as the soil conditions of adjacent excitation sites change more significantly and the soil types vary from the soft to the firm along wave-traveling direction. In addition, the bridge tends to be more vulnerable if the soil condition of the reference site becomes softer for the general excitation case. Spatial variability effects, especially incoherence and site-response effects, should be considered in the fragility analyses of this type of bridges.