# Numerical Assessment of the Seismic Vulnerability of Bridges within the Italian Road Network
## 1 Introduction
Fragility curves have also been studied in the work of [PERSON] and [PERSON] [6], which proposed a methodology to develop bridge-specific fragility curves in order to improve the reliability of loss assessment in road networks and the prioritization of retrofit interventions. The method, which defines critical limit state thresholds for the components of the bridge, can be applied to a large number of bridges within a network. The approach presented by [PERSON] and [PERSON] [7] employs machine learning to generate bridge-specific fragility curves. The method has been tested through a case study consisting of a multi-span concrete bridge class, which can be found in California. The method is reliable and can be employed in risk assessment platforms, but additional studies are required to check if the methodology can be applied to other bridge configurations. [PERSON], [PERSON], and [PERSON] [8] studied the fragility of highway bridges. The research presents a fragility calculation method that takes into account multidimensional performance limit state parameters. Column ductility and transverse deformation in the abutments were considered as performance limit state parameters. The method can be employed to assess the vulnerability of bridges sensitive to multiple response parameters in a more reliable way, allowing also for implementation in loss estimation for the road network. In 2014, [PERSON] and [PERSON] [9] presented a parameterized fragility-based Multi-Hazard Risk Assessment procedure for the assessment of a portfolio of highway bridges exposed to earthquakes and hurricanes. The annual risk, measured as the annual probability of damage, is obtained by combining fragility functions and regional hazard data. The framework has been applied to multi-span simply supported concrete girder bridges, allowing the gain of insights on the influence of bridge geometry and hazard exposure on the risk. The framework can be extended to include other hazards, bridge types and regions, and concurrent occurrence along with independent hazards such as scour and collisions. [PERSON] [10] studied the use of Fiber Reinforced Polymer (FRP) composites in highway infrastructures. The use of these composites started around 1996 and is common in strengthening interventions. The long-term durability of FRP composites still requires additional research. In 2018, [PERSON] and [PERSON] [11] studied the effect of aftershocks on the seismic response of multi-span concrete bridges. Currently, aftershock effects on structures are not taken into account in design codes. Considering reinforced concrete (R.C.) continuous bridges, aftershocks can increase the system fragility, the displacement of the bearings, and the curvature of piers. The research of [PERSON] and [PERSON] [12] shows that the effects of multiple earthquakes during the life of a structure can produce a reduction in its seismic reliability. The study considers highway R.C. bridges. A degradation model has been developed and the results show that the seismic vulnerability of R.C. bridges can increase as a consequence of the seismic degradation in the columns. A recent work [13] studies multi-span R.C. bridges typical of Iran. Many existing bridges, designed at a time when there were no specific requirements in terms of cap beam-column joints, have poor details. The research analyzed the fragility functions of these bridges, highlighting that the seismic fragility of the structure is highly influenced by the fragility of the joints. The research is limited to regular straight bridges with multi-column bents, not including irregular structures in the fragility analysis. The work of [PERSON] et al. [14] provides a literature review on the seismic behavior of bridges and on the analytical methods that can be employed to assess bridge performance, including the methodology to develop fragility curves. Research by [PERSON] et al. [15] presents the comparison between four common approaches used in the literature in the seismic fragility framework, assessing their accuracy and applicability.