# Seismic Risk Analysis of Existing Link Slab Bridges Using Novel Fragility Functions
## 1 Introduction
Indeed, the common practice, according to the existing literature, is that of cataloging bridges within homogeneous fragility classes [23; 24; 25], performing fragility analysis focusing on either the overall performance of the bridge or based on a unique response parameter [26; 27; 28], where often an \"in-series\" system assumption is invoked for the evaluation of the global failure [29; 30; 31; 32]. Some effort was made by a few authors to address the problem of multiple critical components in seismic assessment of bridges [33; 34; 35; 36; 37]. Figure 1: (**a**) Typical consequences of the expansion joints permeability: degradation and corrosion of a cylindrical hinge bearing device. (**b**) Debris and materials accumulation within an expansion joint compromising its functionality. However, the main difference of the strategy adopted here with respect to the common approaches currently available relies on the capability of the novel fragility functions to retrieve more specific and detailed information on the possible failure modes, without limiting the analysis to the global failure conditions but also considering several intermediate damage scenarios (including one or more damage mechanisms), and providing insights on the numerosity of elements involved within a given damage scenario. For instance, while classic risk analysis approaches do not permit a wide spectrum of information on the expected damage conditions but only permit a global assessment (e.g., global attainment of a given limit state), the proposed methodology is capable of providing the probability of attainment of a given limit state by a specific structural component or by a group of two or more components. A set of case studies is presented, consisting of LS RC bridges with different geometries, which have been preliminarily designed according to the codes that were enforced in Italy during the 1970s. These systems are modeled in OpenSees and Multiple-Stripe nonlinear time-history analyses are carried out to build proper demand models, from which various types of fragility functions are determined according to two limit states, the damage onset and near-collapse. Mean annual rates of exceeding are thus estimated for both limit states through the convolution between the hazard and the fragility. The results shed light on the main failure mechanisms characterizing this bridge typology, highlighting how different levels of risk (hence, safety margins) can be associated with failure scenarios that differ in terms of elements/mechanisms involved and damage extension. A comparison in terms of annual rates of failure is made considering the different bridge geometries. The paper structure is as follows. The methodology is presented in the former part of the manuscript in order to highlight the novelty and the strengths with respect to classic seismic vulnerability analysis. Case studies are then introduced providing details about the geometry, the simulated seismic design process, the numerical modeling strategy and the considered response parameters and related capacity thresholds. In Section 4, results are presented in terms of both fragility functions and mean annual rates of exceedance considering the damage onset and collapse limit state and quantitative insights concerning the reliability level achieved by these systems are provided. The paper ends with a conclusive section in which all the most relevant results are recapped.