# Seismic Risk Analysis of Existing Link Slab Bridges Using Novel Fragility Functions
## 1 Introduction  
Bridges play a critical role within transportation and infrastructure networks. Their disruption can have a significant socioeconomic impact and their failure can jeopardize people's lives [1]. Over the last few decades, we have witnessed a significant growth of scientific literature focusing on vulnerability and risk assessment of bridges under diverse sources of danger. For instance, numerous studies have been focused on seismic-related problems (hazard, design, assessment, retrofit) [2; 3; 4; 5]; other works have been dedicated to flood and scour [7; 8; 9; 10], which are also serious phenomena undermining bridge stability and integrity. Some recent studies have been dedicated to special subjects, such as the reliability of existing prestressed bridges [11; 12], structural health monitoring strategies [13; 14], bridge inspection data analysis [15], and safety assessment under traffic loads [16]. Within such a wide context concerning bridges, the current paper focuses on the seismic reliability analysis of a widespread typology of bridges characterizing a broad percentage of the existing infrastructural networks worldwide. The systems at hand are represented by the class of multi-span simply supported reinforced concrete (RC) Link Slab (LS) bridges, based on a technology that has been widely employed over the past 50 yearsto realize structural joints in bridge superstructures [17; 18; 19; 20; 21]. It is known that expansion joints are traditionally provided and designed to accommodate deformations induced by temperature gradients in order to avoid structural problems, and they usually are effective in this aim, though some issues may arise when water drains through them, penetrating the substructures (piers and abutments), and thus contributing to and accelerating the degradation process of bearing devices and substructure themselves (Figure 1a). These joints are moreover prone to ruin because of the gradual accumulation of materials within them (Figure 1b). Continuous bridges can represent a solution to the aforementioned issues, but at the expense of generally higher complexity in the design process. A widely used alternative strategy to realize jointless bridges without renouncing the advantages of simply supported static schemes is exploiting a link slab solution. This allows the connection of the decks belonging to adjacent simply supported spans without resorting to specific expansion joint devices. In general, this solution is employed to realize one or more kinematic chains, composed of a given amount of jointless spans and a limited number of traditional expansion joints located at the end of these chains (and usually in correspondence with one of the two abutments), with the advantage of increasing the smoothness (consequently the safety) of driving, eliminating problems relating to atmospheric agents penetration on substructures. The large presence of existing bridges adopting this technology, designed and built before the entrance in force of proper and detailed seismic codes, is the main reason behind this study. Indeed, a thorough analysis of the seismic reliability offered by existing link slab-reinforced concrete bridges is, to date, missing in the scientific literature. A comprehensive probabilistic framework is thus proposed and adopted in this study to perform seismic reliability and risk analysis of these systems. One of the key points of the framework is represented by a novel practical-oriented procedure for fragility analysis recently proposed by [PERSON] et al. (2022) [22] with the aim of overcoming some limits of classical approaches and providing rapid and useful data to directly support the decision-making process.