# Retrofitting of Bridge Slabs for Safety Railing Refurbishment in Italy: A State-of-the-Art Review
## 1 Introduction
In this code, the focus is the safety of the bridge structural members, while the railings are accounted as accessory elements with lower importance and scarce potential effects on the users' safety. Several Italian road management bodies have started the requalification of road railings (e.g., Figure 1), even though the extension of the national road network requires huge investments that should be allocated considering precise criteria for prioritization, based on the risk generated by the traffic volume (average daily traffic, representing the exposure) and the adequacy level of installed railings, which represents the vulnerability. Figure 1: Photo and scheme of pre- (**a**) and post- (**b**) railing refurbishment intervention on a reinforced concrete bridge. Such investment needs are increased by the inadequacy of supporting elements of bridge barriers. Most available research on the topic has been focused on evaluating the response of safety railings to accidental actions (crashes) [15; 16], neglecting the adequacy of supporting elements like the slab. According to [5], in case a railing is replaced, an H2, H3, or H4 class new railing must be installed depending on the type of road (motorways, extra-urban roads, and urban roads) and traffic volume (also as a percentage of commercial vehicles with mass higher than 3.5 tons). H2, H3, and H4 barriers have increasing containing capacity and are usually installed on bridge edge curbs through chemical anchors. Figure 2 compares old bridge barriers and new ones [17]. These latter (shown only as illustrative models among the wide variety of commercially available devices) are taller than the old ones and are equipped with a 3-wave profile instead of a 2-wave profile. Moreover, connecting elements placed at the top of the barrier are more robust allowing a better collaboration between consecutive posts, thus increasing the containing capacity of the device. In most cases, the bridge slab has a structural capacity insufficient to allow the installation of an up-to-date railing. In fact, the higher the resistance of the barrier, the higher the stresses on the supporting elements. This forces to carry out strengthening interventions on the bridge slab, with a consequent increase in time and cost to carry out works. Furthermore, there can be cases in which the curb is not geometrically suitable for the new railing solution, and works are needed to adapt it. It is worth noting that the bridge edge curb is the part most sensitive to material deterioration possibly impairing the railing effectiveness. Recent studies have shown that this issue can be solved using composite materials not affected by corrosion [18]. However, the structural integrity and durability of bridge edge curbs are not the focus of this study, being devoted to bridge slab structures. This paper is devoted to illustrating the assessment and design methods as well as the most frequently used strengthening techniques to increase the slab structural capacity making it suitable for the railings' installation in Italy. It is worth noting that possible aerodynamic issues on cable-stayed or suspended bridges due to railing installations are not treated here, and they should be addressed in a specific work. This study deals only with single- and multi-span bridges not subjected to aerodynamic problems, representing by far most Italian bridges.