# Retrofitting of Bridge Slabs for Safety Railing Refurbishment in Italy: A State-of-the-Art Review
## 3 Slab Assessment and Retrofitting Approaches  
### Structural Assessment  
When the guardrails on a bridge are replaced with newer and more resistant ones, the forces transferred in case of an accident, especially due to trucks, can be significantly higher. For this reason, the structural assessment of the elements supporting the barriers is mandatory. When installing a new railing (Figure 4a), checking the needed geometric requirements is necessary. In particular, the dimensions of the edge curb should fit the barrier base plate dimensions. If this check gives a positive result, the effect of the barrier failure in case of a crash must be evaluated. In this case, it can be assumed that the railing posts are subjected to plastic deformation as happens in crash tests performed to approve a safety device. Therefore, the plastic bending moment of the post must be evaluated as a consequence of the truck crash (Figure 4c). Given that they are made of ordinary steel, simple structural engineering methods may be adopted. Based on the post actions, sections 1, 2, and 3 in Figure 5a must be checked. Sections 1 and 2 are subjected to shear, bending moment and axial load, while Section 3 is subjected to shear and overturning moment. Figure 4: (a) Bridge deck section with reinforced concrete slab, (b) guardrail supporting elements and critical sections, and (c) truck impact position. Once the post plastic moment \(\mathrm{M_{rd,pl}}\) is calculated, the horizontal crash force \(\mathrm{F_{h}}\) should be derived taking into account a height of 1.00 m from the road pavement, as reported by the Italian and European codes [29; 30; 31]. It is worth noting that \(\mathrm{F_{h}}\) represents the tensile axial load acting on slab sections 1 and 2 (Figure 5a). Section 1 has a width equal to \(2a+b\), where \(b\) is the barrier plate width, and \(a\) is the slab cantilever length (Figure 5b). This assumption is based on the commonly adopted \(45^{\circ}\) stress diffusion, even though more refined methods can be used (e.g., finite-element analyses). Once the crash loads are computed, they must be increased by a factor of 1.5 according to the Italian code and combined with other live and dead loads. Among the live loads, the weight of the truck wheel applied near the curb (Qk in Figure 4c) must be considered (200 kN according to the Italian code [29]). The load combination must be applied to a simple structural scheme represented by the bridge slab cantilever extending from the external beam. Safety checks in sections 1, 2, and 3 must be performed based on an accurate knowledge of the existing bridge. Information on geometry, material properties, and structural details must be gathered through inspections and in situ and laboratory tests. Figure 6 shows investigations for the design of a safety railing refurbishment of an RC bridge. Note that the parapet in Figure 6a,b is made of provisional elements installed only for the safety of workers, while the type of guardrail to be installed is similar to that shown in Figure 2 (H2, H3, or H4). In particular, the investigations of Figure 6 are devoted to detecting the type and number of rebars placed in correspondence with the external beam axis, which is the most stressed section of the slab. This must be performed by removing road pavement and concrete cover until reaching the reinforcement. Moreover, further investigation is necessary on the edge curb (Figure 6a). The number of these investigations should be set based on the availability of bridge design documents as well as its total extension. It is worth noting that most bridges built in the period 1950-1970 have no design documents, and, in those cases, the in situ investigations should be more accurate since the structural knowledge must be obtained starting from scratch. Figure 5: (a) Crash actions on the railing and (b) plan view of the effective slab sections. In the occasion of these investigations, material sampling is also to be performed to determine strength values to be used in safety checks.