Issue 46

F. Bazzucchi et alii, Frattura ed Integrità Strutturale, 46 (2018) 400-421; DOI: 10.3221/IGF-ESIS.46.37 410 Throughout the same years, the Akragas Viaduct (S.S. 115-AG, Agrigento, 1970) was erected in Sicily. The design, by Morandi, considered a total length of 1400 km skewed viaduct with 31 spans, each 44 m long (Fig. 13(a)). The deck, 10 m wide, was realized by a grillage of 3 unbonded prestressed I-beams, 5 transverse beams, and a precasted pavement (Fig. 13(b)) [23]. Support for each beam consisted in a couple of reinforced concrete A columns, with a maximum height of 60 m. To date, these latter elements represent the key vulnerability of the structure. Each column was erected through a concrete concave precast box that works both as scaffolding (in the pouring phase) and as shear resisting element (Fig. 14(a)). It is reasonable to think that visible damage is due to the concave shape of the external box. When shear forces required confinement, the bars pushed against the box bulged the internal part as visible in Fig. 14(b). Together with the static problems, the retrofitting intervention has the aim of improving the seismic behavior by providing sufficient shear strength and ductility: a new element and the recovering of a confined state for the concrete of the core. Figure 14 : Column details (a) ; state of decay of the columns (b) . Petrulla Viaduct characteristics have been discussed in section 1. The oxidation of the reinforcing and of the prestressing cables (Fig. 2(a), Fig. 2(b)) occurred due to an inadequate protection by carbonation and water seepage. Through the results of the vulnerabilities, four different restoration interventions have been proposed, corresponding to the observe damage degree (Fig. 3(a), Fig 3(b)). For the level one (G), the removal of the actual concrete coverage and corroded bars, followed by their complete refurbishment, was suggested (Fig. 15(a)). Considering the second level (Y), to assure the adequate safety factor, the installment of a metallic plate was suggested to reinstate the base of the I-beam. This plate was supposed to be connected to the web through two lateral bolts and a glued to the base of the I, previously abrase. The injection of epoxy resins realized the final sealing and the protection from further corrosion. For the third level (B), the intervention is the same of the discussed previous one with the additional injection into the prestressing cables with low- viscosity epoxy (Fig. 15(c)). Concerning the worst damage case (R), the corroded section area of the strand must be recovered to fulfill the safety factor. In order to do so, an external prestressing was suggested, connected to the sealing steel plates and the cable header (Fig. 15(d)). Considering now the case of La Reale Viaduct (Fig. 7(a)). Durability problems are overcome by the peculiar shape of the deck and its modular assemblage. To avoid a fragile collapse, the structure must improve its robustness. Since the analyses of the safety of the infrastructure are still under exploitation, different levels of intervention are suggested towards the observed damage pattern. For the spans that will evidence lack of cable protective grout, epoxy injection would be necessary to stop di advancement of corrosion. This operation could result particularly difficult to do because of the inaccessible boxed section. A frequent problem in bridge concrete walls is concrete spalling and exposure of reinforcement. This situation is particularly dangerous when the exposed reinforcement realizes the primary load carrying system, i.e. dapped-end corbels (Fig. 5(a), Fig. 5(b)). Under this circumstances, health of the steel is essential to exclude a sudden collapse due to shear failures. Considering the numbers of the existing artifacts, sometimes just blocking the advance of corrosion represents a good strategy to keep reasonable safety factors while retrofitting is pending. This strategy cab be implemented by the use of sacrificial anodes (galvanic protection) directly connected to exposed reinforcements (Fig. 16) [24]. These anodes, usually realized in zinc-based compounds, guarantee local protection to the