PSI - Issue 62

Giuseppe Colombo et al. / Procedia Structural Integrity 62 (2024) 377–384 Colombo, Mariani, Lambrugo, Giardina/ Structural Integrity Procedia 00 (2023) 000 – 000

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As a result of the above, Prof. Martinez proposed a series of interventions that would be carried out after the completion of the doubling of the river crossing and the diversion of the traffic on the new structure. These interventions consisted of: demolition and reconstruction of the upper slab with thickness increased to 0,35 m; increase in thickness of the web of the beams ends adjacent to the Gerber saddle, for a length of 4,5 m and realization of a crossbar above the support section; increase of thickness of web of box girders close to the Gerber saddle; formation of an external cable prestressing system for both buffer (fig. 3) and box beams; replacement of the elastomeric bearings at the Gerber saddles, modification of the top of the piles and installation of pot bearings.

Fig. 3. Prestressing cables installed on external web of buffer beam

1.3. In-depth inspections of 2016 In 2015, following the results of periodic visual inspections, an in-depth investigation campaign was contracted to assess the state of degradation of the work and verify the efficiency of the interventions realized in 1992. The investigation consisted of a series of geometric and visual reliefs of the work, extended both internally and externally to the caissons, and to the buffer beams, as well as the extraction of many concrete samples, elements of reinforcing bars and of prestressing tendons, from the different parts of the deck. The state of deterioration of the piles and the abutments of the bridge was also assessed. To evaluate the tension in the external prestressing cables, the individual strands were stretched, determining the detachment force and therefore the pre-existing tension. The investigations have allowed us to reach a level of knowledge of the work classifiable as LC3. In summary, it was highlighted that the prestressing with external cables had significantly lost his effectiveness, the additional thickness of concrete casted over the upper slab was not sufficiently connected with the pre-existing one, the Gerber saddles were affected by a serious state of deterioration due mainly to the percolation of water from the overlying joints and to the contact between the box girders and the buffer beams. Several strands of the prestressing tendons were totally inactive, some of them resulted with a length very shorter than the cable, finally the protection of strands was realized using a corrugated pipe totally inadequate for the function requested. 1.4. Evaluation of warning class and safety verification The results of the in-depth investigations on the state of deterioration of the structure were taken as the basis for the development of a structural restoration project, that later, after the issuance of the NTC 2018, was updated and integrated, also providing for the requalification of the structure against seismic loads. The project was completed by a safety assessment (level 4 according to the “ Bridges Guidelines ”) which led to the limitation of northbound carriageway traffic to 2 lanes. This limitation was materialized through the installation of two alignments of New Jersey barriers to ban the emergency lane and the fast-overtaking lane. After the issuance of the "Bridges Guidelines", the overall warning class of the viaduct was determined by applying the multi-criterion methodology described in them (fig. 4).