Recovery and requalification of bridges using innovative techniques and materials

Three interventions in Emilia-Romagna The Leo Bridge The Leo Bridge spans the Leo stream on the S.P. 324 “Passo delle Radici” road, near the town of Fanano in the Upper Modenese Apennines. The bridge crosses the Leo stream with a single span, using a double arch solution with an upper theoretical span of approximately 50.00 m and a rise of 9.00 m.

The reinforced concrete arches, connected by crossbeams, support the deck with the help of pillars. The cross-section has a total width of 7.85 m, including the parapets. Prior to the intervention, the structure exhibited evident signs of structural deterioration, along with additional critical issues discovered during the investigations, including:

• Cracks on the intrados of the arches at the abutments.
• Advanced deterioration of the concrete, particularly on the intrados of the key arch, with exposed and deteriorated reinforcement.
• Absence of reinforcement bars in the arches, which instead featured a sort of steel mesh made from recovered material and used as temporary formwork during construction. The effectiveness of this mesh as reinforcement is uncertain, especially regarding issues of adhesion.
• Low concrete strength revealed by material tests, with particularly low results for the arches and pillars, as well as a general scarcity of reinforcement in the reinforced concrete.

The intervention involved the structural upgrading and seismic improvement of the bridge through the jacketing of reinforced concrete elements using fiber-reinforced concrete with a thickness of approximately 8 cm, along with appropriate reinforcement. Other measures included reducing the inert material fill, replacing the expansion joints with suitable ones capable of accommodating static and seismic movements, consolidating the abutments by repairing the damaged parts of the stone walls with squared rubble masonry, and reinforcing them with micro-piles immediately upstream.

The Albergone Bridge The Albergone Bridge spans the Lamone River on the former S.S. 253 road, located between the towns of Lugo and Bagnacavallo (RA). It is a reinforced concrete bridge with three spans measuring 19.00 m, 23.00 m, and 19.00 m. Prior to the intervention, the bridge exhibited widespread exposure of the reinforcement, with oxidation, as well as systematic deterioration of the Gerber saddles.

Significant reinforcement interventions were required to address the aforementioned deterioration and to adapt the structure to increased traffic loads compared to the design loads of the structure. To accommodate static loads, the beams were reinforced for bending and shear using “carbon fibers” bonded to the existing structure with epoxy resins.

The deck was also made continuous by eliminating the intermediate joints, which also eliminated the systematic deterioration affecting the saddles. Pre-compression bars, such as Dywidag bars, were introduced at the beam joints near the Gerber hinges. The design of the Dywidag bars was carried out to balance the entire load action transmitted by the carried beam to the supporting corbel.

For seismic retrofitting (required due to the aforementioned structural scheme change), hydraulic dampers (shock transmitters) were installed, and the abutment supports were replaced with multidirectional supports to ensure the transfer of loads to the abutments. The abutments were properly reinforced with lateral micro-piles and tension ties placed behind them.

Some overall and detailed schematic diagrams are provided to illustrate the interventions, particularly regarding the carbon fiber reinforcements.

The Long Bridge of Brisighella The Long Bridge of Brisighella, serving the former S.S. 302 and crossing a transverse depression of the Lamone River, features two box-shaped reinforced concrete abutments (with a deck consisting of beams and crossbeams), two side access decks with a span of 10.65 m, and a central span with an arched solution of approximately 35.00 m.

The design and renovation works of the bridge aimed at a significant widening of the roadway, capacity upgrade for loads of the then first category, and a marked seismic improvement. The structural renovation with strengthening of the deck structures, both the ones with spans and those on the volumes of the abutments, was achieved through the application of carbon fibers in appropriate configurations.

From a technical and technological perspective, the project and subsequent implementation involved significant interventions on all structural components, including the widening and continuity of the entire deck from abutment to abutment. Supporting the deck widening required the construction of challenging transverse corbels at the frame locations on the arches.

The significant seismic improvement led to a significant increase in horizontal forces attributed longitudinally to the arch system and transversely to two important frames. The frames also include the original rows of pillars (gathered in two large reinforced concrete columns) connected by a metal structure with symmetric diagonals relative to the center of the column and arranged in an inverted V shape to contribute significantly to the ductility of the column.

The deck’s stiffness in its plane determines collaboration between the piles and arches, which has been well investigated and identified through spatial finite element modeling.

Materials Used For structural reinforcements with FRP (Fiber-Reinforced Polymers), the Betontex® system from Fibre Net (https://www.fibrenet.it/context/infrastrutture/application/) was used. It consists of carbon fiber fabrics, nets, flakes, laminates, and preformed bars, combined with epoxy matrices. Thanks to their high mechanical properties, lightweight, and corrosion resistance, Betontex® fiber-reinforced systems are used for structural restoration, improvement, and seismic upgrading of infrastructure works.

The use of Betontex® systems allows for:

• Reducing deformation and bending stresses.
• Increasing loads.
• Improving performance in cases of degraded or insufficient internal reinforcement, ensuring durability and long-term structural performance. The Betontex® system has the Technical Assessment Certificate (Certificato di Valutazione Tecnica, CVT) and can be used for preventing local collapse mechanisms and/or global collapse mechanisms. The fiber-reinforced cladding allows for increased shear strength, flexure in-plane and out-of-plane of masonry.