A5 motorway “Turin – Quincinetto – Aosta”. Reconstruction of a damaged span of the Bessolo Viaduct deck.

Project objective

During works aimed at restoring the structural conditions of the deck of the “Bessolo” Viaduct on the A5 “Turin – Quincinetto – Aosta” motorway, the structural conditions of one span suddenly worsened, leading to the immediate closure of the carriageway.
Given the damage to the deck, its full replacement with a new structure was required, and our Company was entrusted with the Executive Design.
The design had to allow the controlled “deconstruction” of the span and its “reconstruction” within a very short timeframe to enable rapid reopening of the carriageway, considering that the motorway connects Northern Italy to France via the Mont Blanc Tunnel.

Project description

The “Bessolo” Viaduct is 213.00 m long and consists of 10 spans. The deck is made up of four girders connected by transverse beams in a simply supported grillage static scheme.
Built in 1960, it was the subject of studies that highlighted deterioration of the edge girders, particularly in the fourth span.
The concessionaire ATIVA S.p.A. had prepared a “structural restoration project”; however, there was a sudden worsening of span no. 4 (southbound carriageway) due to the failure of an edge girder caused by rupture of wires of the prestressing tendons, making replacement of the span deck necessary.

“Deconstruction” plan
A detailed plan for controlled deconstruction of the deck of span 4 was developed through sectioning of the structural elements using diamond blades and diamond wire saws and core drillings for slinging, followed by dismantling and removal using two mobile cranes positioned on the adjacent spans. The operations were planned to avoid damage to piers and adjacent spans, ensuring safety and control at every stage.

“Reconstruction” plan
After the “deconstruction” of the deck, restoration of the bearing seats at the beam supports was planned, followed by reconstruction of the deck by placing four precast prestressed reinforced-concrete girders and an upper slab on predalles. For erection of the girders, not feasible from the spans, a 400 t mobile crane operating from ground level was used. The intervention was organised with h24 works and monitoring of the involved structures and the adjacent ones, enabling reopening in a very short time.