The diagnosis performed by Freyssinet on the bridge built in 1989 revealed a severe deflection of the concrete deck. The stay cables showed signs of corrosion, degradation of their individual ducts and diverse tension levels between strands of the same cable exceeding the allowable service limit state.

  • Name of the owner and client
    Loire Departmental Council
  • Delivery date of the project
    June 2019
  • Partners of the project
    Arcadis (client’s consultant)
Additional prestressing with external PT cables to reinforce the deck

Strengthening the deck with additional prestressing

The project began in September 2017 by strengthening the deformed deck. The aim was to prevent the level of deformation from worsening further, rather than actually restoring the bridge’s initial geometry. Freyssinet installed two additional longitudinal prestressing tendons (27T15) and eight additional transverse prestressing tendons (4T15 S) in the first two crossbeams on each side of the deck. Access was required to the deck’s underside to anchor the cables. There were initially plans to provide access by erecting fixed tower scaffolding on the riverbanks. But Freyssinet ultimately set up a flying scaffolding system from the bridge deck to avoid encroaching on the footprint of the River Loire’s water levels.

23 pairs of high-tech stay cables

Once the deck had been strengthened, the next stage involved replacing the 23 existing pairs of stay cables, pair by pair. Since the stay cables could not be dismantled, they had to be detensioned strand by strand. Special jaws were used to carry out this tricky operation, since they provide accurate control over the detensioning level of each strand prior to cutting. Then the new Freyssinet H2000 stay cables (from 19T15 to 27T15) were installed in pairs, complete with an aerodynamic general sheath to fully protect and seal the cables. This technology includes an anchoring system that can be completely replaced and removed for even easier maintenance. New damper systems have also been mounted on the longest stay cables to eliminate vibrations and thereby ramp up their fatigue resistance.

New stay cable system installation
Alternate one-way traffic system during works

Traffic as usual during the repair work

The client wanted to keep the bridge open to traffic throughout the repair work. Freyssinet’s teams incorporated the client’s requirements into the work programme and methodology. An alternate one-way traffic system was set up, along with a vehicle measuring system to reduce waiting times at the temporary traffic lights.
The project was ultimately signed off in June 2019 and acts as a real showcase for Freyssinet’s expertise. In addition to carrying out additional prestressing and replacing the stay cables, micropiles were installed to strengthen the abutment on the left bank. Bearings were also replaced, and several concrete repair techniques were used, including cathodic protection, modified hydraulic binders (MHB), dry process shotcrete and Foreva carbon fibre fabrics.

Due to the sheer range of techniques used, the complete repair of the Pertuiset Bridge is an excellent showcase of Freyssinet’s expertise and demonstrates our ability to lead a project as a contractor.

Jean-Claude  
Works director, Freyssinet France

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