The local council in Verdun-sur-Garonne was particularly concerned about longevity of cables on its new suspension bridge, with the clear aim of keeping future costs to a minimum.

  • Owner and client
    Conseil Général du Tarn et Garonne
  • Delivery date
    2012
  • Partners
    Designer: EGIS-JMI Bordeaux
    Contractor: Groupement Sogea, Dodin Campenon Bernard, Freyssinet
    Architect: Lavigne Cheron
From design to installation of the whole suspension system

The structure is the longest suspension bridge equipped with Cohestrand technology and first one with a built-in-place suspension cable

As the implications of capital-investment decisions on whole-life costs become more widely acknowledged, there is a noticeable trend to give more weight to solutions that can extend the lifespan of elements such as cables, bearings and so on.

The structure is the longest suspension bridge equipped with Cohestrand® technology and first one with a built-in-place suspension cable. Execution was conducted following specific Freyssinet procedures.

  • 154m
    Span of metallic deck
  • 185
    Cohestrand® cables
  • 21m
    Height of metallic pylons
Verdun Garonne suspension bridge - Cohestrand technology

Cohestrand technology for the main cables

Such issues can affect bridges of all sizes in this part of France, and on some structures, full replacement of the main cable system had been required. Hence the client commissioning a replacement road bridge, was naturally concerned about durability and future maintenance costs.

With this in mind, the client chose to specify Freyssinet’s Cohestrand technology for the main cables and H1000 multistrand range for the hanger cables in place of a traditional locked-coil cable solution.

The triple corrosion barrier of Cohestrand technology offers a long-lasting solution

Verdun-sur-Garonne Bridge was built to replace the ageing structure at the same location and has a steel deck suspended from the main cables by 20 hangers along each edge. The steel towers are splayed outwards by 10°, with the inclination of the hangers decreasing gradually from 9° to fully vertical at the mid-span.

The triple corrosion barrier of Freyssinet’s Cohestrand technology was well suited to providing the necessary durability for this type of application. Some of the elements that had been designed for the prototype Kanne Bridge in Belgium – notably the hanger collar – were developed and improved for Verdun-sur-Garonne.

Verdun Garonne suspension bridge - cohestrand technology
Verdun Garonne suspension bridge - cohestrand technology

Improving offer

Here the hanger collars were designed with a bolted, rather than welded, assembly so that they could be easily removed or replaced if required. Likewise, for ease of construction the HDPE sheath was provided in two halves that were clipped together around the main cable once all the strands had been erected and the collars clamped, rather than strands having to be threaded through the sheath.

With the main cables anchored behind the bridge abutments, multihole deviation saddles were provided at the top of the towers and the cables were assembled by threading one strand at a time through individual ducts in the saddle made of a steel casing with high-performance fibre-reinforced concrete.

Assembly line

A more traditional erection method was employed at this site, to suit the size of the bridge and the construction process, with the cable assembled in its final position. The deck was first erected on temporary supports and a working platform was installed to give access to the tower tops once a few of the cable strands had been erected.

Verdun Garonne suspension bridge

The design and installation of the cable system was a challenge; it remains to date the largest use of Cohestrand technology for this type of application with 185 strands per cable. Each collar is clamped onto a cable composed of 40% HDPE; while the HDPE improves durability, its resistance and thermal expansion properties also create complexities for the structural system. With this project, Freyssinet again demonstrates that it is the leader in precision work for civil engineering activities.

Constance  
Project manager, Freyssinet major projects
Strands bundle
Close-up on strands through saddle
Collar hydraulic clamping
Collars and hangers’ installation
Hangers installed
Bridge finishings

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