As part of the Atlantic motorway, the North-South backbone of Galicia, the Rande bridge was the largest cable-stayed bridge in the world when it was commissioned, in 1981.

Spanning the Rande straits on the Vigo river, it is considered as a major civil engineering infrastructure in the country, with its 400-metre span and four traffic lanes.

An additional stay cable system was required when it became necessary to broaden the bridge to extend its load-bearing capacity.

  • Name of the owner
    Spanish Ministry of Equipment
  • Name of the client
    Highway concessionaire & Project Owner: Autopistas del Atlántico
  • Delivery date of the project
    November 2018
  • Partners of the project
    Engineering office: MC2 Estudio de Ingenieria & Manuel Juliá Vilardell
    Main contractor: JV Dragados & Puentes Infraestructuras (Puentes Group)
    Technical support to main contractor: Fhecor & Pondio JV
    Technical support to Project Owner: MC2 Estudio de Ingenieria & WSP Spain-APIA XXI
Widening the bridge to overcome traffic congestion

Overcoming traffic congestion

In 2006, 25 years after its inauguration, the average daily traffic flow of the bridge had reached 55,000 vehicles, a value close to the useful load-bearing capacity of the structure.
An initial analysis was requested with a view to widening by two lanes, one in each direction of traffic, by adding two new carriageways. After this initial analysis, the motorway operating company tasked MC2 Estudio de Ingenieria with the design of this innovative bridge widening project.
In 2015, the work contract was awarded to Dragados & Puentes Infraestructuras and Freyssinet for the implementation of the stay cables.
The widening of the Rande bridge had become an absolute necessity, with peaks of more than 70,000 vehicles per day. It had to address at the same time significant technical challenges.

An engineering challenge

A number of bridge extension projects have been carried out around the world, but most of them have been carried out on box girder bridges (steel or concrete) or on suspension bridges. There are few cases of cable-stayed bridge widening, and none on a scale as large as the Rande Bridge.
Impeccable planning and implementation were key factors in the success of the project, which had to comply with the following conditions:

  • No impact on traffic on the bridge and its access roads, with maximum safety throughout the works.
  • No environmental impact on the bay of Vigo.
  • Optimum resilience and maximum use of the strength of the existing bridge.

The enlargement project consisted of adding two additional steel decks on either side of the existing deck.
These new decks had to be placed on the outside of the pylons, with no continuity between the original and the widening lanes. The connection between the original and the new deck is made by means of spherical hinges in order to achieve an efficient behaviour of the structure. These elements have been subjected to specific tests due to their innovative use and structural impact.

Connecting steel deck with spherical hinges
New stay cable system

Visually harmonious stay cable system

The side decks were suspended by HD stay cables, anchored in the pylon struts, recreating the shape of the original stay cables. The stay cables were also anchored inside the box girder, which is 1.5 metres wide and 2.3 metres high. They could hence be inspected from the widening decks for maintenance purposes.
The longitudinal interval of the anchorages of the new stay cables on the deck also coincided with that of the existing stays, so that the entire stay system was visually perceived as parallel and orderly. Quite the opposite of the “cobweb” effect expected with so many stays. The cables of the stay cable system are Monostrand® cables, with a cross-section of 150 mm. The number of strands per stay varied from 44 to 91 for the outer ends.

High productivity and safety requirements

Because of the size of the widening decks (7 m wide) and the need to work without interrupting traffic, the Freyssinet team had to develop specific procedures to guarantee the safety of road users and site personnel, while meeting the contractual deadlines. More than 918 tons of stay cables had to be installed in less than 6 months, i.e 3 to 11 cables each week!
In addition, as the decks were transversely articulated, the anchor points were subjected to rotation exceeding 50 mrad and stress in the order of 10% of nominal values during construction. Thanks to the tension filter of Freyssinet HD anchorages, no auxiliary elements were required.
The viscous dampers have been redesigned to avoid any interference with the guard rail. The three pistons have been grouped together in the same area, an ingenious solution that would not alter the working axis of the displaced piston, and therefore the operation of the whole system. Thanks to this innovative solution, any movement of the strand bundle activated all 3 pistons.

  • 12
    Completion time for the bridge widening (months)
  • 80
    Number of new HD stay cables installed by Freyssinet
  • 411
    Biggest quantity of steel installed within 3 weeks (tons)

In order to face up the challenges inherent to innovative projects, the collaboration of all the people involved is required. Thanks to a good planification from the engineering team on site and a meticulous design from Freyssinet Technical Department, we were able to complete the works without traffic interruption, in conditions of maximum safety for the road users and the workers.

Jorge  
Cable Structures Manager, Freyssinet Spain
Improvement of the stay cable system fatigue behavior

A technical masterpiece from a structural viewpoint

The project has succeeded in minimizing the impact on the existing cable stays of the additional loads due to the bridge widening, and even virtually eliminating them.
The cantilever design of the additional decks allowed the existing stay cables to be relieved, even for permanent loads, when upward loads occurred at the interfaces with the central deck.
On the other hand, changes in amplitude of the stresses to which the cables were subjected as a result of overloads on the deck considerably improved their fatigue behavior.
Lastly, the wind behavior of the structure had also been improved by presenting a slender and aerodynamic profile in cross-wind, as well as a lower wind resistance.

Extending the service life of the whole structure

The widening of the bridge extended the useful life of the whole structure.
To guarantee this lifespan, an inspection and maintenance plan was drawn up and budgeted for upon commissioning. This plan included initial refurbishment work, particularly on the main pylons, abutments, deck, joints and original cables.

The bridge is now used by 95,000 vehicles per day, 20,000 more than before the widening work.

Extending the service life of the cable-stayed bridge