Fatigued stay cables on the oldest of two bridges carrying the A50 motorway over the Waal River near Nijmegen were identified for replacement as part of a full renovation of the crossing, and a nationwide scheme to renovate the country’s steel bridge stock.

  • Name of the owner
  • Name of the client
    Combinatie Versterken Bruggen v.o.f.
  • Delivery date of the project
    March 2016
  • Partners of the project
    Arup (Engineer)

Complex structure

But the unconventional articulation of the structure, which featured hinged connections at the base of the pylons and lower cable deviation saddles, posed a headache for the specialists appointed to carry out the work. Freyssinet’s experience of working with complex bridges came to the fore during the tender procedure, when the company’s experts were able to reassure the main contractor and bridge owner that these technical challenges could be resolved.
Although the scheme bid documents proposed that the original locked-coil cables be replaced like-for-like, Freyssinet put forward an alternative that simplified the replacement process; we also brought the technical know-how to prove that it was feasible.

Space at a premium

Replacement with a different cable type had not been proposed by the scheme designer due to constraints on the saddle arrangement within the tower and the anchor zone in the deck. Physical space at both these locations was already highly restricted, but the introduction of a multi-strand cable could not be implemented without also replacing the saddles and cable anchors.
On the other hand a like-for-like replacement, by the very nature of fixed-length locked coil cables and the arrangement of the saddles, carried the risk that the desired final profile would not be achievable in the renovated structure.

Made to measure

Freyssinet had the necessary experience to provide reassurance that modern saddle and anchor designs could be adapted to fit the tower top and deck geometry, and also to propose a safe and practicable procedure to achieve the desired outcome. What’s more, the adjustability of multi-strand cables could easily accommodate any final profile corrections.

  • 1,055
    Length of structure (m)
  • 262
    Length of Cohestrand T15.7 installed (m)
  • 270
    Length of main span (m)

Work sequence

The order in which the cable system was replaced had to be carefully planned and analysed by Freyssinet. There was no option to introduce temporary props below the bridge deck and the hinged connections of the pylons and lower saddles had the potential to destabilise the structure. Work focussed on one pylon at a time, with the lower cable replaced first and its new saddle fixed into position as a temporary measure to stabilise the pylon before the upper system was renewed. A very detailed plan of action had to be set out and closely observed, in order not to introduce unwanted forces into the bridge structure.

Saddle upgrade

Replacement of the upper saddle was carried out with the top of the steel pylon removed to enable the new unit to be lowered in by crane. However the only way to replace the lower saddle was to manoeuvre the new one in from the side of the pylon in four pieces, and a complicated arrangement of temporary works including beams and winches was designed for this operation. The old beams on which the saddles were supported were retained but needed reinforcement and renovation, including CNC machining, which was carried out with them in situ.