THE NETHERLANDS – Late last year, work commenced on the widening of the two existing horizontally curved box-girder bridges in the northern portion of the Holendrecht junction in Amsterdam. To the best of our knowledge, the project, for which Haitsma Beton has produced specially designed box girders, is the first of its kind to be carried out in the Netherlands. The biggest challenge: obtaining a precise fit between the new curved box girders and the existing bridge.
The widening of the Holendrecht junction was prompted by the need to ensure efficient traffic flow in connection with the widening of the Gaasperdammerweg portion of the A9 motorway (Amsterdam). As part of the project, the two existing link curves over the A2 motorway are being widened to include additional traffic lanes. Building consortium IXAS (consisting of Ballast Nedam, Fluor, Heijmans and 3i Infrastructure), which is currently expanding the section of the A9 motorway between Holendrecht and Diemen, is in charge of the project. Having already supplied IXAS with the colossal prefab bridge girders for the new A9 bridges spanning the River Gaasp, Haitsma Beton was involved in the planning for widening the Holendrecht junction as from the early stages.
Widening box-girder bridge
It might seem the simplest solution just to demolish the existing fly-overs and build new ones, but there are many more aspects involved in such a project than just the costs. The negative effects from traffic, environmental issues and construction time are all important factors. After considering all the options, widening the existing horizontally curved box-girder bridges emerged as the best solution – as it turned out, a unique solution, as, to the best of our knowledge, this has never before been done in the Netherlands.
The widening of the bridges is realised employing box girders on either side. By means of a compression layer, the girders are structurally connected to the existing deck structure. The northern fly-over has five intermediate supports, the southern fly-over, six. In addition to their curved shape, the design of the girders conforms in all other respects to that of the existing box-girder bridges, yielding extremely slender detailing (height: only 800–900 mm; maximum length: 26 metres). For aesthetic reasons, the outermost girders, which also form the edges of the bridge, are bevelled and will subsequently be provided with a boundary element.
Millimetre precision
The biggest challenges presented by the project are: obtaining a precise fit between the box girders and the existing bridge, and the resulting cambering. The cambering of the girders has an extremely tight tolerance, calling for millimetre precision. And it was only after many a headache that a way was found to get such a substantial amount of prestressed reinforcement into the slender cross-sections of the girders.
Mounting
The mounting of the horizontally curved girders started late last year. Mounting activities are planned for six weekends in total, with a portion of the road network being kept open to traffic each time. The last mounting weekend is expected to take place in mid-2017. Jasper Doornbos, project manager at Haitsma Beton: “Despite its complexity, mounting went entirely to plan. The fit turned out to be just right and the upward curvature of the girder is in perfect harmony with the contours of the existing deck. We can look back on successful mounting weekends.”
