When planners in the Netherlands needed to increase the capacity of two major flyovers, they called on the expertise of prefabricated concrete specialist Haitsma Beton. The company has manufactured nine horizontally curved box-girders, engineered to fit precisely to the existing structures.
As part of a larger project to widen the Gaasperdammerweg portion of the A9 motorway in Amsterdam, building consortium IXAS (consisting of Ballast Nedam, Fluor, Heijmans and 3i Infrastructure) needed to add additional traffic lanes to two flyovers at the Holendrecht junction. Rather than replacing the structures, the consortium chose to widen them, to minimise disruption to traffic and impact on the environment. That decision presented significant technical challenges, and is believed to be the first time in the Netherlands that such a project has been attempted on horizontally curved flyovers.
Precision curves
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 from its early stages. To widen the existing box girder bridges, the prefabricated concrete specialist has manufactured nine new box girders – seven for the northern bridge and two for the southern. The new components are up to 26m long, 2.9m wide and weigh as much as 90,000kg.
To permit the new girders to be structurally connected to the current bridge decks, they needed to be manufactured with great precision, so their form exactly matched the curve of the existing structures. At only 900mm high, the girders are also extremely slender, which made incorporating the required amount of pre-stressed reinforcement an additional challenge.
Haitsma Beton achieved the required millimetre tolerances by continually monitoring the shape of the girders during construction and adjusting the tension of the reinforcing elements to control their camber. 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.
Installation
The installation of the horizontally curved girders started late last year. Installation activities are planned for six weekends in total, with a portion of the road network being kept open to traffic at all times. The last installation weekend is expected to take place in mid-2017. “Despite its complexity, installation has so far run entirely to plan,” says Jasper Doornbos, project manager at Haitsma Beton. “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.”