The Rijksweg 7 Sneek project was commissioned by the Province of Friesland, Rijkswaterstaat Noord Nederland (Ministry of Waterways and Public Works for the northern Netherlands) and the Municipality of Sneek. It consists of two wooden bridges, which are actually viaducts, over the new southern A7 ring road. As part of the first phase, a new bridge was placed in the Akkerwinde location at the end of November. The second bridge is planned for the Molenkrite area.
The new bridge consists of a steel deck and two vertical, wooden arches that are 32 metres long and 16 metres high. Bolts and legs join the arches together. The bridge was designed by OAK architecten.The wooden arches were built by contractor Schaffitzel from Schwäbisch Hall in Germany.
"Such an extraordinary structure needs a special approach on heavy transport and lifting and this early stage co-operation finally led to a smooth and well controlled logistic operation," says Wagenborg Nedlift.
At the construction yard, some 1.5 km from the bridge's final position, the wooden arches were put together piece-by-piece using sections prefabricated by Schaffitzel in Germany. Wagenborg Nedlift assisted with a 90 tonne capacity Liebherr all terrain.
Wood on wheels
In mid-November the heavy lift work began and Wagenborg Nedlift's role in the project became more prominent. Both arches, weighing 130 tonnes each, had to be put upright and fixed onto the steel bridge deck.
Intensive lift engineering led to a solution in which each section would be lifted with three large mobile cranes, says the company. In total six all terrain cranes were used, (see crane list)
The shape and material of the arches meant close attention was required to ensure the lifts were successful. Another challenge was the communication between crane operators who had to lift the structures simultaneously.
The first job was to rig the cranes at the construction yard. This had to be carried out one at a time due to the narrowness of the site. First in was the Grove GMK5250, followed by the Demag AC 650. When the conterweight trucks of both cranes were ready to leave, the Demag AC 1200 and Liebherr LTM 1300 drove in. The AC 500 and LTM 1400 were the last two to be installed.
During the day the rigging for each crane was also prepared at the site and, by 8 p.m., installation was complete. The erection of the first arch beagn the next morning, using the AC 650, GMK5250 and AC 1200. This was followed by the erection of the second arch.
The lifting operation was carried out smoothly in just a few hours, says Wagenborg Nedlift. Both arches were then fixed on to the bridge deck and connected at the top.
A couple of weeks later the bridge, now weighing 450 tonnes, was transported from the construction site to its final foundations on highway A7. Before the journey could start, however, the bridge had to be jacked up from its initial 1.6 m level to a 5.1 m level, using Wagenborg Nedlift's new synchronic climbing jacking equipment. On the night of Saturday 29 November, a large crowd of local residents gathered at the jobsite to watch the final journey of the bridge. Two sets of two x 12 lines of Scheuerle SPMT with two power packs were positioned under the bridge and the 1.5 km trip began.
With the SPMT in carrousel configuration, the 450 tonne giant was turned carefully and transported. Using the trailers' hydraulic system, the wooden landmark was placed onto its foundations.
Length: 32 m
Width: 14.6 m
Height: 15 m
Weight of steel deck: 150 tonnes
Weight of wooden arches: 300 tonnes
Quantity of wood: 690 cubic metres
Six cranes used during the installation of the bridge
Crane model Capacity (tonnes) Additional specifications
Grove GMK5250 250 100 tonne counterweight
Liebherr LTM 1300 300 87.5 tonne counterweight
Liebherr LTM 1400 400 100 tonne counterweight
Terex Demag AC 1200 400 96 tonne counterweight
Terex Demag AC 500 500 Guyed main boom
160 tonne counterweight
Terex Demag AC 650 650 Guyed main boom
160 tonne counterweight