Mammoet has removed the bridge, which was in a confined city-centre setting in Vienna, Austria.
More than 30 years ago, a junction was built on the Vienna southeast tangent freeway but it was never put into operation., The final bridge section of this ‘closed exit’ needed to be demolished as part of a redevelopment programme.
The presence of an elevated road below and confined space around the tangent meant that the 43m-long, 550t bridge could not be demolished in a conventional way.
In order to develop a safe solution, client ASFINAG contacted Mammoet at an early stage.
The planning phase of the project started twelve months before its execution. Mammoet worked in close contact with the client to engineer the technically complex crane lifting phase. Several approaches were explored before the optimal solution was confirmed.
The solution that was developed involved lifting the bridge section in one piece and placing it at the side of the tangent. Work could only be carried out on one side of the road due to the congested surroundings; Mammoet determined that only a Demag CC 8800-1 crane could be considered.
The crawler crane, which is one of the largest in Europe, was configured for the application with a main boom length of 78m.
During execution, a section of the southeast tangent - a busy route in Vienna - had to be fully closed in both directions. Two short time windows were planned for the work in order to disrupt traffic as little as possible. In addition, the crane’s location was in the airport's approach corridor, which made air traffic control measures necessary.
"For the heavy lift, it was particularly important to exactly calculate the centre of gravity of the bridge in advance and to precisely adapt the rigging equipment to it,” said Gernot Öder, manager of crane and transport projects, engineering and project management at Mammoet. “In this case, a 31m-long special spreader beam for a load of 650t was required. The weight of the rigging equipment alone was 70t. An ‘integrated stinger’ as fitted to the superlift of the 1,600t crawler crane also enabled the fast changes of the load.”
Mammoet finished the work ahead of schedule. After the end of the construction work, a large part of the area is to be returned to nature as a local recreation area.