Above the Neckar valley, "Germany's castle road", near Karlsruhe, Germany, a major construction site is currently attracting attention: as part of the new Horb bypass, the Karlsruhe Regional Council is building a 667-metre-long, 65-metre-high "Hochbrücke Horb" bridge to carry the B32 federal highway over the river. For this lifting operation, Wiesbauer GmbH & Co. KG mobilized two Liebherr cranes, a crawler crane LR 1700-1.0 and a mobile crane LTM 1650-8.1, to install imposing steel plates under the two bridge decks.
The design of the "Hochbrücke Horb" bridge is based on the "extradosed" principle, a modern technique combining the advantages of cable-stayed and prestressed concrete bridges. Its relatively low pylons and slender concrete decks give the structure a light, elegant silhouette. To ensure resistance to high bending loads, continuous steel plates were fastened to the underside of the decks using thousands of anchor bolts. These elements are anything but light: their thickness varies from 7 to 14 cm, for lengths of up to 157 meters.
Rather than welding the plates section by section on the bridge, a method that would have delayed the work by several weeks, Wiesbauer chose to assemble them on the ground in complete elements. The result: loads of up to 70 tonnes per plate, increased to 85 to 102 tonnes with lifting accessories. These assemblies were then hoisted to a height of 65 metres to be secured under the bridge.
For these operations, the LR 1700-1.0 was equipped with a 132 m main boom, a 12 m fixed jib and 375 tonnes of counterweight. As for the LTM 1650-8.1, it was equipped with a Y-guying system, 155 tonnes of counterweight, a 16 m telescopic extension and a 38.5 m lifting jib. Positioned in the center of the valley, the LR 1700-1.0 was able to carry out the heaviest lifts alone. For more distant positions, a tandem lift with the LTM 1650-8.1 proved necessary. The crawler crane first placed the plate on an accessible area of the deck, before the two machines moved the load to its final position with millimetre precision.
The VarioTray and V-Frame systems played a key role in the success of the operation, enabling the counterweight radius to be continuously adjusted from 13 to 21 meters. " Without VarioTray and V-Frame, this mission would not have been possible ," confides crane operator Ralf Paladey. " We had to adjust the counterweight radius constantly to keep the perfect balance. " During the tandem lifts, the crawler crane reached a working radius of 96 meters.
The installation of the cranes itself represented a major logistical challenge. The site, wedged between the Neckar to the north and a railroad line to the south, left little room for manoeuvre. All components had to be transported on eight-axle trailers to access the valley floor via winding roads. " Even assembly was a precision operation ," emphasizes Ralf Hofmann, driver of the LTM 1650-8.1. " When the dart was installed, there was only one meter of clearance left. " Prior to the operation, Wiesbauer simulated all movements and constraints using Liebherr LICCON planning software and a CAD tool. " In this type of operation, experience makes all the difference ," explains crane operator Tim Moll. " Calculations are not enough: you need to have the right 'feel' for the load and the position of the counterweight. "
