German crane and transport services provider Wiesbauer used two Liebherr cranes to install four steel plates on a bridge being built across the Neckar Valley in Germany. The cranes utilised were an LR 1700-1.0 crawler crane and an LTM 1650-8.1 mobile crane.

The bridge is 667 metres long and around 65 metres high. It will carry the B32 Horb bypass over the river Neckar and has been commissioned by the Karlsruhe Regional Council.

The cranes were used to install steel plates on the underside of the two carriageway spans, a key part of the bridge’s ‘extra dosed’ construction technique.

In order to speed up construction the steel sheets were welded together on the ground before being lifted and fitted in place. This meant each section weighed 70 tonnes. The weight being lifted was even greater, though, as each section was attached to a lattice crossbeam meaning the total loads being lifted weighed 85 and 102 tonnes, including lifting gear.

The loads were lifted to a height of 65 metres. To do this Wiesbauer used the LR 1700-1.0 with a 132-metre main boom, 12 metre fixed jib and up to 375 tonnes of ballast and the LTM 1650-8.1 with Y-guying, 155 tonnes of ballast, 16 metre telescopic extension and 38.5 metre luffing jib.

The LR 1700-1.0 was set up approximately in the centre of the valley directly in front of the bridge section where the heavier steel plates had to be mounted. This enabled the crane to cope with these loads on its own.

For the other loads tandem lifts were necessary due to the larger radius, with the crawler crane working with the LTM 1650-8.1. The LR 1700-1.0 first placed the 85-tonne load in an accessible position on the bridge; from there the two cranes jointly slewed it to its final position and set it down.

The combination of the LR 1700-1.0’s VarioTray and V-Frame were key in the confined operating conditions, as the site was between the Neckar river and a railway line. The VarioTray and V-Frame enabled the ballast radius to be continuously adjusted between 13 and 21 metres depending on the radius. With a small radius the small pallet of the VarioTray with 100 tonnes of ballast was primarily used.

“Without VarioTray and V-Frame the job would not have been possible in this form,” says crane operator Ralf Paladey. “During the lift we had to constantly adjust the ballast radius in order to maintain the exact balance.”

During the tandem lift, the working radius of the crawler crane reached up to 96 metres.

The confined working conditions also posed challenges when it came to the assembly of the cranes. All the components had to be reloaded onto eight-axle low-loaders in order to negotiate the winding roads to the crane site in the valley.

“Even the assembly was precision work,” reports Ralf Hofmann, driver of the LTM 1650-8.1. “When installing the luffing jib, we had just one metre of space to the end of the path.” Positioning closer to the bridge was impossible as the projecting edge only left about one metre of clearance at the lift.

Wiesbauer looked at various options including the use of a more powerful crawler crane. “Our LR 11000 could have handled the load from the stand alone,” says project manager Jochen Wiesbauer, “but the ballast radius would have required slewing over the river – and that wasn’t possible.” A larger nine-axle LTM 1750-9.1 mobile crane was also considered as the LTM 1650-8.1 was working at its limit. The dimensions of the LTM 1750-9.1, however, did not allow it to travel down into the valley.

The deployment was planned using the Liebherr tool LICCON deployment planner and a CAD system to simulate all movements and loads. Some of the work, however, was left to experience – especially when fine-tuning the cranes in tandem operation.

“Experience is essential here,” says crane operator Tim Moll. “Not everything can be calculated in advance. It is crucial to have the right sense of proportion when picking up the load and positioning the ballast pallet.”

After several days of work all four plates were securely mounted.