Tandem lift sets 32-tonne bridge sections 64 metres up at Horb

An extradosed bridge with awkward numbers

The Neckartal bridge near Horb runs 667 metres and stands 65 metres above the valley floor. As an extradosed structure — a hybrid between a girder and a cable-stayed bridge — it demands precise placement of steel elements at height, in this case two 24-metre-long sections weighing 32 tonnes each, lifted to 64 metres.

Crane service provider Wiesbauer put its newly delivered AC 7.450-1 on the job, rigged with a 76-metre main boom and 120 tonnes of counterweight. The second crane came from Munich-based partner AKM. It was the machine’s first outing: operator Jannik Weigle, who had driven it away from the handover in Zweibrücken, was also the man in the seat.

Two hooks, one load

The technical problem in any tandem lift is synchronisation — keeping the load balanced between two hooks throughout the movement. The teams worked to a lifting concept prepared in advance and ran the operation on radio, with a spotter and both operators in constant contact so that no one lost sight of the load’s attitude. On a tandem lift there is no margin for one hook running ahead of the other: an out-of-balance load transfers capacity from one crane to the next without warning, and at 64 metres there is nothing to be gained from finding out late.

“The lifting concept developed by our team beforehand proved to be extremely effective – we lifted the two 24-meter-long structural elements as planned and positioned them with centimeter precision at a height of 64 meters. Everything worked perfectly.”

— Jannik Weigle, crane operator, Wiesbauer

Why the boom length decided it

Weigle’s verdict on the crane comes down to the 80-metre telescopic boom and what it saved him. A smaller machine would have needed a jib fitted to reach the placement height; a larger crane with sufficient boom would not have fitted the standing area available on the site. The AC 7.450-1 sat in the gap between the two — a seven-axle crane that keeps a six-axle footprint while offering boom lengths normally associated with bigger machines. For a bridge site hemmed in by falsework, rail and a live road, that combination is worth more than raw capacity.

Managing director Sissy Wiesbauer framed the choice in the same terms: “We master such challenging operations with state-of-the-art crane and lifting technology, for which the AC 7.450-1 is a prime example.”