Fischer meets Lorch bridge demolition challenge

15 February 2011

The B297 road bridge over the B29 provided contractor FWA Fischer with a 3,000 tonne headache

The B297 road bridge over the B29 provided contractor FWA Fischer with a 3,000 tonne headache

Transport authorities in Germany had decided on some major road construction near the town of Lorch, Hesse, where the B297 road crossed over the B29 on a 3,000 tonne, two bay, reinforced concrete bridge. This bridge had to be removed as a part of the reconfiguration of the road layout but its design and geographical environment meant that it was a challenge for FWA Fischer, the demolition contractor assigned the task of removing it.

First, the B297 bridge had to be removed without any damage being caused to the carriageway of the B9 below it. It also featured not only a longitudinal and transverse slope but also a curvature with a 280 m (919 ft) radius to the horizontal. In addition, a local access route that was slightly offset and 15 m (50 ft) below it had to be kept open for emergency vehicles at all times.

The above required that Fischer develop a demolition plan that described every single demolition phase in precise detail to ensure that work was carried out in a controlled manner that never put personnel, machines or the environment at risk. The works began with the complete closure of both roads and the removal of crash barriers. An impact bed was then laid on the B29 carriageway, using recycled materials, to act as protection.

Fischer then started work on the demolition itself, using a mix of tools (five Atlas Copco breakers and four Atlas Copco CombiCutters) which were mounted on a Cat wheeled excavator and five Cat tracked machines. Fischer simultaneously broke up the bridge deck from above and removed the bridge caps. The 4 m2 (43 ft2) concrete bottom chords were then demolished. Once the longitudinal reinforcements were accessible, they were cut into lengths and removed, and finally the bridge abutments were demolished. All concrete debris was conditioned on site and crushed so that it could be used as fill on other road projects.

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