Demolition of Lahntal Bridge

Movable scaffold forms the hub

The 397 meter long superstructure of the old Lahntal Bridge near Limburg was demolished segment by segment. For the spectacular project, commissioned by DEGES Deutsche Einheit Fernstraßenplanungs und -bau GmbH, the contractor worked with thyssenkrupp Infrastructure to develop a special proposal involving a movable scaffolding system. Key to the success of the project were the main girders of the movables caffolding system, made from the HV21 modular girder system developed by thyssenkrupp Infrastructure, which were designed and used in this size for the first time. During the project the movable scaffolding system was supported solely by an auxiliary scaffold built around the abutments and piers of the bridge and spanned the openings between the piers. In this way the old bridge and the movable scaffold formed a joint support system whose stability was analyzed separately for each phase of the work.

World first

The main segments of the bridge superstructure with spans of up to 68 meters were demolished segment by segment on the movable scaffold so as to minimize interventions and transport operations in the valley below. The old bridge was demolished in the direction in which it was built and not in the opposite direction – a world first. For this a way had to be found to cut through the old structure between the tendon anchorages. Auxiliary load-bearing scaffolds were placed around the bridge peers and heavy construction equipment fitted with demolition cutters and hydraulic breakers was positioned on the movable scaffold. After breaking open a three meter wide section the tendons were cut in the coupling joint, with the stress in the rest of the structure remaining intact. Demolition of the superstructure could then continue with the debris falling into the formwork surrounding the scaffold and being transported away via the remaining sections of the bridge.The movable scaffolding system over the Lahn was dismantled after the demolition of the penultimate segment and the final segment was demolished from the ground in the conventional way.