Bahnhof Hengstey bridge

A bridge with high static requirements

The “Bahnhof Hengstey” bridge on the A1 highway near Hagen is an 87-meter-long three-span structure that crosses a German Rail (DB) mainline at an oblique angle of 77 gon (approx. 70 degrees). This oblique angle presents considerable structural challenges. The project was accordingly demanding. The side sections each have a span of 25 meters, the center section a span of 37 meters. The structure no longer meets modern-day requirements so it is to be replaced by a new bridge.

The client is DEGES (Deutsche Einheit Fernstraßenplanungs- und -bau GmbH) acting under a contract from the state of North Rhine-Westphalia. The contract for the demolition and replacement of the bridge was awarded to the Brücke Bahnhof Hengstey consortium, consisting of the companies BeMo Tunneling and Metrostav.

Controlled deconstruction

The two side spans can be demolished conventionally. However, eight rail tracks run under the center span. The distances between the tracks are so small that auxiliary support for demolition is not possible, which made the job so unusual. After examining various options, the consortium finally decided on a special proposal from thyssenkrupp Infrastructure GmbH.

The proposal involves spanning the structure from the 2nd pier to about 10 meters behind the abutment with two HV21 steel box girders from our movable scaffolding program. This corresponds to a span of 77 meters. A movable girder grid is mounted on the upper chords of the HV21s. 48 core holes are drilled into the center span, through which the superstructure is attached to the girder grid by means of crossbars and tension bars suspended below. A hydraulic press is attached to each tension bar. These presses are connected to our computer-controlled synchronous lifting system. In order to preempt deformations of the steel box girders and avoid overloading the tension bars, theHV21s are pre-stressed against the superstructure. After the center span is separated from the rest of the superstructure by two cuts parallel to the two piers, it is raised by approx. 2.30 meters with the aid of the synchronous lifting system. The synchronous lifting system monitors and controls all press forces and all movements. This ensures that the superstructure is lifted parallel to its original position without overloading a tension bar.

Finally, the raised center span is moved towards the abutment and dismantled step by step in the area between the abutment and the HV21 support tower.