New technique to erect a bridge applied in Austria

A new technique to erect a bridge was applied for the first time in Austria.

The new method, known as the balanced lowering technique, was developed at the Technical University of Vienna (TU Wien). This technique follows a radical approach as the bridge is constructed vertically and it is then placed in the horizontal direction by rotation.

The method was initially tested in 2010 but its first actual application was conducted in February 2020, on the Fürstenfeld Highway S7. The endeavor was successful as a 116-meter bridge that links the opposing banks of two rivers, was erected with no issues. Another 100-meter structure was also achieved using the same method.

Conventional bridges are erected with the utilization of scaffolding or they are built gradually through piers that bear the weight of the structure.

The new method was conceived by scientists at the TU Wien in 2006. According to the developers, it is less time consuming, cost-efficient and can be applied at harsh terrains without disrupting the natural landscape. “Erecting bridges using scaffolding usually takes months. The elements for the balanced lowering method on the other hand, can be set up in two to three days, and the lowering process takes around three hours," Johann Kollegger, a Professor of Structural Engineering at the TU Wien who leads the project, stated.

How does it work

The method utilizes two supporting beams attached to a pier at a vertical position. The girders are joined together at the top of the pier and they are gradually unfolded to create the span of the bridge (Click the video below to understand the unfolding mechanism). To stretch out the beams, a powerful hydraulic system is used.

The beams are initially hollow precast elements that are reinforced with steel. After the system's rotation and when they have been placed in the horizontal position, they are filled with concrete. 

The empty space between the unfolded grinders and the abutments of the bridge is covered using additional suspended beams.

Engineers had to overcome critical issues before implementing the new technique. Those included the design of the joint connection between the two grinders that should bear large forces during the unfolding procedure and the development of hydraulic jacks capable of performing the rotation. 

Researchers wish to establish the new method as a common erection technique in bridge engineering.