A First: New Bridge Building Technology Successfully Used in Austrian Alps

as Kollegger emphasizes. The balanced lowering method (or lifting method when building bridges with high piers) is particularly advantageous for the erection of bridges in difficult terrain or terrain that should not be disturbed – for example a nature reserve, as was the case for the Lafnitz Bridge that is now being erected.

Innovation
ASFINAG is currently building the new S7 Motorway, which will pass Fürstenfeld over the Lahnbach and the Lafnitz Rivers. “ASFINAG attaches great importance to the highest quality and it is always very important to us to build as environmentally friendly as possible,” says Bernhard Streit, project manager at ASFINAG. “With this innovative construction method, we were able to meet both of our requirements for this sensitive area. We are therefore very happy about the successful cooperation with TU Wien,” Streit explains.

The bridge crossing the Lahnbach was erected in several phases between October 2019 and January 2020. The first lowering process of the somewhat longer bridge over the Lafnitz took place on 27 February 2020. 

“This is a huge success for us, and we are very pleased that ASFINAG is taking on a global pioneering role here,” says Johann Kollegger. He has been working on the new bridge construction method for years: the idea was patented in 2006, in 2010 first large scale tests were carried out by TU Wien. Many question concerning the detail design had to be resolved over the years – from the metal joints, that have to withstand the forces during the lowering process, to the hydraulic jack, which are needed for the gradual lowering of the entire construction.

“Now that we have proven that the method is well-engineered and works perfectly,” says Kollegger, “we hope that it will prevail and will soon become one of the common bridge building methods that are used around the globe and that the S7 Motorway will become an international pioneer.”

Technical Data
The rotated girders of both bridges were 36 meters in length, resulting in a span of 72 meters post lowering or unfolding. Each girder weighed approximately 54 tons. Once unfolded, the gaps between the unfolded bridge and the abutments were spanned using suspended girders, resulting in a total length of approximately 100 meters in case of the Lahnbach Bridge and 116 meters in case of the Lafnitz Bridge. For each of the two bridges, four such lowering processes were carried out side by side in order to obtain the necessary width for the motorway carriageway.