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- Green fischer dowels in the world's first zero-energy high-rise
The idea to convert the old water tower dates back to December 1997. At that time, the young architect Norman Räffle noticed the unused tower. Together with his father Jürgen, they developed a concept for a new use of the water reservoir, which the local Milchwerke GmbH had used until 1979. In 2002, the construction company Räffle & Sons finally acquired the dilapidated tower.
During the following planning phase, the idea was born in 2006 to convert the 30-meter-high tower into the world’s first zero-energy high-rise. To achieve this goal technically and economically, Thorsten Räffle submitted a hundred-page application for funding as a demonstration project to the Federal Ministry for the Environment, the KFW, and the Federal Environment Agency, which was approved in October 2008.
During the conversion phase from 2008 to 2016, the tower head was first reduced to a shaft height of 21 meters, then extended by five new floors made of reinforced concrete. Since Radolfzell is located on the edge of earthquake zone 2, the finished tower with its final height of 50.5 meters must also withstand the strongest shocks without damage. This in turn required both secure structural constructions and high-quality fastening systems.
„The higher the tower grows,“ says planner Norman Räffle, „the more weight it has to bear. In the end, it is about 2,500 tons! That’s why, when renovating the old walls and for the new concrete construction, we needed fastening systems that meet the highest quality requirements and all seismic regulations. So far, we have had very good experience with the company fischer from our region in our construction company. That’s why we also used their products for this construction project. They are guaranteed safe and innovative.“ About 2,200 injection anchors were installed to repair the 39-centimeter thick tower shaft wall. These anchors had to be precisely adapted to the stone strength class 20 and mortar group III a of the old brick masonry. „It paid off,“ emphasizes Norman Räffle, „that these anchors easily went through the old plaster without needing to remove it.“
The fischer injection system used, consisting of the powerful hybrid mortar FIS V, the anchor sleeve and the threaded rod or internal thread sleeve, has proven itself from the client’s perspective. As the first injection mortar system approved for all relevant building materials, it provides the necessary safety for the entire tower. Perfectly coordinated, it can carry very high loads. In addition, thanks to the optimized grid structure of the anchor sleeve, the mortar consumption could be reduced by up to 80 percent. Undoubtedly, an equally important advantage for the planner.
Furthermore, about 1,200 fischer bolt anchors FAZ II of different lengths were used for the assembly of the metal substructure for the ventilated curtain facade in the access tower and tower head. The international approvals, which also apply to applications in earthquake areas (seismic), guarantee optimal safety and high load distribution; just by the fact that the anchoring depth in the wall fully utilizes the maximum performance of the anchor and the concrete. Only a few hammer blows are needed and the anchor sits firmly. Given the long construction period, this noticeably fast assembly was another important decision criterion for the client.
The higher the tower rises, the more weight it has to bear. In the end, it's about 2,500 tons! That’s why we needed fastening systems that meet the highest quality standards and all seismic regulations when restoring the old walls and for the new concrete construction.
