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- Green fischer anchors in the world’s first zero-energy high-rise
The idea of renovating the old water tower dates back to 1997 December. At that time, the young architect Norman Räffle became aware of the unused tower. Together with his father Jürgen, they developed a concept for a new use of the water high tank, which the local Milchwerke GmbH had used until 1979. In 2002, the construction company Räffle & Sons eventually acquired the decaying tower.
During the following planning period, the idea was born in 2006 to convert the 30-metre-high tower into the world’s first zero-energy high-rise. In order to achieve this objective both technically and economically, Thorsten Räffle submitted a hundred-sided application for funding as a demonstration facility to the Federal Ministry of the Environment, the KFW and the Federal Environment Agency, which was approved in 2008 October.
During the renovation phase from 2008 to 2016, the tower head was first reduced to a shaft height of 21 metres, then increased by five new floors in reinforced concrete construction. Since Radolfzell is located at the edge of earthquake zone 2, the finished tower, with its final height of 50.5 metres, must withstand even the strongest vibrations undamaged. This, in turn, required both secure static constructions and high-quality fastening systems.
“The higher the tower grows,” says planner Norman Räffle, "the more weight it has to withstand. In the end, it’s about 2,500 tonnes! For this reason, we needed fastening systems that meet the highest quality requirements and all seismic regulations when repairing the old walls and for concrete construction. 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 to be safe and innovative." Around 2,200 injection anchors were used to repair the 39-centimetre-thick tower shaft wall. These anchors had to be precisely adapted to stone strength class 20 and mortar group III an of the old brickwork. “It paid off,” emphasises Norman Räffle, “that these anchors could easily pass through the old plaster without having to be removed.”
The fish injection system used, consisting of the high-performance hybrid mortar FIS V, the anchor sleeve and the threaded rod or internally threaded sleeve, has proven itself from the client’s point of view. As the first grouting system approved for all relevant building materials, it offers the necessary safety for the entire tower. Perfectly matched to each other, it can carry the very high loads. In addition, thanks to the optimised lattice structure of the anchor sleeve, mortar consumption could be reduced by up to 80 percent. This is undoubtedly an equally important advantage for the planner.
In addition, around 1,200 FAZ II bolt anchors in different lengths were used in the installation of the metal substructure for the curtain-mounted rear-ventilated facade in the development tower and in the tower head. The international approvals, which also apply to applications in earthquake areas (seismic), guarantee optimum safety and high load balancing, simply because the anchoring depth in the wall exploits the maximum performance of the anchor and the concrete. Just a few hammer blows are enough and the armature is firmly seated. In view of the long construction time, this noticeably fast installation was another important decision-making criterion for the building owner.
The higher the tower grows, the more weight it has to withstand. In the end, it’s about 2,500 tonnes! For this reason, we needed fastening systems that meet the highest quality requirements and all seismic regulations when repairing the old walls and for concrete construction.
