New support for Hanover's landmark

In the center of Hanover, the Anzeiger high-rise rises 51 m high. The publisher August Madsack had the building constructed, which was opened in 1928. In the high-rise and the adjacent buildings, the builder housed the editorial office, publishing house, and printing press of his "Hannoverscher Anzeiger". Since then, the building has been the scene of more than 90 years of history of German journalism and much more. In 1947, Rudolf Augstein founded the news magazine "Der Spiegel" in the Anzeiger high-rise, and Henri Nannen founded the weekly magazine "Stern" in 1948. Erich Madsack continued the family business in the second generation and launched the "Hannoversche Allgemeine Zeitung" in 1949. After today's Madsack media group moved into the press house on August-Madsack-Straße in 1974, the printing hall of the high-rise was initially used as the club "Rotation". Today, the software company HIS Hochschul-Informations-System e.G. as well as various editorial offices of television and radio stations are housed in the building.

Currently, the Madsack media group is renovating the 7th and 8th floors as the client. The dome cladding and its supporting structure are also being renewed. Planning began at the beginning of 2017. Construction started in 2018 and is expected to be completed externally by the end of 2019. The load-bearing structure of the dome consists of a 60 mm thick reinforced concrete shell, which was realized using the Zeiss-Dywidag method. In this method, a load-bearing lattice structure made of flat steel reinforced with a fine-meshed wire mesh was subsequently covered with sprayed concrete. On the inside, compressed peat boards were also applied to the woven framework. The Anzeiger high-rise documents one of the first applications of this method. In later executions, the lattice was recovered to save material. This approach, which the companies Zeiss and Dywidag had patented in the 1920s, is the precursor of today’s sprayed concrete method for civil engineering structures. It enabled the light, thin-walled dome – thus saving material as well as relieving the building underneath. The copper plates were fastened with dowels wrapped in hemp. However, during an inspection in 2016, it was found that these anchors had come loose. Additionally, it became apparent that the concrete layer on the inside surface of the load-bearing shell was partially crumbling. The existing reinforcement content is also low and poorly executed. Therefore, there was a need for structural renovation.

Special challenges in the renovation project arise primarily from the fact that the concrete shell is only 60 mm thick. This thinness must be preserved in the future to maintain the original character of the listed architecture and not increase the dome's own weight. To preserve the original appearance of the patina that has existed for decades, the new copper was therefore selected pre-patinated in consultation with municipal and state monument preservation authorities. Pre-patinated plates are used, whose material aging and green tone are precisely simulated. Additionally, 60 tension plates made of stainless steel (V4A) will further reinforce the structure. These are radially distributed in the lower third of the dome, dowelled to the ring beam, and fitted with claws to tension the subsequently installed V4A round bars. Additional tension plates made of V4A are anchored in the knee wall and in the roof ceiling.

The fischer injection mortar FIS EM Plus combined with the fischer threaded pin GS 10 x 60 in stainless steel (A4) meets all the requirements for the fastening tasks involved in the dome renovation of the Anzeiger high-rise building. In terms of material quality, corrosion protection, pull-out and shear resistance, as well as all other criteria, the injection system is ideally suited to anchor the wooden substructure for the new copper cladding with stainless steel brackets in the existing sprayed concrete shell. Deviating from the European Technical Approval (ETA) for the fastening system with the fischer FIS EM Plus, the executed anchoring depth here is significantly below the otherwise required minimum depth of 60 mm, at only 40 mm. Pull tests demonstrated that despite the deviation in application during the dome renovation of the Anzeiger high-rise, the injection system can absorb the occurring tensile forces. For this reason, individual approval was granted, with calculations for the use of FIS EM Plus even considering an anchoring depth of only 30 mm to provide additional safety. The load-bearing capacity of the composite anchor is thus maintained with a reduced anchoring and embedment depth of 40 mm or 30 mm in the 60 mm thick load-bearing shell. Using the fischer Zykon drill bit FZUB 12 x 40, undercut holes in concrete are created quickly and without the risk of drilling through.