New stop for Hanover’s landmark

In the centre of Hanover, the Anzeiger skyscraper rises 51 metres high. Publisher August Madsack had the building erected, which was opened in 1928. In the high-rise building and the adjacent buildings, the client housed the editorial, publishing and printing facilities of his “Hannoverian advertisement”. Since then, the building has been a showcase for more than 90 years of German journalism history and much more. In 1947, Rudolf Augstein founded the news magazine “Der Spiegel” in the Anzeiger-Hochhaus and Henri Nannen founded the weekly magazine “Stern” in 1948. Erich Madsack continued to run the family business in the second generation and founded the “Hannoversche Allgemeine Zeitung” in 1949. After today’s Madsack Media Group moved to the press house on August-Madsack-Straße in 1974, the high-rise’s printing hall was initially used as a “rotation” club. Today, the software house HIS Hochschul-Informations-System e.G. as well as various editorial offices for television and radio stations are housed in the building.    

Madsack Mediengruppe is currently renovating the 7th and 8th floors as the building owner. The dome covering and its supporting structure will also be renewed. Planning began at the beginning of 2017. Construction began in 2018 and is scheduled to be completed outdoors by the end of 2019. The supporting structure of the dome consists of a 60 mm thick reinforced concrete shell, which was produced using the Zeiss-Dywidag process. In this method, a load-bearing lattice structure made of flat steels was reinforced with a fine-meshed wire mesh and then covered with shotcrete. Pressed peat boards were also applied to the weave on the inside. The indicator tower documents one of the first applications of the process. In later versions, the grid was reused to save material. This process, which the companies Zeiss and Dywidag had patented in the twenties, is the precursor to today’s shotcrete process for engineering structures. It enabled the lightweight, thin-walled dome – and thus material savings as well as the relief of the building underneath. The copper plates were secured with dowels wrapped in hemp. However, during a 2016 inspection, it was found that these anchorages had come loose. In addition, it became apparent that the concrete application on the inner surface of the support shell was partially crumbling. The existing reinforcement portion is also low and poorly executed. This made static renovation necessary.

Particular challenges in the renovation project arise primarily from the fact that the concrete shell is only 60 mm thick. This thin-walled structure must also be retained in the future in order to preserve the original of the listed architecture and not increase the dead weight of the dome. In order to preserve the original appearance of the patina, which has existed for decades, the new copper was therefore pre-patinated in consultation with urban and regional monument conservation. Pre-patinated plates are used, whose material ageing and green tone are precisely simulated. In addition, 60 tension plates made of stainless steel (V4A) are to further strengthen the construction. These are distributed radially in the lower dome third, anchored with the ring anchor and provided with claws, around which the V4A round bars are then clamped. Additional V4A tension plates are anchored in the threshold and roof ceiling.

The fischer FIS EM Plus injection mortar in combination with the fischer GS 10 x 60 threaded pin in stainless steel (A4) meets all requirements for fastening tasks that arise during the dome renovation of the high-rise indicator building. In terms of material quality, rust protection, pull-out and shear resistance and all other criteria, the injection system is ideal for anchoring the wooden substructure for the new copper flashing with stainless steel angles in the existing shotcrete shell. In deviation from the European Technical Approval (ETA) for the fastening system with the fischer FIS EM Plus, the anchoring depth of only 40 mm will be significantly below the otherwise required minimum depth of 60 mm. The tensile tests demonstrated that the injection system can absorb the tensile force occurring despite deviating use during the dome renovation of the high-rise indicator building. Consequently, approval was granted on a case-by-case basis, for which an anchoring depth of only 30 mm was even expected when using the FIS EM Plus in order to obtain further security. The load-bearing capacity of the composite anchor is thus maintained with a reduced anchoring and embedding depth of 40 mm or 30 mm in the 60 mm thick support shell. With the FZUB 12 x 40 cyclone drill from fischer, undercut holes in concrete can be created quickly and without the risk of drilling through.