MULTI-ROOF

“Germany’s highest cinema” was until recently located above the roofs of Hannover in the dome of the “Anzeiger-Hochhaus”, a building dating back to 1928 and one that was originally planned to be a planetarium. The movie theatre has now temporarily been moved down into the main hall since the dome of the traditional hallmark of the town will be extensively renovated over the next two years. But the dramatics in the dome have not come to a halt with many curious onlookers not wanting to miss the spectacular crane-lift attachment of the MULTI-ROOF by night.

The scaffolding company Schmiedt from Kobern-Gondorf near Koblenz rose to the challenge of scaffolding the entire Anzeiger building and of then equipping it with a weather protecting roof. VARIANT material from the manufacturer scafom-rux was used for the scaffold up to the upper edge of the dome – no less than 54 m in height and the last 16 m free-standing. The scafom-rux MULTI-ROOF system was then attached on top: a supporting structure – which can be optionally equipped with roof cassettes and/or Keder tarpaulins – based on the modular RINGSCAFF scaffolding but one that can be used with any conventional scaffolding systems.

The objective of setting-up the scaffolding was to create working areas and levels around the dome in order to renovate it. Since the dome itself could not be subjected to any loads, the working scaffold had to be designed as a suspended system hung from the roof trusses of the weather protection roof.

And what till then had sounded relatively simple despite all the effort involved – scaffold around the structure, put the roof on, fit the suspended scaffold – became a fascinating and highly complex overall structure due to on-site specifics – a project that needed to be carefully planned by the specialists from Schmiedt Gerüstbau and the Schalksmühle-based Specht engineering office.

The specific situation on-site was that the basic scaffold foundation had to be effected from three positions that were entirely independent of one another and which could not initially be connected with each another. The flanks of the building were interrupted by two lateral extensions and the two corner zones on the rear side were separated by rear-side extensions that could not be subjected to any load so no structure could be fitted on top. Even the northern side could not be subjected to any load over its entire length. Moreover, there was the problem that an extension building with a glass roof was connected over one-half of the side of the building.

The basic scaffold foundation was therefore implemented on the front side (east) along the entire length. The southwest corner was constructed from the extension to the corner (south) and then with one bay around the corner up to the extension buildings connected on the rear side (west). The building with the glass roof on the northern side was initially bridged with a steel structure that served on the one hand as a protective roof and on the other hand as a foundation level for a scaffold. The foundation level here was already at a height of about 12 m which made material supply through the adjoining buildings even more difficult. In this respect, company-own cranes with jib lengths and working radius of some 55 m were used.

The north west and south west corners were connected at a height of about 22 m by means of a 6 m high scaffold bridge, which initially comprised three individual lattice girder bridges. They in turn consisted of scaffold levels of 2 m in height and 25 m in length that had been pre-assembled on the ground. They were then each fitted with a 1 m high lattice girder with additional reinforcement in the upper and lower chords: the scaffold levels themselves were additionally braced using horizontal and vertical diagonals as well as head diagonals in all bays or rows of standards. The three bridges each weighed 3.5 tonnes. When lifting the lowest bridge into place on the north west support just two standards could be targeted, on the south west support it was precisely four. To enable this, the distance between the support scaffolds had to fit exactly, something however that could only be controlled from a height of 22 m. The height of the support scaffolds also had to be identical and this was something that could not be verified up-front. In the case of the other two bridges, the challenge was not only that the six support standards had to fit exactly, but that all 22 scaffold standards would have to fit exactly on the standards fitted below. This went off exceptionally well although the bridges sagged by about 0.5 m at their outer ends as a result of the crane-lift operation.

A steel sub-structure was likewise mounted on the side extensions/balconies (north and south) since the roof surfaces were not sufficiently load-bearing; they were even propped up below with supports going right through the floors of the building. Directly above the balconies, a so-called ‘ring closure’ – the connection of all the individually scaffolded sides – could be implemented for the first time. All elements were now attached to one another through form-fit and friction-locked wedge connections. Thanks to the metric scaffold dimension, the approx. 23 x 23 m-sized object could be completely modified, yet still had its system dimensions.

The assembly of the scaffolding rising above the upper edge of the attic was implemented as a free-standing structure. In this respect, the gable sides (front and rear side) had from the very foundation been constructed as 1.5 m scaffold sections that would be additionally reinforced in the upper half of the building by individual and double head diagonals. The eaves sides were each built as 1 m wide sections, above the height of the balconies an additional 2 m wide scaffold was front-fitted. This was then supplemented by another 2 m wide scaffold section (backpacks) in the area 6 m above and below the attic. The overall depth of the eaves scaffold was as much as 5 m, with sometimes as many as three sections in front of each other.

In a next step at a height of almost 50 m, the steel girders intended as guide rails for the MULTI-ROOF were fitted on the two 1 m wide scaffold sections. Five MULTI-ROOF trusses, each with a length of 26 m and a weight of 3.8 tonnes were pre-mounted on the Steintorplatz in front of the Anzeiger-Hochhaus to be subsequently lifted by a 260 tonne crane into their lowering position on the scaffolding. Since the crane was only able to stand in the middle of the street “Goseriede” running in front of the building, work was only allowed to take place between 21.00 and 6.00 due to the inner-city location. The crane lifted the trusses on to the guide rails at a height of 50 m; an undercarriage was then fitted under the trusses to enable them to be shifted and moved across and beyond the building into their final positions. The lowering and shifting as well as the final positioning of the roof trusses was completed within just five hours, enabling the road to be punctually reopened for traffic. Appropriate Keder rails were then fitted to the roof trusses, into which heavy-duty Keder tarpaulin could be inserted.

Christian Schmiedt from the scaffolding company Schmiedt was obviously satisfied and not only with the precision with which the scaffolding work had been accomplished. Regarding the use of the MULTI-ROOF he said: “The span width of the roof did not really present the real challenge for the system. The biggest advantage was that the roof did not need any tensioning belts. If that hadn’t been the case, then it could only have been pushed over the dome with much higher scaffold sections – and that would have been very difficult to implement from a statics point of view – if at all.”

The roof trusses will shortly be subjected to additional loads when the dome itself is scaffolded – this is planned to be a suspended system. The assembly of the dome scaffolding will be effected downwards from the roof trusses suspended above the dome. Scaffolding the dome will prove to be very challenging in view of the egg-shaped curvature both in the horizontal as well as in the vertical direction. However, the VARIANT material selected will be able to utilise its advantage of stepless circular scaffolding to the full for this job.

The roof will ultimately be prepared for the winter to enable the tarpaulin to be heated from below. The total load resulting in this special situation, including the suspended scaffold, does not allow for any additional snow loads on the trusses. No other snow clearance concept would have been feasible as otherwise pedestrian zones and the roof surfaces of the buildings attached to the sides would have been impaired by the masses of snow from the Anzeiger roof.

In recognition of the performance of his team and all those involved, Christian Schmiedt said: “This project has combined almost everything in terms of challenges that engineering-like scaffolding jobs have to offer. And we can all be very proud of ourselves.”

About two years will pass before the cinema can return to its renovated dome, but until then the considerably scaffolding out of some 220 tonnes of material will give the Anzeiger-Hochhaus its very own appeal.