Tallinn, the capital of Estonia, is the 2011 European Capital of Culture. As centerpiece of the cultural activities, a historical domed structure dating from the time of the last Russian Czar currently is being refurbished and converted into a maritime museum. Contractor Nordecon AS, Tallinn, Estonia, chose the Peri Up scaffolding system, which has been adapted to suit the geometry of the almost 100-year-old reinforced concrete complex and has been used for a wide range of interior and exterior applications.
The structure, with its three impressive domes, was built in 1916-1917 as a reinforced concrete construction; for the time, this was a very unusual feat of engineering. The self-supporting shell-shaped construction without any disturbing intermediate supports was originally designed to serve as a hangar for seaplanes. However, the Russian Revolution prevented later utilisation of the facility. Now, the historical domed structure is being extensively refurbished and should be open to the general public in the summer.
The reinforced concrete renovation work is time and labor intensive: the old reinforcement is exposed by means of an ultra-high-pressure cleaning device, then corrosion protection is applied, followed by injection work along with replacement of any damaged reinforcing bars—all this in order to subsequently install an additional layer of reinforcement and a 50-millimeter-thick shotcrete covering. During all these working operations, the domes have to be temporarily supported so that overall stability is maintained. The detailed scaffolding concept developed by engineers took into consideration that two of the three domes were to be simultaneously scaffolded throughout the short 10-month construction schedule. Here, the scaffold system serves as a spatially adapted working platform with integrated shoring and stair access.
Spatially adapted working platforms
Based on metric grid dimensions of 3x3 meter, a 33-meter long and wide birdcage scaffold was erected underneath each of the two domes using the modular scaffolding system. In order to be able to optimally work on all areas of the underside of each dome, the scaffold solution allowed for stepped working levels in 50-centimeter increments—at heights of 11 meters at the corners and 19.5 meters at the center of the dome. For exact geometrical adjustments in the edge sections, the 3-meter grid of the substructure has been subdivided in each case into two 1.5-meter-wide fields. In addition, cantilevers have been installed using standard node braces thus providing 1.5 meters extended platforms at both ends.
Due to the flexibility of the scaffold system, this means that working levels are geometrically optimally adapted to meet the onsite requirements while the dimensioned birdcage scaffold grid size of the substructure minimizes material costs as well as the amount of assembly work. Furthermore, the large-sized 3-meter-long UDS industrial decks installed throughout feature enormously high individual load-bearing capacities of 4.5 kilonewtons/square meters in spite of each weighing under 20 killograms.
Integrated shoring towers and access technology
So-called lanterns allow natural daylight to illuminate the inside of the building. The ring beams on the opening in the center of the dome are supported during the entire renovation operations with the help of shoring towers. These have grid dimensions of 1.5x1.5 meters and carry up to 40 kilonewtons per leg, with heights of 21 meters. Support under one dome is provided by free-standing units—this means single towers are connected through the use of ledgers. In the other two sections, the shoring towers are fully integrated into the spatial working scaffold used for renovating the underside of the dome. Then, the metric grid dimensions allow not only geometrical but also static adjustments to be carried out according to onsite requirements. In addition, a light-duty aluminium stairway with alternating staircase units, centrally positioned in the working scaffold, ensured safe and easy access to the almost 20-meter-high working level.
Facade scaffold supplements scaffold solution
For the refurbishing work on the outer sides of the domed structure, T 72 facade scaffolding is being used. This provides a high level of safety: the assembly sequence featuring the guardrail in advance without the need of any accessories protects the scaffolder already during scaffold assembly. Likewise, inner guardrails also can be fitted where they are actually required without accessories—an advantage in the case of this maritime museum with missing external walls.
With the scaffold supplements, the same lightweight and high load-bearing UDS steel decking is used. The integrated protection against lifting ensures that when the individual decks are installed and moved sideways during scaffold assembly, they are immediately secured in their final position, again without any additional components. The decks also can be easily removed and refitted at any time during use in order, for example, to transport bulky construction materials through the scaffolding and into the inside of the building. As for the working scaffold, a stair tower is used as safe access to the roof and respective scaffold levels. Fitted with alternating staircase units, it offers shorter walking distances and more headroom than a stair tower with staircase units in the same direction.
Tallinn: The European Capital of Culture
The new maritime museum is the central point of the so-called “cultural kilometre” in Tallinn, a promenade that is gradually being restored to its former splendor where up to just a few years ago, it was still a restricted military and industrial area, where local inhabitants and visitors had hardly any access to the Baltic Sea.