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| Historic reinforced concrete dome becomes attractive museum  Tallinn, the capital of Estonia, is the 2011 European Capital of Culture. As centrepiece of the cultural activities, a historical domed structure dating from the time of the last Russian Czar is currently being refurbished and converted into an attractive maritime museum. The PERI UP scaffolding system has been optimally adapted here to suit the geometry of the almost 100 year old reinforced concrete complex and has been used for a wide range of applications on both the interior and exterior. 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 as a maritime museum. The reinforced concrete renovation work is extremely time and labour intensive: the old reinforcement is exposed by means of an ultra-high pressure cleaning device, corrosion protection is then applied, followed by injection work along with replacement of any damaged reinforcing bars all this in order to subsequently to install an additional layer of reinforcement and a 50 mm thick shotcrete covering. During all these working operations, the domes have to be temporarily supported so that overall stability is maintained. The very detailed scaffolding concept developed by PERI΄s Estonian engineers took into consideration that two of the three domes were to be simultaneously scaffolded throughout the short ten-month construction schedule. Here, the PERI UP scaffold system serves as a spatially adapted working platform with integrated shoring and stair access. Based on metric grid dimensions of 3.00 m by 3.00 m, a 33 m long and wide birdcage scaffold was erected underneath each of the two domes using the PERI UP modular scaffolding system. In order to be able to optimally work on all areas of the underside of each dome, the PERI scaffold solution allowed for stepped working levels in 50 cm increments at heights of 11 m at the corners and 19.50 m at the centre of the dome. For exact geometrical adjustments in the edge sections, the 3-m grid of the substructure has been sub-divided in each case into two 1.50 m wide fields. In addition, cantilevers have been installed using standard node braces thus providing 1.50 m extended platforms at both ends. Due to the flexibility of the PERI UP system, this means, on the one hand, that working levels are geometrically optimally adapted to meet the on-site requirements while, on the other, the generously-dimensioned birdcage scaffold grid size of the sub-structure minimizes material costs as well as the amount of assembly work. Furthermore, the large-sized 3 m long UDS industrial decks installed throughout feature enormously high individual load-bearing capacities of 4.5 kN/m² in spite of each weighing under 20 kg. So-called lanterns allow natural daylight to illuminate the inside of the building. The ring beams on the opening in the centre of the dome are supported during the entire renovation operations with the help of PERI UP Rosett shoring towers. These have grid dimensions of 1, 50 m by 1.50 m and carry up to 40 kN per leg with heights of 21 m. 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 PERI UP grid dimensions allow not only geometrical but also static adjustments to be carried out according to on-site 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 m high working level. For the refurbishing work on the outer sides of the domed structure, PERI UP 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 can also be fitted where they are actually required without accessories a big advantage in the case of this maritime museum with missing external walls. With PERI UP T 72, the same lightweight and high load-bearing UDS steel decking is used as for PERI UP Rosett. 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 can also be easily removed and re-fitted 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. write your comments about the article :: © 2011 Construction News :: home page |