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High, slender und very distinctive - safely and quickly climbed
Donau City Tower 1, Vienna, Austria
Support structure planning was preceded by an extensive range of testing which also included the use of a wind tunnel. This meant it was possible to determine the influence of the wind along with the reaction of the structure itself by taking into account realistic conditions. The horizontal forces are divided by means of so-called outrigger constructions between the core and columns, so that relief is provided for the inner access core when transferring the forces by the columns. Apart from this complex construction, the biggest challenge facing building contractor Max Bögl was maintaining the tight construction schedule. With its comprehensive formwork and scaffolding solution for realising the slabs and columns as well as the three-part building core, PERI ensured that the shell construction work could be completed in the planned time-frame.
Fast forming times for columns and slabs
The building's supports feature a range of different dimensions. The formwork for constructing the columns with cross-sections from 0.60 m x 0.60 m to 1.20 m x 1.20 m and heights of 3.25 m to 6.50 m is based on rentable formwork elements taken from the MAXIMO, TRIO and RAPID systems. In order to minimize the amount of work required on the construction site, PERI delivered the column formwork already pre-assembled to the site. As a result, this could also be used for the inclined columns of the outriggers; furthermore, the constraint points of the gable composite columns could also be taken into consideration.
The 25 cm thick slabs of the standard floors have been formed with SKYDECK aluminium panel slab formwork. The drophead system allows early striking to take place resulting n a reduction in the amount of materials required on site. Although the balcony arrangement on each floor feature a wide range of layouts compensation areas have been minimized. On site, slab formwork requirements for two complete storeys have been maintained throughout; furthermore, two levels of temporary support have been in use as well. The SKYDECK has also served for constructing the 200 cm thick concrete slabs of the outrigger floors. In order to be able to transfer the high loads, the slabs have been concreted in two phases, and additional columns added as an additional measure.
The systematic assembly sequence of the SKYDECK along with the low weight of the components have ensured that the construction crew could maintain the specified forming schedule.
For moving the slab formwork, a customized RCS Material Lifter was designed and supplied. This was integrated into the installation shafts on the front sides of the building and used to move the slab formwork crane-independently for up to four floors at any one time.
Climbing in 4-day cycles
For realising the three core areas of the DC Tower, different versions of the PERI ACS self-climbing formwork (Automatic Climbing System) have been used in combination with the proven TRIO panel formwork. Thanks to their flexibility, these systems have shown themselves to be extremely well-suited to meet the project requirements.
The walls of the building core are up to 1.00 m thick and have a very high level of reinforcement. In order to ensure fast construction progress, the up to 9.60 m high reinforcement cages were pre-assembled and positioned over three storeys. Re-positioning the reinforcement cages has taken place by means of additional mounting brackets on the external scaffolding above the formwork. In some areas, prefabricated sections have supplemented the in-situ concrete - this was integrated by the construction crew likewise in the formwork before concreting took place.
For carrying out the reinforcement work, a PERI UP Rosett Flex scaffold has been used which was installed on the climbing scaffold inside the core. This solution created high additional loads that were transferred via the anchorage points positioned on the areas already concreted. The working scaffold is equipped with hatches that allow the installation of prefabricated stairs in the course of the construction process.
The fact that the cores can be climbed independently of each other provides a high level of flexibility during the construction work. After a short period of training, the construction crew reached a 4-day cycle per 3.50 m concreting section so that three storeys could be completed within 2 weeks on a regular basis.
Safe working conditions on the very distinctive facade The wind tunnel testing formed not only the basis for the structural dimensioning but was also the basis for the planning the climbing protection panels. The temporary enclosure - based on the RCS rail climbing system - secures 3.5 floors at one time and can withstand wind speeds of up to 160 km/h throughout the construction process. As a result, the RCS protection panel guarantees efficient working environment at all levels and situations.
The floor layouts have constantly changed due to the repeatedly buckled facade but the enclosure accordingly matched the geometry without any problems. For this, PERI created a specially-designed anchor solution that has made it possible to vary the inclinations of the protection panels and allowing the hydraulic climbing procedure to take place without requiring any modifications.
For the variable, lateral cantilevers, sliding scaffold elements have provided permanent protection for site personnel. In order to guarantee an all-round protection panel for the variable transverse side of the high-rise building, the construction crew have used additional elements which are installed or dismantled depending on the width of the structure.
Foresighted planning - realised in teamwork
The short construction period had an effect on all planning and logistics processes for the project. Likewise, this called for a fast reaction from the PERI team of engineers. However, in close cooperation with Bögl, they developed an extremely foresighted set of plans. Possible variants, for example the placement of the required anchorage for the climbing formwork, were discussed at a very early stage and taken into consideration during the planning. As building work progressed, all necessary adjustments could then be easily implemented.
The PERI project management has also been on site on a regular basis throughout to ensure efficient coordination and organisation of the formwork and scaffolding planning. This has led to optimized and cost-effective implementation regarding material utilization as well as on-site material requirements.
Vienna DC and DC Tower 1
For several years now, an internationally-recognized centre has been developed on the northern bank of the Danube featuring highly functional and sophisticated architecture: the Vienna DC. In the core area, the DC Towers will dominate the skyline of Vienna. The architects attached great importance to a state-of-the-art design and superior quality. The height of the towers is the result of the architect's ambition to "preserve the compelling aesthetics of slender towers when giving structural shape to their planned cubic content". The DC Tower 1 is the highest building in Austria whilst the planned 168 m high DC Tower 2 will be the fourth-tallest building in Vienna. A striking feature of the two buildings is the very slender appearance and repeatedly indented facade structure.
Currently, Tower 1 is under construction whereby over 60,000 m³ of soil had to be excavated for the basement area. The extreme ratio of the height to the base area of the tower as well as the local conditions regarding settlement behaviour required especially deep foundations with diaphragm walls of up to 35 m high. A diaphragm wall area of around 20,000 m² was required for the construction of the 4.00 m thick bottom slab which weighed 10,000 t. The rising structure consists of the core, the reinforced concrete and composite columns along with reinforced concrete slabs. The skeleton construction will subsequently be covered with an element facade. Parallel to the shell construction work, the interior finishing work for the hotel facility is taking place on the lower floors - this is due for completion in September 2012. In order to ensure that the planned construction schedule is maintained, up to 600 workers are currently employed on a daily basis which includes shift operations.
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