Frankfurt impresses (once again) with the rapid expansion of its high-rise skyline: During the construction phase of OMNITURM, a total of five skyscrapers are under construction in Frankfurt at the same time: Grand Tower, Henningerturm, Marienturm, OMNITURM and WinX. This is unprecedented in the history of Frankfurt, not even in the early 1990s, when Messeturm, Westend Tower and Trianon were built. Nevertheless, OMNITURM stands out as unique among these giants – both in terms of design and multifunctionality.
When space is scarce, divert into the third dimension
Urbanization is a dynamic process that can contribute to more sustainable land use development. In 2007, the world population reached a turning point: for the first time in human history, more people lived in cities than in rural areas – and the trend is intensifying. In this context, cities with well-designed high-rise buildings are an important part of the solution for future living spaces.
Architects and developers have a great responsibility towards society, the environment and generations to come. Since skyscrapers have an extreme impact on their surroundings, these huge structures must be designed and constructed with great care and consideration. They must be tailored precisely to the needs of the people who live and work there in order to create a healthy urban society in the long term.
Regarding its urban development, Frankfurt combines a typically European, organically grown town with the skyscraper city of a modern metropolis into a vibrant ensemble of buildings. OMNITURM is located in the heart of this architectural mixture of high and low. Its name (Latin: omnis 'all') is an allusion to the coexistence of residential and work life in the high-rise building.
Distinctly designed from the inside outwards
In OMNITURM, spaces with various functions are streamlined and efficiently stacked on top of each other. Variations in the interior spatial concept induce sculptural movements in the exterior shape. On street level, the floor areas are shifted back and forth to create vegetated terraces with a view of the park. Halfway up the silhouette, where the high-rise building transforms to a residential structure, the slabs project in a helical motion, creating outdoor spaces for the residents, before it resumes the rectangular, linear cliché of a tower upwards.
BIG architects have designed a tower that expands at its centre to accommodate the optimum spatial dimensions for each respective function. The OMNITURM incorporates two distinct office environments as well as living and public areas, each shaping the exterior appearance of the tower. The OMNITURM unites its working and living spaces in a logical design with artistic symbolism.
Architectural design as a challenge for structural design
A central feature of the architectural concept is the "hip swing", an alternating cantilevering of the 15th to 22nd floors by up to 5 metres in different directions. This presented several challenges to the structural designers. The high-rise building itself forms a spiral by shifting the storeys along its vertical axis. Above, the tower returns to rationally optimized floor areas and thus completes its rotation to realign with the structure outline beneath. The interior function leaves a visible footprint in the exterior design. The cantilevered slabs form terraces for a total of 8,200 m² of living space in a prime location of Frankfurt's real estate landscape.
Bollinger + Grohmann are forerunners among structural designers when it comes to making extraordinary constructions become reality. After the Danish architectural office around Bjarke Ingels, BIG architects, won the architectural competition, the engineers conducted a feasibility study. The aim was to optimize the geometry of the column strands “in order to minimize inclinations and deflections of the columns. At the same time, the decision not to use corner supports required the development of a support system that can renounce these structural elements.”
The OMNITURM was structurally designed as a high-rise building with main and secondary precast reinforced concrete beams, cast in-situ slabs and a reinforced concrete core. "Building projects with this type of structural design are ideal for precast concrete construction, because only a few connection details need to be developed, which are repeated over and over again," explains Thorsten Heskamp, who supervised the project in Peikko's Customer Engineering.
Precast elements in a high-rise building
Due to the construction method with precast elements and thus eccentric supports, the components are subject to torsion. Therefore, the load must be centered by a tension connection. Peikko HPKM column shoes and anchoring couplers in the precast beams avoid torsional moments on all levels above the second floor – wherever a beam is supported by a concrete corbel or a main beam rests on a secondary beam. The use of HPKM column shoes was dimensioned for horizontal installation by Peikko's technical support team and designed individually for the OMNITURM. Anchoring couplers, designed to be manufactured and threaded in precisely calculated lengths to match the standard formwork, are a vital component of the connection system.
This individual Peikko solution combines the benefits of transferring tension forces through the joints of a cast-in-situ structure with quasi-monolithic behavior with the fast assembly of the precast construction. In addition, the column shoe meets all requirements including the fire resistance of R120 for the load-bearing structure. This requirement is fulfilled by the verification according to ETA-130603 approval and by indenting the component deeper into the precast element.
For high-rise buildings, a precast concrete structure is ideally suited, since it is important to make quick and efficient progress building upwards. Peikko is an expert for connection technology used in precast elements, constantly developing creative solutions for demanding structural situations in cooperation with designers and architects. In the end, the quality of a building with the size and effects of a high-rise building is always better the smoother the cooperation between the people involved in the construction is. The example of OMNITURM illustrates that precast construction is fast, efficient and safe.