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Scraping the sky with precast

The OMNITURM of Frankfurt proves that a precast concrete structure is ideal for making quick and efficient upwards progress in a high rise.

Designed as an architectural eye-catcher, the floors between 15 and 22 shift up to 5 meters (16 ft) in different directions and form a spiral by shifting the levels along its vertical axis.
The benefit of the cantilever slabs is the total of 8,200 m² (9,800 sq yd) of vegetated terraces in a prime location of Frankfurt's real estate landscape.

Challenge to the structural designers

After Bjarke Ingels and his BIG architects won the architectural competition, the Bollinger + Grohmann engineers conducted a feasibility study.

Structurally, the OMNITURM was designed as a high-rise building with main and secondary precast reinforced concrete beams, cast in-situ slabs, and a reinforced concrete core.
“Projects like this are ideal for precast concrete construction, because only a few connection details need to be developed. These details are then repeated over and over again,” explains Thorsten Heskamp, who supervised the project in Peikko's Customer Engineering.

Developing a custom support system

The aim was to optimize the geometry of the column strands to minimize inclinations or deflections of the columns.

With precast elements and eccentric supports, the components are subject to torsion. That’s why the load must be centered by a tension connection. To avoid torsional moments on all levels above the second floor, Peikko HPKM® column shoes and COPRA® anchoring couplers were specified, wherever a precast beam is supported by a concrete corbel or a main beam rests on a secondary beam.

A custom design for the OMNITURM, the HPKM® column shoes were dimensioned for horizontal installation. The COPRA® anchoring couplers – another vital component of the connection system – were designed in precisely calculated lengths to match the standard formwork.
This solution transfers tension forces through the joints of a cast in situ structure with quasi monolithic behavior and allows for the fast assembly of the precast construction.

HPKM® Column Shoes were used in this project instead of BECO® Beam Shoes due to the tested R120 fire resistance requirement. This is fulfilled by the verification according to ETA 130603 approval and by indenting the component deeper into the precast element.

An example of moment resisting connection between primary and secondary beams designed for OMNITURM.


This article has been published originally at Connections 1/2020 magazine.