The Power of Concrete: Twisted Tree-Shaped Supports and Beams

HeidelbergCement’s new headquarters consists of three sections interconnected at different heights. Each building section has an atrium that provides ample light and luminance. The building opened June 2020, and offers up to 1,000 employees a state of the art work environment. As a general planner, the architectural firm AS+P Albert Speer + Partner, based in Frankfurt, was responsible for the project. W+Architektur provided the consulting office for client’s project manager.

PERI, a leading manufacturer of formwork and scaffolding worldwide, and HeidelbergCement, a building materials manufacturer, combined their concrete and architectural expertise to execute this project. This allowed PERI to expand its concrete construction capabilities. Special PERI formwork elements were used to realize the architectural highlights of this project.

Customized PERI formwork in use

The new group headquarters of the building materials manufacturer HeidelbergCement makes an impact with its bright, light-flooded rooms and the radially shaped elements made of white concrete. Image © Thilo Ross Fotografie
The new group headquarters of the building materials manufacturer HeidelbergCement makes an impact with its bright, light-flooded rooms and the radially shaped elements made of white concrete. Image © Thilo Ross Fotografie
With green inner courtyards and numerous other highlights, the new building meets the highest standard of the German Sustainable Building Council (DGNB). Image © Thilo Ross Fotografie
BIM Model of the new HeidelbergCement headquarters. Image Courtesy of AS+P Albert Speer + Partner GmbH

The entire project was a huge undertaking. Thomas Mehl says that the total construction time was 16 months and involved approximately 31,500 m3 concrete, 97.500 m2 formwork, 7,500 tonnes of reinforcing metal, 250 m3 masonry, and 31,500 m3 concrete. Thomas was the project manager and managed the entire project with the help of his team at the PERI Frankfurt branch and the Free-Form Concrete technical bureau under Johann Bergmiller.

Twisted Supports, SB 4 Architectural C Concrete

 Within a 16-month construction period, almost 97,500 m of formwork solutions were used for this project – including customised PERI special formwork elements. Image © Thilo Ross Fotografie

Three X-shaped supports, which act as the building’s structural root and take the shape of trees, are the focal point of the new atrium. Johann Bergmiller and Thomas Mehl agree that the highlight of this project was the concrete formwork and concreting of these supports in SB 4 architectural cement quality. These supports support the 700 m2 and 1,200 t ceilings of the atrium, which is approximately 11 meters high. Each support consists of three cross-sections that are square and inclined in the same direction. They cross over at approximately a third of their total height.

Planning Evolution

The complex construction was realised with a 3D special formwork made of steel elements with an overall height of 150 mm. Image © Thilo Ross Fotografie

The engineers at PERI pushed technical limits to achieve the formwork design required for tree-like supports. Because of the unique geometry of the supports, the three-dimensional characteristics and overlap of the three pillars required creativity. Due to the extremely high architectural concrete requirements and the structurally important fresh concrete pressure of 200kN/m2, as well as the tight space constraints in the atrium, it was impossible to use traditional special-purpose timber formwork.

To be reused for other supports, the formwork below the intersection needed to be completely non-destructive. This added another layer of complexity to the construction process. Bergmiller, who was responsible to plan the special-purpose formwork, said that after discussions with the client, they decided to use a complex 3D formwork made of steel elements and a construction height 150mm.

The time it took to plan, deliver and install Heidelberg materials was two and a quarter months. The basis of three-dimensional planning – which was done using CAD systems PERI CAD, and RHINO – was a 3D model the tree-like supports. This included the element separation points. Planners of the formwork construction faced another challenge when these separation points had to be seamlessly integrated into the building’s architectural concrete. The support’s entire height was limited to a single panel joint. Visible fixing screws, tie holes, and formlining joints must be avoided.

Elegant Honeycomb Structure

PERI delivered formwork and falsework from one single source that were fully compatible. Image Courtesy of PERI

Bergmiller says that the support structure for the completed pillar formwork can be viewed as a honeycomb structure, consisting of no less than 63 CNC-laser-cut individual components. Bergmiller explains that the individual components were assembled using a plug-in system to eliminate time-consuming welding in equipment.

Each component needed to be completely reconstructed and statically dimensioned. The construction involved the use of approximately 12.7 tonnes of steel. To withstand high levels of concrete pressure, a 5-mm thick steel formlining was attached to the support structure. Bergmiller says that the most difficult problem was the formwork solution where the arms of three tree-like supports intersect. With the express purpose of counteracting deformation of steel, additional rigging structures were added.

Delivery on-time

The large amount of materials needed for the project meant that the bulk of the structure had to be pre-assembled at the factory before being delivered to Heidelberg. The tree-like supports were assembled on site, one by one. The reinforcement was also installed on site. Additionally, the formwork was seamlessly integrated into the PERI UP Flexible falsework that was already in place. PERI’s compatibility was a key reason why the customer chose to work with us.

Pushing the Envelope

Before construction started, the team responsible knew that the task of erecting tree-like supports was a difficult one. Ingo Lothmann, HeidelbergCement’s chief architectural concrete coordinator, was aware of this and worked with engineers from PERI to devise a technological solution. It was also difficult to place concrete due to concrete technology requirements for the color and structure of architectural concrete surfaces. Concrete was not placed from the top like in most other cases.

Concrete distribution systems poured 30 m3 concrete in three sections at once and forced it upwards using three pumps hoses embedded in the formwork. Slide gate valves were used to inject concrete. They were placed so that they would not be visible after completion. PERI sensors embedded in the formwork allowed for the measurement of the concrete pressure during concreting and monitoring it via a mobile phone with the PERI InSite construction Web Application. The formwork pressure data provided a detailed overview of the concreting process.

The project’s final outcome was a great success. Johann Bergmiller summarizes: “With this project we have once more broadened the scope of what is technically possible in special-purpose formwork building.”

Feature Wall at SB 4 Quality

The new headquarters features more architectural highlights than the tree supports. The building’s feature wall, or foyer wall, is distinguished by its recessed radial design. It is made up of several prefabricated concrete elements which were retrofitted to an in-situ concrete wall. Additional to the requirement for architectural concrete of SB 4 standard, white, there was an additional requirement that no tension holes or fastening points be visible. This would adversely impact the appearance. At the height of the galleries, there are no visible vertical joints. There are only two horizontal joints. An overcut concealed the butt joints. The project-specific PERI formwork was used to realize the prefabricated concrete elements that measure 8 cm thick (4 cm in the recesses).

Uneven Cross Vault at SB 4 Grey Concrete

The feature wall consists of several prefabricated concrete elements of the highest architectural concrete quality, which were subsequently mounted to the in-situ concrete wall. Image © Thilo Ross Fotografie

The domed ceiling was another challenge. It consists of an uneven cross vault with an circumferential edge stand in SB 4 gray concrete. This ceiling was to be formed at a height up to 7m and with a slab thickness of 25cm. The result was a smooth, butt-free joint without any visible fixing points. The formwork solution developed by PERI for the execution of the cross vault included 82 3D-designed architectural concrete timber founders.

Recesses with Diamond-Shaped in the Casino

The 11.75 m2 high facade columns enhance the eye-catching appearance of HeidelbergCement's new group headquarters even from the outside. Image © Thilo Ross Fotografie
The 11.75 m2 high facade columns enhance the eye-catching appearance of HeidelbergCement’s new group headquarters even from the outside. Image © Thilo Ross Fotografie
The dome ceiling was made with 82 factory pre-assembled, 3D-designed architectural concrete timber formers. Image © Thilo Ross Fotografie
The dome ceiling was made with 82 factory pre-assembled, 3D-designed architectural concrete timber formers. Image © Thilo Ross Fotografie

A striking design is also featured in the casino located on the ground floor at the new headquarters. The space offers HeidelbergCement employees plenty of seating and a commercial-sized kitchen. The special reinforced concrete ceiling features radial, sharp-edged beams. These interventions are made in SB 4 white concrete and the underlying ceiling is SB 2 grey concrete. The striking use of colours and shapes makes them stand out. There are no bracing points or fixing points for the beam formwork.

The casino on the ground floor of the new headquarters offers HeidelbergCement employees ample seating and a commercial kitchen. Image © Thilo Ross Fotografie
The casino on the ground floor of the new headquarters offers HeidelbergCement employees ample seating and a commercial kitchen. Image © Thilo Ross Fotografie
The casino's special reinforced concrete ceiling consists of radial sharp-edged beams. These stand out in SB 4 white concrete against the underlying ceiling in SB 2 grey concrete. Image © Thilo Ross Fotografie
The casino’s special reinforced concrete ceiling consists of radial sharp-edged beams. These stand out in SB 4 white concrete against the underlying ceiling in SB 2 grey concrete. Image © Thilo Ross Fotografie

PERI’s special formwork was used for the slab. It was then implemented with 64 pre-assembled box outs in the factory. Four diamond-shaped supports were used to transfer the load. They had different cross-sections within the facade area.