ThyssenKrupp Quarter facades: a giant's gentle skin

Some great buildings pass unnoticed below the radar of architectural intelligentsia. And not because they are small or built in lost places, but because they are too 'client oriented'. If a corporation is satisfied with their new HQ building, its architectural quality must have been low, or so the thinking goes. This post describes a recently finished great group of buildings - two times great, since they are both architecturally compelling and they perfectly reflect their owner and user's vision. If this group of buildings is interesting in a number of ways, one of them is the facade treatment, as I will try to demonstrate here below.

During several decades the architectural landscape of the Ruhr Valley towns in Germany has been dominated by neglected brown fields, industrial ruins and run-down postwar buildings. That is now becoming a thing of the past as architects from all over Europe complete their projects in the former coal-mining region.

The ThyssenKrupp Quarter in Essen is part of a 230-hectare downtown area known as the Krupp belt. The site, kept for years as a wasteland, is a historic place. In 1818, Friedrich Krupp founded a cast steelworks on the same spot, which his son Alfred turned into a global company. Railway tracks were produced here for the United States, and less exciting but quite effective canons were casted in the area for two world wars. It is a place in German history that triggers mixed emotions to say the least. A less known but more interesting tip for architects: the huge 'gerberettes' designed by Rice, Piano and Rogers for the Pompidou Centre in Paris were also built at the Krupp furnaces, not far from Essen. Krupp was the only company in Europe who stood to the challenge of producing the big cast steel pieces that were to play a significant role in the structural concept of the Beaubourg.

Thyssen­Krupp has built its new headquarters in this historic part of Essen at a total cost of 300 million euros. The technology giant, which employs 173,000 personnel in 80 countries, has no interest for skyscrapers. ThyssenKrupp’s chief expectation during the competition was that architects made the essence of its brand visible: transparency, innovation and far-ranging versatility. With the bulk of the masterplan finished this last summer, corporate culture and German industrial power welcome a new symbol. 

Chaix & Morel et associés (Paris) and JSWD Architects (Cologne) won the competition for the campus buildings and developed the ThyssenKrupp Quarter for a working population of 2,000 employees. There is ample space for them here. A 200 meter-long and 30 meter-wide pool forms an axis along which various buildings and generously laid-out boulevards appear. It is quiet around here, too. Cars disappear into car parks and subterranean garages around the plot. All deliveries are conducted below ground. Above this, 68 trees from five continents form a boulevard. There are large expanses of lush green lawn without bushes or perennials. The important aspects here are distance, silence and solemnity. Peter Drucker would have salivated in awe: this is the spirit of the new corporation, built to last.

The main building, known as Q1 and officially inaugurated in June, has a flexible facade layer made up of 400,000 stainless steel slats. This system aims to make air conditioning redundant. A weather station on the roof sends signals to a computer that steers the rotation of the facade slats. The design makes use of the material Nirosta, one of the concern’s branded products. ThyssenKrupp also aims to improve the cladding of high-rise buildings, and replace expensive aluminum profiles. To this end, the company has developed steel sheeting with a zinc and magnesium coating.

There are three elements that deserve to be described in more detail in this post: the glass mullionless curtain walls in the centre of Q1, the sunshades at the external office areas also in Q1, and the flat-rolled steel cladding of buildings Q1 (inside the atrium), Q2 forum, Q5 and Q7 (as the main facade cladding). Let's go with the description, one at a time.

Panoramic windows at the atrium
The large atrium area of Q1 shimmers as a result of its pearl-metallic gold color internal cladding.  But it is primarily the expansive volume of space that captivates. The 50 meter-high building, bonded from two L-shaped structures, is dominated by 'panorama windows', in fact two large tensed cable curtain walls. Both glass constructions are 28 meter high and 26 meter wide. The design and engineering of the panorama windows was done by Werner Sobek from Stuttgart. The facade contractor was Hefi Glaskonstructiv from Talheim, Germany.

View of the main axis pool through the panorama window at Q1

A steel pre-stressed cable net system holds the individual glass panes in place. Each double glass unit is 2.15m wide x 3.60m high, with clamps at the corners and mid height to connect it to the vertical and horizontal steel cables. Pre-stressing in two axes made it possible to eliminate complicated transitional details to the adjacent facade structures. In the vertical direction, with a grid dimension of 2.15m, the grid is composed of pairs of pre-stressed cables with a diameter of 30mm each. They are fixed to a three-story steel truss below the building’s 11th floor. The horizontal net structure, attached at the ends to the story floors, consists of one pre-stressed steel cable every 3.60m, with a diameter of 32mm. The vertical cable disposition in pairs allows the transfer of the glass self-weight via a force couple - tension and compression - into the pre-stressed cables. The horizontal pre-stress per story is 34 tons, while the vertical pre-stress connection is 2 x 15 tons. To transmit these forces the engineers from Werner Sobek chose carbon steel of grade S355. Compared with stainless steel, carbon steel displays a higher strength and a lower thermal expansion. The cables have a tensile strength of 1770N/mm2.

The structural solution followed here is quite similar to the Lufthansa Aviation Centre in Frankfurt, also by Werner Sobek, although in Frankfurt the only load-bearing elements are the vertically tensioned cables.

Atrium with panorama window to the left

The choice of glass was critical too: on the one hand it had to have solar control, while on the other it had to be clear with as little tinting as possible. To achieve the aim of maximum-possible transparency, a custom solution featuring insulated clear glass panes was selected. The structure is as follows: a) 12mm single-pane safety glass, b) 16mm inter-pane space, c) 2 x 8mm laminated safety glass with 1.52mm PVB film for solar control. The type of glazing chosen and the reduced support structure have resulted in an only 45 mm thick membrane that appears completely dematerialized. Despite being so thin, the glazed membrane met all thermal insulation requirements. I have not found any reference to argon fill in the glass cavity, but assume it is the case or the U-value would have been too high.

The images below show the section, elevation and concept details of the glass fixings.

ThyssenKrupp Q1 building: vertical section and panorama window glass elevation

ThyssenKrupp Q1 building: vertical detail of fixing at glass crossing. Two cables run vertical, one cable (sectioned) runs horizontal. All screw heads are embedded on the cast steel piece. 

ThyssenKrupp Q1 building: horizontal detail of fixing at glass crossing, and elevation detail of the external clamp. Two cables run vertical (sectioned), one cable runs horizontal.

The panorama windows viewed from inside

It’s not just the two panoramic windows that contribute to the amount of light that floods the atrium: there is also a large window opening in the atrium roof, supported by a cable net. Its dual-curved outer skin measures approximately 21 x 21m.

The technology of pre-stressed cable net facades is not new, and it's a very German one. If you are interested, there is a good summary in pages 235 to 243 of the highly recommended thesis by Mic Patterson, 'Structural glass facades: a unique building technology'. The first and still best known example of this glass wall system is the lobby of the Kempinski Hotel at the Munich airport, designed by Helmut Jahn and engineered by Schlaich, Bergemann & Parters. The hotel lobby was completed in 1993 and still looks amazing 17 years afterwards. The cable net grid in Munich is much smaller than the one in Essen, but there is only one cable per direction, making the knots less visually imposing than those of the ThyssenKrupp atrium. One could say that the Sobek version is more imposing in size and less innovative in the fixing details than its SBP's counterpart. But Munich was a much less rigid, monolithic glass, not an insulated screen. In any case, at least to me, the real interest of Q1 does not lay on the panorama windows, but on a much humbler element: the sunshades of the office space all around the building.

Sun-shading movable slats
Our industry has been strongly discussing for some years about the energy irrelevance of double skin glass facades. Their former advantage in reducing U-values has been equaled by the triple-glass units with argon-filled cavities and high-performant coatings developed in the last decade. On the other hand, g-value or heat gain coefficient (the % of solar radiation that penetrates through the glass) remains as a serious problem for office buildings in summer period. Renzo Piano was the first one in introducing the 'mediterranean double skin', that is, a continuous glass facade with a set of sunshades on the outside for solar protection. An energy simulation study presented by Mikkel Kragh and Annalisa Simonella from Arup Facade Engineering at ICBEST 2007 has got to the same conclussion: there is no direct correlation between U-value and overall energy performance in a building with high internal heat gains, as an office building. In other words, the main driver is exposure to solar radiation.

The best answer from a energy and daylight perspective, even in a cold climate as the Ruhr Valley, is to combine a lowish Uw-value (around 1,2W/m2ºK for example, achievable with double glass units and high-performant thermally broken profiles) with an effective sunscreen. 'Effective' here means a screen that reduces solar gains when there is direct solar radiation but lets daylight in when there isn't. That is, a moveable sunscreen. Et voilà: this is the solution applied to ThyssenKrupp Q1 facades.

Multiple image with fins at different angles from 0º to 90º

The sun-shading concept was suggested by the architects and developed by the Fraunhofer Institute for Solar Energy Systems in Freiburg. The energy study came out with a proposal to provide a constant horizontal overhang - useful for summer protection and as a catwalk - combined with a vertical set of twisting fins. The fins would twist to achieve an adjustable position between 0º (parallel to the facade: total direct radiation blocking) and 90º (perpendicular to the facade: maximum daylight penetration).

The great idea in this concept was to create a vertical fin made of horizontal cantilevered slats that were connected to a central stud, something similar to vertebrae in a spine. The cantilevered fins at each side of the stud can twist independently, as arms that rotate from widely open (0º) to parallel and intertwinned (90º). The final touch was to provide a shape for the fins that was non-rectangular, thus creating an interesting texture as the fins rotate along the day.
The sunshade elements have been manufactured by ThyssenKrupp Nirosta (the company branch for stainless steel) using a chromium- nickel-molybdenum stainless steel with high corrosion resistance called Nirosta 4404 (that is, EN 1.4404, equivalent to AISI 316L).

The movable fins from inside, with the horizontal catwalk

Each slat is ground on one side and sandblasted on the other. The slats thus appear to be matt or glossy depending on the point of view and incidence of light. The slat surface directs the incoming light indoors in such a way that the offices remain bright enough even if the sun protection is closed.

The manufacturing of the sun protection system must have been demanding. First, the metal strips were processed by ThyssenKrupp Umformtechnik, the group's automotive manufacturing unit. Then, Frener & Reifer, the facade contractor from South Tyrol mounted 116 to 160 slats onto each axis to form electrically driven slat packages. In the process, it was important that the slats remain movable in the center axis and react precisely to the signals of the electrical drive. It's funny that Frener & Reifer motto is 'Starting where others stop', completely adequate to this particular job. The facade contractors did also install the inner curtain wall, made with Schüco elements. Both skins in Q1, curtain wall and fins, are approximately 7,800m2 each.

The virtual animation at the Frener & Reifer page shows the movement game better than my words. The programming is really sensitive: the control system not only detects the seasonal sun position, but also knows what the current weather is like due to the data of a weather station located on the roof of Q1 building. On cloudy days, for example, all the slats will be turned outwards so that the sun shades remain open. Even when the slats are closed directly in front of the facade, employees can open the windows and access for maintenance is always possible.

There are in total a number of 1,600 motors to activate the fins movement. This seems as a maintenance nightmare, but it doesn't have to be so. Movable facade elements are more and more common lately, with motor costs going down and system reliability moving up every year.

This is a revolutionary design move, not in concept but in results: I suspect we will see many more moveable sun-shades in the near future. There is an interesting joint venture between Buro Happold and Hoberman, called Adaptative Building Initiative, that provides nothing but moveable facade elements to control solar gains and light levels at the same time.

External steel cladding

Sheet metal has long been considered a second rate cladding material – an impression the buildings of the ThyssenKrupp Quarter had to change. The final image of the buildings around Q1, finely glimmering in a champagne hue of metallic elements, consist of nothing other than sheets of steel.



ThyssenKrupp Quarter, Q2 Forum building facade clad in coil coated steel sheets.



Not just any sheet steel but a high-quality, fine sheet steel organically refined using a coil coating method. Fine sheet metal, coated using the hot-dip method, can be shaped, welded and painted. The 3m long and 0.67m wide, chamfered steel panels of the Quarter are resistant to wind, weather and UV radiation. Here, one percent of magnesium is added to the molten zinc for the fine sheet metal. As a result, improved corrosion protection is achieved with a thinner coating, which means that the valuable raw material zinc can be used sparingly.



Q2 Forum facade mock-up on site

The fine sheet metal, with a thickness of 0.8 to 1.2mm, is more affordable than a comparable facade element made of aluminum sheets of 3mm, at least so the ThyssenKrupp guys say. The material is called PLADUR ZM Premium steel; used as cladding for the walls of the atrium inside Q1, the interior of the ground-floor lobbies in Q2, Q5 and Q7 buildings, and the exterior facade areas on Q2 forum, Q5 and Q7. The material owes its appearance to a multi-layer coating in a color named Pearl Metallic Gold. Thanks to special pigments, the color shade of the surface changes depending on light conditions and the angle from which it is viewed. The term “Premium” refers mainly to the quality of the top coat, while the abbreviation ZM means that the surface of the steel is first protected against corrosion with a zinc-magnesium alloy coating before the paint system is applied. This alloy provides roughly twice the corrosion protection effect of conventional hot-dip galvanizing.


TKQ, Q5 and Q7 facades



It's fair to record that the façade area consultant for the Quarter has been Priedemann Fassadenberatung from Berlin. No information can be found at their Webpage about the project or their contribution though.

Let me finish this long post in silence. No more words - there have been too many! Just some selected images of Q1 and the sun-shading slats that struck me when I first knew about this project. In awe...