Innovative window technology: bi-folding windows 4.4 m high
09 Apr 2020

UBER headquarters with computer-controlled natural ventilation. At UBER's new corporate headquarters, employees will soon be able to enjoy the fresh sea breeze from the San Francisco Bay. The numerous atria in front of the offices are naturally ventilated via innovative bi-folding windows which have been developed recently. Computers control the opening and closing of the 4.4 m high and 3 m wide windows in the glass façade.


These two-piece windows, which were developed by the German façade specialist Gartner, fold outwards to form a triangle which is open to the inside, with air flowing in from above and below. These 160 bi-folding windows make up approx. 20 percent of the highly transparent building envelope. They blend harmoniously into the breathing façade, as the size of their operable frames corresponds to the dimensions of the fixed façade units. Each window consists of two sashes, each 1.5 m wide, connected by folding hinges, with ultra-clear low-iron laminated safety glass.

To ensure that the large two-piece windows open and close reliably, Gartner had to develop a new sustainable and efficient mechanism. Originally, the architects had proposed a linear actuator in the façade surface so that the windows open perpendicular to the surface. Since this solution would have required large forces for the opening mechanism, additional motors would have had to be installed. However, this was contradictory to the requirements of the customer, who was primarily focusing on appearance and performance.


New kinematic concept with a sustainable and efficient opening mechanism

Load-bearing components had to be designed with sharp edges and be reduced to minimum dimensions. Instead of the intended aluminium frame, Gartner therefore suggested to use steel. Thus, cantilevered scissors and levers could be avoided. In addition, drives and actuators were to be concealed in the base frame to create homogenous views of the façade. In addition to these aesthetic requirements, the foldable windows primarily had to meet criteria of building physics such as air and water tightness, but also wind and earthquake loads as well as thermal insulation. Further criteria for the operable windows included mobility, durability, reliability and safety.

Kinematic solutions had to take into account a rectangular frame with a central intermediate mullion and an opening area of 3 square meters. The two-piece windows were to be designed top-hung, guided by the lower crossbar. Obtrusive fittings of linear drives, for example, contradicted the required very slim design. Chain drives, as used for side-hung windows, were also to be avoided for architectural reasons, just as extra-long connecting rods of scissors drives which were rejected for esthetical reasons.


Top-hung hinged windows with double hybrid rollers and controls integrated in the mullions

Since none of these options could fully meet the design requirements, Gartner chose to use top-hung hinged windows which are supported on newly developed double hybrid rollers. These rollers support the dead weight and enable smooth movement. Cantilevers, which bridge the distance between the rails and the hinged windows, improve the tightness through their movement path. In this way, both lateral stability and minimal material requirements of the structure could be guaranteed. A chain drive with a traction and chain pressure direction of up to 1.5 kN maximum force is concealed in the intermediate mullion. With a stroke of 900 mm, the window can be opened in a controlled manner over an area of 3 square meters.


All control units that allow mechanical synchronization are integrated in the mullion. After the closing movement of the window is finished, it is locked subsequently. Circumferential safety bars are fitted and combined in the frame to allow for emergency shutdown. Various tests including crash tests and long-term performance tests have proven the air and water tightness of this 750 kg structure. With regular maintenance, the motors, chains, drive systems and rollers maintained their function over a period of up to 20,000 cycles without failure.


Youtube video explains the bi-folding window
Watch the YouTube video to learn more about the breathing façade and the bi-folding windows.

Ph.: © Jason O'Rear
UBER HeadquartersSan Francisco | USA
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