Famous facades

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By Gerhard Hope  www.constructionweekonline.com

The O14 development took over four years to build, and is one of the few projects to have been formally launched at the Business Bay development.

The 41cm-thick concrete facade of the O14 tower is perforated by 1,000 circular openings.
The 41cm-thick concrete facade of the O14 tower is perforated by 1,000 circular openings.

The 27,870m2, 22-storey commercial tower features a unique 41cm-thick concrete façade perforated by 1,000 circular openings, and against a window wall enclosure.

A 1m space between the facade and the glass surface creates a chimney effect to allow hot air to rise for passive cooling. The perforations provide light, air and views, while the façade also acts as a sunscreen. O14 was a collaboration between New York City-based Reiser + Umemoto, RUR Architecture PC and Dubai Properties.

Part of the larger ‘city within a city’ Business Bay precinct, O14 is located along the extension of Dubai Creek, occupying a prominent location on the growing waterfront esplanade. Perched on a two-storey podium, the building is named for its site designation. Quite coincidentally, the perforations in the tower’s façade resemble ‘Os’ upon first glance.

However, a closer look reveals that the openings more closely resemble oval or diamond shapes.

An experimental design, the O-perforated shell was wholeheartedly embraced by Dubai Properties business development manager Shahab Lutfi, who encouraged Reiser + Umemoto and RUR Architecture to be innovative.

Jesse Reiser, lead architect of O14, explains that concept was initiated with a competition last year held by Dubai Properties and led by Lufti, who thereafter commissioned Reiser to come up with the design for the new tower.

“The plan was originally mixed-use, but the market changed, so it became an office tower,” explains Reiser.

“The tower evolved from a large tower of complex curves and curtain wall, all prohibitively expensive, into a window wall where there would be glazing from slab to slab. Since Lutfi wanted column-free space, we moved to the idea of just a core that works with gravity, and an exoskeleton that takes the lateral forces.

It is a very efficient structure that, in its simplest form, is a concrete diagrid with openings that modulate via four different scales ranging from 2.5m to 6.5m. This generated benefits because the concrete façade could work as a sunscreen in such a hot climate.”

The space between the perforated façade and the window wall enclosure creates a chimney effect whereby hot air rises and draws cooling air along the glass surface. This contributes to the cooling-system efficiency for O14, thus reducing energy consumption and costs.

Reiser points out that mitigating the use of air-conditioning for O14 was a fortuitous by-product of the design, and helped reduce the cooling load.
“In the development, we realised we could generate a chimney effect, so we worked toward it,” says Reiser.

“Essentially, there are slabs attached to the shell through little tabs or tongues. Even though the shell stands free of the slabs, the voids between those tongues allow an open zone to the ground, so that allows for that chimney effect.” Reiser notes that the passive cooling deployed will ease the load of Dubai’s district cooling providers, which are often overstressed by the scorching summer heat.

Another famous façade is that of the Burj Khalifa in Dubai, the world’s tallest building, which used SunGuard Solar Silver 20 and ClimaGuard NL from Guardian Glass, which has 27 float plants around the world, including one in Ras Al Khaimah.

The glass processor was White Aluminium of Abu Dhabi, while the cladding was provided by Far East Aluminium and Arab Aluminium. The 828m-high tower achieved a world record for the highest installation of an aluminium and glass façade, at a height of 512m.

The glass surface of the building comprises 26,000 glass panels, covering 150,000m2. The proportion of laminated glass is not high when compared to the entire glass façade, with about 5,300m2 of laminated glass installed in the area below 0.7m in terms of outfall security regulations.

The glass used comprised the following:
• 5,000m2 Lami 44.2 + Coating ClimaGuardNL (2x4mm floatglass with 0.76mm PVB layer)
• 300m2 Lami 55.2 + Coating ClimaGuardNL (2x5mm floatglass with 0.76mm PVB layer)
• The biggest size was 3,200mm x 1,800mm

Heat-strengthened glass was mainly used, unlike tempered glass, which tends to be the norm in Europe. One of the main reasons for this was to avoid the risk of spontaneous breakage due to nickel sulfide inclusions that can occur more easily in tempered glass than in heat-strengthened glass.

In addition, heat-strengthened glass presents a better optical quality than tempered glass in terms of distortions. This is mainly due to the cooling process, which differs to tempered glass in that it runs slower.

Guardian says it first got in touch with SOM, the architect of the Burj Khalifa, in 2002. This was followed up UAE sales managers and later Guardian Europe.

The complex and global nature of the design and construction commenced with meetings in Chicago, Germany and Switzerland. The first requests about the glass started in 2003, with different calculations carried out in terms of the technical values of the insulating glass units (IGUs).

Glass-thickness calculations were based on a windload of 3,0kN/m2, which corresponds to a windspeed of 250km/h. Temperature and movement calculations for the IGUs included looking at temperature differences between the ground floor and top (in terms of production of the IGUs and their installation) and also between the different seasonal temperature variations.

Guardian plants in Germany and Luxembourg produced the coated glass for the Burj Khalifa. The company also supplied the glass for the Burj Residence project, comprising six towers that surround the Burj Khalifa.
The Burj Residence uses Guardian SunGuard HP Green 63, produced at Guardian’s Rayong, Thailand float glass plant and coated at Guardian’s Bascharage, Luxembourg float glass plant.

Guardian explains that the decision to use its products was taken as late as 2005. The first IGU was installed in August 2007. The good optical appearance was not only due to the heat treatment, but also due to the segmented positioning of the glass elements.

The initial idea of the architect was to have a matt silver, reflective colour, without the use of any tinted glass. The main stipulation was a solar factor of around 15 to 17, with a shading coefficient of 0.18.

One of the main issues in terms of the glass was the temperature difference between production and installation. For example, an IGU was produced in Abu Dhabi where the temperature was 26°C, and installed in August when the temperature in Dubai was 48°C, with a solar intensity of 900W/m2 (In Europe, the maximum for a vertical façade is 750W/m2).

The subsequent calculations in terms of stress and deflection impacted the final decision as to the glass thickness used.

Interestingly, even though the Burj Khalifa was built before sustainability and green building became buzzwords, low-emissivity glass was considered a ‘must have’ right from the inception of the project. This assists in keeping the heat out of the building at night, when indirect heat gain is still a factor given the high temperatures.

The surrounding areas of the building’s environment absorbs the intense heat generated during the day, and then continues to radiate this throughout the night. Low-emissivity glass not only helps to reflect long-wave radiation, but also helps reduce condensation on the exterior glass.

Another famous façade is that of the Yas Hotel in Abu Dhabi. The skin of the grid-shell comprises about 5,000 diamond-shaped glass panels that vary in size. These panels enable the complex geometry of the façade to be a medium for sequenced lighting or moving imagery.

In this way, the building adds both to the racetrack atmosphere and the hotel’s brand image. The glass panels have a carefully-selected coating and frit pattern that balances visual transparency with light-responsive properties according to different local conditions.

They are each lit individually with a bespoke RGBW LED luminaire designed to give asymmetrical light distribution. Of architectural and engineering significance was the main feature of the project’s design, a 217m expanse of sweeping, curvilinear forms constructed of steel and 5,800 pivoting diamond-shaped glass panels.

This grid-shell component afforded the building an architectural shape comprised of an atmospheric-like veil that contains two hotel towers and a link bridge constructed as a monocoque sculpted steel object passing above the Formula 1 track that makes its way through the building complex.

The grid shell visually connects and fuses the entire complex together, while producing optical effects and spectral reflections that play against the surrounding sky, sea and desert landscape.

The design as a whole acts as both an environmentally responsive solution, as well as an architecture of spectacle and event. The unique façade of the Yas Hotel has transformed it into a significant landmark destination on Yas Island for Abu Dhabi.

Safety glass
Schott Middle East FZE MD Kiomars Dabbagh explains that this German company provides technical glass solutions such as fire-resistant glazing in roofs and façades, partitions and transoms and doors and windows.

Pyran S is a monolithic, fully-toughened borosilicate glass with special strength and impact resistance. It is approved for 30, 60, 90 and 120 minutes integrity in fire-resistant glazing. With maximum dimensions up to 1,600mm by 3,000mm, it gives the freedom to think and build in bigger dimensions, including special frameless constructions.

Pyranova is a compact laminated composite glass meeting the requirements of fire-resistance category EI. It provides a physical barrier against flame, hot gases and smoke, as well as a reduced surface temperature and resistance against spontaneous ignition on the unexposed side up to 120 minutes. Double-glazed units are suitable for internal and facade glazing.

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