Al Bahar Towers ... one of top 20 innovative buildings.
WORK is well under way on the Abu Dhabi Investment Council’s (ADIC) new headquarters, which has been ranked as one of the most innovative buildings in the world.
The twin 25-storey towers – known as Al Bahar Towers – feature on the Council for Tall Buildings and Urban Habitat’s (CTBUH) “Innovative 20” list of buildings that “challenge the typology of tall buildings in the 21st century”.
The project were chosen because of its dynamic facade based on the mashrabiya shading system – a popular form of wooden lattice screen found in Islamic architecture – which was developed by Aedas and Arup to screen the building from direct sunlight while optimising views from inside at other times and reducing the need for artificial light. It features translucent components that will open and close as the Sun moves round.
According to Peter Oborn, deputy chairman of Aedas Architects, the system will reduce solar gain by 50 per cent.
“The design seeks to create a building that is both culturally and environmentally responsive, while also respecting the emergent Abu Dhabi 2030 Plan. The building is targeting a Leed (Leadership in Energy and Environmental Design) Silver rating and is on schedule for occupation at the beginning of 2012,” says Oborn.
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Typical floor plate illustrating the sky garden on the south elevation, which will further reduce solar heat gain. |
Aedas was appointed to design the ADIC headquarters in February 2008, following an international competition for the twin landmark office towers that would provide a contemporary design using modern technology while taking into consideration the region’s architectural heritage together with the status of the client’s organisation.
The towers – each 145 m high – comprise two basement levels with parking for more than 750 vehicles, a ground floor, podium and 25 upper storeys offering 70,000 sq m of space to accommodate 2,100 staff. The ground floor and podium levels provide access to a variety of shared facilities including restaurants, prayer rooms and an auditorium.
Enabling works on the project started in March 2009, with work on the construction of the towers having commenced in November 2009. The project is targeted for occupation on the first quarter of 2012.
An enabling works contract was awarded to achieve an early site start comprising secant piles, main piles and blinding concrete. The building sits on a bored pile foundation while the substructure comprises in-situ concrete. The main contractor has slip-formed both towers concurrently while simultaneously proceeding with construction of the basement and podium block. Erection of the steel-framed superstructure in ‘honeycomb’ pattern has followed closely behind the cores with mechanical and electrical (M&E) first-fix and cladding starting on completion of the in-situ floor slabs.
The turnkey project includes full fit-out and FF&E (furniture, fixtures and equipment) together with bespoke joinery package.
Elaborating on the design, Oborn says: “In order to generate the form of the towers, Aedas applied the principles of geometric composition derived from Islamic architecture. Geometric composition has been a defining characteristic of Islamic architecture for centuries, the circle and rotation reflecting the concept of unification and unity evident in nature; an important concept in Islam and in the emerging science of biomimicry.
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A mock-up of the mashrabiya and (below) computer models of its various positions. |
“Following an intense period of analysis, and influenced by both the client’s brief and also the orientation of the site, Aedas began to develop the distinctive form of the towers using parametric design techniques to generate a defining geometry. The starting point was two cylindrical towers; a circle producing the most efficient form in terms of wall-to-floor area whilst also creating the greatest volume with the least surface area.
“The circular plan form was articulated to reduce solar exposure on the most heavily exposed elevations and, in so doing, began to generate a natural orientation. The form of the towers was then sculpted around the core, narrower at the base and at the top, but broader around the intermediate floors. The crown of the tower was cut at an angle to maximise solar gain for roof-mounted photovoltaics. Sky gardens were introduced in the most heavily exposed southerly elevation to further reduce solar gain while providing an amenity space for users.”
Having established an underlying geometry, the team was then able to erode the elevation in order to generate the structural and cladding grids. The resulting honeycomb structure performs well in terms of its seismic response (due to the number of vertical elements), bracing (due to the number of diagonal elements), redundancy (due to the number of alternate load paths) and wind loading (by providing an aerodynamic profile).
Mashrabiya
At the same time as the form of the towers was being developed, the team was keen to find a way to protect the building from the expected extremely high levels of solar heat gain. Drawing upon their knowledge of the region’s vernacular architecture, the practice became intrigued by the use of ‘mashrabiya’ as a device for achieving privacy while reducing glare and solar gain.
Aedas has reinterpreted the concept of the mashrabiya at ADIC by developing a series of translucent umbrella-like components which open and close in response to the movement of the sun.
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“Each shading device is driven by a linear actuator and dramatically reduces the amount of solar gain striking the façade,” says Oborn. “The dynamic screen avoids the need for heavily-tinted glass, thereby reducing the requirement for significant artificial lighting while providing better views for occupants. This is the first time such a moveable façade has been used at this scale, enabling a reduction in solar gain of over 50 per cent. The façade will be controlled via the building management system, creating an intelligent façade system.”
Some 2,000 separate ‘mashrabiya’ components will be used on both towers.
R&D
Working closely with colleagues at Arup, the Aedas team drew upon the skills of its in-house research and development (R&D) group to apply advanced computational design techniques in support of the project. The group developed bespoke applications to simulate the movement of the façade in response to the sun’s path and went on to support the detailed design development by undertaking a variety of simulations.
The same advanced techniques were later used to derive the geometry from which a single integrated building model was created and this model was in turn used to ensure proper coordination of the various building elements.
Landmark
By applying traditional design techniques in a contemporary manner, Aedas has produced a distinctive solution, which is entirely rooted in its culture and its environment. Aedas has developed a solution for the ADIC headquarters in which form and function are combined into what could be called a ‘new vernacular’. The buildings will create a distinct gateway and a landmark on approach to the city.
