Council on Tall Buildings and Urban Habitat
 

Al Bahar Towers, Abu Dhabi
Featured January 2013
Al Bahar Towers was recognized as the "CTBUH Innovation Award Winner" and a "Best Tall Building Middle East & Africa Finalist" in the 2012 CTBUH Awards Program.
Other Featured Tall Buildings

“The façade has an interactive relationship to the environment which is reminiscent to the opening of a morning glory flower to the sun.”
- Richard Cook, CTBUH 2012 Awards Chair, Cook+Fox Architects 

Location
Abu Dhabi
Completion
2012
Height
145 m (476 ft)
Stories
29
Primary Use
Office


Owner/Developer
Abu Dhabi Investment Council
Design Architect
Aedas

Structural Engineer
Arup
MEP
Arup
Project Manager
Mace Ltd

Contractor
Al-Futtaim Carillion

In looking to innovate high-rise design, nature and culture are the most resilient sources of inspiration. The Al Bahar Towers relies on both of these in the execution of the advanced screening system which was designed to integrate the building with its cultural context and respond directly to the climatic requirements of the region. The “mashrabiya” form of the screens directly anchors the buildings in the Islamic tradition of the Middle East, while the dynamic movement of each of the individual units recalls the response of native plants.

The use of highly developed modern technological methods facilitated this approach, through the use of parametric and algorithmic modeling. Pushing the envelope in terms of computing capabilities, the design concept was refined without sacrificing the ideals of the project. In the end, a new paradigm has been created in the innovative design of tall buildings.

Figure 1. Overall view from the north
Figure 2. Façade close-up view showing shading panels

Abu Dhabi has been the center of a large amount of newly constructed tall buildings in the last decade, but as concerns have grown over environmental impact and sustainability, some design teams have moved toward implementing unique ways to building in the desert while reducing their carbon footprint.

Al Bahar Towers took inspiration from a traditional Islamic motif to design an innovative and visually interesting external automated shading system for the building. The dynamic façade has been conceived as a contemporary interpretation of the traditional Islamic “mashrabiya”; a popular form of wooden lattice screen found in vernacular Islamic architecture and used as a device for achieving privacy while reducing glare and solar gain. The project brief called for two 29-story towers to create an outstanding landmark that would reflect the region’s architectural heritage together with the status of the client’s organization while providing a contemporary, sustainable building using modern technology.

The tradition of tall buildings in the Middle East has relied upon designs typically coming from North America, which generally do not address the radical climate differential. Many existing towers rely primarily on high-performance reflective curtain wall systems which utilize tinted glazing. While this system may deliver acceptable results, it usually provides poor external views, lack of optimal daylighting, and introduces excessive glare to the exterior. Alternatively, fixed shading devices have been employed in some applications with positive effects, but are only optimized for one condition and can therefore never provide ideal results.

The “mashrabiya” at Al Bahar Towers comprises a series of transparent umbrella-like components that open and close in response to the sun’s path. Each of the two towers comprises over 1,000 individual shading devices that are controlled via the building management system, creating an intelligent façade.

Figure 3. Comparison of shading units fully closed (left) and fully open (right)
Each unit comprises a series of stretched PTFE (polytetrafluoroethylene) panels and is driven by a linear actuator that will progressively open and close once per day in response to a pre-programmed sequence that has been calculated to prevent direct sunlight from striking the façade and to limit direct solar gain to a maximum of 400 watts per linear meter. The entire installation is protected by a variety of sensors that will open the units in the event of overcast conditions or high winds. The effects of this system are comprehensive: reduced glare, improved daylight penetration, less reliance on artificial lighting, and over 50% reduction in solar gain, which results in a reduction of CO2 emissions by 1,750 tonnes per year.

Working closely with colleagues at Arup, the Aedas team also drew upon the skills of its in-house research and development group to apply advanced computational design techniques in support of the project. During the competition stage, the group developed customized applications to simulate the movement of the façade in response to the sun’s path as proof of concept and, following award, went on to support the detailed design development by undertaking a variety of additional simulations.

An integrated building model involving both the formal geometry of the buildings as well as the dynamic shading devices was created, providing a full view of the project at any given time. During the design stages of the project this model facilitated a variety of performance optimizations, while during the construction stages the model was used to ensure the proper coordination of the various building elements, including the concrete core, the structural steel frame, the façade, and the “mashrabiya.” It is a testament to the robustness of the model that, despite the complexities of the project and the various tolerances and movements that had to be accommodated, no significant coordination issues were experienced throughout construction with any members of the supply chain.

The overall form of the towers was optimized to complement the shading system. The design began with two simple cylinders, the circular plan giving the most efficient shape in terms of wall-to-floor area while also creating the greatest volume with the least surface area. The circular plan form was then articulated based on a combination of circular geometries to reduce solar exposure, and 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.

Figure 4 and 5. Solar analysis diagrams
The building also incorporates the use of solar thermal panels for hot-water heating and will be one of the first buildings in the Gulf to receive a LEED Silver rating. While subsidized energy tariffs in the Gulf region prevent any meaningful cost–benefit analysis from being undertaken, it is believed that the Al Bahar Towers project will contribute to the wider discussion concerning such issues as cost-in-use and whole-life costs.

Internal sky gardens exist along the southern façade of the building which, in addition to the exterior shading, help alleviate the effects of solar exposure. These areas also serve as an amenity to users, who utilize the spaces for meetings or breaks.

The podium accommodates a range of shared facilities including prayer rooms, restaurants, and an auditorium, while enabling segregated access to be achieved for various categories of users including members of the public, staff, and VIPs who are provided with discreet access from the upper landscaped deck. There are two levels of basement parking and a mezzanine area is provided within the podium as a meeting point for staff.
Figure 6. Typical office suite.
Figure 7. View within sky garden
The façade system challenges the typical high-rise typology of the area, suggesting that more responsive and dynamic solutions to climactic conditions are more appropriate than attempting to statically handle them through designs based on non-regional traditions. Al Bahar Towers seeks to provide both a contextual and culturally sensitive design while also utilizing modern technology to meet higher standards of efficiency.

The design of Al Bahar Towers may also be seen as a response to a number of other initiatives that were being launched within the Emirate at the time of their conception, including publication of the Abu Dhabi 2030 Plan, comprising a comprehensive development framework based upon the principles of cultural and environmental responsibility, together with development of the Estidama environmental management standard and promotion of the Masdar initiative on renewable energy.
Figure 8. Detail view of shading units.

Related Links
CTBUH Skyscraper Center Profile:
Al Bahar Tower 1
Al Bahar Tower 2

Al Bahar Towers was recognized as the Innovation Award Winner and a Best Tall Building Middle East & Africa Finalist in the 2012 CTBUH Awards Program.
Download Al Bahar Towers 2012 CTBUH Awards Book section

2012 CTBUH Awards Book

The CTBUH would like to thank Aedas for their assistance with this article.
Photography © Aedas