This is one in a series of blog posts covering the intelligent, functional, and sustainable features of the Capital Market Authority (CMA) building, an 80-story class-A office skyscraper designed as a joint venture by Omrania and HOK, which establishes a new architectural and engineering benchmark for Riyadh while transforming the city’s skyline.
Rising from the heart of the King Abdullah Financial District — for which Omrania also served as design adviser — the CMA tower is visually distinguished by its sharp-faceted, articulated profile. Yet its most exciting features are its efficient and sustainable systems, starting with the high-performance enclosure system incorporating solar shading, photovoltaic (PV) solar energy collection, and integrated facade cleaning, via the following elements:
- A triple-glazed IGU (insulated glass unit), unitized-type glass curtain wall, which mitigates solar heat gain and reduces the cooling load.
- A horizontal catwalk made of coated aluminum, located externally at each floor, serving at once as an external shading device and part of the façade maintenance system.
- An array of 400-millimeter-deep glass fins with an offset frit pattern arranged diagonally across the building facade, for shading. The position and angle of the fins, connected to the catwalk, are optimized to account for solar tracking, reducing direct light exposure while enabling views and transmitting a respectable 35% of visible light.
- A PV farm in the tower’s crown, generating 300,000 kilowatt hours annually.
- An innovative building-maintenance system integrated with the curtain wall. Three platforms suspended from the tower roof are guided up and down the facade (which is not vertical), using adjustable arms to attach to the catwalk/shading devices at each level. A monorail track along the underside of each catwalk allows workers to easily connect a retractable lanyard to their safety harness and dismount onto the catwalk below. There, they find a cart equipped with cleaning supplies that rolls securely along tracks at the catwalk level. This system allows the tower’s exterior to be cleaned 15 times per year, compared with only four times per year using a conventional suspended-gantry system without catwalks — very important in a climate where windblown sand quickly accumulates on building surfaces. The system is also designed to facilitate replacement of the facade IGUs.
The high-performance envelope design and integrated facade-access system of the CMA tower represents a unique and integral solution to the challenges associated with facade design for super-tall structures in Riyadh and elsewhere in the region.
Turning constraints into design opportunities
Sited on an irregular, trapezoid-shaped parcel within the densely planned King Abdullah Financial District (KAFD), the CMA building conforms to the goals and requirements of the KAFD masterplan. In addition, the super high-rise tower was engineered to withstand powerful wind loads without sacrificing usable floor area. The tower is internally divided into three vertical office blocks separated by “sky lobby” and mechanical floors.
The crystalline profile of the CMA building helps reduce the severity of wind vortex shedding on the structure. Faceted from base to crown, the tower does not significantly taper as it rises. Its prismatic form is consistent with the aims of structural stability, maximum interior area, and aesthetic distinction.
The use of concrete-filled steel tubes for perimeter columns — an uncommon design solution in Saudi Arabia — reduces column section sizes to improve the efficiency of both construction and interior space allocation. Perimeter columns supporting the tower floors are located at the apex and pleat points of the polygonal shaped floor plan, with intermediate columns running up the middle of each face of the building. Inclined columns or pylons rise from the base of the tower to the fifth floor, where they converge to support the perimeter mid-side columns above on each face of the building. At the base of the tower, the inclined columns merge with the perimeter apex and pleat columns. The inclined columns enhance the tower’s visual profile and create wider openings for pedestrian circulation within lobbies at ground to third floor levels.
Each office floor-plate contains a gross area of 2,500 to 2,600 square meters. To maximize usable floor area and achieve a blended efficiency ratio of 70% gross to usable space, it was essential to make the core of the tower as compact as possible. The key driver of core volume was the size of the elevator banks. Given this parameter, the project utilizes the space-saving technology of Thyssenkrup’s TWIN elevator system developed for local zone elevators.
Efficient use of internal space, innovative vertical transportation, and advanced structural performance are just a few of the reasons why the CMA headquarters building represents the vanguard of Riyadh’s transformation into a leading hub for Middle Eastern business.
Article courtesy of Omrania
Written by: Philip Willmetts, CMA Project Manager (Detailed Design)