Let the Games begin

All eyes will be on Doha on 1 December as the Olympic Flame is lit to signal the start of the 15th Asian Games. Arup director Gregoir Chikaher and Bassam Al Awar, MEP manager for the Midmac-Six Construct joint venture give an insight into the engineering behind the tower that will hold the flame aloft for the event.

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By  Alison Luke Published  December 2, 2006

|~|7p19main.gif|~|A 12m-high Olympic Flame will be produced in a specially designed cauldron at the top of Aspire Tower. After the Games a ‘flame’ will be recreated with water. |~|After years of preparations, the athletes taking part in this year’s Asian Games are limbering up for their moment in the spotlight.

But before the cameras swing towards the winners podiums over the coming fortnight, the focus will fall firmly on the efforts of another team of players – the construction firms behind the venues hosting the event.

A series of landmark stadiums have been constructed in preparation for the Games and the one that is likely to capture the imagination of the viewing public the most is the Sports City or Aspire Tower.

At 300m tall, the tower is the tallest building in Qatar and for the duration of the Games the Olympic Flame will burn at its peak.

Sited next to the new Khalifa Stadium, the tower comprises 17 floors of hotel, conference and banqueting facilities, apartments, a health club with a swimming pool overhanging 80m above ground level, sports museum, observation deck plus a revolving restaurant.

The circular structure is formed by a concrete cylinder that reduces from a diameter of 14m at the base to 11m at the top. This core houses MEP service risers, staircases, two 6m/s express lifts and two 3.5m/s goods service lifts.

The external facades comprise stainless steel meshes of gradually varying densities and the tower is topped by a ‘petal’ structure that stretches 77m above the top level and will cup the Flame (see box ‘Meeting an Olympic challenge’).

Midmac and Six Construct won the design and build contract for the project in a joint venture bid in April 2005. The firms awarded the architectural design and development to Arep and the structural design to Arup. Arup was also responsible for the design of the MEP services to scheme phases, with Six Construct producing the detailed design.

One of the main challenges for the construction team was the fast-track nature of the project, with just 21 months to design and build the tower and an immovable completion date. For the MEP installation the main design considerations included comfort, reliability, life safety, energy efficiency, space for plant and the speed of construction.

The building envelope had to be designed to achieve maximum thermal efficiency and comfort levels within the occupied spaces, while enabling visitors a panoramic view of the city. Detailed studies were carried out including a building physics exercise that involved the use of simulation software to determine the best glazing and mesh properties to reduce the overall cooling load and reduce the energy consumption.

The tower is divided into discrete blocks of accommodation connected to the central core. To maximise the speed of construction and usable floor space, the amount of MEP services that could be contained within the core was limited.

In addition to the main lifts, the chilled water, electrical and water installations supplies are contained here, connecting to technical plant levels in the basement, health club, museum and restaurant levels. Each technical plant level includes air intake and exhaust points for the air handling plants serving the local areas.

The estimated electrical demand for the tower is 7MVA, with a peak cooling load of 7MW. Two independent 11kV power supplies are connected to the network. These operate simultaneously, sharing the load, however each can supply 100% of the load in the event of the other failing to ensure high resilient power supply for life safety and hotel operations.

In addition, standby generators are provided to serve the life safety equipment, security systems, commercial operations and data/communications systems. The local distribution network is served via 11kV switchrooms located at basement and revolving restaurant level.

A 350mm diameter chilled water connection is connected to the main energy centre with flow and return temperatures of 6.5°C/14.5°C respectively and a chilled water flow rate of 223l/s. The chilled water system comprises a series of sealed pressurised circuits, operating on variable flow to match the anticipated high diversity factor within the tower and reduce energy demand.

The cold and hot water consumption of the building is expected to be around 45,000l/day and 18,000l/day respectively. As the incoming cold water temperature may exceed 47°C during summer, the incoming water will be chilled.

The cold water services are divided into three categories: cold chilled potable water, cold unchilled potable water and non-potable water. A silver-copper ionisation treatment system for the potable water ensures adequate protection against bacteria, in particular legionella, and allows the hot water temperature to be reduced to 41°C instead of 65°C.

The building is divided into four pressure zones through plate heat exchangers that function as pressure breaks. All terminal units and air handling plants have been designed using two-port control valves to offer controllability for maintaining the required enthalpies.

Because of high ambient water temperatures, the swimming pool water is also cooled by means of plate heat exchangers to maintain a water temperature of 30°C.

The total cooling demand of the tower is 2,000T. Space cooling is mainly provided by fan coil units, with air handling units supplying treated fresh air. For energy efficiency, the exhaust air is routed back to plate heat exchangers to assist in cooling down the fresh air intake before being exhausted to the outdoor.

One challenging design issue was the space cooling of the hotel atrium. With a volume of over 107,000m³, standard comfort cooling systems were not practical. To predict comfort levels a computational fluid dynamics (CFD) model, STAR-CD, was used to calculate the air temperature distribution and air movement within the atrium.

Light ray tracing software, Radiance, was used to calculate the direct and diffuse solar radiation distribution as inputs to the CFD model. This included the complex transmission, absorption and reflection properties of the external shading elements and glass facade combination.

The solution involved the creation of a two-zone environment by the use of air supply nozzles mounted around the inner core at level four and a series of binnacles in the lobby area.

Both the nozzle and binnacle supplies were optimised to provide an acceptable balance of air temperatures and airflows within the occupied zones. The external mesh and facade glazing properties combined to reduce direct solar transmission to acceptable levels.

To minimise the plantroom space needed and improve the efficiency of the mechanical systems, terminal cooling units and air handling plants were selected to control the cooling and dehumidification requirements of the tower.

The acoustic design of the building raised two interesting issues. As the tower is clad with mesh, its height and the local wind climate pointed to high levels of wind generated noise. Specialist suppliers tested the mesh surface with a wind turbine with established wind magnitudes and frequencies, with the mesh profile around the Presidential Suite area being adjusted as a result.

In a second move, a three-dimensional animation model was used by Arup Acoustics to develop the acoustic analysis of the large atrium area at ground level, the results of this modelling were used by the architect and interior designer to determine the final design and materials used within the space.

With an architectural lighting design scheme completed by Scottish-based Kevan Shaw Lighting Design, the tower will be making as much of an impact on the city’s skyline after dark as it does during daylight hours.

The elements of the system were chosen for the ease of installation, maintenance and control. The building facade will be lit by 4,000 colour-changing light emitting diodes (LED). Custom-designed by Solar GB for the project, the 6W LED are DMX-controlled and have been produced to suit the high temperature environment they will endure.

In the building core, 200 colour-changing floodlights illuminate the core structure, revealing the transparency of the mesh skin and adding vivid colour to the grey concrete core. Again, these 36W lamps were custom-designed and manufactured for the project.

Nine 7,000K searchlights complete the picture, continuing the shape of the tower towards the sky and highlighting its location from all the surroundings, ensuring that the tower will remain in the spotlight long after the Games are over. ||**||

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