Hands-on client involvement was key to the design and management of Chek Lap Kok and its massive terminal building. The Airport Authority assumed direct control over all aspects of design and construction with work awarded on a contract by contract basis after competitive tendering.
The Mott Consortium, comprising Mott MacDonald subsidiary Mott Connell (Australia), Foster & Partners and BAA, won the job of designing the 516,000m2 passenger terminal, the world's biggest, in 1995.
'Design had to be broken down into packages and reassembled to suit construction. We would naturally have anticipated the terminal as one contract package,' says Airport Authority project director Douglas Oakervee.
The Mott Consortium used engineers and designers based in Britain, Australia the US, Europe and east Asia. It also established an office on a single floor of the AA's headquarters in Hong Kong. Starting with 60 people, it rose to 230 strong at peak. According to Foster director Grant Brooker, being together in one place was very important in design terms. 'It created a single work culture and was good for information exchange.'
The office had 20 months to design and document every aspect of the scheme, 'from the carpet to baggage handling', says Brooker. A mix of CAD and 1:1 scale modelling was used to work out design details, but the scale of the project demanded simplification. Repeat elements which could be prefabricated off site were chosen to cut time. The 18ha roof was drafted on 36 drawings.
Computer simulations tested the building functionally and structurally as the tight construction schedule did not allow prototypes. Detailed structural design by Mott Connell, was exacting. Around 6,000 bar bending schedules (the terminal building contains 67,000t of reinforcement) were submitted at tender stage.
In concept, the HK$17bn (£1.33bn) terminal building is simple, organised into distinct functional strata. Departing passengers are delivered from external road and rail connections directly to the first floor check in departures concourse. Below this, at ground level, is the arrivals concourse. Baggage handling and stores are housed below ground level, with tunnels for services, baggage movement, and an automated poeple mover beneath. The APM will move passengers between the entrance of the terminal and the furthest gates, 1.3km away, and when a second, westerly terminal is constructed, it will connect the two buildings.
The departure and arrival concourses are open spaces with clear views out to the apron and aircraft. The 18ha roof, for which Ove Arup & Partners was the consortium's subconsultant, is regarded by Foster and Mott as one of the most significant design and engineering features. A single, continuous element with few support columns allows for easy passenger orientation.
The roof rests a 36m grid of cantilevered, reinforced concrete columns. The columns themselves are 1.2m in diameter and up to 22m tall, and contain conduits for electricity and rainwater ducting. At the roof's outer edges, the columns have to resist lateral thrusts of up to 300t and, because of blasting from jet engines and the typhoons common in the area, they also have to accommodate 50mm of movement in the wall plane.
Designed as a modular structure to save time and reduce cost, the roof is a 36m high vault stretching 1.3km at its longest point, and comprises 129 barrel vault sections, each 36m by 36m and weighing up to 120t. Though part of a modular system, every section has its own geometry. Fabricator Watson Steel cut and prepared the steelwork in Britain with component parts welded together on site before being lifted into place.
In plan the departure concourse at its deepest point is 150m from an external wall. The roof is therefore an important source of natural light, its panels transmitting and, with the aid of suspended reflectors, diffusing light. It also has to provide acoustic and thermal insulation.
Initially the vaults were clad insitu, but it was realised early on that better time could be made if they were finished on the ground and lifted complete. Though the roof is light by conventional standards, craning it aloft was a challenge.
On a project like Chek Lap Kok 'every contract becomes the biggest in the world. At every level you were testing the capacity of the industry concerned,' says architect Foster & Partners' project director Michael Jelliffe.
The global make up of the Mott Consortium was typical of all work at Chek Lap Kok. Contractor BCJ, a joint venture between Amec, Balfour Beatty, China State Construction Engineering Corporation plus Kumagai Gumi and Maeda Corporation of Japan brought together skills and muscle from around the world.
One of the main challenges presented by the terminal building - and the airport as a whole - has been logistics. Everything had to be transported to the site by sea, including the 6t of rice eaten daily by the army of 21,000 construction workers. The project also created a global design and supply network, so the ability to detail brief all collaborating parties was crucial.
Already, the terminal's first phase of expansion - a second terminal wing and a second runway - is in progress. And a second phase involves construction of an X-shaped building. The airport has been also designed for the next generation of super-jumbos, and is flexible enough to accept extra elements such as new plant or mezzanine levels.