Airport Terminal in Beijing

Architects: Foster + Partners, London
Norman Foster, Mouzhan Majidi, B. Timmoney, L. Law, S. Chiu, J. Parr, M. Gentz, L. Fox, R. Hawkins, M. Atkinson, C. Foster, M. Gamini

Structural engineer: Arup, London
M. Manning, H. Falter, J. Kerry, P. Cross, Y. Asaoka, G. Thyer

At more than 3 km long, the new Terminal 3 at Beijing Capital International Airport is one of the world’s largest buildings. It will accommodate fifty million passengers per year by 2020. Despite the vast scale, the clearly organised symmetrical floor plan helps passengers orientate themselves. The building fans out at either end to accommodate large halls: located in the south is Terminal T3A for national flights; in the north, T3B for international destinations.

The form is heightened by the singular gesture of the double-curved roof surface; its overall area is 350,000m2. Integrated skylights bring daylight into the spaces. The roof structure is a modular space truss, supported by cantilevered steel columns up to 28m in height.

The ceiling surface is made of slender aluminium louvers, through which the structural members can be discerned; the louvers’ fine lines contribute to the hall spaces’ lofty, dynamic atmosphere. These open spaces — equipped with galleries — step back on each level, enabling views deep into the halls. The colour scheme — of the columns, ceilings and facade supports — is gradated, ranging from red in Terminal T3A, which also serves as the airport’s entrance, to golden yellow in T3B. The terminal levels were constructed as reinforced-concrete decks with downstand beams and round columns on a 12-metre grid. These multi-level frames furnish elasticity, a crucial characteristic in the earthquake-prone Beijing region.

The roof is stabilised solely by the cantilevered steel columns. From a structural point of view this allowed a relatively unrestricted expansion of the roof and made it possible to erect the entire main body of the roof without any movement joints.

Initial studies indicated that in view of the large number of different elements and the tight construction schedule, a space truss with bolted connections was the ideal structural system. Functionality, required floor space, head height, and the maximum roof height (45m) dictated the roof levels in various areas.

A diagonal grid with 36-metre intervals was developed for the roof columns. The spaceframe’s construction grid measures 4.5m. The connections and members all vary due to the curvature of the roof. In order to optimise the weight of the steel components, the members were dimensioned individually. There are more than 18,000 construction points and about 70,000 connecting members. In order to manage this great quantity, a modular system was developed which implemented prefabrication and expedited assembly on site.

The building’s symmetry is not reflected in the space truss design, as it was an architectural requirement that all triangles forming the top layer of the space truss be oriented in the same direction. Some of the members in the bottom layer were omitted, thereby transforming the triangulated bottom layer into triangles and hexagons. For the connections in the bottom layer, the Mero system (steel connection) was used — the patent on it had expired, and it was incorporated in the Chinese code. One steel sphere connects as many as eight rods.

The upper node was planned as bowl node — a hemisphere with cylindrical upper node — by which squared hollow sections and rectangular hollow sections are joined; the metal deck of the roof was to be directly attached to the hollow sections (see detail drawings). The client, however, decided not to realise this detail. The bowl node was replaced with a conventional spherical connection. Due to this change it was not possible to support the roof’s metal deck directly on the top layer of the space truss; an offset layer of secondary steel work became necessary.

All bolted connections which could be executed with the material available locally were carried out as planned. Connections requiring greater load-bearing capacity were welded. This required a scaffold covering the entire roof area, significantly changed the construction stages and put the emphasis on fabrication and welding on site rather than prefabrication in the shop. This example illustrates how design criteria are valued differently in different cultures.

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This article is an excerpt from DETAIL — Review of Architecture

   

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