Modeling the Swiss Re Tower
As such, the parametric model becomes a "living" model — one that is constantly responsive to change — offering a degree of design flexibility not previously available. The same technology also allows curved surfaces to be "rationalized" into flat panels, demystifying the structure and building components of highly complex geometric forms so they can be built economically and efficiently.
The team used software from Bentley Systems to rapidly explore design options. The parametric approach and a scripting interface allowed them to quickly and accurately generate in minutes complex geometric models that once took days to generate manually.
Three QuickTime animations posted on the Foster and Partners Web site dramatize, respectively, the conceptual form-making, the role of the spiraling light wells in the building's appearance, and the effect on the overall form of the building of changing various control parameters.
The Swiss Re Tower has a circular plan that widens as it rises from the ground and then tapers towards its apex. This form responds to the specific demands of the small site. The building appears less bulky than a conventional rectangular block of equivalent floor area; the slimming of the building's profile at its base reduces reflections, improves transparency, and increases daylight penetration at ground level. Mid-height, the floor plates offer larger areas of office accommodation, and the tapering peak of the tower minimizes the extent of reflected sky.
The aerodynamic form of the tower encourages wind to flow around its face, minimizing wind loads on the structure and cladding, enabling the use of a more efficient structure. Wind deflection to ground level is reduced, helping to maintain pedestrian comfort and safety at the base of the building.
Wind tunnel tests have shown that the building will improve wind conditions in the vicinity. Natural air movement around the building generates substantial pressure differences across its face, which can be used to facilitate natural ventilation within the building.
The 590-foot- (180-meter-) tall tower is supported by an efficient structure consisting of a central core and a perimeter "diagrid" — a grid of diagonally interlocking steel elements. Some traditional central-cored buildings of this height would use the core as a means of providing the necessary lateral structural stability. Because of the inherent stiffness of the external diagrid, the central core is required to act only as a load-bearing element and is free from diagonal bracing, producing more flexible floor plates.
Besides receiving the 2004 Stirling Prize, this building was nominated for a Bentley Award of Excellence honoring the design team's imagination and technical mastery.
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Foster and Partners is a London-based architecture, interior, planning, and product design firm founded more than thirty years ago by Norman Foster. Other projects of note include London_City Hall, Hongkong and Shanghai Bank, and the Millau Viaduct.
Portions of this article originally appeared in Digital Fabricators, published by the University of Waterloo School of Architecture Press. It is reprinted with permission of the authors.