by Achim Menges
Foster + Partners won an invited international architecture competition in 2004 to design a new courtyard enclosure for the Smithsonian's National Portrait Gallery, housed in the Old Patent Office building in Washington, D.C. Early in the project, the firm's Specialist Modelling Group was brought in to advise the project team on modeling techniques, to develop new digital tools, and help solve the complex geometric issues involved.
Norman Foster's early sketch shows a diagonal grid of structural elements gently flowing over the central courtyard. The undulating roof structure is supported by eight columns arranged in three domes, the central peak being the highest and having the greatest span.
Instead of simply translating a sketch, capturing design intent involves the development of a digital schematic that can be easily used by the designers to control and manipulate the complex geometry. Design constraints are encoded within a system of associated geometries. Three surfaces, column markers and a computer script control the entire roof geometry.
Constraints such as edge beam location, dome heights and drainage locations are informed by the design surface, which is created from a series of simple control lines. The parameterization of the grid surface sets out the plan locations of the design nodes, while the height location is given by the design surface.
The relationship between these surfaces and a third surface controls the beam twist. The set-out geometry performs as a mechanism to control the parameters of a generative script.
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This article is excerpted from the March/ April 2006 issue of Architectural Design (Volume 76, Issue 2, "Instrumental Geometry" by Achim Menges), with permission of the publisher, John Wiley & Sons.
