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Long-spans amplify the collaborative relationship between architects and engineers

By Sara Hart

Continuing Education Use the following learning objectives to focus your study while reading this month’s ARCHITECTURAL RECORD / AIA Continuing Education article. 1 LU/1 HSW Learning Objective: After reading this article, you will be able to: 1. Discuss innovations in long-span roof structures. 2. Describe the complexities in drawing and constructing domes. 3. Explain the structural systems used in dome structures.

Islands of compression in a sea of tension!” was Buckminster Fuller’s poetic definition of tensegrity. He also offered a more extensive one in his seminal book, Synergetics (1982), in which he coined the term as “a contraction of ‘tensional integrity.’ Tensegrity describes a structural-relationship principle in which structural shape is guaranteed by the finitely closed, comprehensively continuous, tensional behaviors of the system and not by the discontinuous and exclusively local compressional member behaviors. Tensegrity provides the ability to yield increasingly without ultimately breaking or coming asunder.”

Illustration courtesy Yamaguchi and Geiger Engineers This diagram shows how David Geiger translated Buckminster Fuller’s tensegrity dome into his revolutionary Cabledome. By lowering the profile, he created a more aerodynamic structure that would be self-supporting rather than pneumatically supported.

New York structural engineer Guy Nordenson, who worked for Fuller in 1974, parses the definition more succinctly: “Tensegrity structures are self-contained networks of cables and posts, sometimes of regular geometry, sometimes quite free-form. The basic principle is always the same: posts—that is, compression members—are suspended in a net of prestressed cables. The tension in the cables is what gives the system its stiffness and, as a result, the structures tend to be quite springy.”

This principle is important to understand, because not only was it the theoretical basis for Fuller’s revolutionary geodesic domes, its evolution has made spanning great distances possible today. Because technology didn’t catch up with theory until the 1980s, Fuller’s round, freestanding structures of the 1950s and ’60s never grew very large in diameter. It wasn’t until structural engineer David Geiger simplified the construction of Fuller’s domes that the long-span domes that now cover sports stadiums, airport terminals, and convention centers were developed. Geiger, who died in 1989, engineered the first tensegrity structure at a large scale and patented it as the Cabledome. In essence, his system became the prototype for most long-span, tensile-membrane roofs.