Sunday, April 5, 2009

Space Structures

The development of space trusses led to the creation and application of truss systems with specific types of node: MERO, Unistrut, Triodetic, Moduspan, Harley Mai Sky, Catrus, Pyramitec, Nodus and others. The MERO system in fact was one of the first space grid systems and it was introduced in the 1940s in Germany by Dr Max Mengeringhausen. To this day it remains one of the most popular in use. It consists of prefabricated steel tubes, which are screwed into forged steel connectors, the so-called MERO ball. Up to 18 members can be joined with this system without any eccentricity.

The two basic types of these systems are the flat skeletal grid and the curvilinear forms of barrel vaults and braced domes. In the flat skeletal double-layer grids two parallel lane grids are interconnected by inclined web members. The grids may be laid directly over one another (direct grid) or be offset from one another (offset grid). These basic relations lead to different geometries of the system. Lamella domes and vaults consist of interconnecting steel or aluminium units. An important innovative step was the invention by Buckminster Fuller of the geodesic domes, to which reference has been made earlier.

The space grid systems mostly use circular or tubular members and their nodes may be characterized as solid or hollow spherical nodes, cylindrical, prismatic, plates, or nodeless. Most of these systems are double layered in that a top and a bottom layer composed from linear bars are interconnected by vertical or inclined, equally linear, members. The bars of single-layer space grids are usually positioned on a curved surface. A recently proposed new type of space grid is the ‘nexorade’, which is assembled from ‘nexors’. Nexors have four bars (eventually scaffolding tubes) and these are connected at four connection points, two at the ends and two at intermediate points by swivel couplers (Baverel et al., 2000). The various space grids provide abundant inspiration for creating different structures including domes, vaults and irregular structures and, thereby, have an important role in architectural design.Domes and vaults assembled from space trusses have taken on a great variety. One of the world’s largest is the hypar-tensegrity Georgia Dome (structural designer: Mathys Levy in cooperation with his co-workers at Weidlinger Associates, 1992). It has a sophisticated structural scheme. Its ridge cables make rhombs and its cables lie in two planes.

Georgia Dome, Atlanta, Georgia, USA, 1992, structural design: Mathys P. Levy, Weidlinger Associates.
Widespan roof, the longest span hypar-tensegrity structure made.

Deployable structures make temporary scaffolding unnecessary. Mamoru Kawaguchi designed the Pantadome system employing a series of hinges so that the completed dome can be raised all at once (Robbin, 1996). Kawaguchi’s first Pantadome was built in Kobe in 1985. He also designed the Barcelona Pantadome in cooperation with architect Arata Isozaki, which was at first preassembled and then raised with jacks and temporary support towers. Tensile structures may be two dimensional (suspension bridges, cable-stayed beams or trusses, cable trusses), three dimensional (cable domes, truss systems), or membranes (pneumatically stressed surfaces, prestressed surfaces).

Palau Sant Jordi, Pantadome, Barcelona, Spain, design: Mamoru Kawaguchi and Arata Isozaki.The space frame was built in the arena floor bowl, then raised with jacks and temporary support towers; in total 12 000 parts, specified with only 40 Formex expressions.

Structural design must deal with specific risks related to thin, tensile structures: non-linearity, wind uplift, buckling, stiffness, horizontal instability, temperature conditions, boundary conditions, erection methods.

Sebestyen, Gyula. 2003. New Architecture and Technology.

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