Rationalisation of the geometry for production of the 80-m glazed Sphere for the Expo 2017 in Astana

Abstract

The emblematic entrance pavilion for the Expo 2017 in Astana is the so-called ‘Sphere’, which with its 80-m diameter is worldwide the largest closed sphere completely covered with glass. The continuous external surface of the Sphere was designed to be built with spherically curved glass panels of parallelogramic shape. The panels are fixed at their perimeter to a structural grid of bent round tubes of steel. This secondary grid is fixed in turn to a coarser primary structural grid at evenly spaced supports. The purpose of this article is to give insight into the constructive geometry design of the Sphere. One of the main targets of ‘geometric design for production’ is to specify the geometry of a construction in such a way that fabrication and installation procedures can be simplified and carried out with a minimum of effort, cost and time. The main measure for the Sphere was to simplify the basic grid by replacing all original three-dimensional free-form curves with series of interconnected circular arcs. Thus, a typical curved tubular segment could be bent on the plane with a constant radius. A further approach to get a simple and sound construction eliminating geometric torsion and minimising eccentricities among construction subsystems, for example, glazing, sealing, fixings and substructure, was the extensive usage of conical systems inherent in the geometry of the sphere for orienting and positioning the various subsystems components. These two geometric simplification measures were determinant for the practical and economic implementation of the construction, fabrication and installation of the Sphere.