Research And Design Of The Architectural Form Of The Spoke Structure

Spoke structure is mainly composed of inner tensile rings, outer compressiverings and between them, radial cables or cable trusses. It is a self-balanced structure,also well-known for its lightness. For this reason, during recent years it’s widelyused when building stadiums, with membrane as the roof material. This article isfocused on the architectural form of the spoke structure, in order to further promoteits application in China.First, the initial state of equilibrium has to be found. As the modern grandstandof the stadium is often bowl-shaped, it is hard for an architect to give an exact initialstate of the spoke structure just from instinct. So it may not be practical to follow theprocess of “finding force according to the given shape”. In this article, the forcedensity method is devoted to the purpose of finding the initial state of equilibriumfor the spoke structure. And it proves to be very effective and concept-clear. Theplanar projection of the structure is the only factor that dictates the distribution modeof force densities, which will further establish the3-dimensional shape of thestructure. The above process goes from shape to force and then back to shape. Nowthe convergence difficulties often encountered during using general force densitymethod no longer exist.After establishing the initial state of equilibrium, the influence of planarprojection over structural characteristics of the single-layer spoke structure isanalyzed. It is found that the similarity between the shapes of inner and outer rings isvery important to the static behavior of the outer ring. Dissimilarity will arise hugebending moment in the outer ring. So, a balance ring is proposed to eliminate theoverlarge bending moment and it works well. Afterwards, research into the role ofsecondary-rings and layout of radial cables is conducted. Parameter analysis showsthat the force density not only decides the initial form, but also the vertical stiffnessof the cable system.As for the two-layer spoke structure, more attention is paid to the variation of the form of cable trusses. Altogether three forms of cable trusses are compared,including the basic form, the concave one and the convex type. The convex cabletruss is apt to lose its lateral stability, so detailed theoretical analysis is conducted tofigure out the reason. To prevent that from happening, several measures areproposed. New forms of spoke structures are also presented. Moreover, advices onthe preliminary design of concave/convex cable trusses are suggested. On the basisof the above research, we further analyze the possibility of simplifying the originallycomplex inner rigid rings used in the old gymnasia, Beijing Workers’ Gymnasiumfor instance.After the above work finished, Bao’an Stadium is presented as an engineeringproject example to illustrate some problems encountered during design process, suchas the lateral rigidity of the whole structure and the stability of the outer compressivering, etc. Besides, a1/10scale model test of Bao’an Stadium is introduced. Themodel test provides a lot of meaningful experience; including the detailed making ofthe joints, tension process, static and dynamic behavior of the cable system, etc.