State-Finding Of Cable-Truss Structures And Dynamic Characteristics Of Tensioned Cable-Membrane Structures

The architect' task is search for minimal and primitive architecture. Our times demand lighter, more energy-saving, more mobile and more adaptable, in short more nature buildings because our space, land, material and energy are very limited. Fortunately, membrane structure is just the result of which countless architects and designers unremittingly are searching for.Membrane structures are susceptible to low frequencies load such as wind because of their less stiffness and lighter, so the analysis of dynamic reaction is the necessary part of membrane structure design and analysis. However, dynamic reaction is based on the analysis of dynamic characteristics, so it is very important to analyse structures' dynamic characteristics. It is well known to us that dynamic characteristics depends on the mass and stiffness of structures. For membrane structures, the influence of mass on dynamic characteristics is simpler than stiffess and the variety range of mass is very small. But the factors involved in the stiffness are very complicated. Among them, the influence of prestressing, sag-span ratio, span of structure have notable influence on stiffess and their variety range are very great.The paper utilizes the software CAFA for tensioned cable- membrane structures design and analysis (Qingshan, Yang, 2004) to carry out the shape-finding. The mass matrix and stiffness matrix are ascertained after this. Then we can solve the frequencies equation with the corresponding computer procedure. Dynamic characteristics of tensioned cable-membrane structures are analyzed and the influence of prestressing on membrane, prestressing on cable, ridge cable, sag-span ratio, span of structure and the supporting system is discussed. The results show that its frequencies distribute closely and continuously and a number of frequencies overlap each other. The frequencies of membrane structure with short span and stiff edges are not low. Those of large flat membrane area are low and much closely spaced. Supporting system and ridge cable has less influence on frequencies, but great influence on vibration mode.Cable-truss structure is composed of a series of sunken cables to resist loads and protruding cables to stabilize the structure coupled with the connected members between them. The original shape and stiffness of the structure are defined by equilibrium equations according to the prestressing on cable and edge condition because cable can not resist loads without prestressing on it. The process is called Shape-State Analysis. In this paper, State-finding of cable-truss structures is analyzed by using finite element method and corresponding computer procedure is developed. It showed that the presented method is feasible and the convergency speed is fast. A frequency analysis by subspace iteration method is carried out to investigated the natural frequency and the vibration mode of the structures base on the shape-state analysis.