Design And Analysis For Joints Of Grid Structure

Grid structure includes space truss and reticulated shell. It is a tri-dimensional member structure composed by a series of members arranged in a certain order and connected by joints. With good mechanical properties, wide scope of application, attractive appearance and so on, it is widely used in large span structures such as stadiums, exhibition centers, airport terminals and etc. Grid structure is the most wide-ranging and the fastest developed space structure. Joints of grid structure can connect crossed members and transfer internal force. Moreover, the type selection and design of joints can affect the mechanical properties, installation of production, construction costs and etc, so joint is an important component of grid structure.Taken the steel roof space grid structure of Huangshi stadium as engineering background, forces of members are obtained by global analysis with software SAP2000.In order to check the authenticity of analysis, measure points are setted on free joints and some beams, measured value of stress and displacement are compared with theoretical value of the structure under gravity. Based on the global analysis, this paper introduces the design method of large welded steel-plate joints and cast steel joints; it also checks the strength of these joints. The element model and the solid finite element model are established to calculate the stiffness. As to the welded steel-plate joints, using the APDL language to compile the program file and simulate the welding process, and the stress field is calculated by using the ANSYS thermal-structure coupling analysis function. Results between software and theory are compared and good agreements could be obtained. For having a further understanding about characters of welded steel-plate joints and cast steel joints, this paper analyses these two types of joints from the ways of fabrication, installation technique, mechanical properties and economic properties.The calculation and analysis results show that the welded steel-plate joints are easy to make and low cost, but the body of joints are large. Welded steel-plate joints can connect members which have complex space angles. Although they maybe create stress concentration at intersections of members and joint shell, but the regions of stress concentration are not large when material nonlinearity's influence is taken into account. Finite element software can simulate the welding process and predict the distribution and magnitude of welding residual stress. Cast steel joints are poured by cast steel material. They have the characters of form flexible, attractive appearance, high cost and force uniform. Cast steel joints have no obvious stress concentration phenomenon. Both the welded steel-plate joints and cast steel joints are fit for grid structures which have great forces in joints, many crossed members, or complex space angles. Moreover, these two types of joints have different characters, if they used in the suitable structure, they can meet design demands and produce economic benefits. This is a way for joints optimal design of grid structures.