Study On Optimization Of Prestressed Composite Space Truss

Prestressed Composite Space Truss is composed of reinforced concrete,steel and cables.The structure can be either the load-bearing or the maintenance, by applying prestress, whose internal force is improved, the peak stress is reduced, the structural stiffness is enhanced, the deflection is decreased, making use of strength of materials fully, the bearing capacity is increased, the amount of steel is saved and is more economic. Prestressed Composite Space Truss possess so much advantage, which is applied to the large span complex spatial structure system widely.In Prestressed Composite Space Truss1s design, designers first have a problem how to determine its prestressed value, span-depth ratio, number of grids. For these parameters, designers make choice according to the relevant experience or in trial way usually, lack of scientific basis, which not necessarily obtain the optimal solution. Prestressed Composite Space Truss is complicated, which has plenty of design variables whose optimization problem is complicated, and engineer is difficult to master it. Therefore, by the optimization theory, study Prestressed Composite Space Truss’s geometry shape, which provides a basis for Prestressed Composite Space Truss’s structural form selection, and is meaningful.According to the loading characteristics of pre-stressed composite space truss, the paper by APDL sets up finite element entity model. Based on three stage design method, under the effect of three kinds of load condition, the paper analyzes its deformation and stress of the components in detail. In combination with the stress of the component performance, this paper selects prestressed composite truss’s height, span, number of grids, prestressed value, rod cross-sectional area, the width and the height of rib beam as design variable, regard total cost of structure as the objective function, taking into the strength, stiffness, stability, cross-sectional dimension, pretensioned limits, structural deflection as constraints. Through the zero order optimization design method, the paper conducts optimization design of the structure. From all results, selecting3%within the optimal solution, the paper use method of regression to discuss the relationship between span, height, length number of grids, prestressed value and structure cost. Conclusions are stated as follows.1. When Prestressed Composite Space Truss’s prestressed value, span-depth ratio, number of grids simultaneously reach their optimal solution, cost access to optimal value.2. The Optimal span-depth ratio of Prestressed Composite Space Truss is basically constant, which has a broad zonation, and should be taken as16-193. Length has little effect on the number of grid, the optimal number of grids of Prestressed Composite Space Truss depends on short span, and should be taken as (6～8)+0.2L2(L2is short span)4. The best prestressed value of structure is fixed value in principle which has a broad zonation, and should be35%～45%of structure’s total load.