| Due to the advantages of light weight,high strength,beautiful appearance,good corrosion resistance,easy molding and construction,domestic aluminum alloy truss pedestrian bridges are more and more widely used.However,due to the low elastic modulus of aluminum alloy materials,the main girder has low stiffness and large structural deformation.When the main girder structure is stressed into the plastic state,the geometric nonlinearity has a greater impact on the ultimate bearing capacity,which leads to the reduction of the live load bearing capacity of the aluminum alloy bridge.Therefore,increasing the stiffness of the aluminum alloy bridge has become an urgent problem to be solved,and the application of prestress is one of the effective ways to improve the stiffness of aluminum alloy truss girder,which can also improve the stress state of main girder members and increase the live load bearing capacity of aluminum alloy truss bridges.A prestressed CFRP-aluminum alloy truss bridge system is constructed on the basis of literature analysis.The method of combining theoretical analysis,model testing and numerical simulation is used to study the effect of prestress on the stiffness and bearing capacity of aluminum alloy truss bridges,with structural optimization measures proposed.The main research content and conclusions of the thesis are as follows:(1)Construct a prestressed CFRP-aluminum alloy truss bridge system.By comparing the properties of steel strands and various fiber-reinforced composite materials,carbon fiber(CFRP)tendons are selected as prestressed tendons.The external prestressing mode is adopted to compare and analyze the prestressed tendon linear layout,section design,anchoring method and anchor type.Based on the analysis of existing domestic and foreign literature,the effect of different prestressed tendon linear layouts on the force of aluminum alloy truss beams is comparatively studied.(2)With reference to the concept of prestressing degree of prestressed concrete bridges,the concept of prestressing degree of aluminum alloy truss bridges is proposed.By comparing the structural deformation and component stress distribution of aluminum alloy truss bridges under live load with different prestressing degrees,a reasonable value range of prestressing degrees is proposed.(3)Carry out prestressed aluminum alloy truss bridge model tests.According to the model similarity theory,the aluminum alloy truss beam was scaled to 1:10 to obtain the test model.After prestress was applied,it was loaded step by step to obtain the displacement,stress and prestressed tendon tension of the model bridge,and compared with the numerical simulation results to verify the accuracy of numerical simulation.(4)Through the finite element numerical simulation,calculate the stress and deflection changes of the aluminum alloy truss bridge before and after the prestress in the static state,and perform linear elastic and nonlinear stability analysis to obtain the bearing capacity of the structural system on the aluminum alloy truss bridge with different prestress levels.After the aluminum alloy truss bridge is prestressed,the structural deformation decreases,and the live load bearing capacity increases from 23.04 N/m~2to 50.28 N/m~2,which is 2.2 times the bearing capacity before prestressing.(5)To further increase the bearing capacity of the bridge,the structure of the prestressed aluminum alloy truss bridge is optimized,that is,transverse bracing is added at the bottom of the truss beam.After adding transverse bracing at the bottom of the beam,prestress is applied to the main beam,and then linear elastic and nonlinear stability analysis are carried out.It is found that the live load bearing capacity of the aluminum alloy truss bridge has increased from 23.04 N/m~2to 58.25 N/m~2.The load-bearing capacity of the pre-stressed front main girder is 2.5 times,and the structural optimization increases the load-bearing capacity of the aluminum alloy truss bridge by 15.8%.The paper has 46 pictures,38 tables,and 89 references. |
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