Mechanical Analysis And Experimental Research For Rail Cable Launching Technology About Suspension Bridge With Separated Tower And Stiffening Girder

The erection of stiffening girder has always been the key and difficult point in the construction of long span suspension bridge in the mountainous area. Based on the flexible cable theory and nonlinear finite element theory and closely combined with the engineering practice of rail cable launching (RCL) new technology for the long-span suspension bridge in mountainous area, the key problems including non-loading form finding and loading solving were studied from the global mechanical analysis of this new technology. The accuracy of solving is manifested by reduced-scale experimental model test and the feasibility for this technology is also demonstrated. The followings are the detail research contents and results:1) From the working mechanism of RCL new technology, the systematic stress and deformation compatibility relation in non-loading condition are analytic researched. The multi-stage linear cable element and piece-wise parabolic element are respectively used to simulate rail cable. The main cable and sling are simulated by the segmental catenary element and line cable element respectively, and the elastic extensions of cable are taken into account. With the unknown initial geometrical condition of RCL system, the equilibrium equation is established on the configuration of post deformation. The real internal force and shape of the rail cable are determined by the iterative computations with the assumptions of initial force and configuration. The enough accuracy for this method can be achieved in the simplified calculation process and it can be adopted in the practical engineering.2) The working mechanism of carrying stiffening girder segments in RCL new technology is deeply investigated. On the modeling basis of carrying beam system in non-loading condition, the rail cable segments for the beam carrying trolley are simulated by the multiple linear cable elements and other rail cable segments are simulated by the single linear cable elements. From the systematic stress and deformation compatibility relation, the stress and deformation compatibility relation for the system in the typical stiffening girder segments carrying working condition are researched by using the analytical method, and the analytical equation is founded for solving.3) With the application of nonlinear finite element theory the global finite element model for the RCL system is established. In this model, the main cable, sling and rail cable are simulated by the segmental catenary element, linear cable element and segmental catenary element respectively. The working conditions include non-loading cable state, rock anchor cable tensioning, rail cable tensioning, deck erection gantry moving, stiffening girder segments carrying trolley on its place and erecting for each stiffening girder segments. And the considered systematic responses for each working condition are main cable configurations and forces, sling forces, rail cable forms and forms, tower deviations and forces of rock anchor cable etc.4) According to the similarity principle, the reduced-scale experimental model for Aizhai suspension bridge is designed, produced and installed, also the RCL system and measuring system are established. The installation process for the global model test are discussed, the implementation process for the RCL project is investigated, which can provide the reference for the construction of practical bridge. The calculated and measured values of main cable deflections, main cable forces, sling forces and rail deformations in each construction stages for main beam in the model test are in good agreement with each other and have similar regularities, which verified the correctness of the presented calculation method. The calculated theory truly reflects the actual mechanical performance of the structure. And the structural deformation can be fully controlled by the existing calculation theory. The precision of the designed testing system satisfies the test requirements.5) The rock anchor cable tensioning device was set up on the basis of reduced-scale experimental model test. The rock anchor cable force in the working conditions of non-loading cable state, main girder constructing and bridge deck constructing are researched, the sequences and time for tensioning are optimized, which can be used as references for the practical bridge constructions.6) The mechanical properties of the practical suspension bridges with the isolation of tower and beam are analyzed in combination with the characteristics of the three pairs of rock anchor cables. On the maximum living load effect of vehicle, the measured values of tower deviations, tower bending stress, main cable force, the maximum cable force increment, main cable mid-span deflection increment, steel truss stress and main girder beam deflection increment all satisfy the design requirements. The measured values match well with the theoretical calculated values, and the calibration coefficients are mainly locating between 0.9-1.0. The reasonable matching of the position and cable force settings for the three pairs of rock anchor cables under the living load of the vehicle is demonstrated.