Research On Suspender Tensioning Scheme For Long-span Self-anchored Suspension Bridges

The self-anchored suspension bridge is increasingly preferred by the engineering field for its beautiful structure,good place adaptability and good economic performance,which has become the most competitive bridge type in cities.Sometimes it is impossible to erect the main girder by the former support method due to the limitation of terrain and navigation conditions,so the construction method use cable stayed before suspension has become an effective construction scheme.Because of this method does not have any successful cases for reference,mechanical properties of self-anchored suspension bridge system conversion process are worthy of study because there are still a series of key technology issues need to solve such as if stress of each component meets the requirements of strength in the transformation from temporary cable-stayed bridge to self-anchored suspension bridge,pushing space and the right pushing moment of main cable saddle,dismounting sequence and the right moment of dismount of stay cable etc.According to the actual bridge project,based on elastic catenary theory and geometrical nonlinear theory,the finite element model for the whole bridge is established by the large-scale commercial software Midas/Civil which can analyze mechanical characteristics of reasonable bridge stress state and the construction stage to select the optimal tension scheme.The main contents of this paper are as follows:(1)Research on completed bridge state of long span self-anchored suspension bridge,including reasonable cable shape and reasonable suspender cable force.Firstly,using the principle of internal force equilibrium method to make sure that the ratio of maximum stress of upper flange and material tolerance to allowable stress is equal to the ratio of the maximum stress of the lower flange and the allowable stress of the material under the action of constant load and live load,thus the reasonable hanging cable is obtained.Then,the nodal line method and the nonlinear precise iterative method are used to solve the cable shape and the stress free length of the main cable under the reasonable bridge.Finally,the inverted cable is analyzed by the principle of no stress length of the main cable and the reasonable cable shape is obtained.(2)Modeling technology research on long-span self-anchored suspension bridge.The structural characteristics,design parameters and constraints of self-anchored suspension bridge are analyzed and the finite element analysis model is established based on Midas/Civil platform.The stiffened girder,beam,main tower,pier,all adopt beam element model,the main cable and the sling adopt the cable element model which can only transfer axial pulling force.Considering the connection mode and the basic boundary of the structure,a beam element with large tensile and elastic stiffness is adopted to simulate the launching process of the saddle;Transformation of construction process is simulated through element birth and death and different working condition.The correctness of the above modeling method is proved by an example.(3)Research on calculation model of system transformation.The cable-stayed bridge can be analyzed by the reasonable bridge state,and the geometric of the suspender is obtained by the disassembly and analysis of the bridge model,but the two are independent models which must be coupled before they become the basic model of the late tensioning calculation.Based on the principle of non-stress length,the cable control point of the suspension bridge and the control point of the cable-stayed bridge are coincident and the stress-free length of the main cable is given then the coupling model of the cable is obtained.(4)Simulation method research on tensioning process of long-span self-anchored suspension bridge.Simulate the cable process by changing the stress-free length,the element birth and death and the different working conditions of the sling.The results show that the method can be used to simulate the cable process accurately with high precision,simple method and good result.(5)Research on cable suspender tensioning scheme of long-span self-anchored suspension bridge.On the basis of reasonable bridge state,3 feasible hanging cable schemes are proposed primarily by using different primary girder initial alignment,the optimal cable scheme is determined by construction process simulating analysis to load and deformation of the sling,main cable,main tower and main girder and comparing the feasibility,safety and economy of the scheme.