Research On Longitudinal Pylon-girder Inter-restriction System Of Ultra-long-span Cable-stayed Bridge

Cable-stayed bridge(CSB)is a structure in which girder,stay cables,and pylons are the main load-bearing members.With clear action mechanism in each part,CSB becomes one of the most competitive long-span bridge types.For ultra-long-span CSB,different structural system have the relevant working mechanism,and the comprehensive performance of the structure is very sensitive to the choice of structural system.Based on the engineering background of Changtai Yangtze River Bridge,the basic finite element model is established,studying the effects of different longitudinal pylon-girder inter-restriction systems,containing semi-floating system,longitudinal-fixed system,longitudinal-elastic restriction system and temperature-adaptive restriction system,on the performance of cable-stayed bridges and exploring the working mechanism of different CSB structural systems through comparative analysis.The natural vibration characteristics and seismic time-history dynamic analysis of semi-floating system and temperature-adaptive restriction system are studied to explore the effect of CFRP member on the dynamic structural performance.The analysis of the semi-floating system and the longitudinal-fixed system shows that,compared with the semi-floating system,the latter has better performance in the optimization of the longitudinal structural stiffness and longitudinal load transmission path of CSB,but it also greatly limits the release of longitudinal temperature deformation in girder,causing the structure to generate a greater temperature secondary internal force.Using the longitudinal stiffness of pylon-girder inter-restriction as the independent variable,the mechanical response of the longitudinal elastic-restriction system is studied.The analysis results show that the longitudinal elastic restriction is effective for increasing the longitudinal structural stiffness and optimizing the longitudinal load transmission path,but has unfavorable effect on the structural performance under the effect of system temperature load.Therefore,in terms of bending moment at the bottom of pylon,the comprehensive structural performance of the cable-stayed bridge can reach the related optimal state only if the elastic restraint stiffness is appropriate.Based on the analysis of the action mechanism of the longitudinal elastic restraint system,the proposal and working principle of the temperature-adaptive longitudinal restriction system are expounded.The finite element model of the new structural system is established and analyzed.Compared with the longitudinal elastic restraint system,according to the results,when they both have the same longitudinal restriction stiffness,the longitudinal structural stiffness of the new structural system and the longitudinal elastic restriction system can achieve the same optimization effect,and the new structural system can also achieve the same structural performance as the semi-floating system under the effect of system temperature load.As for the natural vibration characteristics,the second-order natural vibration period of temperature-adaptive longitudinal restriction system,reduced by 15.4% and characterized by first-order longitudinal girder drifting,is the most different from that of semi-floating system,so the effect of CFRP member on the longitudinal structural stiffness is reflected in terms of inherent attribute.As for the seismic time-history dynamic analysis,compared with semifloating system,the extreme values of longitudinal girder-end displacement,longitudinal pylon-top displacement,and pylon-bottom bending moment are effectively reduced.The results of the study show that temperature-adaptive restriction system has well-performed dynamic structural performance.Based on the well-performed static and dynamic structural performance of temperatureadaptive restriction system,this new structural system could be used as the first choice for the scheme of longitudinal pylon-girder inter-restriction system in the design of kilometer-scale ultra-long-span cable-stayed bridge.