Study On The Mechanical Behavior Of Y-shaped Rigid Frame Suspension System Of Steel Box Girder Arch Bridge

The Y-shaped rigid-frame suspension bridge with a basket-handle arch is a type of composite bridge with a complex formation process and a complicated construction procedure.Compared to the swallowtail cable-stayed arch bridge,the Y-shaped structure eliminates support columns and straightens the cantilever arms,transforming its load characteristics to that of a beam with bending as its primary stress.Furthermore,in order to achieve the spatial basket-handle arch structure,the Y-shaped rigid-frame structure requires a spatial configuration with inward cantilever arms and twisted cantilever sections,making the study of its structural construction and load-bearing performance particularly necessary.This paper presents the design concept of a steel-concrete Y-shaped rigid-frame based on an ongoing pre-stressed concrete Y-shaped rigid-frame suspension bridge,combining research conclusions and engineering practices from the Caiyuanba Yangtze River Bridge and steel-concrete composite beam bridges.The study focuses on the co MParison of static performance between pre-stressed concrete and steel-concrete Y-shaped rigid-frames,analysis and optimization of design parameters for the Y-shaped structure,analysis of the transmission mechanism for the steel-concrete combined section,and optimization of the Y-shaped structure’s construction process.The main research content is as follows:(1)Considering the limitations of construction methods for pre-stressed concrete Y-shaped rigid-frames and the insufficient overall load-bearing capacity of the Y-shaped structure,the design concept of a steel-concrete Y-shaped rigid-frame suspension bridge with a basket-handle arch is proposed.Using the finite element analysis software Midas/Civil,a structural analysis model for the steel-concrete composite Y-shaped rigid-frame suspension bridge is developed and tested.A co MParative analysis of the structural responses of the steel-concrete composite and pre-stressed concrete Y-shaped rigid-frames under self-weight and ultimate bearing capacity conditions is conducted.The steel-concrete composite Y-shaped rigid-frame is selected for the stress analysis during the entire bridge construction phase,and the most unfavorable internal force state of the steel-concrete combined section under various loading conditions is extracted for subsequent chapters on the local stress analysis of the steel-concrete combined section.(2)Based on the single-factor geometric parameter analysis and RSM(Response Surface Methodology),the key design parameters of the steel-concrete composite Y-shaped rigid-frame are optimized.Firstly,the independent geometric parameters of the Y-shaped rigid-frame structure are analyzed in detail,and the influence laws of the key section internal forces are investigated.Based on this,the key design parameters of the steel-concrete composite Y-shaped rigid-frame are further optimized using a combination of response surface methodology and optimization algorithms.(3)Based on the FEA/NX software,a local finite element solid model of the steel-concrete composite connection section is established,and the most unfavorable load conditions during construction are considered.Through calculation and analysis,the stress and deformation laws and the transmission mechanism of the steel structure and concrete structure in the connection section are obtained.(4)In consideration of the phased tensioning of the tie rods during the construction process and the conversion of the edge-span and middle-span structural systems of the Y-type rigid frame lifting cable-stayed arch bridge,an optimization scheme for the loading process of the edge-span and middle-span was discussed.An optimized scheme for tie rod tension and tensioning sequence was proposed.The principle was to use the tie rod tension as the adjustment vector and to reasonably simplify the i MPact matrix of the tie rod tension on the control target during the construction process.The tie rod tension was then constrained within the feasible domain.The optimized tie rod tension scheme effectively controlled the longitudinal bending moment and its peak at node O of the edge-span Y-shaped structure,as well as the longitudinal horizontal displacement at node O’,thereby avoiding excessive tensile stress in the concrete during construction,which could lead to structural cracking.The local finite element solid model of the steel-concrete connection segment was established based on the FEA/NX finite element analysis software,and the most unfavorable load conditions during the construction process were considered.Through calculation and analysis,the stress and deformation laws and force transmission mechanism of the steel and concrete structures in the connection segment were obtained.