Study On Mechanical Characteristics Of Steel-concrete Composite Beam And Shear Performance Of High-speed Railway Cable-stayed Bridge

Steel-concrete composite box beams make full use of the materials of steel and concrete,and have many advantages such as large stiffness,high natural frequency,fine stability,and easy construction.In recent decades,steel truss beams have been mostly applied in railway cable-stayed bridges,but rarely apply steel-concrete composite box beams on account of the large load intensity and the ratio of live load to dead load of railway trains.Therefore,there have few researches on steel-concrete composite box beams of cable stayed bridge of railway and high-speed railway.Ganjiang Bridge is the first long-span hybrid beam cable-stayed bridge of high-speed railway with speed of 350km/h in china which consists of prestressed concrete box beam at side-span,steel-concrete composite box beam at mid-span and steel-concrete composite joints.As the mid-span structure of high-speed railway hybrid cable-stayed bridge,steel-concrete composite box beams have complex structure and prominent characteristics,whose mechanical characteristics under load need to be further studied.As the shear connectors of steel-concrete composite box beams,the shear performance of studs has important effect on that.Based on the engineering example of Ganjiang Bridge,the finite element(FE)method is carried out to study the mechanical characteristics of steel-concrete composite box beams and the shear performance of studs,and the main research contents and conclusion are as follows:1.Based on literature investigation,the research results of steel-concrete composite box beam and two kinds of common shear connectors at home and abroad are summarized and the mechanical behaviors and failure mechanism of studs in composite box beams are analyzed.Based on the Eurocode 4,the shear performance indexs and evaluation method of studs are introduced.The formulas for calculating shear capacity and stiffness of studs given by codes at home and abroad and scholars are introduced in detail.2.Considering the three nonlinear problems of geometry,material and contact state,according to the push-out test of studs completed by N.Gattesco,Abaqus is used to carry out the nonlinear FE calculation,and the nonlinear FE model is validated through a comparison between results derived from the FE analysis and measured test.3.For the studs of steel-concrete composite box beam of Ganjiang Bridge,the shear performance of studs is analyzed by preceding approach and the load-slip curve and key shear performance indexes are obtained,and the stress states of studs are investigated.The influence of concrete strength,steel beam strength,stud strength,stud length,and stud diameter on shear performance of studs is investigated through single factor parametric analysis,and the stress distribution law of stud is also investigated when these parameters change.4.For the steel-concrete composite box beams standard sections of Ganjiang Bridge between M8~M9 stay cable whose forced state is most dangerous,the FE model consisted of solid-plate-nonlinear spring elements is established by Ansys.Based on the results of FE analysis,the stress distribution of the main components and force transmission mechanism of steel-concrete composite box beams under calculating loads are studied,and the deck deformation of steel-concrete composite box beam under high-speed railway train loads is investigated.The shear force and slip distribution of group studs and the impact of internal forces types on the slip of group studs is analyzed.The research show that the steel-concrete composite box beams have fine deck stiffness.The stress distribution of main plates is uniform which is in elastic working state.The stress and displacement of the side webs and middle webs along the direction of beam height are non-linear,while the displacement is basically linear.The concrete slab is the main component of axial force transmission,and the route of “upper flange to side webs to inclined bottom flange” is the main path of force transmission of the steel box beam.The shear force and slip distribution of group studs is similar under calculating load,the transverse shear force and slip of group studs is M-shaped,and the slip effect between steel and concrete is small.The axial force has a significant inhibitory effect on the slip effect of group studs,which proves the rationality and advancement of the application of steel-concrete composite beams adopted by the mid-span structure of Ganjiang hybrid beam cable-stayed bridge.