Study On Limit State And Bearing Capacity Of Embedded Perfobond Rib Shear Connectors

As an key component of the joint zone of a steel-concrete composite bridge,the perfobond rib shear connectors(in German,perfobond leiste,or,in short,PBL)are widely applied in recent years.PBL can be sorted as two types:one is located in composite beams whose perfobond ribs are welded on the exposed steel structures and convered by the thin concrete paltes,so this type can be called as "composite PBL";the other is embedded by large blocks of concrete thus it is called as "embedded PBL".The studies on composite PBL are relatively complete,while,however,some research results show the significate difference between composite PBL and embedded PBL.Therefore,the limit state and ultimate bearing capacity of the embedded PBL is studied in the present work based on some experimental study and finite element analysis,on the following five aspects:(1)The existing experimental and theoretical researches are summarized.Many PBL tests have been carried out by scholars with different dimensions.The measured ultimate loads and ultimate slips by different authors are different due to the different judgement about the limit state.Detailed FEA(finite element analysis)may suffer from poor convergence and low computational efficiency while simplified model can not reflect the local stress.Based on the anchorage system test for the 4th Yangtze River Bridge in Nanjing,the design parameters and dimensions of embedded PBL are described,and the related test results are summarized and analyzed.(2)In order to simulate the failure mechanism of concrete dowel,concrete damaged plasticity(CDP)model is used.A new formula is deduced to calculate the damage factor in CDP model through combination of Sidoroff energy equivalent principle(SEEP)and concrete constitutive relationship from "GB50010-2010 Code for Design of Concrete Structures".SEEP method is simple and reliable in comparison with other calculation methods.(3)Some detailed FEA models are built according to the anchorage system experiment of the 4th Yangtze River Bridge in Nanjing,and static standard analysis,extend finite element method(XFEM),virtual crack closure technique(VCCT)and dynamic explicit analysis are applied.Some conclusions can be drawn by comparison with these solution methods:XFEM and VCCT can not simulate 3D cracks in solid element with poor convergence and limited consititutive relationship.Dynamic explicit analysis can greatly improve the computational efficiency by introducing the Arbitrary Lagrangian Eulerian(ALE)technique and Subcycling Integration Algorithm(SIA),but introducing the mass scaling factor and material damping coefficient cause result to distort.The result of load-slip curve by static standard analysis is quite true to the test result,therefore,static standard analysis is most suitable for this case.(4)Six groups FEA models are built by single variable method to investigate the influence factors on the ultimate bearing state of embedded PBL.The results of these models show that:the diameter of hole in the steel slab,the diameter of rebar,the axial compressive strength of concrete,and the strength of rebar have a great influence on mechanical properties of embedded PBL,whereas steel slab's thickness have no influence on mechanical properties when its thickness is equal to the diameter of rebar,the reinforcement ratio can not affect the mechical properties of embedded when the ratio is low in 4 times the diameters of hole in the steel slab region concrete.(5)Based on the embedded PBL engineering characteristics and load-slip curve,bearing capacity limit state of embedded PBL can be setted as the yield stage indicated by a dimensionless variable.Bearing capacity fomula can be deduced by the analysis of influence factor,and this foumla calculation result by comparing with the test results shows a great accuracy.By dimensional analysis,the parameters which influenced embedded PBL mechanical properties can be rearranged into two dimensionless variables fitting a power function through which the load-slip relation of embedded PBL shear connectors can be represented.