Research On Shear Performance Of Large Stud Connector In Steel-UHPC Composite Structure

When ultra-high performance concrete（UHPC）material is used as a composite layer between the orthotropic steel deck（OSD）and the asphalt pavement layer,the magnitude of fatigue stress and the risk of fatigue cracking can be decreased effectively.In the past few years,this type of composite structure has been analyzed by different researchers and applied in steel bridge structure extensively.Stud shear connector is the key member to ensure the co-working between OSD and UHPC material.At present,in the most research about steel-UHPC composite structure,the diameters of studs are from 10 mm to 16 mm.When this type of composite structure is used in some places where the magnitude of shear force is very large,many studs are needed to satisfy the force requirement since the contribution of each stud is small because of the small diameter.However,many potential problems such as the inconvenience for construction and the welding quality problem for each stud may be generated because of the increase of studs.These problems described above may be solved with the use of large stud shear connectors（diameter equal to or larger than 16 mm）in OSD-UHPC composite structure.In order to understand the application prospects of large stud shear connector for OSD-UHPC composite structure,the analysis model of push-out specimen was established based on the practical application dimensions of this type of composite structure through ABAQUS software.After the validation of the finite element model using the experimental data,the parameter analysis was conducted.The mechanical characteristics of the large stud,the factors affecting the bearing capacity of the large stud and the influence law under material failure mode and pull-out failure mode were investigated,respectively.Lastly,the calculation formula for the bearing capacity of stud under stud material failure was proposed through the fitting analysis of the finite element analysis results,and the limitations of this formula were given.The main conclusions are as following:（1）Because of the limitation of the thickness of OSD,the large studs whose diameters are larger than 22 mm are not suggested to be applied in the OSD-UHPC composite structure in order to avoid stud pull-out failure.（2）The factors affecting the bearing capacity of stud are different for different failure mode.For the stud material failure,the diameter and the tensile strength of stud are the two main factors affecting the bearing capacity.The function forms similar with d^1.75 and linear function are suggested to be used to describe the effect of the two factors on bearing capacity,respectively.For the stud pull-out failure,except the diameter and the tensile strength of stud,the length of stud and the compressive strength of UHPC material also have great effects on the bearing capacity of stud.The bearing capacity can be increased by 35%when the length of stud is increased from 20 mm to 35 mm.When the compressive strength of UHPC material is increased from 80 MPa to 150 MPa,the bearing capacity can be increased by20%.However,this improvement effect will be decreased with the larger diameter of stud.（3）The main factors affecting the stiffness of stud are the diameter of stud and the elasticity modulus of UHPC material.The effect of compressive strength of UHPC material on the stiffness can be neglected.（4）The calculation formula proposed under the stud material failure mode has a great agreement with the calculated value from finite element analysis.The limitations for the formula are:13 mm≤d≤19 mm,300 MPa≤f_s≤550 MPa,80 MPa≤f_c≤150 MPa.（5）The main factors affecting the minimum value of length-diameter ratio of stud under the pull-out failure mode are the dimension and the tensile strength of stud,and the compressive strength of UHPC material.The minimum value of length-diameter ratio will be increased with the increase of stud tensile strength and the decrease of UHPC material compressive strength.In another word,the stud is more likely to be pulled out with the higher tensile strength of stud or the lower compressive strength of UHPC material.For the different strength of stud and UHPC material,when the length-diameter ratio of stud is above 2,the pull-out failure will not occur in the OSD-UHPC composite structure.