Research On Anti-cracking Design And Shear Key Durability Of Steel-concrete Composite Beams In Negative Moment Region

When the composite girder is subjected to negative moment,the steel girder suffers compression while the concrete deck is subjected to tension.,which may cause tension cracks and weaken the stiffness and durability of the composite beam.In the adverse circumstance,the girder is vulnerable to chloride ion erosion and its fatigue performance is prone to be reduced.In the perspective of design,parametric analysis under negative bending moment for anti-crack schemes were conducted.Besides,in the perspective of operation,the research on the durability of deteriorated shear studs suffering corrosion was studied.The main contents include the following aspects:(1)With the finite element software ABAQUS,23 schemes are carried out to assess the effect of crack resistance based on 5 crack arresting methods including fulcrum jacking,midspan weight,pre-stressed tension,stiffness-lag shear key,and UHPC composite layer.Moreover,the crack width,economy and other indicators were considered as the crucial factors to evaluate each plan according to the fuzzy mathematics comprehensive evaluation method.The results show that 35 cm jacking is the best scheme.(2)Specimens of C50,ECC and UHPC composite beams with cracks were soaked for 6months to study the chloride ion erosion path of stud connectors,and the ability of erosion resistance of the three materials was compared.The results indicate that chloride ion in C50 specimen is more likely to invade from the concrete surface while UHPC has the strongest ability to resist chloride ion erosion.Secondly,considering the most unfavorable corrosion path,the corrosion pits are preset at the roots of stud to compare those without defects.Then four pushout specimens were loaded under static load.It can be seen that the preset corrosion pits have no obvious influence on the bearing capacity of shear connectors,but cause the increase of slip.The reliability of the numerical simulation is verified by comparing the finite element analysis results with the test results.(3)In order to study the fatigue performance of studs under corrosion,fatigue tests of seven push out specimens were carried out,and three of them were subjected to fatigue load coupled with electrical accelerated corrosion method.In detail,fatigue life,residual slip,dynamic slip and shear stiffness were utilized as damage variables to analyze the deterioration mechanics of shear studs under the corrosion-fatigue condition.The results show that coupling effect leads to the reduction of fatigue life and stiffness,and mainly affects the development stage of fatigue damage,which is related to corrosion rate.(4)The corrosion-fatigue life prediction model was established considering both shear cracking failure mode and fracture mechanics.The fatigue crack growth path of shear connectors was studied.the numerical model with FRANC3 D and MATLAB was verified by the test resuls.The results show that the theoretical values are in good agreement with the test values,which proves the feasibility and rationality of the prediction model.