Failure Mechanism And Interface Mechanical Properties Of Angle Steel Connector

With the continuous improvement of the road level and the expansion of the construction scale,the required span of the bridge is increasing.the bridge type is constantly enriched,the structure is constantly lightened.the steel-concrete combination structure bridge has the advantages of both concrete and steel bridges.and is increasingly used in the project.The steel and concrete are jointly stressed by shear connectors;thus,the design of shear connectors is a key step in the design of steel-composite bridges.The study on shear connectors mainly focuses on pinned connectors and PBL connectors,and there is still a gap on angle shear connectors.Unified bond strength calculation formula and load slip curve model has not been proposed.This paper takes a large span continuous box girder bridge with corrugated steel webs in Gaoguang high speed in Shandong Province as the background.In this bridge,the corrugated steel webs are connected to the concrete by angle shear connectors.Based on this connection method,the mechanical properties of the angle shear connectors are studied.In this paperr the pust-out tests of 73 angle shear connectors model were carried out based on 200-ton servo loading equipment.The model tests considered the effects of concrete strength,angle thickness and angle spacing on the bearing capacity of shear joints.A high-precision displacement meter was used to measure the relative slip between steel and concrete,and the loading equipment was connected with the acquisition system to achieve simultaneous force and displacement acquisition.The acquisition frequency was set to 1Hz.The test used the combination of force and displacement control for loading.The force control loading was used in the early stage of loading,which was changed to displacement control loading when the concrete cracks in the specimen was pust out.until the specimen completely losed its bearing capacity.The full process load slip curves of angle shear connectors were obtained for the first time by this loading method.A three-dimensional dynamic digital image correlation(DIC-3D)method was used to test the concrete strains in some specimens to achieve the acquisition of concrete strain fields.By analyzing the concrete damage of the specimen.the wedge-shaped damage mode of the concrete below the angle in the angle shear joint was proposed,and the relevant parameters in the wedge-shaped damage body were measured.Based on the limit theory analysis method in classical elasto-plasticity theory.the equation of balance between the power made by the external force Fmax and the energy dissipation rate of the wedge-shaped damage surface is established,and the calculation model of the bond strength of angle shear connectors is derived,and the predicted values of the model are compared with the measured data of three groups of validation samples to verify the validity of the model.Based on the curve characteristics of the rising and falling sections of the full process load slip curve of the angle shear joint.the expressions for the calculation of the load slip segments of the angle shear joint were assumed.and the relevant parameters in the model were analyzed theoretically to obtain the expressions for the calculation of the bond slip segments of the angle shear joint.This paper establishes a three-dimensional numerical model considering the plastic damage of concrete with the finite element software ABAQUS,and carries out the analysis of the influencing factors of angle steel shear connectors based on the numerical model.The breakage pattern of the unilateral double angle model in the pust-out specimen was analyzed,and a study of the damage pattern between adjacent angles by spacing was carried out.Based on the experimental test data.the correction coefficient of the angle spacing on the calculation of the bearing capacity of multiple angle joints was proposed.Theoretical equations for load slip curves based on individual angle shear connectors to react to the damage of angles and concrete through the damage of nonlinear spring units.A two-dimensional simplified model of the angle shear key group with real bridge dimensions was established by DIANA,and the analysis of the effect of different spacing on the shear force distribution and bearing capacity of the angle shear key group was carried out based on the simplified model.The main conclusions obtained in this paper are as follows:1)Fit to obtain the expression of the relationship among the angle y of the breaking surface of the wedge,the width H of the top surface of the wedge-breaking ring and the thickness of the angle2)Derive the expressions for calculating the bond strength of angle shear connectors3)Obtain the expression for the calculation of the bond strength corresponding to the slip value S0 and the model for the calculation of the bond slip segmentation of the angle shear joint4)Show that the thickness of the angle,the length of the angle and the strength of the concrete have obvious effects on the bearing capacity,while the effect of the width of the flange can be neglected.5)Propose the correction coefficient for the shear key bearing capacity when the angle spacing is less than the height of the wedge,and fit to obtain the expression for the correction coefficient.6)Show that the characteristics is large in the middle and small at the ends when the shear bond group reaches the ultimate load and the angle spacing is negatively correlated with the bearing capacity when the angle spacing is greater than the damage height of the wedge.