Study On The Flexural Behavior Of Steel Box-concrete Composite Beams Under The Influence Of Interface Slip Effect

The steel box-concrete composite beam connects the steel box beam with the concrete flange slab through the shear connector to work together.In recent years,it has been widely used in practical engineering because of its characteristics of high stiffness,high bearing capacity,good seismic performance and convenient construction.However,the interface slip between the steel box beam and the concrete flange slab is caused due to the commonly used flexible shear connectors such as studs and friction high-strength bolts will deform during the bearing process of composite beams.It will have a certain influence on the mechanical properties of composite beams,especially on the partial shear connection steel box-concrete composite beams.In order to explore the influence of interface slip on the mechanical properties of steel box-concrete composite beams with different shear connection degrees,this thesis combines bending test,finite element numerical simulation and theoretical analysis to carry out a series of studies.The main work and conclusions are as follows:(1)Three steel box-concrete composite beams with different shear connection degrees were tested for bending resistance.The failure characteristic,bearing capacity,interface slip,deflection and strain development law of the test beams were analyzed.The results showed that the overall failure modes of steel box-concrete composite beams with complete shear connection and partial shear connection were basically the same.They showed obvious plastic bending failure characteristics.But with the decrease of shear connection degree,the reticulate staggered cracks and longitudinal splitting cracks on the top of the concrete flange slab and mid-span bending cracks of the test beam were more developed.(2)The yield and ultimate flexural capacity of the test beams decreased with the decrease of the shear connection degree,but the decreased degree was less than 8%.So the degree of shear connection had no significant effect on the flexural capacity of steel box-concrete composite beams.The interface slip between the concrete flange slab and the steel box girder of each test beam experienced the non-slip stage,the initial slip stage and the slip development stage in turn.The interface slip was symmetrically distributed and the development speed of slip strain increased with the decrease of shear connection degree.Therefore the influence of interface slip cannot be ignored when calculating the bearing capacity of steel box-concrete composite beams with partial shear connection.(3)Refined numerical models of steel box-concrete composite beams were established on the basis of considering the contact relationship between studs and concrete flange slabs.Then the influence law of web height and web spacing of steel box girder,thickness of concrete flange slab and number of studs on bending performance were obtained.The load-deflection curve calculated by the numerical model was in good agreement with the test curve,which can well reflect the whole process bending behavior of steel box-concrete composite beams with different shear connection degrees.(4)Using the elastic method,the normal stress calculation formula of steel box-concrete composite beams under serviceability limit state was derived.And based on the simplified plastic theory and the limit equilibrium plastic calculation method,the formulas for calculating the flexural capacity of steel box-concrete composite beams with full and partial shear connections under the ultimate state of bearing capacity were established respectively.Comparing the theoretical calculation value with the finite element calculation value and the experimental value,the theoretical calculation value was safe and accurate.So it can be used to calculate and analyze the flexural capacity of steel box-concrete composite beams with different shear connection degrees.