Experimental Research On Interfacial Sliding Behavior Of High Strength Steel-UHPC Composite Beams

The high strength steel-ultra high strength concrete composite beam formed by the combination of high strength steel（HSS）,perforated plate connector（PBL-Perfobond Leiste）and ultra-high strength concrete（UHPC）has strong crack resistance,high bearing capacity and good durability,and is very competitive in the field of new small and medium-span highway bridges.Previous studies on the basic mechanical properties of composite beams with conventional materials have shown that the relative slippage of the interface between the steel beam and the concrete slab will weaken the overall performance of the two and reduce the flexural bearing capacity of the structure.The connector is the key component that affects the sliding behavior of the two interfaces.For the HSS-UHPC composite beam,the shear performance of the PBL connector used on the joint surface is significantly different from that of the traditional welding stud connector,and the interface slip behavior under external load is not clear.The applicability of the existing traditional welding stud composite beam analysis theory to the HSS-UHPC composite beam interface slip calculation needs to be further verified.Based on this,experimental research and theoretical analysis on the interface slip behavior of HSS-UHPC composite beams and its calculation method was conducted.The main research work and results are as follows:（1）The latest research progress of steel-concrete composite beams at home and abroad and their interface slip behavior analysis methods were summarized.The influence laws of parameters such as shear member type,shear connection degree,material properties and composite beam geometry on the interface slip behavior of composite beams were summarized.The key influencing parameters were determined to provide a basis for the design of subsequent interface slip tests.（2）The degree of shear connection,the bearing form of the perforated plate,the size of the concrete slab and the distribution form of the shear parts were used as the test parameters,and the HSS-UHPC composite beam was designed and fabricated for the flexural loading test,including 10 positive moment test beams and 8 negative bending moment test beams.The test results showed that the HSS-UHPC composite beams basically satisfies the assumption of plane section in the elastic stress stage.The ultimate state of the composite beam under the action of positive bending moment was mainly controlled by the yielding of the steel beam and the crushing of the concrete slab,and the ultimate state of the composite beam under the action of negative bending moment was mainly controlled by the yielding of the tensile reinforcement in the UHPC slab and the local buckling of the lower flange of the steel beam.（3）Based on the measured results of the interface slip of the composite beam,it was found that the maximum interface slip occurred first at L/4 of the composite beam,and the peak position of the slip gradually moved to the beam end with the increase of the load.Increasing the degree of shear connection and the pressure bearing at the end of the perforated plate could significantly enhance the anti-slip capability of the composite beam interface,and the anti-slip performance of the composite beam interface with PBL uniformly distributed along the beam length was better than that of the non-uniform arrangement of PBL.The UHPC board size（board width and thickness）had little effect on the elastic anti-slip stiffness in the positive bending moment area of the composite beam,but increasing the UHPC size could effectively improve the interface anti-slip stiffness in the negative bending moment area.In addition,the maximum interface slip in the negative bending moment area of the composite beam measured by the test was 1.46 mm,which had little effect on the flexural performance of the structure.（4）Based on the section analysis method,a theoretical model suitable for the calculation of the interface slip and deflection of the HSS-UHPC composite beam was established,and the interface slip of the test beam was calculated using this model.The results showed that the proposed theoretical model had good calculation accuracy.Based on the validated computational model,the effect of shear connection degree and concrete slab size on the interface slip behavior was further analyzed.Based on the experimental and theoretical analysis results,a calculation method for mid-span deflection of HSS-UHPC composite beams considering the influence of interface slip under positive bending moment was presented.