Experimental Research On Negative Bending Behavior Of Steel-UHPC Composite Beams

Ultra-high performance concrete(UHPC)is the most advanced cement-based engineering material.It has ultra-high compressive strength,tensile strength and durability.Its compressive strength can reach 150?200MPa and tensile strength can reach 7-10 MPa.UHPC's excellent mechanical properties are used to solve the typical mechanical problems in bridge engineering,such as the cracking of composite beam bridge decks.In order to study the tensile properties of UHPC in the negative bending moment region of steel-mixed composite beam and the influence of connection mode on the bearing performance of bridge deck,this paper uses the bridge deck continuous steel-mixed composite beam to carry out relevant experimental research and analysis.The research contents are as follows:(1)For the cracking of the bridge deck in the negative moment region,this paper combines UHPC's ultra-high tensile and compressive properties,and proposes to replace the ordinary concrete with the UHPC in the negative moment region of the composite beam to form a new form of composite beam-steel-UHPC composite beam.Three steel-UHPC composite beams with different joints in negative moment region are proposed.The loading process was completed by a unique rotation loading method.The key data such as rotation,critical cracking load and critical cracking strain were obtained.(2)Based on the Abaqus concrete plastic damage model,the nonlinear finite element model of the test beam was established.The test process was simulated in detail.The test results are in good agreement with the finite element results,which lays a solid foundation for the subsequent deeper analysis of the actural project.(3)Combining the test and theory,the crack resistance of the steel-UHPC continuous composite beam was analyzed.The analysis results show that UHPC can improve the cracking load of the composite beam in the negative moment region,and the crack spacing is small,which obviously inhibits the development of concrete cracks,and can effectively solve the cracking problem of steel-mixed continuous beam bridge deck.Based on the theory of bond-slip theory and comprehensive analysis theory,a simple UHPC crack width calculation formula is proposed.Considering the shrinkage properties of UHPC,the effects of curing conditions,reinforcement ratio and steel fiber blending on the crack resistance of UHPC were analyzed.(4)Combining the French and American standards,the loading capacity of the test beam was studied;the MATLAB program was used to perform nonlinear analysis on the weakest section of the test beam.The analysis results show that the welding length of the continuous web after the simple bending of the negative bending moment region is increased,and the loading capacity of the structure is greatly improved.(5)Based on the theoretical and model test analysis results,the structural stress analysis of the supporting project is carried out,and the reasonable interface form of the negative bending moment area and the reasonable longitudinal laying length of UHPC are proposed.