Experimental Study On Mechanical Performance Of Steel-UHPC Continuous Composite Beam

To solve the problems of prone to crack in hogging moment and heavy deadweight of traditional steel-concrete composite girders,UHPC(Ultra-High Performance Concrete)material with high strength and high performance is introduced into this structure,and a new type steel-UHPC continuous composite girder structure is proposed.By utilizing the excellent mechanical properties of UHPC,the purpose of improving the crack resistance,reducing the deadweight,and enhancing the span and durability of bridge structure is achieved,so as to solve the above problems existing in traditional composite girders radically.This paper conducted preliminary investigations on the mechanical properties of steel-UHPC continuous composite girder from experimental study,numerical simulation,and theoretical investigation.The main completed work are as follows:(1)Two large-scale models(including a steel-UHPC continuous composite girder(SUCB)and a prestressed steel-concrete continuous composite girder(SCCB))were tested under static load.The test results indicate that the bending capacity of SUCB is 1.2 times that of SCCB;the cracking strength of SUCB is larger than 20 MPa,much higher than the conventional one;the cracks appeared in UHPC slab dominated by micro-cracks with smaller length are numerous and intensive;the relative slip between the steel beam and the concrete slab is small as a whole,which indicates that the group stud connector can effectively combine the two into a whole stress.(2)A nonlinear finite element model of SUCB is established by using the FEM software ABAQUS,in which the material nonlinearity and geometric nonlinearity are considered in the model,and concrete plastic damage(CDP)model is adopted in UHPC.The results of finite element analysis are consistent with the test results.(3)After the applicability of the FEM is verified,the influence of primary design parameters on the flexural capacity of SUCB is clarified.These parameters include:UHPC top plate thickness(ht),UHPC slab rib height(hr),UHPC slab longitudinal reinforcement ratio(rl),cubic compressive strength and axial tensile strength of UHPC(fc and ft),the web thickness,bottom plate thickness and yield strength of steel girder(tw,tb and fy).The results indicate that the strength grade of steel,web and bottom plate thickness play an important role in improving the bending capacity of SUCB;the axial tensile strength of UHPC,rib and top plate height of UHPC slab can enhance the bending capacity to a certain extent;the reinforcement ratio of UHPC slab has little effect on the bearing capacity of SUCB.(4)The adaptability of the calculation formula of the maximum crack width on the surface of UHPC in three kinds of current codes.The results show that the calculation accuracy of MC 2010 is relatively high,that of French UHPFRC-2013 is more conservative,and that of Leutbecher-Fehling model is more error.(5)Considering the UHPC tensile strength,the formula of the section flexural capacity of SUCB is derived based on the plastic theory.According to the calculation method of the amplitude modulation coefficient after considering the UHPC tensile strength,the rigid plastic analysis results of SUCB are obtained The results are compared with the results of SUCB without considering the UHPC tensile strength and the results of traditional composite girder.The results show that the tensile properties of UHPC improve the flexural capacity of the section in the sagging and hogging moment areas,while reducing the rotation capacity and amplitude modulation demand of the plastic hinge in the sagging moment areas.