Research On Bending Behavior Of Narrow-Width Steel Box-UHPC Composite Beams Under Negative Moment

Tensile cracking under negative moment and steel box buckling under compression are two common problems of steel box-concrete continuous composite beams.In this paper,on the basis of Normal Concrete(NC)partially filled narrow-width steel box continuous composite beams,A new type UHPC(Ultra-High Performance Concrete)-NC composite beam with narrow steel box was proposed.By replacing NC flange with UHPC-NC flange,the problem of premature withdrawal of composite beam due to tensile crack is improved,so as to further improve the durability and mechanical performance of composite beams.In this paper,relying on the project of National Natural Science Foundation of China,on the basis of the research group’s existing research on the NC partially filled narrow-width steel box,the UHPC-NC composite beam with narrow-width steel box was analyzed by experiments and ABAQUS finite element software respectively.The main achievements are as follows:(1)The reverse static loading test was carried out on 9 narrow-width steel box-UHPC composite beams.The crack development and failure pattern of composite beams were analyzed based on four parameters,namely the ratio of wing reinforcement,UHPC steel fiber content of wing plate,UHPC relative plate thickness and the filling degree of concrete in steel box.The load-deflection curves,load-strain curves and load-maximum crack width curves of the whole span of the test beam are obtained.(2)A nonlinear fine model of PSCB2 narrow-width steel box-UHPC composite beam was established by ABAQUS finite element analysis software.The whole loading process of the test beam was simulated,and the results were compared with the test values.The whole loading process and the characteristics of stress deformation and failure of the two beams were in good agreement.Therefore,the narrow-width steel box-UHPC composite beam established according to the experiment can better simulate the bending process of the composite beam,and it also shows that ABAQUS finite element analysis software has a certain applicability.(3)The effects of three different UHPC constitutive relations and three different UHPC plate thickness parameters on the initial cracking load and ultimate bearing capacity and the overall mechanical performance of composite beams were analyzed by ABAQUS finite element refined model.It is verified that the UHPC constitutive relation used in this model is the best UHPC constitutive relation.(4)Based on the converted section method,the elastic analysis is carried out without considering the tensile effect of UHPC.Based on the simplified plastic theory and considering the tensile action of UHPC,a formula for calculating the ultimate flexural capacity of composite beams is derived,and the calculated value is in good agreement with the experimental value.