Study On Structural Load Bearing Performance Of Steel-UHPC Composite Girder Bridges Under Hogging Moment

The steel and concrete combination girder bridge has been widely used in Bridge Engineering.But due to the low tensile strength of ordinary concrete,the concrete in the negative moment region of the continuous girder bridge is easily affected by tensile open crack problems,which affects the performance of the bridge.A UHPC(Ultra-High-Performance Concrete)can effectively solve such problems.Applying UHPC and steel beams to form a new type of steel-UHPC combination beams through shear connections can overcome easy cracking of bridge panels in negative bending moment zone and improve bridge engineering carrying capacity.In recent years,domestic and foreign scholars have gradually studied the mechanical properties of steel-UHPC combination beams under a negative bending moment.However,the relevant research is still relatively small.In this paper,a set of numerical and theoretical analysis methods for the whole flexural bearing capacity of steel-UHPC composite beams is studied.The influence of various parameters on the flexural performance of composite beams under the action of negative bending moment is studied.The uncertainty of the calculation model of ultimate flexural bearing capacity based on plasticity theory is also studied.The main research contents and results are as follows:(1)A numerical analysis method of the whole process of the anti-bending carrying capacity of steel-UHPC steel mixing beam was developed.Firstly,the basic simulation framework of the numerical analysis method was established.Secondly,the solution was determined for the numerical simulation framework’s critical technical problems,such as material nonlinearity,steel mixed contact,nonlinear solution and convergence criterion.Finally,the numerical analysis and comparison were carried out using this method combined with the test results of steel-UHPC combination beams based on the existing literature.The results demonstrate that the carrying force’s error range is within 6%,the cross-section load-deflection curve is the same,and the deflection error corresponding to the maximum load is 5%.The stress-strain course variation law can be well-matched,which shows that the numerical analysis method is reliable and accurate.(2)A Model of steel-UHPC combined beam scale test beam was established with a practical project.The effect of different structural parameters on the anti-bending performance of the test beam was studied through the whole process of numerical analysis.The analytical parameters involved includes the strength grade of UHPC,thickness of UHPC,rib ratio of the UHPC bridge panel,the layered height of UHPC,strength level of steel beams,the thickness of the abdominal plate,thickness of the rigid ribs,number of bolts and cross-sectional area of the bolts.The results indicate that the strength grade of the steel beam,rib ratio in the UHPC plate,and the abdominal plate thickness significantly affect the limit of bending carrying capacity of the combined beam.Increasing the cross-sectional area of the bolt improves the limit of the anti-bending carrying capacity of the combined beam,but the increase is not significant.Increasing the thickness of the UHPC also improve the cracking and bending moment of the combined beam,but it has less impact on the carrying capacity.Using UHPC instead of traditional ordinary concrete can improve the combined beam’s overall stiffness and make the combination beam have a better delay.In contrast,the remaining parameters have little effect on the limit of bending carrying force of the combined beam.(3)The reliability of the calculation method of the steel-UHPC carrying capacity was studied.First of all,the calculation formulas for the flexural bearing capacity of the steel-UHPC composite beams were established based on the elastic and the plastic theory.The calculation results were compared with the experimental results and it was found that the calculation formulas based on the plastic theory were closer to the experimental results.Secondly,combined with 105 groups of steel-concrete composite beam test data collected in the literature,the model uncertainty of the plastic theoretical bearing capacity calculation formula was analyzed.The ultimate bearing capacity calculation model with a deviation coefficient of 1.06 and a coefficient of variation of 0.10 is obtained.Finally,combined with a domestic steel mixing beam,the bridge’s structural reliability under the current design load is analyzed using plastic theory.The results show that the bridge’s calculated reliability level is 4.06 under the maximum negative bending moment.