Numerical Analysis Of Temperature-induced Mechanical Responses For Long-span Steel Box Girder Suspension Bridge

Temperature load is one of the important loads on bridges,which has a significant impact on the mechanical responses of bridge structures.It causes degradation of bridge performance,and even serious safety accidents.Therefore,it is necessary to calculate effectively the temperature field distributions and the temperature-induced mechanical responses of bridge structures with appropriate numerical analysis methods.In this paper,the temperature effects of bridges are studied.And then,a long-span steel box girder suspension bridge is selected as the research object to study the temperature field distributions and the temperature-induced mechanical responses of bridge structures with finite element numerical analysis methods.The main contents are as follows:(1)Theoretical analysis of the temperature influence on structural mechanical responses are studied.And the temperature influence on structural boundary are analyzed from three parameters: beam end constraint stiffness,vertical bearing stiffness and axial force.Through a example,the influences of temperature-induced changes of various boundary conditions on frequencies are compared.And then,an experiment system of the simply supported box girder is established and placed in natural environment.Through by static and dynamic tests and finite element analysis,the accuracy and effectiveness of the structure frequency-temperature calculation are verified.(2)A long-span steel box girder suspension bridge is studied.The two-dimensional finite element thermal analysis models of the cross-sections of each component are established.The thermal boundary conditions of the bridge are confirmed and applied to the finite element models to calculate the distributions of time-varying temperature fields in natural environment.And the calculation results are compared with the measured one,which verifies the correctness of the numerical analysis method of the temperature field.The three-dimensional finite element structural analysis of the whole bridge model of the suspension bridge is established.The calculated temperature field is applied to calculate the mechanical responses of the structure,which are compared with the measured one.It verifies the accuracy and effectiveness of the numerical analysis method of the temperature-induced mechanical responses.(3)Through the control variable method,the influence of the temperature changes of different components on vertical displacements in mid-span are compared.It is found that the change of vertical displacement is mainly caused by the temperature changes on the main cable and the steel box girder.Through analyzing the relationship between the lateral inclination in mid-span and the lateral temperature gradient of the steel box girder,it is found that the absolute value of the lateral inclination increases as the temperature difference between the east and west web plates rises.(4)The thermal strains of key nodes on the steel box girder,main cable,hanger,and tower are analyzed.The research shows that the temperature-induced strain changes between different components and different positions of the same component are quite different.In the operation stage,the thermal strain changes of the towers are mainly affected by the self-temperature load and the temperature effect of the main cable and the steel box girder.And there is a difference in the strain change between the side facing the main span and the side facing away from the main span.(5)The former 20-order frequencies and vibration modes of the suspension bridge structure are analyzed.It is found that the structural frequency decreases when the temperature rises,and the change rate of the frequencies of each order is not the same.Through analyzing the temperature effect on the modal curvature,the conclusion that the temperature effect on the modal curvature is negligible is verified.Through the control variable method,the influences of the temperature changes of different components on the frequencies are compared.The temperature variations on different components have different influences on the structural frequencies,ranking high to low: the steel box girder,the cable-hanger structure,the boundary conditions and the towers.