Aerostatic Stability Of Long-Span Combined Highway And Railway Suspension Bridge

With the rapid development of national economy and people’s increasing imperious demands for transportation, long-span combined highway and railway suspension bridge has been taken seriously as an alternative in the strait-crossing super infrastructure solution. Under the action of the wind, with growing main span length of suspension bridge, the static and dynamic response of a suspension bridge will be more significant. Wind tunnel tests show that under the action of wind load, the static instability of long-span bridge is likely to precede the dynamic instability. Therefore, it is necessary to study the static stability characteristics of long-span combined highway and railway suspension bridge under static wind load.The engineering background of this thesis is a certain strait-crossing long-span combined highway and railway suspension bridge. First of all, on the basis of considering the static wind load nonlinearity and structural geometrical nonlinearity factors, a command stream program which was used to analyze structural aerostatic stability was compiled with ANSYS Parametric Design Language. And the stability and accuracy of the results calculated by the program was proved by numerical examples; secondly, the full-range analysis of static response of the combined highway and railway suspension bridge under the action of static wind load was carried out. Characteristics of aerostatic instability were summarized. Considering the influence of initial wind attack angle and component of mean aerodynamic force coefficient, comparative analyses of the failure mode and aerostatic instable critical wind velocity of long-span combined highway and railway suspension bridge had been made; thirdly, a comparative analysis of the differences in calculation of aerostatic instability critical wind speed with linear and nonlinear aerostatic instability theory had been made. The influence of material nonlinearity on the aerostatic stability characteristics of long-span combined highway and railway suspension bridge was discussed preliminarily. Further, the aerostatic instability mechanism of long-span combined highway and railway suspension bridge was summarized; last but not the least, based on the bridge’s situation, the influences of different railway deck system and sag to span ratio of main span on aerostatic instable critical wind velocity were analyzed. Simultaneously, aerostatic stability characteristics during the erection of stiffening girder via rigid connection method were analyzed.Research shows that only on the basis of thinking through the nonlinearity of static wind load and structural geometrical and material nonlinearity, a reasonable evaluation of the static stability characteristics of long-span combined highway and railway suspension bridge can be achieved. This research also indicates that the aerostatic instability of long-span combined highway and railway suspension bridge is the result of static wind load and structure interaction. When the increment of structural resistance is less than that of static wind load, the structure goes into unstable state. Meanwhile facts show that using the command stream program compiled with APDL to analyze the static stability characteristics of long-span combined highway and railway suspension bridge has the characteristics of high efficiency, fast calculation speed etc, which indicates that the method is not only feasible but also has practical significance to solve complex special problems in practical engineering.