Reliability Research Of Flutter And Aerostatic Stability For Long-span Bridges

With the ever-growing span of bridges, wind resistance of bridge structures is faced with unprecedented challenges. Since uncertain conditions of bridge structure and the wind circumstance should be accounted for, occurrence of flutter and aerostatic instability is therefor uncertain. In this dissertation, a reliability research is achieved to correctly evaluate flutter and aerostatic stability of long span bridges. First of all, the status quo is reviewed about the reliability research on flutter and aerostatic stability of long-span bridges, then a further research is conducted to solve the problems and shortcomings in existing methods. At last, an improved limit state equation of reliability analysis is constituted, and a set of analysis method with little calculation, practical reliability is formed to meet with the engineering precision requirements. The major contributions of the research center on:(1) A new set of flutter reliability analysis method considering the uncertainties of structure is formed after indepth systematic study in existing domestic and international bridge reliability analysis methods. In this way, the calculating speed and operability are improved. Then the method is applied to the reliability analysis of the flutter of the Yamen Bridge and the Huangpu Bridge on North Bridge.(2) The limit state equation of aerostatic stability reliability analysis is established based on the deterministic analysis theory of aerostatic stability, and considering parameters uncertainty. Then, the method applied in the flutter reliability analysis is also performed in the reliability analysis of the aerostatic stability of the two cable-stayed bridges.At last, it is applied to the reliability analysis of the aerostatic stability of the two cable-stayed bridges.(3) Comparison analysis between aerostatic instability and aerodynamic instability (flutter) of the two long-span bridges is presented. The analysis has practical value for wind-resistant design in the future.The main conclusions obtained are listed as follows:(1) The proposed methods are successfully applied to the reliability analysis for flutter and aerostatic stability of the Yamen Bridge and the Huangpu Bridge on North Bridge. The results show that the annual probabilities of failure due to flutter for the two bridges are 3.4455×10^-4 and 1.1702×10^-4, respectively. And the annual probability of failure due to aerostatic instability for the two bridges are within 10?8 .The results are so reasonable, that the method is correct and practical.(2) The critical wind speed of the aerodynamic instability is compared with that of the aerostatic instability for the two bridges in the sense of probability. Results indicate that the probability of the event that aerostatic instability occures before flutter instability is within 10^-4 for the Yamen Bridge, and within 10?6 for the Huangpu Bridge on North Bridge. Therefore, the design for the two bridges can satisfy the engineering requirements.(3) The parameter sensitibity analysis for flutter and aerostatic instability of the two bridges are shown that:①Sensitive factors for flutter of the Yamen Bridge are related with the parameters of the girder, such as cross-sectional area, torsional inertia moment, inertia moment of line quality, line quality, and so on. But in view of the Huangpu Bridge on North Bridge, the tower elasic modulus should also be taken into account beside the above parameters.②The sensitive factors for aerostatic instability of the Yamen Bridge are related with the girder, and also coefficient slope of lift moment. And for the Huangpu Bridge on North Bridge, the tower elastic modulus is also necessary to be considered beside the above parameters.So the variability of the sensitive factors should be reduced by certain measures in order to guarantee the stability safety of flutter and that of aerostatic stability.