Reliability Analysis And Robustness Evaluation Of Bridge Quasi-steady Steady Galloping Stability

The girder,bridge towers,arch ribs and other blunt body sections of the bridge may gallop.Galloping is a speed-dependent,damping-controlled single-degree-of-freedom aeroelastic instability phenomenon.Under "high reduced wind speed",when the speed is higher than the speed of the vortex shedding lock,there is no substantial interference from the vortex shedding The quasi-steady theory is applicable,and the galloping in this case is called quasi-steady galloping.However,at present,there is no clear value for the "high reduction wind speed",that is,the scope of application of the quasi-steady galloping theory is vague.At the same time,due to the complexity of environment and the structural system itself,there are many uncertain factors for the quasi-steady galloping stability performance.At present,the quasi-steady galloping stability checking method based on the safety coefficient method cannot meet the requirements.This paper introduces the reliability theory to analyze the quasi-steady galloping stability of the bridge.In the meantime,in the face of the extreme wind loads that the bridge may encounter,it is necessary to further evaluate the galloping stability of the bridge to reflect the bridge's ability to resist extreme wind loads.This paper introduces the concept of quasisteady steady galloping robustness.The research contents of this article are as follows:(1 For a small width-to-height ratio(B/ D ?1 bridge cross-section where quasi-steady galloping may occur at high reduced wind speeds,the application scope and analysis process of the quasi-steady galloping theory are clearly proposed.In view of the shortcomings of the calculation method of the quasi-steady critical wind speed of galloping based on the classic Den Hartog criterion,if the wind angle of attack is not considered and the calculation may bring a large error,this paper proposes a more accurate quasi-steady galloping analysis method considering the angle of attack of the wind.(2 Considering the various uncertainties existing in environment and the structural system of the bridge,this paper proposes a reliability analysis method for quasi-steady steady galloping of the bridge to overcome the deficiency of the quasi-steady steady galloping calculation method based on the safety factor method in the current wind resistance design of bridges,the critical wind speed of quasi-steady steady galloping is regarded as a random variable obeying the normal distribution,and the randomness of the design standard wind speed is considered.In addition,a random parameter is proposed considering the gust influencing factors,the modified first-order second-moment method is used to calculate the quasi-steady steady galloping reliability of the bridge.(3 Considering the extreme wind speeds that the bridge may not encounter before,this paper introduces the concept of quasi-steady galloping robustness and proposes a robust analysis method for the quasi-steady galloping of the bridge.It is expressed in the concept “return period”,and the robustness index is calculated in modified first-order second-moment method.