Analysis Of Aerostatic Stability Of Long-span Cable-stayed Bridge In Inhomogeneous Wind Fields

Aerostatic instability has great destructive effect on the bridge structure.It is one of the important safety indicators for the wind resistance performance of long-span bridge structures.It is very important to analyze the static wind stability of long-span bridges.On the other hand,due to the requirement of mountain line indicators,mountainous long-span bridges usually straddle mountainous valleys with complex topography,which will lead to uneven distribution of wind speed and wind angle of attack along the bridge across the bridge site,and will affect the wind resistance performance of the bridge.It is of great significance to carry out the analysis of the static wind stability of large-span bridges based on the characteristics of inhomogeneous wind fields in the complex topography of mountainous canyons.To study the effects of inhomogeneous wind fields induced by the mountain-gorge complex terrain on the aerostatic stability of long-span bridges,a long-span cable-stayed bridge straddling a typical mountain-gorge terrain was regarded as the engineering background.Firstly,the wind characteristics at the bridge site were analyzed by using the computational fluid dynamics(CFD)software FLUENT,and the inhomogeneous wind speeds and inhomogeneous wind attack angles along the bridge main beam were calculated.Then,the nonlinear program which can analyze the aerostatic stability of long-span bridge under the inhomogeneous wind speeds and inhomogeneous wind attack angles was developed.Based on the above,the effects of inhomogeneous wind attack angles,inhomogeneous wind speeds and both the inhomogeneous wind speeds and inhomogeneous wind attack angles on the aerostatic stability of the long-span cable-stayed bridge state and the construction state of the largest single-cantilever and the largest double cantilevers were comprehensively investigated.The research results of aerostatic stability of bridge structure under inhomogeneous wind fields show that the peak position of aerostatic responses under the inhomogeneous wind speeds or inhomogeneous wind attack angles is located between the peak position of wind loads and the position of mid-span,which is different from that under the homogeneous wind fields.Then,it is the peak position of aerostatic responses rather than the position of mid-span that should be paid more attention when analyzing the aerostatic stability of long-span bridge under the inhomogeneous wind fields.The critical wind speed of the aerostatic instability under the inhomogeneous wind attack angles is much smaller than that under the inhomogeneous wind speeds,and the performance of the aerostatic stability under the inhomogeneous wind attack angles mainly depends on the maximum wind attack angle rather than the average value of those inhomogeneous wind attack angles at the main beam.The critical wind speed of the aerostatic instability under the inhomogeneous wind speeds is influenced both by the average wind speed and the maximum wind speed at the main span.The shapes of vertical displacements and torsion angles mainly dominated by the wind attack angles.However,the lateral displacements are relatively independent,of which the shapes are generally symmetrical about the mid-span,and the values are mainly determined by the wind speeds.The research results of aerostatic stability of bridge construction state under inhomogeneous wind fields also show that the inhomogeneous wind speeds and inhomogeneous wind attack angles of the main beam of the construction structure are different from the homogeneous wind field,and the aerostatic response varies greatly;the largest single cantilever state is more prone to aerostatic instability than the largest double cantilever state;Inhomogeneous wind attack angles plays a leading role in the aerostatic stability of the construction structure.