Study On Wind-induced Response Of A Landscape Cable-stayed Bridge Under Mountainous Terrain

The rapid development of tourism promotes the construction of cantilevered glass landscape cable-stayed pedestrian bridges in scenic spots,which gradually develops towards the direction of longer cantilevered and higher altitude.Compared with the traditional bridge,the landscape pedestrian bridge has lighter weight,less stiffness and lower damping.The wind environment in the mountainous area of the bridge site is complex and more sensitive to the wind,resulting in potential safty risks.It is of great economic and social significance to comprehensively consider the wind load characteristics of this kind of landscape pedestrian bridge.Therefore,in this paper,a landscape cable-stayed pedestrian bridge in a complex mountain terrain is taken as the core researched object.Combined with theoretical analysis,finite element analysis,wind tunnel test and other technical means,the wind environment of the pedestrian bridge site and the wind-induced response of the pedestrian bridge are comprehensively analyzed.The wind speed and direction observational data of three meterorological stations around the pedestrian bridge are analyzed and compared by using the joint probability method of wind speed and direction with variable separation probability distribution,and the basic wind speed with 50-year return period of each wind direction is obtained.The results show that the joint distribution of wind speed and direction should be considered in determining the basic wind speed at the complex mountainous bridge site,and the basic wind speed will be overestimated if the wind direction is ignored,so the wind direction difference can be evaluated by the wind direction reduction coefficient.When calculating the basic wind speed at the complex mountainous bridge site,the distance between the bridge site and meterorological station,geomorphic difference and other factors should be considered.According to the mountain terrain around bridge site,the wind tunnel test of terrain model is carried out to obtain the mean and fluctuating wind characteristic parameters.The results show that there is no obvious canyon wind acceleration effect at the valley bridge site.When the wind blows along the valley,the climbing effect is obvious,the positive correlation between wind speed and attack angle is obvious,the turbulent intensity is the smallest,and the turbulence integral scale is large.The design wind speed of bridge site will be more conservative when the influence of wind direction and terrain effect is ignored.The comprehensive effect of wind direction and geomorphy should be considered to determine the design reference wind speed of bridge in mountainous terrains.The finite element model of pedestrian bridge is established and the time domain analysis of wind-induced response is carried out.The results show that the first six modes of the pedestrian bridge differ greatly.When the wind blows from the transverse direction of the bridge,the maximum transverse direction displacement response occurs in the middle of the bridge span rather than in the far end of the bridge cantilever,and the displacement response of the tower on the windward side is slightly greater than that on the leeward side.The displacement of the middle of the cable span is large,which have a significant influence on the wind-induced response of the pedestrian bridge,and the force transmitted to the bridge body will increase the response of pedestrian bridge.Wind tunnel test of aeroelastic model of pedestrian bridge is carried out.The displacement and acceleration responses under different wind speed and direction were measured.The results show that the displacement and acceleration responses of the pedestrian bridge increase with the increase of wind speed.The displacement response increases significantly in the case of oblique wind flow,while the torsion effect of bridge body is not obvious,and the effect of turbulence should not be ignored.There are aerodynamic damping and stiffness in the pedestrian bridge.The overall damping ratio is generally positively related to the wind speed,and negatively related to the wind azimuths.The test results of static wind response and buffeting response in uniform flow field and uniform turbulent flow field are in good agreement with the calculated values.The design of equivalent static gust wind load in the wind code of bridge is conservative.The vertical comfort of pedestrian bridge basically confirms the national standards,while the horizontal comfort confirms the national standards only in a few inclined winds.