Research On Wind Response Of High Steel Pipe Lattice Support Of Sea-Crossing Bridge In Typhoon Area

Lattice high support has the characteristics of large slenderness ratio and strong flexibility,which is very sensitive to wind load.When building a cross-sea bridge in typhoon area,the high lattice support system is not only affected by harsh natural conditions such as the thunderstorm,heavy fog and tide,but also affected by strong wind and typhoon,so the structural design and construction technology are faced with great challenges.To ensure the safety and stability of lattice high support in typhoon area is one of the issues concerned by bridge engineering field.In this dissertation,taking the lattice high support of the newly constructed cast-in-place highway beam bridge,the Fuping Railway Pingtan Strait Road-Rail Bridge-Daliandao Grand Bridge,as the research object,the mechanical performance of lattice high support under wind load is studied by means of wind tunnel force test,particle image velocimetry(PIV)test,aeroelastic model test,field monitoring,numerical simulation and theoretical calculation,so as to solve the wind engineering problem of lattice high support in typhoon area.The main research work and results of this dissertation are as follows:(1)The ANSYS was used to establish the models of the four-legged and six-legged lattice support,and the modified finite element method and time-domain method were utilized to calculate and analyze the downwind wind-induced response of the lattice support.The results show that the first sixth-order vibration mode of the four-legged single-column support and the six-legged single-column support are basically the same.The resonance contribution of the first two modes of the multi-legged single-column lattice support is more significant,and the lateral stiffness of the lattice high support in the transverse direction is greater than the lateral stiffness in the longitudinal direction.There is torsion and translation at the sides and the center line of the lattice high support structure,while the torsion of the lattice high support structure under the transverse bridge wind direction angle is not obvious,under the action of asymmetrical load of the lattice high support,the displacement of the top of the support RMS increased by about 12%,and there is a significant torsion effect,the main load-bearing components of the lattice high support are vertical members and diagonal rods,and the inclined rods on the windward and leeward sides of the high support have a significant stress increase due to the torsion effect.After considering the superstructure,the displacements of both four-legged and six-legged lattice supports are significantly reduced,indicating that the superstructure is imposed to facilitate the displacement control of the structure.(2)The three component force coefficients of the model under different wind direction angles in uniform flow and turbulence were measured by wind tunnel test of the lattice high support scale model.Particle image velocimetry(PIV)was first used to visualize the horizontal plane flow field and vertical plane flow field of the high pier steel tube support model.the vortex intensity and turbulivity of the vortex center in the single-column PI V test and the double-column PIV test of the support model were quantitatively analyzed,and the law of the influence of the flow direction on high aerodynamic characteristics was obtained.Research shows that the resistance,lift and torque of the lattice high support have obvious changes in wind resistance calculations,and the influence of static wind loads in three directions should be fully considered,when ?=45°.the vortex motion is violent,and the vortex intensity and turbulent kinetic energy intensity are the largest,as a result,the average aerodynamic force and pulsation value of the model are large.The vortex intensity and turbulent kinetic energy at the vortex center of the six-legged lattice high-support model are both smaller than those of the four-legged lattice high-support model,and there are obvious construction disturbances among the components of the lattice high support,and the three-dimensional characteristics of space should be considered in numerical simulation.(3)Three-dimensional design wind load of latticed high support based on piecewise estimation method,equivalent wind loads were applied to four-legged and six-legged lattice high supports,the correlation formula between the wind grade and the displacement of each segment of the lattice high support was obtained.The single variable grey prediction model DGM(1,1)was used to calculate the displacements of the high lattice support under the action of different wind levels in the erection stage of construction,finally,the calculating formulas of wind load grade and construction segment displacement of four-legged and six-legged lattice high support were fitted.By comparing the calculated results with the field monitoring displacement,the results show that the displacements of each support structure is larger than the actual values when calculated by the building load code and time domain method respectively,which is close to the calculated value according to the equivalent wind load,the calculation of equivalent wind load is more consistent with the variation law of support displacement.(4)Based on wind load test on the full bridge aero-elastic model the with reduced scale of 1:40 of lattice high support,the vibration responses of the structure under different parameters such as wind speed and wind direction angle were analyzed.The results show that the acceleration response of lattice support is positively correlated with wind speed and height,at some wind direction angles,the displacement response of the transverse wind direction is equal to or even greater than the downwind displacement response,and the wind vibration coefficient is obtained and the torsional response and torsional wind load are analyzed.The angular acceleration response of the left and right transverse wind direction is basically symmetric and anti-phase,the root mean square of torsion angular acceleration at each wind speed is basically the maximum at the wind direction angle of 0°,and the minimum at the wind direction angle of 90°,and it increases with the increase of wind speed.(5)The optimization criterion method was proposed to optimize the design of lattice high support,the following conclusions can be drawn as follows:it is better to choose 4 columns with high lattice structure,the segment length should be controlled within 15m,and the total height should not exceed 70m,moreover,the column spacing should be controlled between 7m and 8m,in the design optimization process of the lattice high support,the top displacement limit of lattice high support plays a controlling role,the wind load time-history and equivalent static wind load need to be updated,and the influence of wind load time-history is greater than the equivalent static wind load.