Analysis Of Measured Wind Parameters In Mountain Canyons And Research On Wind-Resistant Performance Of Bridges

As China’s modernisation moves into a new stage of development,the implementation of infrastructure interconnection projects in the central and western regions is steadily advancing,opening up roads in every mountain and building bridges in every river,and more and more large span bridge structures are being built in the mountainous valleys of central and western China.Due to the complex topography of mountain valleys,their wind characteristics are different from those of the open plains,and the existing wind codes at home and abroad provide little description of the wind characteristics of mountain valleys.In order to provide a reliable basis for the wind resistance design of large span flexible bridges in mountain valleys,it is necessary to further investigate the wind characteristics of mountain valley bridge sites in depth.This thesis takes the Murong Bridge in the V-shaped gorge on the western Sichuan Plateau in Ganzi Tibetan Autonomous Prefecture,Sichuan Province as the research object,and mainly uses field measurements and numerical simulations to systematically analyse the wind characteristics of the mountainous bridge site and carry out research on the wind resistance of the bridge under a large angle of attack,mainly as follows:(1)Establishing a wind environment observation system at the bridge location of the Murong Bridge and carrying out on-site actual measurements.Based on MATLAB programming,the measured wind data at the bridge location were processed to obtain wind environment parameters such as mean wind speed,basic wind speed,wind angle of attack,turbulence intensity,gust factor,etc.,and fitted to obtain the pulsating wind power spectral density function.(2)The wind environment parameters of a typical mountainous deep-cut V-shaped canyon were compared and studied with the similarities and differences of the parameters of the benign wind field.It was found that the mountainous deep-cut V-shaped canyon had obvious acceleration effect on wind speed,strong locking effect on wind direction,large angle of attack effect,slightly lower turbulence intensity and gust factor than the normative given values,and the measured wind angle of attack was mainly distributed between-4° and 10°,which was larger than the recommended range of wind resistance specification for highway bridges in China.(3)ANSYS and MIDAS were used to build finite element models of the bridges to compare and analyse the structural dynamic properties and to verify the validity of the models.Combining wind tunnel tests and CFD numerical simulations,the three-part force coefficients for each typical section of the main girder were fitted to obtain the three-part force coefficients as a function of the wind angle of attack,and the derivatives of the three-part force coefficients were calculated for each wind angle of attack to lay the foundation for the analysis of the static wind and vibration response of the bridge.(4)Based on the expressions of the three-part force coefficients of the bridge section calculated in the previous section,the three-part force at 0° angle of attack is calculated as the initial static gust wind load;based on the measured pulsating wind power spectral density function,the spatial pulsating wind field in the bridge site area is simulated based on the harmonic synthesis method,and the static wind load and jitter load are time-domain processed.ANSYS was used to develop an APDL program to analyse the static wind gusts and shuddering response of the bridge under the maximum single cantilever construction condition and the completed bridge condition.The results of the analysis show that the bridge structure is safe under static wind and jittery vibration,with the lateral displacement not exceeding 40 cm,which has little impact on the safety performance of the structure;the vertical displacement under self-weight reaches 73.6cm,which requires corresponding maintenance measures to be taken during the construction process to ensure construction safety.The internal forces and displacements of the structure under pulsating winds have a significant amplification effect compared to the static gust response,and should be fully considered in the design of the bridge against wind.