Research On Wind Vibration Characteristics And Wind Vibration Coefficients Of Large Cooling Tower Based On Field Measurement And Wind Tunnel Test

Standard 5% damping ratio for high-rise reinforce concrete structures is generally used for the current damping ratio value of cooling towers,but considering the unique configuration and material attributes of large cooling towers,the actual damping ratio must be far smaller than the recommended.Field measurement is the most direct and effective way to study structural responses and dynamic characteristics,the existing field measurements of cooling towers are generally intended to obtain the wind pressure distributions on the external surfaces of the towers.With the development of the cooling tower,the wind effects have become the control factor of the structure design of such large cooling tower.Meanwhile damping ratio as the important input parameters of wind vibration dynamic analysis,the wind resistance safety of cooling tower will be affected by its value.However,the research of field measurements and damping ratio for large cooling towers has been conducte.At the same time,the comparison of wind vibration characteristics and wind vibration coefficients of large cooling towers based on field measurement and wind tunnel test methods has become the lack of of cooling towers.In view of this background,a large cooling tower standing 180 m in northwestern China in the domestic was selected for the field measurements,and the field measurement researth of acceleration responses of large cooling tower under ambient excitation was carried out,and acceleration vibration signals at representative positions of the tower were obtained.Firstly,ARMA,Peak Picking and HHT meathods were applied to analyze the frequencies and damping ratios for the first ten order modes,and the cooperation and error analysis between measured values and results of the finite element calculation were carried out.Following the line of thought of modal combination,an equivalent synthetic damping ratio of the cooling tower was derived.Then,pulsating wind pressure of the cooling tower were obtained as the input parameters of wind load based on wind tunnel test,meanwhile the equivalent comprehensive damping ratio was used as the parameter for complete transient analysis of cooling tower wind vibration responses.On that basis,the spectral characteristics,probability statistical properties,correlation,coherence,non-gaussian and nonstationary characteristics of acceleration response are studied emphatically.The average,pulsating and extremum of the cooling tower wind responses are summarized.The distribution of wind vibration coefficients and the value proposition under different responses and equivalent tagerts in condition of the criterion peak factors and response peak factors are discussed.Finally,the differences of Wind vibration responses and wind vibration coefficients between the measured and finite element analysis results are analyzed.The results show that the measured first ten frequencies of the cooling towers are consistent with the results of finite element analysis,and distribution of identified damping ratios is discrete.Following the line of thought of modal combination,equivalent synthetic damping ratio of the cooling tower was derived;the value is 2.13% less than 5% of standard.The corresponding frequency position of the energy peak of local modal of power spectral density between the finite element and the measured responses are in good agreement.The minimum difference of the measured and finite element acceleration response is 8.4%.The wind vibration coefficient is equivalent to the mean value of the absolute mean value is closest to that of the measured average wind vibration coefficient.The wind vibration coefficient is equivalent to the maximum value of the absolute mean value is greater than the measured average wind vibration coefficient.The minimum difference between the finite element and the measured wind vibration coefficient is 0.036.Wind vibration responses and wind vibration coefficient characteristics of large cooling tower structure are studied in detail by the methods of field measurement,wind tunnel test and finite element analysis.The present research provides valuable clues for the determination of wind load for large cooling towers.