Field Measurement Of Wind Load On Large-span Spatial Structure

Numerical simulation,wind tunnel test and field measurement are three major methods for obtaining the wind load characteristics on building surfaces.Although each method has its own advantages and disadvantages,field measurement is the most direct and basic research method and is the only standard for testing the reliability of other two methods.During field measurement test,surface wind pressure measurement has more importance than wind speed measurement.However,each current pressure measurement test has more or less deficiencies,and there is no appropriate equipments yet for wind load measurement on the surface of large-span roofs.Therefore,the necessary condition for the field measurement research is developing a suitable wind load field measurement system.This article starts with the field measurement equipment development.Through refering to the advantages and disadvantages of the existing measured system,this article designs a wind load measurement system for large-span roofs.The system realizes long-time continuous synchronous data acquisition with high sampling rate in large area,which meets the requirements for wind load field measurement on large-span roofs.In order to ensure that the data measured by the system is true and reliable,this paper conducts experimental exploration and parameter calibration of the performance of the system.Secondly,because there are few large-scale wind load field measurement for large-span roofs,there are few references for practical application of the measurement system.Therefore,this article proposes corresponding solutions to the problems that may be encountered in practical applications.During measurement point arrangement,a pressure measurement node grid encryption method based on the dichotomy method is conducted,which can achieve a reasonable layout of wind pressure measurement nodes.When reconstructing the missing wind pressure data,the BP neural network can reconstruct long-period dynamic wind pressure accurately.In addition,rapid spatial interpolation of wind pressure data can also be achieved through the BP neural network,so as to achieve real-time visualization of the wind pressure contour map.Thirdly,the wind load measurement system is applied to the surface of a large-span roof with a relatively standard appearance.This not only verified the performance of the measured system designed in this paper but also explored the characteristic of measured wind load on the large-span roof.This paper analyzes the wind load characteristics and compares them with the specified values in different load codes.The result shows that the turbulence intensity under the type B surrounding in China code seriously underestimates the turbulence of the real wind speed at the height of 40 meters.When estimating the local wind pressure coefficient of the double-pitch roof with a relatively small slope,the gust factor should be calculated according to the Eurocode.And the coefficient value on the lee wind side should be appropriately increased.Through correlation analysis of the measured data,it can be found that no matter fluctuating wind speed or fluctuating wind pressure have the phenomenon of migration at the average wind speed.As the vortex travelling forward,its turbulent characteristics gradually change.When the distance between measuring points is relatively small,there is a obvious correlation between the measured data,and the dynamic data contains certain travel wave effect.When the distance is greater than 100m,the correlation between the measuring points is small,and the dynamic loads of the two points are independent from each other.Therefore,the correlation characteristics of these dynamic loads should be taken into consideration when performing wind-induced vibration analysis.Finally,this paper takes the Zhejiang University Sports Center(Zhejiang University Stadium)as the measured building,and conducts several long-term field measurements under the monsoon wind field,and compares the measured results with the wind tunnel test results.Because the quantity of the field measured samples is relatively large,the characteristics of the real wind field and wind pressure are statistical studied.The measured average wind pressure coefficient is consistent with the wind tunnel test.The measured mean pressure coefficient results have similar trend with wind tunnel test under different wind directions,field measured results are basically within the envelope value of the wind tunnel test.However,the field measured fluctuated wind pressure coefficient results are obviously larger than wind tunnel test result under almost all wind directions.Most of roof area of the near-spherical stadium are not affected by vortex shedding,thus the wind load power spectrum is prominent in mid-frequency.In the ridge area on the top,wind load is obviously affected by vortex shedding,thus the wind load power spectrum is prominent at high frequencies.Wind tunnel test can accurately simulate low-middle-frequency fluctuating wind pressure,but for high-frequency fluctuating wind pressure caused by local turbulence,wind tunnel test underestimates its energy.If wind tunnel test results are used for designing peak wind load in the area which is 10m～20m behind the sharp edge,proper amplification should be performed.In a conclusion,this paper performed a large amount of field measurement tests on the real building through the self-designed wireless field measurement system.The first-hand measured wind load data on the surfaces of the large-span roofs are obtained and compared with the wind tunnel test.The ideas and field measurement results of this paper can provide effective reference for future wind resistance design of large-span roof structures.