Several Key Technical Problems Of The Base Balance And Its Application In Wind Resistance Research Of Super High-rise Buildings

The base balance method is one of the main test technologies in wind engineering research,and has been widely applied to the study on wind effect in high-rise buildings.The generalized base balance includes the high frequency force balance(HFFB)and two-degree-of-freedom aero-elastic balance(AEB),which are used for aerodynamic measurements of super high-rise buildings and for aero-elastic tests considering the wind-structure interaction(WSI).This paper focuses on the wind effect study on significant high-rise buildings and the theoretical and technical requirements of wind resistance design,and makes a detailed study on several key technical problems related to the generalized balance.It is of great theoretical and practical value in improving the technology of wind resistance research,the accuracy of wind effect estimation and the technical level of the wind resistance design of high-rise buildings.The main tasks of this paper are as follows.(1)Dynamic signal calibration method of the HFFB test:A correction method for dynamic signal distortion of balance model system(BMS)is proposed.The second-order blind identification(SOBI)method is used to achieve effective decoupling of measured signals of BMS.Then the accurate parameter identification of the decoupled signal is performed using a parameter fitting method that combines the actual aerodynamic characteristics.Finally,the dynamic distortion signal of BMS is corrected accurately.In practice,due to the inevitable non-rigid effects of the model and the complex WSI effect,non-proportional damping problems of BMS may occur.This paper further uses the signal decoupling method based on the complex mode theory called CSOBI and the modified bayesian spectral density parameter identification methods.As a result,a universally applicable dynamic calibration method of HFFB is formed.The proposed method is applied to the data processing of the dynamic signal of the HFFB test of a 528m super high-rise building and compared with the existing methods.The results show that the proposed method has strong adaptability to signal decoupling.The parameter identification strategy can effectively improve the calibration accuracy of the signal in the resonance region.The comparison with the existing methods shows the superiority and reliability of the proposed method.(2)Calculation method of three-dimensional coupled wind-induced response of complex super high-rise buildings based on HFFB test:The concept of modal distribution coefficient matrix is proposed,and the modal coupling degree between different modes is described by modal distribution coefficient matrix.Based on the signal dynamic calibration,the chapter deprives the calculation method of the coupled wind-induced response and equivalent base internal force of super high-rise buildings based on the HFFB test.Taking the actual engineering as an example,the effects of modal coupling and signal dynamic calibration on the wind-induced response and loads of the structure are discussed.The results show that according to different engineering and model conditions,the wind-induced response calculation of uncalibrated signals will cause the wind load and wind-induced peak acceleration of the structure to be overestimated by 35.8%and 58.8%,respectively.Modal coupling can significantly affect the distribution of structural dynamic loads under physical coordinates.To obtain more accurate structural wind-induced loads and responses in the wind-resistant calculation,the modal coupling effect of the actual structure must be considered.(3)Wind tunnel test method and wind effect characteristics of multi-tower structure with weak connection:Based on the multi-HFFB synchronous test technology,the calculation method of the wind effect of the twin-tower structure with weak connection is established.First,the frequency domain method is used to derive the calculation method of wind effect of the multi-tower structure based on the HFFB technology.According to the multi-balance synchronous test data,the wind-induced response and load and the interference effect between two towers are analyzed.The displacement correlation between towers and variation of the relative displacement at the bridge are investigated.The results show that the maximum and minimum relative displacements in the along-bridge direction are 0.26 m in the along-wind direction and-0.26 m in the crosswind direction,respectively.The channeling effect formed by the surrounding buildings is the main cause of the maximum cross-bridge displacement.Relative displacement response can be reduced by increasing the structural damping.The displacement correlation between the two towers is weak,thus the influence of the correlation between the two towers can be ignored for the along-bridge relative displacement.The results of the HFFB and high-frequency pressure integral tests agree with each other,thereby indicating the reliability and effectiveness of the proposed method.The two methods verify each other,indicating the reliability and effectiveness of the proposed method.(4)Aerodynamic damping identification method considering aerodynamic characteristics of super high-rise buildings:This method is used to identify the modal parameters of an aero-elastic test of an 838m super high-rise building.The results show that CSOBI can effectively separate the coupled signals due to the very close two-order modal frequencies of the aeroelastic model.The coupled signal of AEB is decoupled by CSOBI method.According to the existing research results,a universal aerodynamic model is proposed,and the Bayesian spectral density parameter identification method(NewBSDA)considering the influence of colored noise is established.The proposed method is applied to the parameter identification analysis of aeroelastic test of a high 838m super high-rise building.The results show that CSOBI can effectively separate the coupled signals generated by the close proximity of the two-order lateral modal frequencies of the aeroelastic model itself.The results of NewBSDA are significantly more reasonable than BSDA due to the consideration of the characteristics of actual aerodynamic forces.The comparison shows that near the critical wind speed,BSDA significantly underestimates the structural aerodynamic damping.This result also confirms the conclusion obtained by using the BSDA method to identify the modal parameters of the simulated narrowband excitation response.In addition,due to the solution to the decoupling problem of complex coupled response signals,when the AEB method is used for the aeroelastic model test,no artificially added constraints or stiffness are required to separate natural frequencies in the two oscillating direction,which makes the test simulation closer to the actual situation and also improves the test efficiency.