Identification Of Nonlinear Aerodynamic Damping Of Crosswind-excited Super-tall Buildings And Its Application

Crosswind loads and response determine the wind-resistant design of super-tall buildings in strong winds,and the aerodynamic damping is crucial to the assessment of crosswind response.At the vicinity of vortex lock-in wind speed,the crosswind aerodynamic damping changes nonlinearly with varying wind speeds and vibration amplitudes,which can only be quantified through wind tunnel tests currently as it is so complex that developing a theorectically analytical model is tricky.There are two major methods,involving the forced vibration method by which the aerodynamic damping can be identified from the self-excited force,also the random vibration method where the aerodynamic damping can be extracted from stochastic crosswind response.As the latter needs simpler equipment,it has been widespread.However,the existing identification methods are not accurate enough.It has become a problem of great importance in wind research field that setting up an efficient analytical model,which can be applied to precisely identify the crosswind aerodynamic damping and predict response.Theoretical analyses,numerical simulations and wind tunnel tests were combined to investigate the identification of crosswind aerodynamic damping of super-tall buildings and its application deeply.Firstly,based on the nonlinear stochastic vibration theory,an analytical model of nonlinear aerodynamic damping related to crosswind response statistical characteristics was developed,and the identifications of aerodynamic damping model based on response statistics and probability density functions of amplitude process were put forward.United with equivalent nonlinear equation technique(ENLE),the analytical solutions of crosswind response were determined.As a result,a complete analytically theoretical framework from the identification of aerodynamic damping to the prediction of crosswind response was established.The correctness and reliability of the proposed analytical framework were validated through numerical simulations and comparing with the results calculated based on the methods in related literatures.Then,this framework was applied to identify the aerodynamic damping of super-tall buildings in boundary layer flows,the influences of approaching flow on crosswind aerodynamic damping were studied,and the mechanism of random buffeting force acting on crosswind response was discussed.At the end of this dissertation,the effects of alongwind vibration on the crosswind aerodynamic damping and response were analyzed.Main works are as follows:(1)A complete analytically theoretical framework involving identifying aerodynamic damping and predicting response of crosswind-excited super-tall buildings was established.Firstly,an analytical model of nonlinear aerodynamic damping related to crosswind response statistics was developed.For a given wind speed,the aerodynamic damping was expressed as the nonlinear function of time-varying vibration velocity,and the nonlinear differential equation for crosswind vibration was obtained.According to nonlinear stochastic vibration theory,on the basis of solving state-space moment differential equation,the nonlinear aerodynamic damping model was acquired utilizing non-Gaussian moment closure technique and moment-based Hermite translation model.The analytical solutions of probability density functions(PDFs)of amplitude process and response statistics were derived from ENLE.Secondly,the methods of extracting nonlinear aerodynamic damping based on crosswind response statistics and PDFs were put forward.The statistics and PDFs of crosswind response of a super-tall building at varying wind speeds and levels of structural damping ratio were gained through aeroelastic model testing,and the nonlinear aerodynamic damping model was identified through solving linear equations and nonlinear optimization.Random buffeting force was measured through high-frequency-force-balance(HFFB)testing or identified as an unknown parameter.The amplitudes and PDFs were used to establish linear equations,and the nonlinear aerodynamic damping model was extracted through solving linear equations and nonlinear fitting.When the identified aerodynamic dampin was combined with ENLE,the crosswind response of other super-tall buildings with unchanged building shape but different mass ratio and structural damping ratio can be predicted.(2)The numerical simulation was utilized to validate the correctness and efficency of proposed analytical framework.Based on given nonlinear aerodynamic damping and wind load spectra,the displacement time histories of a square-section super-tall building at different levels of structural damping ratio and reduced wind speeds were generated through POD-based spectral representation and Newmark-? linear acceleration approaches,and response statistics and PDFs were obtained from time history analysis.The nonlinear aerodynamic damping model was identified with response statistics and PDFs in terms of the analytical framework.Also,the response statistics and PDFs were calculated,which matched the target values well.Besides,the aerodynamic damping was extracted with the methods in relevant literature,which was used to predict crosswind response.The results further confirmed that the analytical framework could identify crosswind aerodynamic damping accurately and predict crosswind response efficiently.(3)HFFB testing and aeroelastic model testing of a super-tall building in different boundary layer flows were carried out.First of all,HFFB tests of a square-section super-tall building model with aspect ratio of 10 were conducted in open and suburban terrains to acquire the power spectra of crosswind base bending moment coefficients.Then,aeroelastic model tests of the building for crosswind vibration and twodegree-of-freedom vibration were performed to obtain alongwind and crosswind response at different wind speeds and levels of structural damping ratio,which provided the data for identification the aerodynamic damping and parametric analysis.(4)According to the experimental results,the aerodynamic damping was identified and crosswind response was predicted,which were compared with that calculated from the method in relevant literature.The influences of approaching flow on the aerodynamic damping were studied,and the mechanism of random buffeting force acting on crosswind response was discussed.In addition,the effects of alongwind vibration on crosswind aerodynamic damping and response were investigated.These results further illustrated that the proposed analytical framework is correct and effective,also has higher value in engineering application.When applied to the practical project,it would promote the efficiency of structure design.