A Study On Damage Identification Of Steel Frame Structure Bolt Looseness Based On Hilbert Spectrum Sensitivity

In the steel frame structure,the bolt connection is a very common connection method.The presence of the bolt will cause the structure to have localized stiffness and discontinuity of damping at the connection part.Under the action of non-stationary vibration load,The nonlinear behavior of adhesion sliding and gap collision may occur.Under the influence of these behaviors,the dynamic response of the structure shows a complex nonlinear vibration phenomenon.Both the Fourier transform and the wavelet packet transform can only deal with the stationary linear signal,but the HHT is a new method with strong adaptability to deal with non-stationary and nonlinear signals.In this paper,the damage identification method based on Hilbert spectral sensitivity is used.The finite element analysis software is used to simulate and analyze the intact state and different damage states of a four-story steel frame structure,and a four-layer plane-scale assembly frame model is used to conduct an experimental study,the following conclusions were obtained:?1?The model of the bolted structure can be a simplified model with two degrees of freedom,which has bending stiffness at both ends of the unit,means that the unit can be viewed as a non-linear spring with only relative angles at both ends and no relative displacement.Through a numerical simulation analysis of a cantilever beam,comparison of displacement response curves of models without bolt connections and bolted connections,the results show that the simplified model of the bolt is correct.?2?When the dynamic response of the structure exhibits complex nonlinear vibration characteristics,the structural reaction enters the elasto-plastic stage,and the structural member also undergoes elastic-plastic deformation.At this time,the structural resistance and displacement do not maintain a linear relationship:Fs?K₀*?u?,but become a function of the displacement:Fs?28?Fs??u??.When the bolt is loose,the bending moment and the relative rotation corner of the connection part are not kept in a linear relationship.The relationship between the bending moment and the relative rotation corner when the bolt is loose is obtained through experiments.?3?EEMD can effectively solve the problem of modal aliasing of EMD and carry out Hilbert transform on each order of IMF of EEMD.The Hilbert spectrum can be obtained.The sensitivity matrix and sensitivity equation of the damage parameters of the Hilbert spectrum can be used to obtain the properties of the damage parameters before and after the structural damage,and to determine the structural damage.?4?Hilbert spectral sensitivity based frame structure damage identification method can achieve the qualitative,localization and quantification of the damage of the four-story frame structure.This method can accurately identify single damage and multiple damage.