Research On Instantaneous Frequency Identification Of Building Structure Based On Improved Synchroextracting S Transform

Building structures are often subjected to extreme loads and long-term working loads in the process of use.In essence,they are nonlinear structural systems,and their dynamic response signals are non-stationary.It is more reliable to study the dynamic parameters of structures as nonlinear structures.The instantaneous frequency is one of the important parameters of non-stationary signal,which can directly reflect the healthy and safe state of the structure.In order to improve the recognition accuracy of instantaneous frequency,an improved generalized S-transform and synchroextracting transform are used to identify the instantaneous frequency of nonlinear structures.The work is as follows:(1)Firstly,the basic theory of time-frequency analysis method is introduced;secondly,the advantages and disadvantages of S-transform and its improvement methods are introduced,and then several post-processing methods of time-frequency distribution are introduced.Finally,through numerical simulation,it is found that compared with the traditional timefrequency analysis method,the energy of the post-processing time-frequency map is more concentrated and the frequency resolution is higher.(2)Combined with the generalized S-transform of Gaussian window,the S-transform is improved.The improved window function can describe the frequency by multiple term coefficients.Based on the principle of energy concentration,the improved parameter optimization algorithm of generalized S-transform is derived.Then,the synchroextracting algorithm based on improved generalized S-transform is proposed,that is,improved synchroextracting generalized S-transform.(3)Firstly,by analyzing amplitude-modulated and frequency-modulated analytical signals,it is verified that the instantaneous frequency identified by the improved synchroextracting generalized S-transform is closer to the theoretical value.Secondly,numerical simulations of nonlinear system under free vibration and frame structure under forced vibration show that the instantaneous frequency curve identified by this method is more accurate and smoother.Finally,a three-story reinforced concrete frame structure is established by Open Sees finite element software,and dynamic response of this structure is analyzed by applying seismic load.The time-frequency analysis of response signal of this structure is carried out by this method.It is verified that the method can effectively identify the instantaneous frequency of the structure,and has high practical value.(4)Based on the cable test,the stiffness of the cable is changed by applying different pulling forces to the cable.The instantaneous frequency of the cable structure is identified by using the improved synchroextracting generalized S-transform.The experimental results show that the instantaneous frequency identified by this method is basically consistent with the theoretical frequency,and the accuracy is higher.Meanwhile,a nonlinear support beam structure is designed,and the random load and pulse load are applied to it,which verifies that the instantaneous frequency energy identified by this method is more concentrated and the value is more accurate.Finally,through a seven-story reinforced concrete shear wall structure test,it is verified that the instantaneous frequency burr phenomenon identified by this method is weak,the frequency curve is smoother and the readability is higher.