Research On Structural Strain Mode Identification And Experimental Verification

Strain mode and displacement mode are different manifestations of structural vibration characteristics,which are essentially the same,have the same modal frequency and damping.Therefore,the strain mode can replace the displacement mode to assess the quality of structure or improve the design work,especially in the structural health monitoring and fault diagnosis,the strain mode is more sensitive to damage,making it of high value in its engineering application.However,in the process of strain modal identification,it is difficult for the existing testing equipments to make an effective response to the large-scale structures such as large-scale offshore platforms,high-rise buildings and large-span bridges,so the traditional testing methods of modal parameters identification are too limited.In order to solve this problem,we first describe the theory of strain mode based on displace mode,and analysis the relationship between beam strain modal shape an displacement modal shape,then we studied the general theory of stochastic subspace identification.The method can identify modal parameters effectively without measuring the input excitation,thus solving the problem caused by traditional testing methods.In order to further illustrate the effectiveness of the basing displacement mode and stochastic subspace identification in the identification of strain mode,the finite element simulation and experimental study of two clamped beams are carried out.Based on the identification of strain modal parameters,the paper proposes improving theory of beam element modal strain energy damage identification method,established the strain mode damage location index and quantitative damage identification equations and carry out corresponding research.Based on the theory of strain modal identification based on stochastic subspace method,the work of the software design of modal identification is carried out.In this paper,the finite element simulation and experimental results show that the covariance driven stochastic subspace method and data-driven stochastic subspace method can identify modal parameters of strain.Based on the strain mode modal strain energy damage identification method can effectively identify the damage location and damage degree,and compared with the traditional method of damage identification based on displacement modal and modal expansion,the improved method is simpler to calculate,good noise resistance,and with good engineering application prospects;based on the random subspace method of modal identification software to meet the design requirements.