Strain Modes Identification And Application For Beam Bridges

Strain mode is a key parameter for health monitoring of bridges, which can reflect the dynamic strain distribution of the structure. The strain mode parameters are more sensitive than displacement mode parameters to structural damage. However, the commonly method of strain mode identification is based on the relationship between displacement and strain, which is not a direct strain modes identification method. Thus, the direct strain modes identification method based on the measured dynamic strain is more practicable.For the beam bridge structure, this paper presents a new method to estimate the strain modes of beam structures based on the measured dynamic strain. Since the cross correlation matrix of the modal coordinates is a diagonal matrix, thus, the cross correlation matrix of the measured dynamic strain is also a diagonal matrix, and the strain modes can be obtained to find the eigenvectors of the strain cross correlation matrix. The strain modes of a simply support beam and a continuous beam subjected to various impulsive excitations are identified from the numerical simulations using the proposed method. Finally, the method is verified through the experiment of a simply supported beam under hammering excitation. Both the numerical and test results show that the proposed method can estimate the strain modes of beam structures.Deflection is one of the critical parameters for bridge health monitoring. In this thesis, the identification method of dynamic deflection based on strain modes is studied and discussed. The strain mode shapes are first estimated from the cross-correlation function of the measured dynamic strain data. Then, the displacement mode shapes can be estimated from the strain mode shapes based on the displacement-strain relation. With knowing the strain mode shapes and strain data, the corresponding modal coordinates can be estimated. The dynamic deflection can then be estimated by the obtained displacement mode shapes and modal coordinates. The method is verified by numerical simulations of a simply support beam and a continuous beam subjected to impulsive excitation, the numerical results show that the proposed method can effectively estimate the dynamic deflection of bridges.