Research On Framed Structure Damage Identification Based On Wavelet Analysis

Frame is widely used in engineering structure. During the using process, the damage may occur due to the impact of external factors. When the cumulative damage reaches a certain level, it can lead to serious security incidents and bring immeasurable loss of people's lives and social property. Therefore, the theory and method of damage identification of frame is not only having important theoretical significance but also having important value in engineering application.Wavelet analysis is a new kind of signal processing method which has a strong analytical ability for stationary signal and has a good suitability for non-stationary signal. Different from the past Fourier analysis which only show signal in a single region, the wavelet analysis can show the local characteristics of signal effectively in time and frequency domain and analyze the signal singularity position and singularity strength accurately.Based on the research of frame in this paper, it was given the damage identification principle of frame in different modal parameters cases. Established finite element model of frame and analyzed the dynamic characteristics. Through the continuous wavelet transform of structure modal parameters, the location of damage could be identified by the modulus maxima of wavelet coefficients.This paper established the damage identification method based on rotation mode, curvature mode and strain mode. Taking a layer of a cross frame, a layer of two cross frame and two layers of a cross frame for examples, after the continuous wavelet transform of modal parameters under three different conditions (column with crack, beam and column with cracks, two columns with cracks, both two columns and two beams with cracks), the location of frame cracks was identified by the maximum of wavelet coefficients. Numerical examples show that three methods can identify the location of cracks effectively, especially wavelet transform method of curvature mode and strain mode which can exclude the singularity interference of Compound just node, so it is more sensitive and accurate to the location of cracks .Based on the damage identification of simple plane framework, the above methods were generalized to more complex three-layer two cross frame structure, through the finite element analysis to get modal parameters under different conditions(column with crack, beam and column with cracks, two columns with cracks, both two columns and two beams with cracks). Identify damage through the location of maximum of wavelet coefficients after wavelet transform of these modal parameters. It is found that the wavelet analysis method of strain mode is more effective than other two methods, in which the wavelet coefficient value is more smooth, singular is more apparent and reflect crack position more accurately. Methods proposed in this paper were not only applied to simple frame but also to complex frame structure. So these methods had significance for damage diagnosis of building structure.