Damage identification of column under the axial load based on wavelet transform and modal data

As time passes, some elements of the structures are affected by local damage, though insignificantly. With the development and expansion of the damage , these structures may be completely destroyed and impose high socioeconomic costs. This study investigated the damage identification problem in the column under the axial load using modal data (frequencies and mode shapes) and wavelet transform analysis. The obtained results showed that by increasing the axial load proportional to the critical buckling load, the frequency value decreases in all modes in healthy and faulty modes. Additionally, under the effect of the same axial load, the frequency of the faulty sample is less than that of the healthy one, and as the damage severity increases, the rate of frequency reduction increases. The wavelet transform input signal was defined on the basis of the angle between the healthy and faulty mode shapes. The output signal details in the damage locations indicated perturbation so that in all the studied modes in different ratios of critical load, the damage locations were identified with high accuracy. Moreover, the results from the research showed that the perturbations in different damage locations are independent of each other and are only affected by the severity of the location damage and the axial load has no effect on the damage detection sensitivity of the wavelet transform algorithm. Furthermore, the sum of the wavelet coefficients of damaged locations in several damage modes is equal to the wavelet coefficients of damaged locations of the sum of damage modes.