The Multi-scale Damage Analysis For Ancient Architecture Timber Structure Based On Wavelet Transforms

With the development of modern transportation, ancient timber structure were havebeen suffered structural damage from complex traffic load in the environment. Forfurther protection of ancient buildings, and establish the ancient timber structuredamage earlier warning theory; put the identification of ancient timber structure damageunder the random environment excitation for a research subject. Specified the unit ofstiffness has been reduced, then using the method of FEM to establish different damageconditions of modal. Using white Gaussian noise simulate randomly environmentexcitation. And then get timber frame acceleration dynamic response under differentworking conditions of damage signal.Constructs the damage variable, only change the designated unit damage variableson the finite element model in order to form contrast signal; make use of waveletdecomposition respectively for the finite element model of the response signal fromthree location of the modal, using the decomposition of wavelet transform highfrequency coefficients for variance analysis.After using the Matlab algorithm by optimized decomposition and reconstructioncoefficient of wavelet packet, different delta function of wavelet packet and variousdecomposition layers will be contrasted as decomposition computation of signal andascertained the criteria by contrasting the change rate of wavelet packet energyspectrum and norm entropy of a complete computational cost, which aims to select asensitive and costless wavelet packet function.By furthering using the energy ratio vector quantity and its rate of change as thenew yard stick to identify the damage signal of timber frame, we found that there is anobvious relation between the absolute value of the rate of change of energy ratio vectorquantity and damage variable D, however, there is no exact correspondence between the variation trend of that absolute value and damage variable and damage place. Theenergy ratio deviation and variance can show the change of every frequency band, thatwe can use it as the early-warning index of the injury degree about timber frame.