The Modal Parameter Identification Of Timber Structure Based On The Theory Of Wavelet And SVD Under The Influence Of Environment

Ancient Chinese timber structure is the treasure among the buildings of world as its unique architectural form and the scientific structural system. It shows wisdom and crystallization of civilization for thousands years. As using years by years and impact of internal and external environment, the safety of the structure should be worried. Modal parameter identification has a great significance to discover the health state of structure and evaluate its security, reliability and durability and reinforce the structure to defense disaster.Basic science laid a solid foundation for the development of modal parameters recognition. Signal processing theory has developed from time domain and frequency domain to the time-frequency domain. The structural modal parameter identifications under environment excitation are often nonlinear and time-varying signal. Wavelet transforms and singular value decomposition theory is a time-frequency analysis method which is suitable for this condition.Under the direction of the key project of national natural science foundation of China (51338001), Condition assessment, safety limit and performance maintenance of the ancient timber frameworks. An ancient house named Zhoufujiu of salt merchant in Yangzhou and Zhunti temple are selected as the research objects to identify modal parameters. The main content of this paper includes:According to the theory, a convenient and fast algorithm based on MATLAB is produced. The algorithm selects correct scale of wavelet, which reserves the frequency band of wavelet transform coefficient. Then measures should be taken to choose the best center frequency and bandwidth of frequency and to process intensive modal and endpoint effect etc. A numerical example of seven degrees of freedom damping system is calculated to verify the scientific of algorithm.The change of modal parameters about Zhoufujiu house is monitored long-term under environment excitation. Timber structure dynamic characteristics in different temperatures under different humidity are observed. According to test results, the change rule is summarized and the influence factors are analyzed. Zhunti temple in Yangzhou is selected to identify the model parameters under two different humidity. The measured data confirmed that the environmental factors have certain influence to the modal parameters of timber structure.By ANSYS to establish model of Zhoufujiu house with semi-rigid mortise and tenon joint nodes. The model set density, elastic modulus, material parameters and Gaussian white noise excitation to identify parameter under environment excitation. Natural frequency, damping ratio and modal shape are compared to the results of measured data.This paper is based on the theory of time-frequency, the experiments and finite element simulation. The theory of wavelet and singular value decomposition for modal parameter identification and analysis of ancient timber structure is confirmed feasible. This method provides a basis for timber structure condition assessment and also can provide a reference to damage identification.