Parameter Identification And Damage Alarming For Large Span Spatial Steel Structure Under Ambient Excitation

With the continuous development of national economy and the construction technology, a lot of large-span spatial structures with unique outline and complex construction are emerging. The health monitoring system that mainly used in bridge structure is applying in large span spatial structures gradually. Parameter identification and damage alarming is the core technology of health monitoring. Because noise ratio of testing data under environmental excitation becomes lower, structural response easy to be affected and other problems, many algorithms are effective in laboratory but failed in practice. This dissertation studies parameter identification and damage alarming method of large span space steel structure under environmental excitation, using National Aquatic Center steel structure health monitoring program as the example to promote practical use of structural health monitoring technology. The detailed research contents of this dissertation are shown as below:Firstly, this dissertation studies optimal placement of acceleration sensor. According to vibration characteristics of large span steel structure, it proposes sensor placement method based on modal energy and step-size optimization. It means that the main contribution mode is selected according to the importance of structural mode responses under environmental excitation, and then applies the optimal sensor placement according to mode shape, feature vector product and confidence level. This dissertation takes National Aquatic Center steel structure as the engineering background to optimize acceleration sensor distribution.Secondly, this dissertation studies the denoising method of vibration signals. Maximum module characteristics of both useful signal and noise are analyzed. In order to overcome the difficulty in determining decomposition level of wavelet denoising and reconstruction order of singular value decomposition, a self-adaptive determination method for decomposition level and reconstruction order is proposed. Numerical signal simulation and the measured data verify the proposed method.Thirdly, this dissertation studies modal parameter identification technology based on wavelet transformation. It proposed a modal parameter identification method with natural incentives and wavelet transformation to solve the problems of low-intensive of large spatial structure and difficulty in motivating with hammer or shaker. This method analyzes the impact of choosing mother wavelet parameter on identification accuracy. According to this analyzing it proposes self-adaptive selection method based on genetic Algorithm and minimum standard deviation of wavelet center frequency and bandwidth. Numerical simulation and field measurement of National Aquatic Center verify the effectiveness of the proposed method.Fourthly, this dissertation studies model updating method considering uncertainty. It proposes finite element model updating method based on range theory and multi-output support vector regression according to the uncertainty of model parameter and too much calculation when updating complex structural model. This method describes the uncertainty of parameters using interval analysis, constructs a sample using uniform experimental designing method, and takes model parameter as input, a number of designing parameters as outputs to get the non-liner mapping relationship between input and output value, then makes use of support vector regression generalization ability to get target value of design parameter, which provide a new exploration for finite element model updating. Numerical models and the National Aquatic Center steel model are used to verify the validity of the method.Lastly, this dissertation studies the early warning of structural damage. It puts forward a damage alarming method based on impulse response function and statistical theory. This method first selects the structural pulse responses under environmental excitation using virtual excitation technique, takes the pulse responses as sensitive indicators, then uses the methods of principal component analysis, support vector machine, control chart, etc. to alarm structural damage. Numerical model of National Aquatics Center steel structure and its measured data verifies the effectiveness of the proposed method.