Study On Key Technologies Of Health Monitoring System For Spatial Lattice Structures

Long-span spatial lattice structure which are composed of bar elements and beam-column elements are a kind of three-dimension spatial structure system, and they are the symbol of the national building science and technology for not only their reasonable force, high stiffness, light weight, good earthquake resistance, short construction period and cheap construction cost but also prolific style and complete function. They have been wildly adopted in the fields of long-span architechtures, such as industrial architecture, civil architecture and public building. Spatial lattice structures are inevitable to suffer from natural disasters, such as environmental loading, fatigue, corrosion, aging and so on. And then the damage accumulates and the resistance attenuates during long service period, and finally the damage or even paroxysmal disasters happened. Therefore, intelligent heath monitoring and damage diagnosis for structures during building and service period at various environment become an important technology to study.Detailed researches were carried out for spatial lattice structures health monitoring by combining the status quo of structural health monitoring (SHM) and structural condition assessment. The related important problems on structural health monitoring system, such as modal parameters identification under ambient vibration, optimal sensor placement, finite element model updatting, spatial lattice structure damage detection, were investigated and one spatial lattice structure health monitoring system was developed also.Meanwhile the laboratory test and field investigations also were finished. This dissertation investigated the theories of modal parameters identification and presented the unified approach for the method of low order time domain modal parameters identification under ambient vibration and the method of high order modal parameters identification under ambient vibration respectively. The similarities and differences of different identification methods were presented as well. All these work is helpful to build the whole unified theory of modal parameters identification methods. By comparing the four useful methods for spatial lattice structure modal parameters identification under ambient vibration, the advantages and disadvantages on their application of these methods were given. And also the validity of the two kinds of methods was verified.Considering the problem of optimal sensor placement on spatial lattice structure, an improved genetic algorithm (IGA) was introduced. The method took the modal strain energy (MSE) and the modal assurance criterion (MAC) as the fitness function respectively, and improved the data storage capacity with the decimal two-dimension array coding method and solved the problem of positional repeatability of sensors with the forced mutation operator. Further the evaluation criterion for sensor placement based on the mean square error between the Guyan Expansion mode shapes and the FEM mode shapes was given.With this criterion, the structure modal parameters identified by Data-driven Stochastic Subspace Identification (SSI-DATA) method using the measured data at different optimal sensor placement were compared. Then the minimal number of sensors for the identification of the first few modes were indicated. This dissertation investigated two optimal sensor placement methods used widely in the field of structural health monitoring (SHM). And then the theoretical similarity between the modal kinetic energy (MKE) method and effective independence (EI) were given by mathematical derivation.Additionally, the differences of the applications of the two methods were pointed, which was helpful to the further development of the optimal sensor placement method. Using the model expansion of MDOF system's FRF matrix, the formulas of average displacement amplitude and average velocity amplitude and average acceleration amplitude were derivated. Further, based on the effective independence method, the effective independence - average acceleration amplitude (EI-AAA) method and effective independence -modal kinetic energy (EI-MKE) method were derivated. Comparing with the effective independence (EI) and the modal kinetic energy (MKE) method and effective independence - driving-point residue (EI-DPR), the advantage of the two proposed methods were verified.An evaluation algorithm based on the modal strain energy theory was given by adopting an overdetermined equation group solved by the non-negative least-squares method to quantitatively identify the damage extent. The method also maintained the sparsness of the stiffness matrix and excluded the approximations and assumptions except the damping ratio. Meanwhile the validity of the method used for the spatial lattice structures was verified by analyzing the two cases of complete and incomplete measured information and comparing with those results obtained by using the minimum rank perturbation theory.Considering the number of the bar is quite larger than that of the node in a spatial lattice structure, a node-oriented multistage damage identification method based on three layers BP neural network was proposed. The method took the normalized natural frequence variation ratio and mode vector norm as the input of neural network, and then determinated the position and size of the damage according to the output of neural network nodes. Then the validity of the method was verified by a plain truss model. Considering the propertities of the concrete spatial lattice structure, the damage identification method directly used the modal information of the damage structure by the surface fitting method of curvature mode was proposed, which localized the damage by the difference between curvature mode and its fitted value. The research results showed that it was suitable for online SHM of the concrete spatial lattice structure.Laboratory work has been done with an autonomous design space truss test model with which the tests of static and dynamic and damage identification have been finished also. A finite element model updating method using the static and dynamic test data was proposed. And with this method, the benchmark model was obtained from the initial model. Analyzing the results using the identification method proposed in the paper, the validity of the damage localization method based on residual modal force was verified once again. And the damage is simulated by the disabled connection nodes and the added node mass. Further the probability of setting the laboratory model as the Benchmark model for the spatial lattice structure was investigated. Finally, the uniform standard test model was given.The dissertation also gave the design approaches of the SHM system for the spatial lattice structure and proposed the system integrated design principles. Also the data acquisition system based on LabVIEW and the structural modal analysis and damage identification system (SMADIS 1.0) based on Matlab were developed, which had the functions such as dynamic data acquisition and its preprocessing, modal parameters identification of the structures under ambient vibration, modal matching, model updating and damage localization and quantification. The application of the two systems verified the developed approach is helpful for the development of the SHM system. Field investigation was carried out on a steel roof of a SPSS structure natatorium in service. The systematic field-work approaches were given. The field visual inspections and static checking were conducted in turn under in-service environmental conditions. Further a three-dimensional finite element model was developed according to its factual geometry properties obtained from the field inspection. By comparing the four useful modal parameters identification methods for spatial lattice structure under ambient vibration, the all-round assessment on structure safe state and service behavior was conducted, then the constructive suggestion of reinforce and maintainance was given, and finally were the relative conclusions.