Research On Parameter Identification Technique And Damage Detection Method For Latticed Shell Structures

Space structures are extensively used as roof structures of competition and training gymnasiums in Beijing Olympic Games. A latticed shell structure belongs one of main structural styles in space structures. It has a large span, a beautiful design, a reasonable stress and a convenient construction, so it is used as the roof structures of some Olympic gymnasiums. For example, the roof of Olympic Cycling Gymnasium is a double-layer spherical latticed shell structure; the roof of Olympic Badminton Gymnasium is a suspended spherical latticed shell structure. A latticed shell structure ensured these Olympic gymnasiums novel, artistic and multiform. But at the same time, its complex dynamical property brings some new challenge to structural parameter identification and damage detection. The main research targets of this dissertation are modal parameter identification, mode localization and transition, damage detection of latticed shell structures. Moreover, for two kinds of common structures, inter-story shearing structures and RC beam structures, the problems of parameter identification and damage detection were also researched. The research results are as follows:1. A modal testing technique for latticed shell structures is presented. The technique combines the technique of single-point transient shock excitation and the complex mode indication function method for modal parameter identification. Through the optimal position selection of single-point transient shock excitation, the mode identified can be isolated or separated to a great extent, and the interference between repeated frequencies modes (or closed frequencies modes) in structural response can be lightened to some extent. The complex mode indication function method is an advanced modal identification method in frequency domain. It can determine modal parameters automatically with a high-speed, so it is better than traditional peak-pick method. Numerical simulation was done to the modal testing technique. The results show that the technique has good validity and accuracy to some extent.2. Mode localization and transition of latticed shell structures were researched systematically. Through a numerical simulation example of a latticed shell substructure, the existence of mode localization and transition phenomena is verified in theory. The mechanism of two phenomena is analyzed by the matrix perturbation theory. It shows that the internal cause of two phenomena is the intensive frequencies of latticed shell structures and the external cause is the slight change of structural physical parameters. Using the modal testing technique presented in this dissertation partly, a model experiment was done to a Kiewitt single-layer spherical latticed shell structure. The experiment results prove that the phenomenon of mode localization is existent indeedly. The important impact of two phenomena is expounded in the areas of earthquake resistant calculation and damage detection of latticed shell structures. And using a single spherical latticed shell structure as an example, structural linear dynamic response under the same ground movement are calculated and analyzed by considering different initial geometrical imperfections. The results show that comparing with the case of ignoring initial geometrical imperfections, the peak values of axial pressure of some members augment remarkably. Thus, mode localization caused by initial geometrical imperfections can make linear dynamic response of latticed shell structures change remarkably, so it should be considered adequately in the seismic calculation of latticed shell structures.3. For the slight damage of latticed shell structures, a damage characteristic vector with good properties is presented based on the phenomena of mode localization and transition. The vector is simple, and it is composed of some low-order modes and a few testing freedoms. Through a numerical simulation example of a latticed shell structure, the properties of the damage characteristic vector are tested. The results show that the vector not only has good identifiable ability, damage sensitivity and noise robustness, and it can keep its adaptability to some extent to the error of structural finite element model. Furthermore, through a damage experiment of a Kiewitt single-layer spherical latticed shell structure model, the properties of damage characteristic vector are verified.4. A trial experiment is done on the damage region detection of latticed shell structures based on the difference of high-order modes. The experiment is to divide a latticed shell structure into several regions and place sensors in accordance to these regions firstly, then to acquire structural high-order modal response by single-point random excitation and identify the modal parameters by random decrement technique and Ibrahim time domain method, at last, to locate damage regions by the difference of high-order modes before and after damage. Through a damage detection test of a single-layer ellipsoidal latticed shell structure model, the feasibility of the method is verified basicly.5. The problem of inter-story stiffness identification for shearing structures under ambient excitation is researched and a new method is presented. In the method, the transition from structural random response to deterministic response is realized by the natural excitation technique (NExT). The parameter-decoupled free vibration equation of shearing structures is deduced, and the equation can simplify the process of identification and reduce the amount of calculation. Through the effective combination of the NExT, the parameter-decoupled method and the extended Kalman filter (EKF) algorithm, a good scheme is presented for inter-story stiffness identification of shearing structures under ambient excitation. Using shearing structures with six-degree-of-freedom and ten-degree-of-freedom as examples, the scheme is tested by numerical simulation and experimental verification. The results show that the inter-story stiffness can be identified with accuracy basically, and the scheme can be applied in frame constructions, continuous bridges and engineering structures whose mechnical models can be simplified as chain multiple degree of freedom systems.6. The damping characteristic of a simple-supported RC (reinforced concrete) beam after damage is researched, and a new index of damping characteristic (adjacent periods'dissipative ratio, APDR) is presented. The relationship between new index and bend-crack damage of RC beam is given by experimental analysis. In the experiment, the accumulated damage of beam is realized by static load test, and the change of damping characteristic with loading damage is tracked by shock load test. The mechanism of damping ratio's change and APDR's change with crack damage states are analyzed and compared deeply. The results show that the APDR index is sensitive to the severity of crack damage, and it has good noise robustness. So it can be used as a damage detection index of RC beams. Keywords latticed shell structure; parameter identification; damage detection; mode...