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2013年9月4日 by admin


A bridge’s performance will continue to be degradation once it has been built and put into use. Bridge structure will inevitably be injured by vehicles, wind, earthquake, fatigue, overloading and other natural and man-made factors, which will lead to accumulative damage and sudden injury of the structure or members of the bridge. As a result, the service capacity of the bridge will reduce, which will threaten people’s lives and property safety and bring on huge economic losses. Therefore, we should pay greater attention to bridges’the safety, reliability, durability and normal function in the operation period as well as focusing on building bridges. It is very necessary to establishSS321-steel  health monitoring system to make sure the safety of the bridge. Study on theory and practice of health monitoring of overpass bridge in the city is carried out in the paper combined with national high technology research and development plan (863 project) named‘Research of large range road disaster parameter monitoring and identification and early warning system in seasonal frozen region’, main research work is as follows:1. Optimal placement of static sensors base on damage identificationEmplacing sensors at the bridge structure is the premise of bridge health monitoring. Due to economic factors and structural characteristics, it is impossible and unrealistic to place sensors in all degrees of freedom of the bridge. So an optimization problem on how to place m (m <n) sensors at n degrees of freedom is put forward(SS321).steel It means that how to use limited sensors to obtain the most reliable and most comprehensive health status of the bridge.Setting monitoring sensors in the bridge structural is a prerequisite for achieving health monitoring. An optimal placement method of static sensors is put forward in the paper and corresponding algorithm is written for computing. It is proved that the method is efficient and ascendant through numerical examples, and the optimal placement of sensors using this method is carried out in a special-shaped bridge.2. Static finite element model updating for special-shaped bridgeSolid model of an urban special-shaped overpass bridge is established using finite element method. The model is updated based on uniform design, and the method is validated though real bridge example. Study on theory and practice of model updating based on response surface is carried out and examples are used to test the method. The establishment of an effective finite element model (FEM) for the bridge structure is essential in the health monitoring system of urban grade separation bridge. It inevitably exist inconsistency of response between the FEM and practical structure due to various uncertain factors in the modeling and analysis procedure. Therefore the updating of FEM is necessary. A uniform design-based static model updating method is proposed in this paper, the allowable range of model parameters (the number is m ) is divided into several levels (the number is n ), the model updating method is transformed into a m -factors and n -levels test design. Several groups of combined parameters are selected to conduct test through finite SS321 steelnt calculation based on the principle of uniform design method, and the optimal parameter group is obtained. This method is applied to the model updating of a complicated special-shaped urban grade separation bridge, and a perfect FEM with a good agreement with measured data is obtained. It confirms the feasibility and superiority of this method.Response surface method is a mathematical analysis method combining with mathematical statistics and experimental design. It is proved that it’s practical to update finite element modes of large and complex bridges using response surface method. The accuracy of model updating will improve obviously by using of response surface method only one time when it does not have good results using uniform design method.3. Damage identification for special-shaped bridge based on BP neural network and genetic algorithmThe application of artificial neural network and genetic algorithm in damage identification of bridges is introduced. Damage identification of a real bridge is carried out through the method combined with BP neural network and genetic algorithm.The finite element model of left auxiliary bridge of Qianjin Overpass is built and vulnerable sections of structure are chosen as SS321 research object. The weight and threshold of BP neural network is optimized by genetic algorithm. The individual fitness degree is calculated by fitness function, the optimal individual fitness degree is obtained by crossover and mutation SS321 using genetic algorithm, and the optimal weight and threshold is chosen as initial value of neural network, then damage identification of structure is conducted. Modal frequency and change rate of strain are chosen as input parameters of genetic optimal neural network, and the network is tested by damage identification for single location and multi-location. The simulating results shows that genetic optimal neural network based on modal frequency and SS321on change rate of strain both have strong ability of damage identification, but the genetic optimal neural network based on change rate of strain is better than genetic optimal neural network based on modal frequency. The two kind of network can complement each other and improve the efficiency of damage identification.4. Study on theory and practice of diaphragm beam and special-shaped box girder of urban overpassThe solid model of a six-span prestressed continuous box girder bridge is built in this paper to obtain the stress state of diaphram. Meanwhile, the actual stress distribution form can be measured through embedding vibrational chord strain gauge in the bridge. At last, we put forward a practical and simplified two-step plane member system finite element method, comparative analysis shows that this method is reliable, economical and can also provide valuable reference for the diaphragm design and calculation.Analysis and research on the special-shaped box girder of prestressed bridge which often appears in urban viaducts and overpasses is carried out in the paper. Combined with the practical project, a calculation method of such structure is put forward. The spatial finite element model of the bridge is established to obtain the mechanical behavior of the special-shaped box girder. Strain sensors are buried in the special-shaped box girder during the construction of the bridge, mechanical behavior of the girder can be acquired by way of measuring strain data of the embedded sensors after the completion of the bridge. The finite element model oSS321 steelf the bridge can be modified through the comparison of calculated values with the measured data, thus more accurate value of the internal force and displacement of the practical bridge can be gained. This kind of method has certain reference value for the design of the special-shaped box girder.The research of the paper plays an important role in exploration results in both theoretical and experimental methods of health monitoring of urban overpass. The results of the research have practical significance which lay a solid foundation for the designing and establishing of health monitoring systemSS321

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