Condition Assessment Research To Large-span Bridges Based On Long-term Static Monitoring Data

Large-span bridges'health monitoring and safety conditions assessment are used to forecast the structural deterioration and prevent the occurrence of disasters, which are major research and application domains in the fields of civil engineering. Based on the high ratio of dead load to total load in large-span bridges, a new safety conditions evaluation method is developed, which utilizes measurement changes in the long-term static monitoring data. The dissertation systematically explores new theories and methods of long-term safety conditions evaluation in the large-span bridge from the views of damage information extraction, damage detection method and optimal sensors placement.The main contents and results are stated in detail as following:â‘ A novel damage information extraction method for long-term static monitoring dataBased on the time scale character of action effects in the long-term static signals, the distribution characteristics in the frequency of signals are analyzed and a new dead load effect extraction method is proposed, which can separate the temperature effect, live load effect, creep and shrinkage effect and measurement error effect from the monitoring signal. Combining the k-means clustering algorithm, particle swarm optimization algorithm, RBF neural network and Butterworth filter, the adaptive band-width temperature separation method is developed. Based on the mathematic prediction model of ACI209, Chinese related regulations and B3 model, the incremental prediction model is presented to separate the creep and shrinkage effects of concrete. According to the distribution location of the live load and measurement error effect in the signal, low-pass filter technique is used to detach them, thus realizing the extraction of the damage information.The experimental verification result of numerical simulation shows that the novel damage information extraction method can accurately acquire the damage information.â‘¡A synthetical damage detection method based on dead load effectThe number of sensors in situ bridge is small compared with the number of finite elements and design variables, so the existing methods of condition evaluation based on model updating can hardly converge to true damage condition and the calculation efficiency of these methods is too low to meet the actual need, which prevents the application of these methods. To solve above problems, a synthetical damage detection method based on dead load signal is developed to detect the degree and the position of the damage part of the Shibanpo Yangtze Bridge in Chongqing.The dimension reduction technique is introduced into this method based on the damage function, and the damage detection is departed into two levels, which are level of marco-cell and finite element cell. The number of design variables to be identified in each level is cut down. Based on the priori knowledge that only several locations will be damaged in the whole structure, the non-change factor is used to modify the non-dominated sorting genetic algorithm II(NSGA-2) in order to reduce the search space of the NSGA-2. The meta-model method which substitutes the finite element model with mathematical model is used and calculation efficiency of NSGA-2 is improved obviously.The experimental verification results of numerical simulation show that the synthetical damage detection method can detect the damage location and level successfully in the condition of sparse sensor location. The calculation efficiency can be improved 10 times in the Shibanpo Yangtze River Bridge in Chongqing.â‘¢A novel sensor optimal location approach for static sensorAccording to the fact that damage effect of dead load can only be reflected in part of the whole structure and based on the rule of maximization sensitivity of damage, the effective influence domain method for optimal sensors setup is developed, and the relative measurement error factor is added into the method in order to select different static measurement types.â‘£Application of the software system developed to a real bridgeBased on the VC++, Matlab and SQL Server database technique, using the damage information extraction method for long-term static data and the synthetical damage detection method proposed, a software system for condition assessment to bridge is developed and applied to Shibanpo Yangtze Bridge. The application results show that this software can realize the condition assessment to large-span bridges under operation environment.