Research In The Applied Condition Assessment Method And Its Application In Long Span Suspension Bridge

The research and its application of bridge condition assessment becomes a hot and important field in civil engineering with the growing attention to the performance and reliability of long span bridges. Meanwhile, the rapid development of correlative techniques such as the vibration test, signal disposal, damage identification makes it possible to realize the online evaluation of long span bridges. Based on existing theory and research, this paper focuses in the research of applied methods of condition assessment and provides some useful reference to the condition assessment system of Runyang bridge.In this paper, the comparatively popular or new methods are comprehensively summarized. To realize the bridge condition assessment, a proper FE model is required, so the model modification of long span suspension bridge and its updating method are discussed first. Based on this, the probability analysis method using numerical simulation is further researched, which is an emphasis of this paper. Moreover, in order to find out the comprehensive performance capacity of bridges, the fuzzy analytic hierarchy process is dedicated and the compositive condition assessment system is set up. The main work of this paper is as follows.1. Model modification and updating of long span bridge for condition assessmentAccording to the need of condition assessment, the FE model modification method using optimization process is provided, and the FE model of Runyang suspension bridge is modified by zero-order method and first order optimization method. The results show that the zero-order method has a rapid converge speed, and when the curve fitting of state variables is by quadratic plus cross terms, the precision of analysis can basically meet the need of model modification. it should be used when the number of design variables is less than twenty. The first order optimization method has a better precision but is rather slow in the converge speed, moreover when the tolerance of objective function is not small enough, the best solution maybe a local one,it can be used when the number of design variables is more than twenty or a more precise analysis is required.2. Simulation of nonlinear behavior under damaged situationIn order to simulate the nonlinear behavior of suspension bridge under service and damaged situations, an adaptive Newton-Raphson arithmetic is introduced after the modification of the original model, the position and stress of cables are calculated precisely .This method provides a nice tool for the updating of the FE model, especially in damaged cases, and finally a more reliable FE model is achieved.3. Research in the theory of numerical simulationIn this part, the key techniques are discussed. Through the compare of Monte Carlo method and Response Surface method, the characteristics, the process and the systemic error are summarized. Based on this, a combined method of simulation is dedicated as a basic tool for the probability analysis of Runyang bridge. The combined simulation method transfers the original complex question of probability analysis into the solution of a series of multinomial, making the efficiency improved significantly so that the precision of analysis is also increased greatly.4. Application of the combined method in reliability assessment of Runyang bridgeBased on this combined method, the probability analysis of Runyang suspension bridge is made, the probabilistic sensitivities, the correlations between random variables and the reliability of structures are analyzed in normal and heavy traffic state respectively. In this paper, several damage situations are simulated to evaluate the reliability of the bridge under the certain damage situation. Those results provide some useful references to the structural health monitoring system of Runyang Bridge.5. Research in the fuzzy analytic hierarchy processTo get a more comprehensive understanding of performance of the suspension bridge during the serviceperiod, combined with the information from the health monitoring system and daily inspection, the fuzzy analytic hierarchy process is further researched upon the probability analysis. In order to embody the fuzzy character in evaluation, the traditional analytic hierarchy process is developed into a fuzzy one. The introduction of triangular fuzzy number can contain more fuzzy information of evaluation. The ranking method for reciprocal judgement matrix with triangular fuzzy numbers is also presented. Based on the mode identification process, the mathematical model of multi-level and multi-object evaluation using fuzzy approach degree is set up primarily.6. According to the process of probability assessment and compositive assessment, the whole reliability evaluation system is set up. The key problems in this system are discussed in detail. Combined with the health monitoring system, the online evaluation of Runyang bridge has been elementarily realized.