The Fuzzy Comprehensive Evaluation And Life Prediction Of The Existing Highway Bridges

With the action of natural environment,increasing vehicle load and material deterioration,the concrete bridges have undergone various degree damages on three levels of material, component and structure as time goes on. And with the accumulation of these damages,the concrete bridge is bearing capacity,durability and serviceability will drop or degrade , so its nonnal service function is influenced.How to evaluate the reliability of existing highway bridge and to forecast bridge is remaining service life rationally has gradually become one of the concerned problems in the domain of domestic and foreign bridge academia.Based on comparing the status of the evaluation of the existing highway bridges,the advantages and disadvantages of various evaluation methods,we use fuzzy mathematics theory, the concept of fuzzy sets and membership to describe and deal with the fuzzy uncertainties factors in the evaluation process. Using AHP to evaluate the durability,the security and the serviceability of the whole structure of the bridge. The durability, safety evaluation generally consider the main influential factors. This model is different from the previous model, and it can better reflect the true status of the bridge structure. Also,it has a good practical significance.The main job includes:1. In the light of the hierarchical features of bridge structures and the inadequacy of existing grade evaluation methods,a method of multi-level fuzzy comprehensive condition assessment for existing highway bridges is presented and studied.The basic frame work and steps of multi-level fuzzy comprehensive condition assessment are established.Methods of determining weight value vectors are studied.And methods of determining assessment grade according to the fuzzy grade vectors obtained by assessment are discussed.2. The fuzzy evaluation criterion was established from three aspects(durability,safety and serviceability).Though analytical hierarchy process,the weight coefficients of item level factors and index level factors were determined. Using fuzzy distribution, relevant degree method and qualitative description method , the degree of membership functions of fuzzy evaluation indcxes,etc.for existing highway bridge were constructed.Thus,the fuzzy reliability distributing vector of bridge could be calculated by multilevel fuzzy synthesis evaluation.Then,the fuzzy reliability grade of bridge was figured out by fuzzy nearness metbod.In consideration of fuzzy reliability evaluation results characteristic,the markov forecast method of concrete bridge evaluated with several states was presented on the basis of constructing transition probability matrix.Through matrix operations of markov process,the remaining servicel life of existing highway bridge could be determinded by boundary of the worst acceptable condition.3. A 18-year-old highway bridge of some a province was evaluated and its remaining service life was forecasted by the research fruits upwards using the method presente . It provides a reference for the concerned department for corresponding strengthening measure.