Research On Safty And Service Performance Evaluation Of Concrete Beam Bridge Based On Variable Weight

At present, transportation networks are being well established, more and more bridges have been built and at the same time the number of old bridges also rises which leads to heavy work in management and maintenance. Due to the design and construction deficiency, loads, environment action and natural disaster, the bridges in service have fault in performance function and safety. Bridge management department should acquire the bridge status as soon as possible in order to improve the bridge service ability and avoid accident such as collapse. How to evaluate bridges quickly and accuately becomes the focal point, so it is important to search suitable bridge evaluating methods.Simply supported beam bridge with continuous deck is taken as research object, the performance of such type of bridge under loads is analyzed by theoretical and numerical method. By comparing with ordinary simple supported bridges, the evaluating of the aimed bridge can be simplified as simple supported bridge assessment with some modification.Based on the analysis of bending stiffness formula, and the experimental results of two T type simple supported beams, the relationship between crack development and the stiffness degradation is discussed. Crack average depth and spacing are taken as two indexes of crack statistics parameters, and non-uniformly distributed strain coefficient of reinforcement is used to present the degradation of stiffness. By numerical analysis of a rectangle beam, a regression equation of crack statistics parameters and non-uniformly distributed strain coefficient of reinforcement is obtained, so the relationship between crack statistics parameters and stiffness degradation can be established and it is verified by test results.In order to improve the assessment method of bridges, quantitative and qualitative evaluating systems of bridge safety and performance are carried out based on analysis of the factors which affect bridge safety and performance. To avoid the dullnesss in constant weight evaluation model which is widely used now, variable weight evaluation model is presented in this paper and used in the evaluating of bridges.In bearing capacity quantitative check, a method based on theory bearing capacity is presented. Theoretical bearing capacity is taken as basic value, then multiplied by section reduction coefficient Zd and structure condition deterioration coefficient Zt which is determined according to bridge investigation results. In safety evaluation, a fuzzy assessing model based on varied weight is established. The bearing capacity reduction degree which can be obtained in quantitative check and actual traffic condition, boundary condition and structure state are taken as assessing factors to obtain the safety grade. In quantitative assessment of service performance, maximum crack width and deformation of beam are taken as indexes and the limited deformation value is modified based on measured data. In qualitative assessment of service performance, a fuzzy assessing model is established with indexes of stiffness reduction rate, vibration property, traffic condition and structure deterioration condition. For assessing vibration property, the bridge and vehicle coupled vibration equation is studied and the results show that the pavement roughness, approach deformation and beam stiffness variation should be considered. Then calculation programming is made in Matlab software and the factors mentioned above are simulated. So the evaluation index, grade division and weight are proposed. At last, several tables are worked out for engineering application and they are verified by several actual bridges.