Damage Assessment Of Simply Supported RC Bridges Based On Reliability

Damage identification, reliability assessment and remaining service life predication are urgent problems to be solved in the engineering field. Simply supported reinforced concrete bridges are typically used in the moderate and small spans. During their operation, such factors as material degradation, reinforcing bar corrosion, being frequently loaded or even over loaded, in addition to natural disaster and traffical accident, will cause the bridges to be damaged or locally failed. Based on the models of resistance attenuation and loading, the limit state equations of carrying capacity of RC bridges are established in this dissertation, then the time-variable reliability is analyzed. In this way, the dynamic reliability theory is related to the damage assessment.Using previous research conclusions as references, the factors influencing resistance attenuation are considered respectively in this dissertation, such as the time-variability of the strength of concrete, reinforcing bars and the cross section of reinforcing bars and the deterioration of bond behavior between the steel and the concrete. On the basis of the models related to the foregoing factors, the structural resistance model is formed. An important aspect is the effect of reinforce corrosion on the resistance deterioration. Two types of corrosion are considered, i.e. general corrosion and localized corrosion.Load is one of the main factors influencing bridges, including dead load and vehicle load, which is considered to be random variables. According to investigation data from home and abroad research, the stochastic models of dead load and vehicle load are introduced in this thesis. The dead load's model submits to normal distribution and the vhehicle load's unnormal which is devided into general traffic and dense traffic states.After completing resistance and load models, the limit state equations of carrying capacity of bridges damaged, which are also called function equations,are formulated. The reliability theory is integrated with the evaluation of bridge structures. As the resistance is time-dependente and the vehicle load is unnormal in these equations, programs of JC method and Monte Carlo Sampling method based on an example are coded respectively. Then the time-dependente reliability index of structural members are computed and compared between the methods. At last, the residual service life of the bridge system is predicted roughly to meet the object reliability. In addition, the effect of various factors is contrasted to discuss their sensitivity.