Reliability-based criteria for corrosion in prestressed concrete bridge girders.

摘要

Probability concepts make it possible to take into account the distribution of the loads that may include environmental loads and resistances. This concept also makes it possible to quantify the level of uncertainty in a way which is consistent with the available information. Therefore, the reliability-based design codes have been developed in various countries. Most of the code calibration effort was directed to the development of the ultimate load criteria. However, serviceability limit states, such as allowable stresses, are often more critical for bridge designs than the ultimate limit states. The allowable tensile stress after prestressing losses, which is one of the allowable stresses, is directly related to cracking due to the applied loads and it is indirectly related to steel corrosion in concrete.; The presented research deals with the development of design recommendations in severe environments and a rational design criterion for chloride-induced corrosion from the reliability point of view. In order to approach the problem, cracking due to the applied loads is initially considered. Utilizing the linear analysis of cracked sections, crack width, the probability of cracking, and crack opening time are calculated. Monte Carlo simulation technique is applied to the algorithm so that distributions of the results can be obtained. The parameters are used to obtain the diffusion coefficient of the crack. Using the diffusion coefficient of the crack, finite element analysis (FEA) with Monte Carlo simulation is carried out to obtain the chloride concentration at the surface of reinforcement. The results are utilized to obtain the probability of the initiation of corrosion as well as the distribution of life cycle cost. From the probability of the initiation of corrosion and the life cycle cost, the design recommendations for various environments are obtained.; The closed-form formula for one-dimensional diffusion problem is improved for cracked sections. Using this formula, a new design criterion is introduced for prestressed concrete bridges in corrosive environments. Sensitivity analysis reveals the influence of the parameters on the chloride diffusion. From the sensitivity analysis, cover depth might be the most important factor for prestressed concrete girder bridges in terms of the chloride-induced corrosion.