RELIABILITY ANALYSIS OF SCOURING AROUND THE BRIDGE ABUTMENTS

Traditional bridge design approaches are commonly based on suciently large safety margin to compensate the uncertainties of the design parameters and the unknowns of the related phenomena. This may lead to the conservative designs. Excessive local scour around bridge piers and abutments induced by hydraulic de- ciencies is known as a major cause of the bridges failure. Complexity of the scouring phenomenon and high degree of uncertainties of the governing parameters lead to unavoidable risks in bridge pier and abutment designs. Thus, to obtain an appropriate level of security and reliability of the bridge structures, their risk of failure due to the scouring phenomenon needs to be evaluated. In the present study, a generalized reliability model based on the static resistance-loading interference is developed for the assessment of reliability of the available formulas in the literature, to estimate local scour around the bridge abutments. By examining a comprehensive set of data, a two-parameter bivariate normal distribution is found to represent the joint probability density function of the resistance and loading. To obtain relevant information for the decision-making in design purposes, the model was applied to obtain a relationship between the reliability and safety factors. Thus, dierent probability distribution functions were tried on the eective dependent parameters, used in the derived equations of the former investigations. These parameters include channel width, abutment shape, sediment median size, and the ow discharge. To evaluate the reliability of each equation, Monte Carlo simulation method was applied and the reliability index of the considered equations was computed. Accordingly, among dierent available equations presented in the literature, the most reliable equation with the least probability of failure as well as the highest index of reliability was chosen as an appropriate equation to estimate the local scour around the bridge abutments. To obtain highly accurate results, the uncertainty of the dependent parameters on the scouring phenomenon at bridge abutment was examined. Among those, uncertainty of the ow depth and the ow velocity are the most signicant factors in in uencing the local scour around the bridge abutments.