Evaluation of Biaxial Strength Deterioration for Coastal Bridge Piers under Non-uniform Corrosion

Coastal bridge piers in the corrosive marine environment inevitably deteriorate over time, leading to a reduction in their strength. In the present study, a biaxial strength prediction method for non-uniform corroded bridge piers under axial force and biaxial bending moments is proposed by extending the applicable range of the load contour method. First, a method to establish the three-dimensional interaction surface is developed on the basis of the fiber-section model, which considers the two-dimensional chloride diffusion, the degradation of reinforcement and concrete. The proposed methodology is verified by a biaxial quasi-static test of the locally corroded bridge column specimens. Then, through further case study, the time-dependent characteristics of the interaction surface for bridge piers in the splash and tidal region and the atmospheric region are investigated. Finally, the expression of surface exponent is obtained from the interaction surface, which can be used in Bresler's load contour method to evaluate the deterioration in the biaxial strength of coastal bridge piers. The analytical results conclude that the expression of surface exponent can be divided into three stages including the constant stage, decrease stage and increase stage during the pier's service life. Axial compression ratio and corrosion degree are two important factors which influence the biaxial strength deterioration for different corrosion regions of the coastal bridge pier.