Three-dimensional Nonlinear Degrading Model for Earthquake Response Analyses of Concrete Bridges

This paper presents a three-dimensional nonlinear degrading stiffness model capable of capturing stiffness degradation in bilateral directions for earthquake response analyses of reinforced concrete bridges. Stiffness degradations due to flexural and shear damage are considered. The model can trace the progress of damage from initial failure through gradual degradation of the member stiffness due to accumulative effects of damage to ultimate collapse. Flexural degradation is quantified by a cumulative flexural damage index, which is computed based on consideration of the maximum rotation and dissipated hysteretic energy of the element. Shear degradation is quantified by a shear damage index, which is derived from the shear demand and capacity relationship. Nonlinear earthquake response analyses of three-span reinforced concrete bridges subjected to bidirectional earthquake excitations are carried out to validate the model. Bridges of ductile dominated and shear dominated behavior structures are studied. Numerical results are presented in terms of the maximum displacement of bridge deck, moment at plastic hinges, local and global damage index and normalized hysteretic energy.