Modeling Residual Displacements of Concrete Bridge Columns under Earthquake Loads Using Fiber Elements

Nonlinear dynamic analysis with fiber-element models is now widely used to assess the seismic response of bridge structures. The ability of such models to accurately simulate response parameters for characterizing the postearthquake condition of bridges, namely residual displacements, is assessed by comparison of analyses of dynamically loaded reinforced concrete bridge columns to experimental data. The models are unable to capture residual displacements, and the cause of the inability to capture residual displacements is investigated through dynamic analysis of fiber-element and single-degree-of-freedom (SDOF) models. A certain type of pinching present in the numerical hysteretic response shape is found to lead to poor residual displacement simulation both in the SDOF models and in fiber-element models. When eliminating this pinching, improvements to residual displacement simulation are found. A modified concrete constitutive model representing damage accumulation from cyclic loading is implemented for the fiber-element analysis that incorporates changes to reloading behavior when moving from high tensile strain back to compression. Analysis using the modified concrete constitutive model leads to improvements in the ability of the fiber-element model to capture residual displacements.