Finite-Element Modeling of a Post-Tensioned Bridge Bent with Tension-Only Replaceable Anchors

A three-dimensional (3D) finite-element model (FEM) of a two-column post-tensioned bridge bent with replaceable tension-only stretch length anchors (SLAs) used as external energy dissipators was developed. The 3D FEM was used to obtain the moment–rotation curve at each joint of the rocking columns idealized as a trilinear rotational spring, which was incorporated in a simplified numerical model in OpenSees (version 3.7.1). The experimental results from six quasi-static cyclic tests of two-column bridge bents at 42% scale were used to validate the 3D FEM and OpenSees models. Three of the specimens utilized unbonded post-tensioning (PT) bars in the columns; the remaining three specimens utilized PT bars in the columns as well as SLAs as external energy dissipators at the joints. Parameters examined included the number of PT bars per column, initial post-tensioning force, and shear key locations in the footings and cap beam. The OpenSees model, built with trilinear rotational springs at each joint, matched the experimental results within 5.0% for peak lateral force, 6.2% for hysteretic energy, and 9.0% for initial stiffness and effectively captured the rocking behavior. The OpenSees model was used to determine the cyclic performance and residual displacements of the experimental two-column bridge bents at high drift ratios near collapse. Once the 3D FEM was developed, it could be used to generate moment–rotation backbone curves for a wide range of other configurations by changing the geometry, number of PT bars, or material properties. The OpenSees model was subsequently used to perform a parametric study for different column dimensions, axial load levels, and post-tensioning levels.