Plastic Hinging Behavior of Reinforced Concrete Bridge Columns

Abstract

The location of inelastic deformations in reinforced concrete bridge columns has been examined to simulate the nonlinear response of bridge columns and estimate the ultimate displacement capacity. In bridge columns, these nonlinear deformations generally occur over a finite hinge length. A model of hinging behavior in reinforced concrete bridge columns will help guide proportioning, detailing and drift estimates for performance-based design. Data was collected during the NEESR investigation of the seismic performance of four-span large-scale bridge systems at the University of Nevada Reno that details deformations in column hinging regions during response to strong shaking events. In order to evaluate the plastic hinging regions, a photogrammetric method was used to remotely track deformations of the concrete surface in the joint regions. The surface deformations and rotations of a reinforced concrete bridge column under dynamic loading has been examined and compared with the results obtained from traditional instruments. This research utilized the experimental data from photogrammetry measurements of bridge column deformations to create a finite element model that realistically represents hinging behavior in a reinforced concrete bridge pier. The three dimensional finite element model of one column was defined with the cap beam on the top of the column and the footing system under the circular column using ABAQUS Finite Element software. The results of the FE model of the bridge column under dynamic loading were obtained and compared with the photogrammetric measurements as well as the data from the traditional instrumentations. Two plastic hinge length expressions for reinforced concrete bridge columns under static and dynamic loadings have been developed by studying the available test results in the literature. Many of the previous tests were conducted using the static loading and for small-scale components. A few of the tests focused on bridge columns and dynamic loading. Expressions that have been developed to estimate the plastic hinge lengths have either been based on the maximum drift at the top of the column, or the spread of plasticity in the hinging regions. An expression to calculate the maximum drift capacity of a bridge column in double curvature has been derived by considering the deformations due to flexure as influenced by the definition of plastic hinge length (lp), and the bond-slip effect of the longitudinal reinforcement at the connections. Drift capacity of a bridge column, which corresponds to a 20% reduction in lateral load capacity on the descending branch of the response backbone curve, has been estimated using the new expression and compared with the results that were obtained from the earlier plastic hinge length expressions. The measured drift of the bridge column from the four-span large-scale bridge system test was also compared with the calculated responses from the expressions. The proposed equations provide the best estimate of plastic hinge length for reinforced concrete bridge columns.