Seismic performance of full-scale reinforced concrete columns

The deformation capacity of a concrete column can be expressed by using different ductility parameters such as curvature ductility, displacement ductility or drift capacity. However, little research has been conducted into the relationship among different ductility parameters. The objectives of this research are (1) to investigate the relationship among various ductility parameters by considering the effects of shear spanto-depth ratio and axial load level and (2) to develop methods and procedures that can be used to estimate the deformation capacity of reinforced concrete columns. Five full-scale reinforced concrete columns were tested at The University of Texas at Austin. Test results indicated that the shear span-to-depth ratio and axial load level were important parameters influencing the relationship among various ductility parameters. Measured plastic hinge lengths of column specimens were also affected by the shear span-to-depth ratio and axial load. The plastic hinge length of concrete columns was investigated by studying the compressive strain profile of the core concrete. An analytical procedure was used to study the effect of various parameters on plastic hinge length. Based on the results of the experiments and a parametric study, a new expression that can be used to estimate plastic hinge lengths was proposed. Two methods that can be used to predict the deformation capacity of reinforced concrete columns were developed. One of these methods can be considered as a state-ofthe-art analytical method, which employs various phenomenological models for confinement of concrete, reinforcing bar buckling, reinforcing bar slip and shear deformations. The other method consists of simple expressions derived by studying the lateral load response of columns as influenced by the P-Δ effect. The use of the rigorous analytical method provided reasonably accurate estimates for the deformation capacity of over one hundred columns tested by various researchers. The use of simple expressions, on the other hand, traced the lower-bound of the measured drift capacities of these columns. The simple expression is recommended for use in performance-based design of reinforced concrete columns.