Analytical Element for Simulating Lateral-Strength Degradation in Reinforced Concrete Columns and Other Frame Members

Abstract

An analytical element is proposed that is capable of simulating the lateral-strength degradation behavior of frame members subjected to seismic loading up to severe loss in lateral strength. Although element capabilities allow simulating the behavior of a wide range of frame members exhibiting loss of lateral strength, they were developed with the behavior of shear-critical reinforced concrete columns in mind. The element consists of a zero-length shear spring that connects in series with a beam-column flexural element. The proposed element can dynamically monitor beam-column elements for user-defined limiting forces and flexural deformations, and initiate degradation when either is reached. Upon initiation of degradation, the material model governing the behavior of the zero-length shear spring changes its constitutive properties to include pinching, strength degradation, and stiffness degradation. Cycle-, energy-, and displacement-based damage accumulation methods were implemented to provide users with the necessary tools to model a variety of frame members. A novel flexural-deformation compensation algorithm was implemented in the element that automatically adjusts the shear-spring stiffness and backbone curve such that a symmetric member response is achieved. The versatile element is shown to possess the necessary capabilities to simulate the nonlinear shear behavior and strength degradation of select reinforced concrete columns with only a limited number of parameters calibrated.