A Practical Model for Beam-Column Connection Behavior in Reinforced Concrete Frames

Traditional as well as performance-based seismic design requires accurate simulation of building response to determine component deformation and load demands. This is particularly challenging for reinforced concrete structures in which concrete cracking prior to yield may change component stiffnesses substantially and for existing concrete structures in which inadequate design details may result in component strength loss prior to yield. In this study analytical models, which are practical for use in design and compatible with commercial software such as SAP2000, are developed for one type of concrete component: planar interior beam-column joints. A dataset comprising 45 joint sub-assemblage tests is used for model development. First, a simple, center-line model is proposed for elastic analysis in which the beam-column joint region is modeled as semi-rigid. Experimental data are used to determine the joint stiffness that minimizes the error in predicted inter-story drift and the new ASCE 41 recommendations are evaluated. A second model is developed for use in a nonlinear pushover-type analysis. For this model, joint flexibility and beam flexural response are represented by plastic hinges at beam ends. A simple empirically-based model is used to determine, on the basis of joint shear stress demand and bond stress demand within the joint, if system response will be ductile or brittle. A joint shear strain limit determines when strength loss will occur in brittle joints. For ductile joints, the behavior of the sub-assemblage is dominated by the nonlinear response of the beams.