Practical Modeling of Reinforced-Concrete Beam-Column Joints in Non-Ductile Structures

摘要

Behavior of beam-column joints can significantly impact seismic performance of concrete moment-frame structures. Models capable of predicting joint performance are needed in the design and evaluation of such structures. One method of modeling joints is to use rigid offsets at the ends of beam and column elements. Rigid offset joint models are provided in ASCE 41. Modifications to these models are proposed. Evaluation of joint behavior using existing and proposed offset models provides accurate prediction of story drift in the linear range of joint behavior. Yet moment frames behave nonlinearly during an earthquake and research has shown beam-column joints can contribute significantly to system flexibility. Identification of joint failure is critical to identifying structures requiring retrofitting, and cannot be achieved using offset models and linear analysis techniques. Models capable of capturing flexibility of joint behavior and failure of joints exist, but lack simplicity for implementation in commercial software. A nonlinear model is proposed that models joint behavior by modifying lumped-plasticity beam elements. Criteria are determined that identify joints as brittle or ductile based on joint shear stress demand and bond demand of beam longitudinal reinforcement within the joint.