Strength of beam-column joint in soft first story RC buildings Part 1: Experiment

Abstract

This study describes the strength of reinforced concrete (RC) beam-column joints in buildings with a soft first story. In such buildings, the sections of first-story columns are usually much larger than those of second-story columns to prevent story collapse. To investigate the strength of the beam-column joints, four specimens are constructed and the test is conducted with two types of joints: 1) the first-story column is extended toward the inside of the building (I-type joint) and 2) the first-story column is extended toward the outside of the building (O-type joint). The test parameters are the hoops in the beam-column joint, beam reinforcements, stirrups in the beam, and axial force. The beam longitudinal reinforcements are effective to prevent the yielding of the beam reinforcements in both types of joint. Stirrups in beam and hoops in joint strengthen I- and O-type joints, respectively. The force-resistant mechanisms of these joints are different from those of usual beam-column joints because sign of the bending moment in the second-story column is the same as that of the first-story column. The failure modes of these joints are also different from those of the usual beam-column joints. Copyright © 2014 Japan Concrete Institute.