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 re-inforcements 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.