Experimental study on seismic behavior of RC column-steel beam joints with whole column-section diaphragm

Abstract

RC column–steel beam (RCS) frame is one of the most popular hybrid structural systems. Multiple types of RCS joints have been proposed in the last few decades. To avoid undesirable bearing failure, complicated strengthening details were required in RCS joints, which caused difficulties in construction. This study proposed a whole column-section diaphragm type RCS joint with simple details. Compared to most RCS joints, the steel web was cut off at the beam-column interface in the proposed joint, which facilitated the arrangement of stirrups and concrete casting. Moreover, the bearing failure could be avoided since the bearing area of concrete was enlarged and the local bearing stress decreased, requiring no additional strengthening details. To investigate the seismic performance of the proposed RCS joint and the impacts of strengthening configurations, four interior joint specimens were designed, fabricated, and tested under cyclic loading. In addition, joint strengths were calculated using the existing methods. The test results showed that joint shear failure occurred in all specimens. The concrete within the hole in the diaphragm has limited influence on joint behavior. The force in flanges could be fully transferred to concrete through the dowel action of longitudinal reinforcements and friction between the diaphragm and concrete. The ductility of joints was significantly improved due to the confinement provided by face bearing plates (FBPs). The orthogonal FBPs could greatly increase the shear resistance of the joint. The predictions for joint shear strengths following the current calculation methods were significantly conservative. It confirmed that adequate shear capacity could be obtained although the simplified details were used. The conclusions of this research can provide a reference for the engineering application of the RCS hybrid frame.