Experimental and numerical investigations on seismic behavior of circular tubed reinforced concrete column to RC beam frames

The tubed reinforced concrete (TRC) column is a special kind of concrete-filled tube (CFT) column where the steel tube is disconnected at the beam–column connection, thereby not directly carrying the axial load while maximizing the confinement effect. Extensive research has been conducted to study the static and seismic performances of TRC columns and their mechanical properties. However, little attention has been paid to study the whole structural system containing TRC columns. To fill this lacking information, an experimental program on the seismic behavior of circular tubed reinforced concrete (CTRC) column to reinforced concrete (RC) beam frames (CTRC frames) was presented in this study for the first time. Two half-scale two-story CTRC frames, with two bays in each frame, were designed and tested under quasi-static loads. The first frame has strong columns and weak beams; while the second frame has rather weak columns and strong beams, implying that plastic hinges may form in the columns under seismic action. The test results indicate that both frames are sufficiently ductile to effectively dissipate energy. However, for the second frame, more severe damages of beams and columns in the first floor were observed, resulting in the instability of the overall frame. A fiber-based finite-element model is established using OpenSees; and the numerical results are generally in good agreement with the test results. Utilizing the numerical model, a parametric study is conducted and the preliminary design suggestions on TRC frames are proposed.