Hysteretic behavior of circular tubed reinforced concrete column to steel beam frames

Abstract Tubed reinforced concrete (TRC) columns have good deformability and energy dissipation capacity under horizontal cyclic loads ; and even with plastic hinges formed at the column ends, the corresponding frame structure may still have sufficient inter-story deformation capacity. Extensive research has been conducted on the static and seismic performances of TRC columns. However, little attention has been paid to the structural system containing TRC columns. To overcome this shortcoming, an experimental study on the seismic behavior of circular tubed reinforced concrete (CTRC) column to steel beam frames (referred as “CTRC frames”) is described first in this study. Based on the previous studies on CTRC columns and joints, two double-bay two-story CTRC frames of 1/2 scale were designed and tested under quasi-static loading: one frame with stronger flexural strength in columns than the beams and the other frame is the opposite. The test results indicated that although the frame failed in column plastic hinge mode had the ductility coefficient of 3.56, a weak story with the maximum story drift ratio of 1/18 formed in this frame, which increased the collapse risk of the overall structure. Therefore, considering the unfavorable deformation mode , the column plastic hinge mode should be avoided in practical designs; and the control of frame deformation modes should be considered when proposing a suitable column-beam strength ratio for CTRC frames. A fiber-based element model using OpenSees software was developed, which showed a good agreement with the test results. Utilizing the numerical model, the affecting parameters to the hysteretic behavior of CTRC frames, such as the axial load ratio, concrete compressive strength , and column-beam strength ratio, were further investigated.