Assessment on the seismic performance of circular tubed reinforced concrete column to steel beam frames using numerical modeling

Tubed reinforced concrete (TRC) is an innovative steel-concrete composite structure in which the steel tube acts as the transverse confinement rather than directly carries the axial load. To study the seismic performance of TRC columns in high-rise buildings, the static and dynamic analyses of the frames containing circular tubed reinforced concrete (CTRC) columns and steel beams were performed in this study. Representative frame analysis models with both the building height and the maximum elastic story drift ratio close to the code-specified limits were established using the software OpenSees. The effectiveness of the finite element model was verified through component and frame tests. The failure mechanisms, story drift ratios, and collapse margins of different frames were compared and analyzed, with the reinforcement ratio and column-to-beam strength ratio considered as the main parameters. In addition, the seismic behaviors of the frames containing CTRC columns (i.e., CTRC frames) were compared with those containing concrete-filled steel tubular (CFST) columns (i.e., CFST frames) under the same column steel ratio. It is shown that the load-bearing capacity, ductility coefficient, and collapse margin of a properly designed CTRC frame are similar to those of a CFST frame; and increasing the column reinforcement ratio is more effective in improving the load-bearing capacity and ductility of CTRC frames, compared with the use of thicker steel tubes. Moreover, when the CTRC frame is designed based on the lateral stiffness, its collapse margin is generally stable as the column-to-beam strength ratio decreases from 1.52 to 0.85. Based on the analysis results, suggestions on the seismic design of CTRC frames, including the allowable building height, maximum story drift ratio, and effective column section forms, are proposed.