Seismic performance of locally FRC replaced tied steel–concrete composite columns

The presence of both steel sections and reinforcement cages in traditional steel‐reinforced concrete (SRC) structures complicates construction, limiting its application and widespread adoption in engineering. Removing the reinforcement cage and replacing all normal concrete with ductile concrete can increase workability while ensuring structural ductility. However, this approach often results in high costs. In this study, a novel solution is proposed: using tie bars between the flanges of steel sections, a technique called tied steel, to replace the reinforcement cage in traditional SRC structures and replacing normal concrete only in the plastic hinge zone of the column, where large deformations occur, with fiber‐reinforced concrete (FRC). This forms a locally FRC‐replaced tied steel–concrete composite structure, combining workability, ductility, and economic efficiency. Two identical locally FRC‐replaced tied steel–concrete columns with the same structural details were manufactured, and pseudostatic loading tests were conducted along different axes of the cross section to evaluate the seismic performance of the new structure under varying seismic loading directions. Finite element simulations were performed to compare the seismic performance of locally FRC‐replaced columns with that of all‐concrete columns and to analyze the impact of localized FRC replacement on improving the seismic performance of tied steel–concrete columns. In addition, the effects of the axial compression ratio, presence or absence of tie bars, spacing of tie bars, and height of FRC replacement on the seismic performance of the new structure were investigated. The results demonstrate that the locally FRC‐replaced tied steel–concrete columns exhibit excellent seismic performance under seismic loads along different axes of the column section. Replacing normal concrete with FRC in the plastic hinge zone significantly enhances the seismic performance of the structure. Increasing the axial compression ratio reduces both the load‐bearing capacity and ductility of the structure. A larger FRC replacement height improves the structure's seismic resistance.