Mechanical Properties of Steel-Reinforced Reactive Powder Concrete Columns with Different Geometrical Dimensions After High-Temperature Exposure

This paper mainly discusses the mechanical characteristics of steel-reinforced reactive powder concrete (SRRPC) columns with different geometrical dimensions after high-temperature treatment. The bearing capacity, axial stiffness, and ductility of 35 SRRPC column specimens after high-temperature treatment are investigated, considering two parameters: concrete cover thickness (30–100 mm) and slenderness ratio (3–50). The findings indicate that (1) the ultimate bearing capacity increases by 26.0–135.7% as the concrete cover thickness increases and decreases by 1.5–92.0% as the slenderness ratio increases. (2) The axial stiffness increases by 18.9–92.5% as the concrete cover thickness increases and sharply decreases by 31.9–92.6% as slenderness ratio increases, and change degree decreases. (3) As concrete cover thickness and slenderness ratio increase, the displacement ductility coefficient declines, and degree of decrease in displacement ductility coefficient becomes progressively smaller. (4) The bearing capacity, stiffness, and ductility are extremely sensitive to concrete cover thickness, followed by slenderness ratio. Considering confining effect of stirrups and section steel on concrete in the core area, methods for calculating bearing capacity after high-temperature treatment are proposed. From the perspectives of preventing buckling instability and cracking of components after high temperature, two methods for determining the critical concrete cover thickness are given. Finally, the calculation formula of the stability coefficient corresponding to various slenderness ratios after high-temperature exposure is provided, which provides a reference for postfire evaluation and reinforcement of SRRPC structure.