COMPARATIVE ANALYSIS OF AXIAL COMPRESSION PROPERTIES OF RECYCLED CONCRETE SHORT COLUMN FILLED CIRCULAR AND SQUARE STEEL TUBE AFTER BEING SUBJECTED TO HIGH TEMPERATURES AND WATER COOLING

In order to study the difference of axial compression properties of recycled concrete filled square(RCFSST) and circular steel tube (RCFCST) short column after being subjected to high temperatures and water cooling, 27 RCFSST and 27 RCFCST short columns were designed for axial compression test, with the variable parameters of recycled coarse aggregate replacement percentage, temperature and cooling method considered. The failure process of specimens was observed, and the mechanical properties such as bearing capacity, initial axial compression stiffness, ductility and energy dissipation capacity of the specimens were compared and analyzed. The results showed that the initial axial compression stiffness and energy dissipation capacity of RCFSST specimens were more affected by cooling method, while the bearing capacity and ductility of RCFCST specimens were more affected by cooling method. With the increase of temperature, the bearing capacity degradation, ductility change and energy consumption change of RCFSST specimens were more significant than that of RCFCST specimens. For the change of initial axial compression stiffness, when the temperature was lower, the degeneration of RCFSST specimens was greater, and when the temperature was higher, the degeneration of RCFCST specimens was greater. The change of the replacement percentage had a great influence on the bearing capacity of RCFSST specimens and initial axial compression stiffness of RCFCST.specimens With the increase of the replacement percentage, the ductility and energy dissipation coefficients of RCFSST specimens increased, while those of RCFCST specimens decreased.