Stress-Strain Behavior of Confined Concrete during Cooling after Heating to High Temperature

The stress-strain behavior of confined concrete under heating and residual conditions has been preliminarily addressed in previous research; however, its behavior at subsequent cooling temperatures after being heated to peak temperature has yet to be thoroughly investigated.It is crucial for determining confined concrete structures' post-fire performance and burnout resistance.The paper presents the fundamental behavior of the confined concrete constitutive parameters and stress-strain curve at subsequent cooling temperatures after being heated to peak temperature.The study includes the stress-stress relationship of a 200 mm diameter cylinder with two distinct confinement spacings of 60 mm and 120 mm.The constitutive parameters for confined concrete were initially determined for a peak heating temperature of 750 C and then modified to establish the stress-strain relationship for successive cooling temperatures of 500 C, 250 C, and ambient temperature.The study results show that confinement has a considerable impact on compressive strength, stiffness, and ductility at ambient and fire conditions.After being heated to peak temperature, the confined concrete compressive strength recovers during successive cooling temperatures, with the recovery dependent on confinement spacing.The established stress-strain relationship can assist in better comprehending structural performance and capacity degradation for different tie spacings, and is useful for the analysis and design of confined RC (reinforced concrete) elements during and after a fire.