Structural performance of reinforced concrete columns subjected to high-temperature and axial loading under different heating-cooling scenarios

High-temperature exposure can considerably affect the structural performance and load-carrying capacity of reinforced concrete (RC) structural elements, leading to a partial or total collapse. This study aims to characterize the structural behaviour of RC columns exposed to high-temperature (about 1150 degrees C) and axial load simultaneously subject to different heating-cooling scenarios. An advanced electric furnace and cooling system is developed to subject RC columns under constant axial loads to high-temperature effects in accordance to ISO 834 standard. In total 16 large scale tests are conducted on 250 x 250 x 1200 mm column specimens. The main parameters of the study are concrete strength (13.7 MPa and 41.4 MPa), heating time (30, 60 and 120 min) and cooling method (water-cooling and air-cooling). A continuously high-temperature exposing scenario is also considered to represent a fire event with no-firefighting intervention. The changes in the stiffness and bearing capacity of the column specimens are investigated for each case. The results indicate that 120 min of high-temperature exposure could reduce the axial load carrying capacity of the specimens up to 9.5% and 35% using air-cooling and water-cooling systems, respectively. It is also shown that the normal and low-strength column specimens experienced a sudden lost in their load-bearing capacity after 210 and 240 min of continuous high-temperature heating, respectively, leading to collapse. The experimental results are then used to develop detailed non-linear finite element (FE) models in ABAQUS as practical tools for the design and assessment of RC columns exposed to high-temperature and axial loading using different cooling methods.