Effect of structural damage on the thermal response of CFST columns

Concrete-filled steel tubular (CFST) members are efficient structural members which are currently increasingly used in the construction industry. Under multi-hazard loading conditions, columns are often subjected to structural damage followed by thermal loading due to fire. This article studies the effect of mechanical damage on the thermal response of CFT columns through a detailed experimental program. Circular and square stub CFST columns were subjected to structural damage by applying axial compression and eccentric compression loading. The columns were loaded to three different levels of damage: (a) no mechanical loading, (b) loading to a maximum deformation of 10 mm at the ends, and (c) loading to a maximum deformation of 19 mm at the ends, respectively. The concentric compression (CC) and eccentric compression (EC) loading were done in a displacement-controlled manner. The corresponding deformation field in the steel tube was recorded digitally using the digital image correlation (DIC) technique. Subsequently, the specimen was unloaded and heated by placing them in a furnace. The temperature in the furnace cavity followed the ISO-834 standard fire curve for 1-hour followed by 2-hour cooling. The insulation effect of the gap created between the steel tube and concrete core, as well as increased resistance to the heat flow due to the development of cracks in concrete, is critical for predicting the temperatures inside the concrete core.