1 Experimental and numerical studies of reinforced concrete columns confined by circular steel tubes exposed to fire Faqi Liu a,b , Yuyin Wang a,b , Leroy Gardner c , Amit H. Varma d a Key Lab of Structures Dynamic Behavior and Control (Harbin Institute of Technology), Ministry of Education, Heilongjiang, Harbin, 150090, China b Key Lab of Smart Prevention and Mitigation of Civil Engineering Disasters of the Ministry of Industry and Information Technology, Harbin Institute of Technology, Harbin, 150090, China c Department of Civil and Environmental Engineering, South Kensington Campus, Imperial College London, SW7 2AZ, UK d School of Civil Engineering, Purdue University, West Lafayette, IN 47907, USA Abstract: Reinforced concrete columns confined by steel tubes, also known as steel tube confined reinforced concrete (STCRC) columns, are a kind of composite column in which the outer steel tube acts predominantly as hoop reinforcement. This is achieved by the provision of breaks to the longitudinal continuity of the steel tube. The compressive behavior and seismic performance of STCRC columns have been extensively studied in the past few decades. However, knowledge of the fire behavior of STCRC columns is very limited. Hence, experimental and numerical studies to investigate the response of STCRC columns under combined thermal (fire) and structural loading are presented herein. Four full-scale STCRC columns and one concrete-filled steel tubular (CFST) column were first axially loaded and then subjected to the ISO 834 standard fire until failure. The measured furnace temperatures, specimen temperatures, axial displacement versus time curves and fire resistance of the columns are presented and discussed. A nonlinear finite element model, employing a sequentially coupled thermal-stress analysis, was then developed in ABAQUS and validated against recent fire tests on STCRC columns and concrete-filled steel tubular (CFST) columns reported in the literature. Following extensive parametric studies, a simplified method is proposed for predicting the temperatures of the steel tube, the reinforcing bars and the concrete. Design rules are then proposed for predicting the load-bearing capacity of STCRC columns exposed to the ISO 834 standard fire,