The confinement effect of the shell on the axial strength of thin wall circular section concrete filled steel tubes

This study uses experimental, numerical, and finite element (FE) analysis to demonstrate the vertical load-carrying capacity of thin-walled circular section concrete-filled steel tubes (TCSCFST) with core concrete and thin-walled unfilled steel tubes (UF). According to the experimental results, the average load factor of the TCSCFST is NE = 4.92 and NE = 5.52, respectively, based on the theoretical value estimated by Eurocode-4, EN 1994-1-1 (2004) part 1-1 for specimens with heights of 320 and 315 mm. Additionally, according to the experimental testing results, the TCSCFS's axial bearing capacity is improved by an average load factor of NA = 4.92 and NA = 5.51 from the theoretical value calculated for 320 and 315 mm height using the American Institute of Steel Construction (AISC) design code. The experiment also reveals that, compared to the theoretical value calculated using the AISC design code, the core concrete's axial bearing capacity rises by a load factor of NCA = 26.68 and NCA = 34.01 for 320 mm and 315 mm height specimens, respectively. In order to know whether a core concrete or shell is highly enhanced by the confinement effect, a FE analysis investigation on TCSCFS and UF steel tube is undertaken. The FE analysis result shows that the axial bearing capacity of the core concrete is increased by a load factor of NCF,E = 13.63 and NCF,E = 13.10 for 320 and 315 mm height specimens, respectively, from the numerical value estimated by Eurocode-4, EN 1994-1-1 (2004) part 1-1. In addition, the axial bearing capacity of the core concrete is determined by FE analysis and also increases by a load factor of NCF,A = 21.40 and NCF,A = 20.38 for 320 and 315 mm height specimens, respectively, from the numerical value estimated by AISC. As per the study, the confinement effect of steel enhances the axial bearing capacity of the inner concrete and the shell; however, Eurocode-4, EN 1994-1-1 (2004) Part 1-1, and AISC design codes show more conservative values than the experimental and finite element analysis results.