Performance of lightweight coconut shell concrete-filled circular steel tube columns under axial compression

The current study aimed to use coconut shell concrete, a structural lightweight concrete, as an infill material in concrete-filled steel tube (CFST) columns and test it under axial compression. Testing was done on eighteen short, intermediate and long coconut shell CFST columns and six normal-weight CFST short columns for comparison. For both types of columns, the axial load-displacement curves and modes of failure were examined. By varying the length-to-diameter and diameter-to-thickness ratios, the axial capacity of steel tubes filled with coconut shell concrete was assessed. The composite action was verified from the results of the confinement index, strength index and the contribution of the coconut shell concrete as infill concrete. Structural efficiency and energy absorption of the lightweight CFST column was contrasted with its counterpart column. The contribution of coconut shell concrete to the strength of the CFST column was the highest at 61.36% and more significant than that of normal-weight CFST columns. The coconut shell CFST columns were 23.63% lighter than the normal-weight columns, contributing to its higher structural efficiency. These columns also had 8.12% more energy absorption than normal-weight columns. Hence, the results of this investigation revealed that coconut shell concrete has the potential to be utilized in CFST columns. Further, compared to the experimental ultimate loads, the predictions made by the existing codes, EC4 and ANSI/AISC 360 are conservative.