Modern-day structures using conventional concrete, which is tall and aesthetically pleasing is in need of torsional strengthening. The ability of a structure to withstand twisting forces about a longitudinal axis is called torsional strength. In this study, torsional behaviour of normal weight concrete (NWC) and lightweight concrete (LWC) is analysed. Coconut shell aggregate is used instead of broken granite to make lightweight concrete. Torsional strengthening is done using crimped steel fibres. A torsion-loaded member will result in torsional cracking commencing before the flexural failure, as the torsional strength is highly dependent on the tensile strength, which is the weakest component in brittle concrete. Steel fibres in optimum amount can impart homogeneous tensile properties in concrete, which in turn increases torsional capacity. Fibres are added in 0.5%, 0.785% and 1% by volume to both NWC and LWC. Basic mechanical properties such as compressive strength, split tensile strength and flexural strength are analysed using cubes, cylinders and prism for 7 days and 28 days. Torsional strengthening studies are carried out on beams of size 1100x150x100 mm. Comparative study of results in NWC and LWC is done with control mixes of corresponding mixes. Comparison between torsional behaviour of NWC and LWC is also done. Torque-Angle of twist responses of all mixes is also found. LWC showed more torque value and angle of twist than NWC. Steel fibres enhanced these properties in both mixes. © School of Engineering, Taylor’s University.