6. Conclusions
The compressive strength capacity of concrete-filled light gauge steel composite columns was experimentally determined in this study by testing fourteen stub columns and twelve full-scale columns. Results from the stub columns were used to assess the effect of confinement, local buckling, and individual contributions of the components to the axial capacity of the full-scale light gauge composite columns. The findings of this study are applicable to width-to-thickness ratio of the encasing steel section of 125. Further experimental studies are required to corroborate these findings for other widthto-thickness ratios. Two parameters were investigated in the stub column tests: concrete contribution including effect of confinement, and encasing steel contribution including local buckling. The test results demonstrated that the concrete strength was increased by approximately 16% due to the effect of confinement. The observed effect of confinement applied only to the stub columns that consisted of shorter encasing steel sections that were not subject to axial loading. The gain in strength due to confinement was negligible for the full-scale columns, where failure was localized at the ends of the columns (end bearing failure). Therefore, the beneficial effect of confinement should not be included in evaluating the strength of full-scale columns encased by light gauge steel. Results from the steel-only stub columns illustrated that local buckling controlled the strength of the steel sections when not restrained by the concrete core. The observed average strength capacity of the steel section was 33% of the tensile capacity of the section. The load capacity of the full-scale composite columns was proportional to the cross sectional area. Columns C12 and C18 sustained approximately double and triple the load of Columns C6. The compressive capacity of the full-scale columns was controlled by end bearing, which is a cross sectional limit state independent of length. The axial strength capacity of the concrete-filled light gauge steel full-scale columns was estimated with end bearing resistance as the limit state according to CSA A23.3-14 and the average strain of the light gauge steel section at mid-length. The calculations did not include any contribution from the internal steel reinforcing bars. The calculated strength capacities were in good agreement with those recorded. The calculated-to-recorded strength was 0.97. In addition, a preliminary limit on the contribution of the steel section of 33% of the yield capacity as observed with the steel-only stub columns was suggested. The predicted-to-recorded strength ratio was 0.94. The limit on the steel contribution provided satisfactory results; however, further testing and validation are required.
