The purpose this study is to produce square CFT columns that do not exhibit degrading behavior due to local buckling. From this, the authors thought placing steel tubes around the perimeter through grout on the critical sections of square CFT columns to suppress degradation behavior caused by local buckling. To further prevent an excessive increase in resistant load due to stiffening, internal voids decided to place within the filled concrete. Therefore, in this study, first conducted compression tests on these stiffened CFT short columns. As a result, the following findings are obtained. i) After reaching the maximum compressive strength, the stresses in the stiffened CFT remained as stable as those in the unstiffened CFT. ii) It is not possible to assess the degradation behavior of stiffened CFT solely for the maximum compressive strength and the compressive stress that stabilizes after reaching it. iii) To conduct a detailed examination of the effects of stiffening effect, it is necessary to improve the construction and quality accuracy of the grout.
