Axially loaded square CFST short columns strengthened with high-strength square steel tubes and concrete jackets

Abstract

This study investigated the axial compressive performance of square concrete-filled steel tube (CFST) short columns strengthened with high-strength square steel tubes and concrete jackets. 22 columns were tested: 1 reference column, 15 columns strengthened with high-strength steel tubes, and 6 columns strengthened with standard steel tubes. The test results showed significant improvements in the load-bearing capacity, ductility, and stiffness of the CFST columns after strengthening by high-strength steel tubes. For strengthened columns, there was a general upward trend in the improvement of load-bearing capacity when Q460, Q550 and Q690 steel tubes were used for strengthening relative to the use of Q235 steel tubes. However, the specimens strengthened with Q690 steel tubes showed corner cracking during loading resulting in a lower increase in load-bearing capacity of some of their specimens than the specimens strengthened with Q550 steel tubes. Therefore, it is recommended to use high-strength steel tubes with strength grades of Q550 or lower for reinforcement projects. A finite element (FE) model was established and verified using the test results. The FE model showed that utilizing high-strength steel tubes enhanced the synchronization of displacements corresponding to the ultimate load of the original and post-cast concretes and improved the bearing capacity of both. Furthermore, a new formula was proposed to predict the load-bearing capacity of columns strengthened with high-strength steel tubes and concrete jackets. The results of this formula showed strong agreement with those of the experiment and FE model.