Axial compressive behavior and design of high-strength square concrete-filled steel tube short columns with embedded GFRP tubes

This paper proposed a hybrid column by embedding glass fiber-reinforced polymer (GFRP) tube into high-strength square concrete-filled steel tube (CFT), named as high-strength square steel-concrete-GFRP concrete (SCFC) column. A total of 13 high-strength square SCFC short columns were tested. The test parameters included diameter and thickness of GFRP tube, width and thickness of steel tube, yield stress of steel, and compressive strength of concrete. Results showed that high-strength square SCFC short columns exhibited post-yield strengthening behavior and stable residual strength. The axial strength, confining effect, and ductility were improved because of the embedded GFRP tube. Detailed finite element models were developed and benchmarked to investigate the strength contribution of each component and conduct parametric studies. It was shown that: (i) the concrete infill and the steel tube contributed >90% to the overall compressive strength and (ii) the strength improvement by embedding GFRP tube was closely related to the section size ratio, confinement ratio of the GFRP tube, and confinement ratio of the steel tube. Evaluation of the current equations showed that they were not accurate enough to estimate the axial compressive strength of high-strength square SCFC short columns. New equations were then proposed.