Flexural behavior of precast concrete-filled steel tubes connected with high-performance concrete joints

Precast concrete-filled steel tube (CFST) columns with connection joints are widely used in building structures, yet research on their flexural behavior when connected with various high-performance concrete (HPC) types is limited. This study presents experimental investigations on precast circular CFST columns subjected to flexural loading until failure. These CFST columns, encased in galvanized steel sheets (GSSs), are connected using HPC joints. Two types of HPC joints were tested: an engineered cementitious composite (ECC) and an ultra-high fiber reinforced concrete (UHFRC). Additionally, the study was conducted varying the development length of the reinforcement/concrete filler joint to 150, 200, and 300 mm. Results indicated that increasing the development length of the reinforcement and the connecting concrete joint enhances both the cracking resistance and load-bearing capacity of slender precast CFST columns with an intermediate joint. Moreover, the combination of GSSs with ECC and UHFRC connections enhances the load-bearing capacity, demonstrating performance comparable to that of a typical precast normal concrete control column without an intermediate connection. The experimental results revealed that ECC and UHFRC connections increased the performance by 11 and 17%, respectively, compared to the control column. Additionally, doubling the development length of the ECC joint improved the cracking force, ultimate force, elastic stiffness, and energy absorption by 20, 15, 133, and 64%, respectively, while UHFRC connections showed improvements of 10, 10, 82, and 94%, respectively.