Research on Mechanical Properties of UHPC Encased CFSTs Under Eccentrically Compressive Loading

Ultral-high-performance concrete (UHPC) encased concrete-filled steel tubes (CFST) have advatages such as superior durability and high bearing capacity. Four CFST columns with varying eccentricity and slenderness ratios were experimentally tested to examine their mechanical properties. Based on the test results, the failure characteristics, load-deformation responses, ultimate eccentric bearing capacity, second-order effects, and ductility were investigated. The results revealed that the incorporation of steel fibers significantly reduced the failure degree of the outer UHPC, while the inner CFST offered the column specimens good ductility. It was noted that the eccentric bearing capacity decreased markedly with the increasing eccentricity, particularly in the range of 0－80 mm. Moreover, second-order effects had a substantial impact on the eccentric bearing capacity, contributing up to 36.5% of the total moment as eccentricity and slenderness ratio increased. The study’s findings were used to discuss the applicability of existing code provisions for calculating the eccentric bearing capacity of UHPC encased CFST columns.