Research on the Compression Bearing Capacity of Special-Shaped Steel-Concrete Columns

Conventional reinforced concrete exhibits weaknesses such as poor ductility, limited load-bearing capacity, and complex reinforcement detailing in beam-column joints. To expand its application scope, this study proposes two novel types of L-shaped and T-shaped concrete-filled special-shaped steel columns, with steel skeletons fabricated from either square steel tubes or H-shaped steel sections, based on built-up steel welding construction. A total of eight column compression tests were conducted under both axial and eccentric loading conditions. The main conclusions are as follows: All specimens exhibited failure modes characterized by external concrete cracking or spalling; axial compression specimens primarily developed vertical cracks, whereas eccentric compression specimens exhibited diagonal cracks. The use of normalized loads enabled comparison across columns with different numbers of limbs. The square steel tube columns demonstrated superior compressive performance compared to the H-shaped steel columns, with an average increase of 17.6%. Eccentric loading resulted in significant performance degradation across all four column types, with the T-shaped columns being particularly affected, exhibiting a 40.9% reduction in normalized load, while the L-shaped columns showed a relatively smaller reduction of 22.1%. Furthermore, a quadratic function fitting method was employed to analyze the stiffness degradation curves of all specimens, effectively capturing the stiffness degradation patterns with minimal dispersion and satisfactory fitting accuracy. Systematic parametric analysis revealed that the curve parameters are primarily governed by the initial stiffness and the displacement corresponding to complete stiffness degradation.