Experimental and theoretical study on the eccentric compression performances of cruciform lower-longitudinal-reinforcements-ratio thin concrete encased steel column

In response to the development demands of prefabricated building systems featuring green, low-carbon, and high-efficiency construction, this study proposes a cruciform lower-longitudinal-reinforcement-ratio thin concrete encased steel column (C-LRTCES). Given that column components in actual frame structures typically behave as slender columns, the eccentric compressive capacity and stability are highly sensitive to the P-Δ effect, leading to complex mechanical behavior. To investigate the compressive mechanism of the column component under eccentric loading, the study were conducted eccentric compression tests and finite element simulations to evaluate the influence of key parameters including aspect ratio of the column limb, stirrup form, eccentricity ratio, and slenderness ratio. The load-displacement curves, load-strain curves, and typical failure modes under both small eccentric compression and large eccentric compression were analyzed. Based on the section internal force and the resistance ratio, two calculation methods for eccentric compressive resistance were proposed. The results indicate that the reasonable increase in the limb aspect ratio is an effective means of enhancing the load-bearing capacity of the C-LRTCES columns. The novel stirrup configuration exhibits a confining effect comparable to that of conventional closed stirrups. Under eccentric compression, the small-eccentricity specimens are dominated by compressive failure, while large-eccentricity specimens are characterized by tensile failure. It is recommended that the eccentricity ratio should be controlled within 0.6 in practical design. Under this condition, the columns exhibit satisfactory ductility and sufficient post-peak load-bearing capacity reserve. Based on the experimental and numerical simulation results, the existing code design methods were refined and improve. Both improved calculation methods demonstrate the good accuracy and can provide reliable references for practical engineering design.