Confinement mechanism and constitutive model of SRC columns with cross-shaped steel sections

This paper proposes a novel confined concrete constitutive model for steel reinforced concrete (SRC) columns with cross-shaped steel (CSS) sections based on the similar characteristics of descending branches in stress-strain curves of confined and unconfined concrete, by considering confinement degradation caused by the buckling of steel section or longitudinal reinforcement. The confined region of SRC columns with CSS sections was divided into four parts: highly steel-confined concrete (HSC), partially steel-confined concrete (PSC), stirrup confined concrete (SCC), and unconfined concrete (UCC). Additionally, relevant effective confinement coefficient expressions were presented. Simulation results of existing tests showed that (1) load-strain curves obtained by using the modified stress-strain constitutive model agreed well with the experimental results, with the error in the descending branch smaller than 5%; (2) the HSC region for SRC columns with CSS sections in the finite element model (FEM) was in a good agreement with that in the proposed region division; (3) concrete confined region boundaries simulation for SRC columns with CSS sections were determined by using plumb lines for improving the calculation efficiency.