Confinement mechanism of cross-shaped steel reinforced concrete columns

A novel confined concrete constitutive model for steel-reinforced concrete (SRC) columns with cross-shaped steel (CSS) sections is proposed. The model is based on the similar characteristics of descending branches in the stress–strain curves of confined and unconfined concrete (UCC), considering confinement degradation caused by buckling of the steel section or longitudinal reinforcement. The confined region of SRC columns with CSS sections was divided into four parts: highly steel-confined concrete (HSCC), partially steel-confined concrete (PSCC), stirrup-confined concrete (StCC) and UCC. Relevant effective confinement coefficient expressions were also derived. Simulations of existing tests showed that (a) the load–strain curves obtained using the modified stress–strain constitutive model agreed well with the experimental results, with the error in the descending branch less than 5%; (b) the HSCC region for SRC columns with CSS sections in the finite-element model was in good agreement with that in the proposed region division; (c) the simulation of confined concrete region boundaries for SRC columns with CSS sections were determined using plumb lines for improving the calculation efficiency.