Investigation on axial compressive behavior of pentagonal section steel-reinforced concrete columns

Special-shaped steel-reinforced concrete (SRC) columns have been widely used in high-rise buildings, while research on the axial compressive performance of special-shaped SRC columns is limited. To address this issue, four pentagonal section SRC columns based on an actual engineering project were designed and tested to examine the failure mode, axial load-displacement response, bearing capacity, ductility, and restoration capacity. The effects of the steel section structure and concrete strength on the axial compressive performance of the pentagonal section SRC columns were investigated. The test results showed that the pentagonal section SRC columns exhibited great axial compressive performance, the SRC columns with distributed rectangular steel tubes connected by steel plates exhibited higher bearing capacity and ductility compared to those with separated rectangular steel tubes, and higher concrete strength resulted in higher bearing capacity but lower ductility. Considering the confinement mechanism of the steel section and stirrups to concrete, the concrete in the SRC columns was divided into three regions: unconfined concrete (UCC), partially confined concrete (PCC), and highly confined concrete (HCC). An analytical model was developed for predicting the axial load-displacement response of pentagonal section SRC columns based on the constitutive relationships for concrete in different regions. Furthermore, a finite-element (FE) model was developed and a parametric analysis was conducted using the verified FE model.