Axial compressive behavior and capacity prediction of concrete-filled cold-formed lipped channel PEC stub columns

The stability and capacity of thin-walled steel columns can be considerably upgraded by filling concrete into hollow spaces surrounded by cold-formed lipped channel (CLC) and external battens. However, there is limited experimental data available, especially for the axial compression behavior of concrete-filled CLC partially encased composite (PEC) columns. This paper aims to investigate the compressive behavior of CLC-PEC short columns and presents an analytical model for predicting the axial capacity of the column. The study explores the influences of cross-sectional dimensions and external batten plate configurations on the compressive performance of CLC-PEC columns through axial compression tests conducted on 12 short column specimens. The results indicate that the failure modes of the specimens involve localized concrete spalling on the exposed side at the lower part of the column, along with a elephant foot-shaped buckling of the cold-formed steel lipped channel. The damage surface of the confined concrete was obtained by circumferential cutting of the buckling location. The findings highlight the significant influence of the character of the CLC section on the ineffectively confined area at the failure surface, with a dumbbell-shaped effective confinement zone revealing the presence of a highly confined area. Based on the calibrated failure surfaces, a numerical model-based study of the axial stress distribution in the concrete core was then carried out to estimate the confinement effect of the columns under peak loading. The study employed multiple regression analysis to quantify the area ratio of the confined zone to the concrete core based on finite element analysis (FEA) results from 143 CLC-PEC columns. The proposed model was evaluated against test results and found to be more reliable than axial compression loads based on the superposition strength method. The proposed axial capacity of short columns takes into account the slenderness ratio of each member.