Stress paths of confined concrete in axially loaded circular concrete-filled steel tube stub columns

•Stress paths of confined concrete in the whole-section-loaded CFT columns and corresponding stress path effects are investigated.•The influences of column parameters upon the stress paths of confined concrete in whole-section-loaded CFT columns are different from those in concrete-loaded CFT columns.•The confinement effects of the concrete in whole-section loaded CFT columns are generally worse than those in concrete-loaded CFT columns.•For the confinement coefficient less than about 0.2, the confinement effects of the concrete in CFT columns under the two loading conditions are nearly the same.•A compressive strength model incorporating the stress path effect was developed for the confined concrete in CFT columns under two loading conditions. Previous study has suggested that the stress paths of confined concrete in concrete-filled steel tube (CFT) stub columns influence the compressive strengths of the concrete, which, however, is based on the test of concrete-loaded CFT columns. In this paper, to fully understand the compressive strength of confined concrete in CFT column, the stress paths of confined concrete in the whole-section-loaded CFT columns are investigated. A detailed parametric study is conducted on the stress paths and their corresponding effects on compressive strength. Test results suggest that the lateral stress of the concrete in a whole-section-loaded CFT column generally occurred in a later stage and less significant than that in a concrete-loaded CFT column. The compressive strength of confined concrete in the whole-section-loaded CFT column with a small confinement coefficient is path-dependent, and the confinement effect of the concrete is generally weaker than that in concrete-loaded CFT column. With the increase of the confinement coefficient, the compressive strengths of confined concrete in whole-section-loaded CFT columns become path-independent. Based on the test results, a compressive strength model incorporating the stress path effect is developed for confined concrete in both whole-section-loaded and the concrete-loaded CFT columns. Good agreement between the experimental results and the ones predicted by the model is found, indicating a high performance of the proposed model.