Passive stress-strain model and ultimate strength prediction for short steel tube confined concrete (STCC) columns allowing for size effect

Steel tubes can significantly enhance the strength and ductility of concrete-filled steel tube (CFST) and steel tube confined concrete (STCC) columns. Existing research work have mainly focused on the former type while the later type of members not only avoid longitudinal steel bulking but also provide better ductility performance to resist seismic loads which is further investigated in this paper. Based on partial-interaction shear-friction mechanics, a passive stress-strain model for short steel tube confined concrete columns is proposed. The main benefit of the proposed model is that it is based on mechanics for rectangular and circular cross-sections which could allow for the size effect. Besides, this model also gives the ultimate strength of steel tube confined concrete columns and is further simplified as a design-oriented approach. The proposed passive stress-strain model and the simplified model for the ultimate strength of concrete columns show good correlation with experimental data. Compared with three other existing approaches, the simplified model could enhance the computing efficiency to a new level. Then a parametric study is conducted to investigate the effect of specimen size on the behaviour of steel tube confined concrete columns.