Analytical model for predicting axial capacity and behavior of concrete encased steel composite stub columns

The axial compressive capacity and force–deformation behavior of concrete encased steel stub columns were analytically investigated. An analytical model was developed for predicting the force–deformation response for composite stub columns with various structural steel sections and volumetric lateral reinforcement. Constitutive relationships were established for materials used in the composite cross section, which included unconfined concrete, partially and highly confined concrete, structural steel section, and longitudinal reinforcing bar. The axial capacity of composite stub columns can be determined from strengths contributed from each material component following the stress–strain relationship. Analytical results show that the axial load-carrying capacity and force–deformation behavior measured in the experiments can be accurately predicted. In addition to the lateral reinforcement, the structural steel section can provide a confinement effect on the concrete and enhance the axial capacity and post-peak strength.