Analytical model for circular F-STC stub columns under concentric compression

The fiber reinforced polymer (FRP)-steel composite tubed (F-STC) column is characterized by high strength and deformability as well as the tube corrosion resistance provided by the FRP. This study aims to find a suitable analytical model for F-STC columns, based on the existing analytical models for confined concrete columns where each typically consists of the stress–strain relationship of actively confined concrete, a lateral strain equation, and the confining stress. A database of 66 tests (61 reported plus 5 added) is established and used to examine the existing analytical models. However, existing models fail to predict the initial stiffness of F-STC columns with lower diameter-to-thickness ratio of steel tube and the correct development of tube stresses. To this end, an incoordination coefficient of axial strains is proposed to account for the different axial strains between the steel tube and concrete. Lastly, after a close examination on the existing analytical models, a modified Teng’s model is proposed. The results predicted by the proposed analytical model generally match well with the test results of F-STC columns.