f Ghobadi - PhD student, Department of Civil Engineering, University of Tabriz, Tabriz, Iran
G.R Abdollahzadeh - Associate Professor, Department of Civil Engineering, University of Babol, Babol, Iran

Due to the presence of the FRP tube, current design methods for concrete-encased steel columns are not applicable to FRP-encased steel-concrete composite columns. An analytical model is developed to predict the behavior of the composite column for various slenderness ratio values. This article presents three areas: (1) analysis methods of composite columns; (2) prediction methods for the mechanical behavior of columns; (3) mathematical representations of the axial force–strain curve. a new exponential model to depict the behavior of composite column is proposed. The parameters of the model are generated from dimensional details of the column, as well as the material properties. Predicted values are found to be in good agreement with the experimental results from tests of six columns ranging from 500 mm to 3000 mm in height. Modeling of columns using the proposed mathematical model can give crucial beforehand information, and overcome the disadvantages of time consuming workmanship and cost of experimental studies.

axial force–strain curve, Component model, Composite columns, Mathematical modeling