Experimental evaluation and theoretical analysis of the effective flexural stiffness of reinforced CFFT columns

This research work presents new design equations to adequately determine the effective flexural stiffness (EIe) of concrete-filled fiber-reinforced polymer (FRP)-tubes (CFFTs) columns. Based on an experimental parametric study and theoretical simulation, factors influencing the effective stiffness of reinforced CFFT columns are discussed. The main variables considered are: the axial load ratio (P-u/P-o), the eccentricity to diameter ratio (e/D) and the slenderness ratio am. Approximately 3,400 reinforced CFFT columns with different combination of specified variables, in symmetric single curvature bending were simulated to generate the stiffness data. Extensive comparison for the proposed stiffness expressions is made with the results of 74 experimental tests conducted by the authors and others. It is shown that the proposed stiffness equations have a good correlation with the test results. The proposed equations are applicable for any load levels including both service and ultimate loads. Since the proposed expressions give a realistic representation of the actual column behavior, they are recommended for general use in the design of FRP-confined concrete columns under different load levels.