Predicting Strain Reduction Factor for Concrete-Filled FRP Tube Columns Incorporating Interface Gap and Prestress

This paper reports the findings from an analytical study into the influence of fiber reinforced polymer (FRP)-to-concrete interface gap and prestressed FRP tubes on strain reduction factor (k_ε) for concrete-filled FRP tube (CFFT) columns. A database that consists of a total of 45 aramid FRP- (AFRP) confined normal- and high-strength concrete (NSC and HSC) specimens with circular cross-sections is presented. All specimens were cylinders with a 152 mm diameter and 305 mm height, and their unconfined concrete strengths ranged from approximately 45 to 110 MPa. Analyses of the experimental databases that consisted of 22 specimens manufactured with FRP-toconcrete interface gap and a further 23 specimens prepared with lateral prestress is presented and discussed. Based on close examination of the hoop strain development on the FRP confining shell, expressions to predict strain reduction factors (k_ε) are proposed. The comparison of the proposed model predictions with the experimental test results of specimens prepared with an interface gap or prestressed FRP tubes shows good agreement.