Fibre-reinforced polymer wraps for slender eccentrically-loaded reinforced concrete columns

Externally-applied circumferential fibre-reinforced polymer (FRP) wraps have proven to be an efficient and effective technique for repairing and strengthening structurally deficient reinforced concrete columns. Guidelines for the design of FRP-wrapped columns are currently available, and field applications of this technique have been successfully implemented worldwide. However, two significant issues that require additional research attention are eccentric loading and slenderness effects on FRP-wrapped reinforced concrete columns. The study presented herein investigates the performance of FRP wraps for slender and eccentrically-loaded circular reinforced concrete columns through an experimental investigation and associated analytical modelling.; The experimental investigation involves the testing of nineteen small-scale columns to failure under monotonic axial compressive load with a constant end eccentricity of 20 mm. The parameters studied include the slenderness ratio, the amount of FRP confinement, and the amount of additional longitudinal FRP wraps. Furthermore, the mechanics of confinement has been investigated by examining the hoop strain distributions in the FRP wraps.; An analytical model has been developed to generate axial load-moment interaction diagrams for short, circular FRP-wrapped columns. The model adopts a layer-by-layer approach assuming strain compatibility and material constitutive relationships to describe the stress-strain behaviour of the concrete, steel and longitudinal FRP in both tension and compression. The model also accounts for the effects of eccentric loading on the confinement mechanism. A very brief parametric study is included to study the effects of confinement and longitudinal FRP wraps on the predicted interaction diagrams.; A second analytical model was developed to generate column strength curves for FRP-wrapped columns. The model adopts an incremental stiffness approach which accounts for the decreasing axial and flexural stiffness of the member as load progresses. Again, a brief parametric study examines the effects of increased FRP confinement and longitudinal FRP wraps.; Overall, it is demonstrated that, although hoop FRP wraps can significantly enhance the strength and deformation capacities of circular reinforced concrete columns, these wraps are considerably more effective for strengthening short columns. In addition, it is shown that the application of longitudinal FRP wraps is an efficient and effective technique for improving the performance of slender FRP-wrapped columns.