Experimental investigation of bond and tube thickness effect on the flexural behavior of concrete-filled FPR tube under lateral cyclic loading

The effect of bond and tube thickness on the flexural behavior of concrete-filled fiber reinforced polymer tube (CFFT) are investigated experimentally in this research. Two different kinds of tubes were used in this research, pultruded tubes and filament winding tubes. Two full scale CFFT column specimens are tested under lateral cyclic load only to study the effect of bond between the concrete core and the tube internal surface under lateral cyclic load only. One of them was prepared with sand-coating on the internal surface of the tube and the other specimen was kept without sand-coating. The CFFT columns were embedded 500 mm into a rigid square reinforced concrete footing with 1200 mm side dimension and 800 mm depth. The two specimens are pultruded FRP tubes having the same mechanical properties and 305 mm exterior diameter. Another two full-scale CFFT columns were reinforced with steel reinforcement and were fabricated with tube thicknesses of 4 mm and 8 mm. These two column were tested to study the tube thickness effect. The columns were embedded 400 mm into rigid reinforced concrete footings, which were anchored to the laboratory floor. The columns were loaded under a constant axial load and lateral cyclic load. These two columns are filament winding FRP tubes were manufactured in the Composite Material Reinforcement Laboratory of the Sherbrooke University with the same interior diameter 324 mm and with two different thicknesses 4 mm and 8 mm. The results indicate a significant improvement in the full composite action of CFFT in terms of flexural capacity and stiffness due to the sand-coating. The increasing of the tube thickness delays the yielding of steel and increases the ultimate flexural capacity of the CFFT. Keywords: Bond, Sand-coating, Flexural behavior, Fiber-reinforced polymer, Concrete-filled FRP tubes, Lateral cycli