Combination of Bamboo Filling and FRP Wrapping to Strengthen Steel Members in Compression

This paper reports on axial compression experiments on 18 specimens that were strengthened using fiber-reinforced polymer (FRP) fabric and bamboo sticks to improve buckling resistance. The core steel members were first bundled with bamboo sticks longitudinally using steel wire and were then wrapped longitudinally and laterally with FRP fabric. The bending stiffness and load-bearing capacity of the members were increased by the strengthening system, and the bamboo sticks acted as lightweight and free-shaped filling between the steel and FRP. Three major parameters were examined: (1) the cross-sectional shape; (2) the nominal slenderness ratio of the steel members; (3) the number of FRP fabric layers. Although global buckling that is analogous to that in unstrengthened specimens was observed, the strengthened specimens exhibited significant local deformation at the end of the steel member and rupture of the FRP fabric at midheight. The load-displacement results demonstrated an increase of 25–114% for load-bearing capacity and a maximum increase of up to 6.7 times for ductility. The load-strain developments also evidenced a reduced effective compression stiffness of the strengthened section. Based on the test results, a calculation method for the load-bearing capacity of the strengthened specimens was proposed.