Plastic mechanism analysis of unstiffened steel I-section beams strengthened with CFRP under 3-point bending

This paper presents experiments and theoretical analysis of 16 steel I-section beams strengthened using externally bonded CFRP under quasi-static large deformation 3-point bending. The main parameters examined in this paper were the section and member slenderness and the location of the CFRP plates. The member slenderness examined in this paper was in the range of Le/ry=40–92. The section slenderness examined in this paper was in the range of b/tf=6.25–16.67. The CFRP plates were added either to the tension flange or both compression and tension flanges or even to the whole section including the web. An expression for the yield and plastic moments of the composite section were obtained by means of an equivalent thickness approach for the web and flange. The newly obtained strength results were compared against the present design rules in steel specifications. The CFRP increased the strength by up to 32% for compression and tension flange strengthening whereas the strength increased only by 15% for tension flange strengthening. The per cent increase in strength for short specimens was mostly affected by the section slenderness where the maximum gain was obtained for the semi-compact section. Plastic mechanism analysis was performed to predict the collapse curves. Good agreement was found between the theoretical and experimental post buckling load–deflection curves.