Behavior of tee-section bracing members retrofitted with CFRP strips subjected to axial compression

This paper presents the behavior of steel tee-section bracing members retrofitted with carbon fiber reinforced polymer (CFRP) strips. The retrofitted sections are monotonically loaded in axial compression. Two numerical approaches, eigenbuckling analysis and nonlinear large displacement analysis, are conducted to predict the axial response of retrofitted sections; these are validated experimentally. A simple analytical model based on virtual work is developed to estimate the out-of-plane displacement of such FRP-retrofitted sections subjected to axial load. The parameters evaluated include the CFRP-retrofit scheme, geometric characteristics of the retrofitted sections, and material properties of the CFRP used. A case study is carried out to examine the effectiveness of the retrofit, based on the acceleration profile of the 1989 Loma Prieta earthquake. The slenderness ratio of the retrofitted sections in the weak axis significantly influence the load-carrying capacity and out-of-plane displacement of the members. The aspect ratio of the webs affects the stiffness of load-displacement (out-of-plane) responses. The CFRP strips reduce the stresses of the retrofitted sections up to 25% when compared to an unretrofit control section, in particular at the web-flange junction where critical hysteretic stress accumulation could occur under seismic loading. The CFRP-retrofit, however, may not be recommended for tee-section bracing members with a slenderness ratio greater than 60.