Abstract: According to the combined analysis with the actual situation that a large number of deleterious concrete bridges which require strengthening, and the bridge mainly suffer fatigue loading, the fatigue life and stiffness degradation rate of basalt fiber reinforced concrete beams strengthened with different layers of basalt fiber are studiedunder constant and variable amplitudes fatigue loading. Research results demonstrates that: (1)Under constant and variable amplitudes fatigue loading, compared with RC beams strengthened with one layer of BFRP sheets, fatigue lives of RC beams strengthened with two and three layers of BFRP sheets are increased by 20% and 40%, separately. With the same BFRP sheets reinforcement layers, fatigue lives of the strengthened RC beams under variable amplitude fatigue loading are reduced by 16% than those under constant fatigue loading. (2) Variable amplitude fatigue loading can fasten steel bar strains and middle span deflections of beams. The curve of the middle span deflection and fatigue times is obviously "concave" shape. (3) The stiffness degradation rate of beams without BFRP sheets under constant fatigue loading is about 0.313 MN·m²/Million times, while the stiffness degradation rate of beams strengthened with one, two, three layers of BFRP sheets under constant fatigue loading is about 0.014 MN·m²/Million times, and the rate under variable amplitude fatigue loading is about 0.050 MN·m²/Million times. It demonstrates that pasting BFRP sheets reduces stiffness degradation rate of the beams, and variable fatigue loading significantly increased stiffness degradation rate of beams.

Key words: BFRP sheets, damaged RC beams, flexural fatigue, constant and variable amplitude, stiffness degradation rate