Flexural Behavior Of High Strength Concrete Beams Reinforced With BFRP Bars And Steel Fiber

Basalt fiber reinforced polymer(BFRP)bar is an environment-friendly composite reinforcement with high strength,corrosion resistance,electrical insulation and superior cost performance.The combination use of BFRP bar and steel fiber in concrete structure will reduce the weight and restrain the development of crack and deformation,as well as increase the ductility,bearing capacity and durability of the structure.The addition of steel fiber only in partial depth of cross section of BFRP bar reinforced concrete structure will achieve the above advantages and reduce the cost of construction.It has a certain application prospect.In this thesis,a total of 18 beams,in which including 1 high strength concrete beam reinforced with steel bars and steel fiber,1 high strength concrete beam reinforced BFRP bars and 16 high strength concrete beams reinforced with BFRP bars and steel fiber,were prepared and tested under four-point-bending.The flexural behavior of fully and partially steel fiber reinforced high strength concrete beams reinforced with BFRP bars was studied.The influences of steel fiber volume fraction,thickness of steel fiber reinforced concrete layer and FRP reinforcement ratio on the failure modes,flexural capacities,load-deflection curves,service loads,load-maximum crack width curves,average crack widths,deviations of crack widths,and ductility of high strength concrete beams reinforced with BFRP bars and steel fiber were discussed.The calculation methods of flexural capacity,stiffness and crack width of high strength concrete beams reinforced with BFRP bars and steel fiber were proposed.The main research contents and achievements are presented as follows:(1)Study on the failure mode and calculation method of flexural capacity of high strength concrete beams reinforced with BFRP bars and steel fiberThe failure modes of high strength concrete beams reinforced with BFRP bars and steel fiber were FRP bar rupture,concrete crushing and balanced failure.The steel fiber volume fraction,thickness of steel fiber reinforced concrete layer and FRP reinforcement ratio had various influences on the failure mode.The flexural capacity can be increased by the addition of steel fiber in the full section of high strength concrete beams reinforced with BFRP bars.The addition of steel fiber only in the tension zone did not show a significant influence on the flexural capacity.The increase of FRP reinforcement ratio had a positive influence on the flexural capacity.(2)Study on the deformability and calculation method of stiffness of high strength concrete beams reinforced with BFRP bars and steel fiberThe service load of high strength concrete beams reinforced with BFRP bars can be increased by the addition of steel fiber.The deflection of tested beam specimens can be restrained by the increase of steel fiber volume fraction,thickness of steel fiber reinforced concrete layer and FRP reinforcement ratio.When the thickness of steel fiber reinforced concrete layer is 0.57 times of the height of beams,the steel fiber produced a same effect on restraining deflection with fully steel fiber reinforced specimens.Based on the analytic and effective moment of inertia methods,calculation methods for predicting the stiffness of high strength concrete beams reinforced with BFRP bars and steel fiber were proposed.(3)Study on the cracking behavior and calculation method of crack width of high strength concrete beams reinforced with BFRP bars and steel fiberThe development of crack can be restrained by the increase of steel fiber volume fraction,thickness of steel fiber reinforced concrete layer and FRP reinforcement ratio.When the thickness of steel fiber reinforced concrete layer is 0.57 times of the height of beams,the steel fiber produced a same effect on restraining the development of crack with fully steel fiber reinforced specimens.A calculation method for predicting the crack width of high strength concrete beams reinforced with BFRP bars and steel fiber was proposed.(4)Study on the ductility of high strength concrete beams reinforced with BFRP bars and steel fiberThe addition of steel fiber in the full section of beam and increase of FRP reinforcement ratio produced positive influences on the ductility of specimens.However,the addition of steel fiber in the partial depth of beam produced a negative influence on the ductility.To restrain the development of deformation and cracking of FRP bar-reinforced concrete beams,increase the service load and decrease the cost of construction,partial steel fiber reinforcement was recommended.However,for the structures with high ductility requirements,full steel fiber reinforcement was recommended.