Experimental Study On The Flexural Behavior Of High Strength Concrete Beams Reinforced With Steel-CFRP Composite Bars

In recent years,the research and application of Steel-Carbon Fiber Reinforced Polymer(SCFRP bar)Reinforced concrete structures with strong corrosion resistance,obvious and stable "secondary stiffness" in corrosive environment(such as Marine construction)has been the focus of civil engineering.However,high strength concrete can significantly reduce the size and dead weight of components,and has the characteristics of high strength and early strength,etc.The application of high strength concrete components with SCFRP bars in Marine engineering construction has been a trend.This paper focuses on the calculation methods of normal section bearing capacity,yield load,ductility,crack width and deflection deformation of SCFRP bar reinforced concrete beams with high strength,so as to lay a foundation for the application of SCFRP reinforced concrete beams in marine engineering.The main conclusions are as follows:1.The stress process of SCFRP bar concrete beams is similar to the reinforced concrete beam,but its existence steel-core reinforced yield after strengthening phase,showed relatively good ductility features,SCFRP bar reinforced concrete beam accord with flat section assumption.2.Under the same concrete strength,the initial crack development height of SCFRP reinforced concrete beams is generally 50%?60% of the beam height,while that of CFRP bars is 80%,and the oblique crack of SCFRP bar reinforced low-strength concrete beams is more likely to have secondary horizontal cracks at the tensile longitudinal bars.When the SCFRP bars yield,the crack width of the test beam increases significantly,and the measured maximum crack width is about 2?3 times of the average crack width.And the crack width decreases with the increasing of steel content.3.The introduction of steel into fibrous materials can effectively improve the stiffness of concrete beams.Under the same conditions(0.6Mu),the mid-span deflection of SCFRP reinforced concrete beams is reduced by up to 37% compared with that of CFRP reinforced concrete beams.4.The shear failure and bending-shear failure of SCFRP bars reinforced concrete beams are mainly caused by the instantaneous slippage of the bars,the ultimate failure mode of the flexural member is changed by the slippage of the reinforcement.The increased stress causes the fiber to fracture in different degree,which causes the steel core strain to be larger than the outer fiber strain at the later stage of loading,at this point,it is not obvious that the ribs with SCFRP bars can not provide enough concrete holding force and damage of SCFRP bars.5.Through the steel core yield strain,the compressive strain of concrete in the compression zone and the height of the compression zone when the test beam is yielding are calculated,and then the yield load of SCFRP bars concrete beams and reinforced concrete beams are solved.The theoretical value of the yield load is in good agreement with the measured value.6.Considering the change of the elastic modulus before and after the yield of SCFRP bars,the theoretical formula of the bearing capacity of SCFRP bars reinforced concrete beams is derived,the ratio of calculated value to measured value is between 0.82 ? 1.20.Considering the influence of potential slippage of SCFRP bars on the calculation of deformation and safety of members,and the damage caused by potential slippage of flexural members,two coefficients are introduced to modify the flexural capacity of SCFRP bars reinforced concrete beams,the ratio of theoretical value to measured value of bearing capacity is 90% ? 106%.7.Based on the technical specification for application of fiber-reinforced composite materials in construction engineering,considering the change of elastic modulus of SCFRP bar after its yield and its bonding performance with concrete,the non-uniform coefficient ?of tensile longitudinal bar between cracks is corrected,and the calculation formula of maximum crack width of SCFRP reinforced concrete beam is proposed.8.Based on the finite moment of inertia method,the short-term stiffness formula of SCFRP reinforced concrete beams is presented.The modified formula reflects the linearity of three sections of SCFRP reinforced concrete beams,and the modified formula is reasonable.