Experimental Study On The Mechanical Behavior Of Concrete Beams Prestressed With FRP Bars

In commom reinforced concrete structures,the tensile strength of concrete is low,the crack resistance is poor,the fatigue performance of internal reinforcement is poor and easy to corrode,these factors restrict the durability of the structure in complex environment to a certain extent.Compared with traditional reinforcement,carbon fiber composite reinforcement(referred to as CFRP reinforcement)have the unique advantages of light weight,high strength,fatigue resistance,corrosion resistance and easy processing,so they are espected to be reforced bars and has a broad application prospect in architecture,bridges,seaports and national defense construction.However,because of its low elastic modulus and poor bond performance with concrete,carbon fiber composite reinforcement has large deflection deformation and rapid crack development in service,which can not meet the requirements of production and life for structural performance.The prestressed concrete structure can improve the crack resistance and control the deformation development of the components by applying the preloading stress to the concrete in advance.Therefore,the application of carbon fiber composite reinforcements in prestressed concrete structures have become an important research of fiber composite materials popularization and application.Compared with the post-tensioning method,pretensioned method has the advantages of simple working procedure,saving steel,economical mass production,small deflection deformation in service,and great engineering advantage.At this stage,scholars at home and abroad pay more attention to the mechanical behavior of external prestressed components and post-tensioned prestressed components,as well as the reinforcement of prestressed composite materials.However,there are few studies on the mechanical properties,especially the fatigue properties of pretensioned prestressed composite reinforcements.Therefore,the experimental study on the static and fatigue properties of pretensioned prestressed composite reinforcements is of great significance to promote the engineering application of the new pretensioned prefabricated components.In view of this,we carried out an experimental study on the static and fatigue properties of prestressed composite reinforced concrete structures.Main research contents and conclusions are as follows:(1)The experimental study on the shear behavior of the interface between additional ribs and composite reinforcements was carried out.The interface properties between additional ribs and composite reinforcements of different specifications were tested.We studied the effects of aluminum alloy tube length,wall thickness and extrusion amount on the shear properties of composite steel-additional ribs interface and selected the additional rib specifications with better performance in order to provide reference and guidance for the Anchorage setting of additional ribs in post-prestressed composite reinforcements beams.(2)The load holding test of the pre-tensioned anchor developed by our research group was carried out,and the test results show that the anchor has good stability and can meet the requirements of long-term load holding,and then through the prestress transfer length test after tension we obtained the law of the variation of prestress transfer length with the level of prestress(3)The bending bearing capacity of pretensioned prestressed composite reinforcements was tested.The stress process,crack development,failure characteristics,ultimate bearing capacity,bond slip between composite reinforcement and concrete,anchoring effect of additional ribs and so on of the pretensioned prestressed composite reinforcements were studied and analyzed.The test results show that the improvement of prestress performance can effectively control the development of deflection,restrain the development of cracks,and enhance the bending stiffness and crack resistance of members,and the additional rib anchoring on the composite reinforcements has little effect on the mechanical behavior of the test beam under static action.(4)The fatigue test and the static failure test after fatigue were carried out on the pretensioned prestressed composite reinforced components.We focused on the failure characteristics,loading and unloading stiffness degradation,deflection deformation,bond slip between composite steel bar and concrete and so on,then studied the indexes of the static test of some components after fatigue.The test results show that under normal stress amplitude,the fatigue performance of prestressed members is excellent,which circulates to 1 million times without failure.And the additional ribs can effectively improve the anchoring performance of composite tendons and reduce the bond slip of composite reinforcements in the fatigue process.