Experimental Study On Flexural Behavior Of Unbonded Partially Prestressed Concrete Beams With CFRP Tendons

In order to solve the problem of corrosion of steel,Fiber Reinforced Plastic(FRP) was introduced to the Civil Engineering as a new type of composite material,with its properties of light-weight and non- corrosive.When the FRP tendons was used in general concrete structures,due to the smaller elastic modulus,the deformation and the crack were difficult to control,material properties couldn't give full play,so we consider FRP tendons applied to prestressed concrete structures.CFRP tendons were high tensile strength,anti-corrosive and so on,but were weak shear strength and anti-squeezing,if using the traditional anchor directly,shear failure occurs in the tensile process,its high-tensile strength cannot be exploited.So the problem of prestressed FRP tendons anchor has become a constraint to FRP further application.In this paper,based on a large number of domestic and foreign research results,reseach the expansive cement steel sleeve bond-type anchor and extrusion-type anchor,and designed the matching tensioning device.Primary studies shown that the use of two kinds of anchors both can meet the requirements,the.extrusion-type anchor has better anchoring efficiency,it is worthy of further study,80% of the load was transferred to steel sleeve by expansive cement.The steel sleeve assumed a large load,so called for a higher bond length and wall thickness.In this paper, the use of reinforced unbonded tendons, the flexural properties of four post-tensioned concrete beams were studied, on the basis of analysis of the experimental data,the main research and achievements are as follows:1. CFRP tendons of unbonded prestressed concrete beams in accordance with the process by force of non-prestressed reinforcement are two different situations:(1)Non-prestressed reinforcement yield point for the ordinary steel, the load-deflection relaship is divided into three stages. From the beginning of the first stage of loading to the specimen cross-section cracking; From the section of the second stage of cracking in tension zone to the non-prestressed reinforcement yield, the deflection of the sample changed little; From the third phase of non-prestressed reinforcement to yield concrete compression zone of the sample was crushed, to speed up changes in specimen deflection, deformation larger, the specimen deformation is still larger after Concrete crushing.(2) Non-prestressed reinforcement is no obvious yield point of the fiber reinforcement, the load-deflection relaship is divided into two stages. From the beginning of the first stage of loading to the specimen cross-section cracking, From the section of the second stage of cracking to the concrete compression zone of the sample was crushed, reduced to speed up the specimen stiffness, the ultimate deformation of the sample is relatively large. Both cases, the specimen after the crack did not exist in significant yield stage.2.the mechanical properties,such as load-deflection curve,load-strain curve of prestressing tendon, load-strain curve of non-prestressed rebars, load-strain curve of concrete compression zone, strongly depend on the non-prestressed rebars of the mechanical properties of its own;3. Non-prestressed rebars can play the role of dispersed cracks,which was the impact of CFRP unbonded partially prestressed concrete beam cracks in the number, width and spacing of the important factors;4. Test results show that the use of FRP prestressed beams as a non-prestressed rebars play a better performance under the normal load, but also to meet the special requirements of the environment, it is worth further study.In addition, based on the analysis of experiment,we used commercial finit element software-ANSYS,nonlinear finite element simulation of prestressed concrete beams with unbonded prestressing CFRP tendens is accomplished.It is modeling method,selecting element,defining constitutive relationship of materials and solution method that are elaborated on in this paper. The analytical results of the prestressed beam specimens,such as ultimate load-carrying capacity, defleetion as well as stresses of prestressing tendons and steel rebars are in good agreement with the experimental results, which is to verify the correctness of the model,providing analysis tools for further research. Test results and studies obtained in this paper can provide scientific principles for CFRP unbonded partially prestressed reinforced concrete structure in the actual application,and in the further study of CFRP tendons have certain reference value.