Study On The Ductility Of Prestressed FRP-reinforced Concrete Beams With The Compression-yielding Block

The Fiber reinforced polymer(FRP)bars have the advantages of light weight,high strength,and corrosion resistance.Using FRP bars as reinforcing materials for concrete structures can effectively solve the durability problems associated with corroded reinforcing steel bars.The prestress on the FRP bars can postpone the crack control the deformation of of the elements.As a consequence,the service performance of the FRP-reinforced concrete beams is largely enhanced.However,the prestree will furture weaken the ductility of the FRP-reinforced concrete beams due to the linear elastic stress-strain behavior.This makes it difficult to conform to the requirement in the correspondding code in terms of ductility.In order to improve the ductility of prestressed FRP-reinforced members,a new method is proposed called compression yielding theory,in which a high ductility compression yielding(CY)block place in the compression zone of maximum bending moment to enhance the ductility of the entire component.The final failure of the member is achieved by the yielding or breaking of the CY block and thereby improving the ductility of the entire member.To verify the feasibility,this paper systematically studies the ductility of prestressed FRP-reinforced concrete beams with CY blocks.The specific contents of the study are as follows:(1)The development of the CY block.the compression test of 13 steel fiber concrete blocks was carried out for different reserved holes,in which steel fiber content is about 10%.The compressive capacity,failure mode,and deformation capacity of each test block were studied.The test results show that the reinforcement of steel cage has no effect on the ductility of steel fiber concrete block;the provision of reserved holes has a very obvious effect on the ductility of steel fiber concrete block.When the porosity of the reserved hole is 3%~ 4%,high ductility can be obtained on the basis of ensuring sufficient yield strength of steel fiber concrete blocks.(2)The development of the pre-tensioned concrete prestressed with CFRP bars(PCPC).In this paper,The pre-stressed construction process of 10 mm carbon fiber composite material was carried out,and the pre-stressed composite material pre-tensioned method was proposed.PCPC was successfully produced by this process.(3)Study on the PCPC beams configured with the CY block.Based on the aforementioned woks,an experimental study on static bending performance of the eight beams was conducted.The variables included in the eight beams were: the type of the prestressed beams(pre-tensioned prestressed beams and near-surface mouted pre-tensioned prestressed beams),the prestress level,construction features of the CY block as well as the geometric features of the CY block.The results showed that: the prestress is capable of reducing the deformation of the beams,suppressing the development of cracks and further improve the serviceability of the beams.As a results,the prestress reduces the ductility of the beam;The CY block has a great influence on the failure mode of prestressed beams.The ductility caused by the compression of the CY block is closely related to the connection between it and its surrounding concrete.The mere chiseling treating on the surface of the CY block is not enough to enhance the ductility of the beam.When a reliable connection is available,the CY block can work together with the surrounding concrete and the ductility is observed to some extent.The compressive strain increases to 37.5%,171% and 158%.Respectively when different CY block was installed at the centre od the top beam and the post-cracked rigidity is lower than that of un-blocked beams,which means more deflection is observed under the same level of the loading.(4)Ductility analysis of the PCPC beams configured with the CY block based on the finite element method.Base on the aforementioned experimental result,this paper established the finite element model using abaqus software programme.The parameters,including the type of CY block,concrete strength and the prestress level,on the ductility of them prestressed beams were compared.The main conclusions obtained from the numerical calculation are: The construction of CY block has great effect on the ductility of the prestressed beams.The type of the CY block investigated in the model increase the ductility form3.44 to 4.24 and 7.03,respectively,which makes it to meet the minimum limits regulated in the corresponding code in terms of ductility;Concrete strength had minor influence on the ductility of the prestressed beams;With the increase of the prestress level,the ductility of the prestressed beams tends to decrease.The ductility coefficient decreasesby16% on average with the increase of 25% of the presress level.PCPC with high prestress levels can obtain excellent ductility by adding CY blocks,which makes it to have good performance in the whole process of stress.