Study On The Flexural Behaviour Of Hybrid BFRP/Steel Reinforced Concrete Beams

It has become a major problem in concrete structures that the service life of the structure reduces because of the corrosion of steel bars,which results in a substantial increase in maintenance costs.Fiber reinforced polymer(FRP)materials with excellent properties such as high tensile strength,convenient construction,light weight and corrosion resistance,which is used to replace steel reinforcement in concrete structures,can effectively solve the problem of steel corrosion.This application has attracted more attention of engineering community in recent years.However,the lower linear elastic stress-strain relationship and elastic modulus leads to the deflection and the crack width of FRP concrete beams greater than that of the reinforced concrete beams under serviceability limit state.To address this issue,many efforts have been made to investigate the mechanical behaviour of the hybrid reinforced concrete structure combining FRP bars and steel reinforcements,which have good durability and serviceability.The main objectives of this paper present herein were to further researching in flexural behaviour of concrete beams reinforced with hybrid(BFRP and steel)bars.Furthermore,a comparison between the theoretical previsions and numerical simulation results has been presented in this work.The main contents are as follows:(1)A total of ten concrete beams,including one reinforced with BFRP,one reinforced with steel,and eight reinforced with hybrid BFRP and steel are designed.Experiment tests are carried out to investigate the effect of reinforcement area ratio on the flexural behavior of hybrid BFRP/steel reinforced concrete beams with a low and high reinforcement ratio.The flexural capacity,failure mode,flexibility deformation,crack distribution and ductility performance of the hybrid BFRP/steel reinforced concrete beams were analyzed and compared with the BFRP reinforced beam as well as the steel reinforced beam.It can be found that the failure modes are divided into two types depending on the reinforcement ratio.The concrete in compression crushes after the yielding of steel reinforcement for the hybrid BFRP/steel reinforced concrete beams with high reinforcement ratio,while the brittle failure of beam occurs following the FRP ruptures after the yielding of steel reinforcement for the hybrid BFRP/steel reinforced concrete beams with low reinforcement ratio.The load-deflection curves of the hybrid reinforced concrete beams show the tri-linear characteristics with the turning points,which corresponds to the cracking load and the yield of the steel bars.The ductility coefficient of hybrid reinforced concrete beams is higher than that of reinforced concrete beams,and the lower the reinforcement ratio,the larger the reinforcement area ratio,the higher the ductility coefficient.In order to satisfy the design requirements of ductility and deflection,it is recommended to set the reinforcement area ratio in the range of 0.6-1.65.(2)The initial crack load,ultimate load,load-deflection curves and width of cracks of the hybrid BFRP/steel concrete beams are calculated according to the American Fiber Reinforced Bar Standard ACI440.06-1R and China's "Technical Specifications for Fiber Reinforced Composites Construction Project".Then the feasibility of the existing guides on the flexural behavior of hybrid BFRP/steel concrete beams is validated by comparing the results of theoretical and experimental calculation.It is found that the theoretical calculated values are in good agreement with the test results.The American Fiber Reinforced Bar Specifications are more accurate in predicting the ultimate bearing capacity,the load-span mid-span deflection curve and the crack width.(3)The 3D finite element model of the hybrid FRP/steel concrete beams are developed through the large software ANSYS.And the numerical simulation of the bending process is carried out based on the test data.By comparing the failure modes,cracking load,ultimate load,crack initiation morphology and load-span mid-deflection curve of the reinforced concrete beam with the experimental results,it can be seen that the numerical simulation in good agreement with the test.Based on above analysis,the effects of factors such as the section height of hybrid reinforcement,the type of FRP bars and the placement of tensioned reinforcement bars on the flexural behavior of hybrid reinforced concrete beams are discussed.