Research On The Flexural Behaviors Of Hybrid Fibre ECC-NC Composite Beams

Engineered Cementitious Composites(ECC)has the characteristics of high ductility and multi-crack.When applied in structural negative moment area,ECC can effectively solve the durability shortage caused by accelerated steel corrosion caused by cracks in the service process of bridges in complex environments.,and can effectively improve the long-term mechanical performance of the structure.This paper focuses on the flexural performance of composite beam structure composed of hybrid fiber ECC and normal concrete(NC),studies the mechanical behavior under pure bending,and proceed experimental research,numerical simulation and theoretical analysis.The results are as follows:(1)The mechanical properties of ECC materials with different fiber types and dosage were studied,and the key mechanical parameters of different kinds of ECC were determined.The material properties test results of ECC showed that the tensile strength and compressive strength of single Polyvinyl Alcohol(PVA)fiber were inferior to that of single Polyethylene(PE)fiber ECC.When the PVA fiber mixed with 0.6% and 1.0% volume fraction steel fiber,the ECC tensile strength of hybrid fiber increased by 80.0% and 72.0%,respectively,which is significantly higher than that of other groups.(2)The flexural tests of 1 NC beam and 10 ECC-NC composite beams were completed,and the effects of different kinds of ECC layers and different reinforcement rates on the flexural performance of the composite beams were discussed.When 0.6% or 1.0% volume steel fiber are added to the 1.7% volume PVA fiber,compared with the single PVA fiber ECC,it exhibits excellent tensile properties and crack control ability,which can dramatically reduce the average crack distance and maximum crack width.(3)By means of digital image correlation technology,the strain of the test beam in the loading process is analyzed,the deformation of the composite beam in the bending process is accurately measured,the time and location of cracks are determined,and the cracking load of the beam is defined.The results show that hybrid steel fibers in PVA can significantly increase the cracking load of composite beams.The strain distribution of hybrid fiber ECC-NC composite beams around cracks is more uniform than that of NC beams and single fiber ECCNC composite beams,which reflects the stress transfer and dispersion effect of fiber bridging.(4)The ABAQUS model of hybrid fiber ECC-NC composite beams is established on the basis of the ECC material constitutive model in accordance with the present paper.The comparison with the experimental results shows that it can effectively simulate the mechanical behavior of the composite beams.Combined with the model,the influence of different reinforcement and the height of composite layer on the mechanical properties of composite beam is further studied.The results show that the reinforcement with low elastic modulus can not exert the tensile properties of the material due to too large deformation.The stiffness and bearing capacity of composite beam can be improved by increasing the height of hybrid fiber ECC layer.(5)A theoretical analysis method for the bending bearing capacity of composite beams based on plane section assumption and material constitutive relationship is established.The stress-strain relationship of the composite beam section at different stages of the stress process was analyzed,and the theoretical calculation formula of the cracking moment,yield moment and ultimate moment applicable to the composite beam is established,and the calculation formula of the maximum crack width is modified based on the specifications.