Flexural Behavior Of Hybrid FRP Concrete Composite Beams With GFRP Tube Setted In Compression Zone

Fiber Reinforced composites (Fiber Reinforced Plastics/Polymers, referred to asFRP) has became a new popular reinforcement material in civil engineering due to itshigh strength and rigidity, good durability and repairability and et al. In recent yearsFRP has been widely applied to solve the problems of poor durability of the currenturban infrastructures and bridge structures, etc. FRP, however, is a kind of linearelastic material with brittle failure and its cost is higher. In order to make full use ofthe advantages of all kinds of materials to achieve the purpose of improving concretestructure mechanics performance, this thesis put forward a new kind compositestructure form which is made of Hybrid Fiber Reinforced composite materials (HybridFRP) with traditional reinforced concrete structure considering the concept of localconstraint. The thesis studied the bending capacity of the composite structure in depth,the main works include the following content:(1) Mechanical properties of materials applied in the specimens were tested inthis paper, mainly including: the uniaxial tensile performance test of CFRP and GFRP,the axial compression test of concrete and the tensile properties test of reinforcement,which provides the basis for the design and experimental analysis of hybrid fiberconcrete composite beam.(2) Based on the material test results in this thesis and the material constitutivelaws that already exist, full-range analysis of flexural performance of hybrid FRPconcrete composite beams with GFRP tube setted in compression zone is carried out.The main contents include stress mechanism analysis of constraint performance ofGFRP tube as well as the stress calculation of confined concrete, the basic equationsfor the full-range analysis of composite beams and calculation method of deformationproperties based on stiffness analysis results, analysis of the two basic failure modesand ultimate bending capacity calculation of these composite beams.(3) According to the material test results of FRP, the FRP layers and crosssections of hybrid FRP reinforced concrete composite beams are designed. FRP shellmolds are made using hand lay-up method. The interface between concrete and FRPshell mold are bonded in two ways, i.e. wet bonding and sticking stones. Then thehybrid FRP concrete composite beams are manufactured and tested based on thedesign results. Through the flexural experiments of1ordinary RC beam (as the control specimen) and10hybrid FRP concrete composite beams with GFRP tubesetted in compression zone under the action of static load, flexural performance ofload-deflection relationship, pre-yield stiffness， buckling stiffness, ductility ofcomposite beams, the load-strain relationship of reinforcement, and the load-strainrelationship between reinforcement and concrete are all analyzed in detail. Theexperimental results indicate that the ultimate bearing capacity of the hybrid structureare greatly increased, and failures of composite beams are in a multi-level fracturemechanism, the post-yield stiffness of composite beams is good and stable, andcomposite beams also possess good ductility performance. Comparing the ultimatebearing capacity of the theoretical calculations with the measured values, the error iswithin a small range, which indicates that the theoretical analysis methods oftheoretical analysis are feasible.