Study On Bending Mechanical Properties Of Composite Beams With GFRP Profiles-concrete Slabs

As a new structure material with light weight,high strength,corrosion resistance and changeable shape,FRP is increasingly favored by the civil engineering field.In order to give full play to the excellent tensile properties of FRP materials and make up for the insufficient stiffness of components caused by the thin size of components and the insufficient shear properties caused by the anisotropy of materials,the design of composite structures with reasonable force transfer performance has become one of the hotspots of FRP application research.The composite form of FRP profiles and concrete wing plates is a typical FRP composite structure beam/plate structure with many researches at present.It mainly relies on the upper concrete bearing and the lower FRP profiles being pulled,which can give full play to the material properties of concrete and FRP to a greater extent.At present,the mechanical properties of FRP and concrete composite structures are mostly studied by experiments.The quantitative design method of composite structures in the current technical specifications for application of fiberreinforced composite materials in construction engineering also mainly relies on experimental regression.In order to ensure sufficient safe storage and simplify calculation,the flexural stiffness calculation formula of frp-concrete composite beams in the code does not include the contribution of FRP webs,so as to offset the errors caused by ignoring the influence of interface slip and shear effect of composite beams,and the analysis method is not perfect.There is little research on numerical simulation of FRPconcrete composite structures at home and abroad,and the damage mechanism of FRP materials is often ignored.It is assumed that FRP materials are linear elastic materials.The numerical analysis of the mechanical properties of the interface between FRP and concrete and the bond failure mechanism in the composite structure is not enough.For this reason,a composite beam composed of GFRP i-beam and concrete wing plate is numerically simulated in this paper,and its mechanical properties and failure mechanism are quantitatively studied.A simplified design formula based on equivalent stiffness is derived,and its rationality is verified by parameter analysis.The vumat subroutine of composite material based on the stiffness degradation criterion of Hashin damage was programmed,and the constitutive model and its corresponding finite element model of GFRP profiles under three-dimensional orthotropic anisotropy were established.The bilinear cohesive force element was used to simulate the interface mechanical behavior of composite beams.The finite element model of GFRP-concrete composite beams is validated by the comparison with the experimental results.At the same time,the influence of concrete strength and section size,adhesive layer type and web height on the bending failure form and bearing capacity of composite beams was studied.The results show that at the initial stage of composite beam loading,the concrete flanges and GFRP profiles are under the cooperative force of effective bonding,and then micro-cracks occur in the tensile zone of concrete,and the interfacial bonding is gradually damaged.The ultimate failure mode of the whole structure is affected by the strength,thickness and width of the concrete wing,and the type of adhesive layer,etc.The interfacial bond property is weakened with the increase of concrete strength.The use of soft adhesive layer with good toughness can effectively connect GFRP with concrete.In a GFRPconcrete composite beam with a small shear span,stiffeners at the support can effectively improve the flexural stiffness of the composite beam.Finally,based on the flat section assumption,and the introduction of composite beam shear and interface slip effect of stiffness reduction factor,considering influence of stiffening rib,established the equivalent flexural rigidity GFRP and concrete composite beams is derived and simplified design formula of ultimate bearing capacity formula is compared with the results of numerical analysis,verify the rationality of the proposed simplified design formula.