The Analysis And Numerical Modeling For The Interfaces Between Steel Bars And Concrete

Reinforced concrete structures have been widely used as a significant part of the infrastructure, such as dams, nuclear power stations, offshore platforms, underground powerhouses, bridges, tunnels, primarily because of its outstanding performance and variety of the structural style. Many new types of rebar, such as enamel-coated rebar, further promote their use in chloride rich regions. The finite element modeling and rational design of RC structures is closely related to the mechanical properties of the steel-concrete interface. The study on the steel-concrete interface mechanical properties based on appropriate numerical techniques is of great significance to the finite element modeling and safety evaluation for RC structures. To further develop the understanding of the steel-concrete interface mechanical properties, this paper modeled the pullout tests of plain bars and deformed bars using mesoscopic damage model, and the results were validated by the fixed crack model. The study includes:(1) A modified procedure for generating the numerical coarse aggregates is proposed in this paper. Based on the investigation into more 3,000 specimen sections, the author records the shapes of coarse aggregates into the database, which are the original shapes of numerical coarse aggregates. The shapes of numerical coarse aggregates generated by the proposed approach have not only randomicity, but also actuality. Also, to assure the aggregate rate, the judging method for embedding of numerical aggregates is a direct method based on the computer graphics. The proposed approach is implemented in the preprocessing soft-PREP_MDFPC for numerically generating random aggregate model.(2) The mesoscopic numerical simulation for the pullout tests of plain bars is conducted. According to the failure mode of the pullout specimen of plain bars, the simulation method in this section uses the failure of interface elements to describe the debonding of the plain bar from concrete. The constitutive model of interface elements, which is a damage-friction type, is derived from the mechanical behavior of the steel-concrete interface. In addition to these, this approach uses the constitutive parameters of each interface elements following to Weibull distribution to describe the inhomogeneity of the interface. Subsequently, the influencing factors have been numerically analyzed by using this method. In addition, the shear stresses of the interface were fitted by the improved radix-4 FFT algorithm. (3) The failure of concrete of the pullot specimen is described by 3-D mesoscopic damage model, which is implemented in ABAQUS by using the user subroutine UEL.(4) The 3-D finite element modeling for the pullout tests of plain bars and deformed bars is conducted by using the fixed crack model. The effects of surface configuration of bars and confining pressure on the adhesive property of the steel-concrete interface have been studied. In addition, conclusions drawed from the study are that both deformed bars and confining pressure can improve the bond strength of the steel.