Meso-damage Evolution Of RC Bonding Interface And Its Action-Mechanism To RC Property Degradation

In reinforced concrete (RC) structures, whether concrete and steel with different properties work together depend on the bonding between concrete and steel. The failure of bonding between concrete and steel is one of the major reasons that cause the deterioration and failure of RC structures. So the bonding behavior between concrete and steel is a hot issue and has been studied by many researchers. However, in recent researches on bonding behavior between concrete and steel, such as pull-out experiments and numerical simulations in which connecting unit is used to simulate bond slip, ignore meso-damage evolution process within the bond area between concrete and steel. In order to overcome the shortage, a mesoscopic numerical simulation method is developed to simulate the meso-damage evolution of the bond area between concrete and steel within RC specimens. In addition, a consistent multi-scale simulation method is also developed based on the developed mesoscopic numerical simulation method coupling an adaptive grid mesh algorithm to simulate the meso-damage evolution of the bond area between concrete and steel within RC structures with lower computational cost. The pull-out process of a RC specimen is simulated using the developed method. From the simulation, the macroscopic mechanical behavior deterioration and mesoscopic damage evolution of the bonding area between concrete and steel within the RC specimen is analyzed during the pull-out process. The effects of different factors on the macroscopic mechanical behavior deterioration and mesoscopic damage evolution of the bonding area between concrete and steel are also analyzed. Mesoscopic mechanism of the bond behavior deterioration between concrete and steel is summarized. Finally, damage evolution of a four point bending RC beam is simulated using the developed consistent multi-scale simulation method. From the simulation, the macroscopic mechanical behavior deterioration and mesoscopic damage evolution within the RC beam is analyzed during damage and failure process. The effect of the mesoscopic damage of the bonding area between concrete and steel on macroscopic mechanical behavior of the RC beam is analyzed. The main work and conclusions can be summarized as follows:Firstly, a mesoscopic numerical simulation method is developed to simulate the mesocopic damage evolution of bonding area between concrete and steel within RC specimens, where in the reinforced concrete material can be modeled as three phases:mortar, coarse aggregate and steel. The generation method of random aggregates is used to simulate coarse aggregate distribution in mortar. Elastic damage constitutive relation is used to describe the mesoscopic elements of coarse aggregate and mortar, wherein maximum tensile strain and Mohr Coulomb criterions are used to describe the stretching damage and compression-shear damage, respectively. The displacement increment method, as well as the mesoscopic simulation method considering the material heterogeneity instead of the complex homogeneous constitutive relation in the traditional numerical simulation methods of bonding area between concrete and steel is used in the developed methods. Based on the developed mesoscopic numerical method and the adaptive grid mesh algorithm, a consistent multiscale simulation method is developed to simulate the mesoscopic damage evolution of the bonding area between concrete and steel within RC structures.Secondly the pull-out process of a RC specimen is simulation. Comparing with between the simulated bond-slip curve and experimental result, it shows that the developed mesoscopic numerical simulation method is feasible and effective. And the pull-out failure process are divided into the following three stages:the segment wherein the adhesion coefficient of performance is steady, and the bonding area has no failure elements, the segment wherein the adhesion coefficient drop quickly, and stretching damage zone grow along the axial reinforcement to about half of thebonding area, and the segment wherein the adhesion coefficient drop slowly and the damage zone extension cannot extend axially.Pull-out process of the RC specimen with different factors, such as elasticity modulus of mortar, the elasticity modulus of coarse aggregate, the confining pressure and the shape of reinforcement, is simulated by using control variable method. It shows that the increment of the initial meso damage and the coarse aggregate modulus of elasticity modestly can reduce bonding properties between concrete and steel; increment of mortar elastic modulus can modestly increase the bonding properties between concrete and steel. Rebar and interface by confining pressure can significantly increase the bonding properties between concrete and steel. The growth rate of stretching damage through the reinforcement axial direction can slightly improve the bonding properties between concrete and steel; once local compression shear zone during the interface emerge, the pulling and extending failure can be restrained and the bonding behavior can be enhanced.The damage evolution of a four point bending of RC beam is simulated. It shows that the developed consistent multi-scale method is effective to simulate the damage and failure process of RC structures by considering mesoscopic damage evolution of the bonding area between concrete and steel with lower cost. For the low steel-concrete interfacial bond strength, bending and shearing girder segment of RC beams can fail through the interface region along the axial reinforcement, and dramatically reduce the overall equivalent beam bending performance.