Date Published: April 16, 2019
Publisher: Public Library of Science
Author(s): Ying Wang, Yuqian Zheng, Xuan Wang, Zhaoxia Li, Costin Daniel Untaroiu.
Damage in the bonding interface is a major factor that leads to the degradation of macroscopic performance of reinforced concrete (RC) structure because the damage generally results in the debonding or slipping between reinforcement and concrete. Based on hierarchical mesh methodology, a multi-scale finite element (FE) model consisting of coarse aggregate, mortar and steel rebar was established to analyze the failure process of RC structure in this paper. In order to develop the mesoscopic FE model, Monte-Carlo method was used to randomly generate the size and position of coarse aggregates; a criterion of mesh reconstruction was proposed to separate the macroscopic mesh into the mesoscopic mesh and the mesh of transitional zone; the damage constitutive relation model for concrete presenting significant difference of its tensional and compressive properties was adopted to control the damage evolution in concrete when loading; the birth-death element method was used to adaptively reform the multi-scale FE model, and finally macroscopic performance degradation of RC structure was evaluated reasonably. A example of standard RC specimen under unaxial load was performed to verify both the accuracy and efficiency of the developed FE model in analyzing failure mode of RC specimen under unaxial tension and compression. By using the developed multiscale FE model, the destruction process of a four-point bending RC beam was analyzed. The simulation results coincide well with the test results from another literature.
From the perspective of mechanics, the degradation of bonding ability in the interface between concrete and steel rebar when loading is caused by the shear stress due to the difference of their material properties. When the shear stress reaches to a critical value, the relative slip between concrete and steel rebar along the anchorage direction is generated in the bonding interface. If the slippage is small, these two materials still can collaborate; while the debonding is generated once the slippage exceeds a certain critical value. Main interactions between concrete and reinforcement in the process of debonding include pullout effect [1–2], tension-stiffening effect [3–5] and dowel effect [6–7].
In order to study the interfacial debonding or slipping of reinforced concrete caused by mesoscopic damage, it is necessary to research the failure process in a mesoscopic level. However, the large volume of concrete structure makes the computation of mesoscopic model inefficient. Therefore, a multi-scale finite element model of the RC structure is developed in this paper, which can simulate the deterioration of the macroscopic mechanical performance of the structure and the mesoscopic damage evolution on the bonding interface at the same time. There are mainly three steps to develop the multi-scale model: 1) developing a mesoscopic model of concrete material with random coarse aggregates, 2) realizing multi-scale modeling of the RC structure by adaptive mesh encryption technology and 3) calculating the damage of each element in every analysis step to simulate damage evolution in the bonding interface.
In order to ensure the accuracy of the multi-scale analysis, it is necessary to make sure that the simulation at the mesoscopic scale is precise. In this paper, the mesoscopic simulation method is verified by simulating the failure process of concrete specimens subjected to uniaxial tension and compression. The glued double-plated device used in the uniaxial tensile test is shown in Fig 7, and the tensile stress on the bonding interface is regarded as uniform distribution . The device used in uniaxial compressive test is shown in Fig 8, and the compressive stress on constrained ends is also regarded as uniform distribution.
In this section, the multi-scale modeling method proposed in Section 2, in which the mesoscopic damage on the bonding interface is considered, is applied to simulate the failure process of a four-point bending RC beam. The effect of mesoscopic damage evolution on macroscopic performance of the beam is investigated, and the simulation method is verified. The test device and the size of the specimen are shown in Fig 14 .
The following conclusions are obtained in this paper: