Numerical Method For Mechanical Properties Of Reinforced Concrete Members On Mesolevel

In terms of the composites of concrete material and researching consideration, there are several different levels:macrolevel, mesolevel and microlevel. All the mechanical properties of concrete are available to be predicted through the levels of macro or micro. On mesoscale, concrete is usually regarded as a three-phase composite, consisting of coarse aggregates, mortar and the bond zone between these two compositions. Among them, the mortar or aggregate can be regarded as isotropic materials, respectively. Mesoscopic Rigid Body Spring Model (RBSM) is an approach to analyze the properties of concrete by the method of RBSM on mesolevel. In this paper, the mesoscopic RBSM is used to simulate the behavior of concrete and reinforced concrete members under static loading. By comparing the simulation results with experimental data, the mesoscopic RBSM is confirmed to be effective and feasible for simulating the mechanical properties of reinforced concrete members. The main contents are summarized as follows:(1) This paper systematically summarizes the theoretical background of the mesoscopic RBSM, covering the generation process of coarse aggregates, the meshing technique of elements, the construction of the mesoscopic RBSM and the development of constitutive law of the springs. In addition, the latest research advances and results on the application of mesoscopic RBSM are reviewed.(2) Regarding of the loading characteristics of splitting test in simulation, the adjustment of element meshing is adopted for the sample in order to be able to represent the test condition. The article simulates the concrete splitting tensile tests under different sample sizes, which is compared with the results from the experiments. It is shown that both the failure modes and splitting tensile strengths are similar with those from test results, and the size effect is more evident in small size samples. The influence of bearing widths on splitting tensile strength of concrete is also analyzed. The results show that ratio of bearing width b to sample width D has a significant impact on splitting tensile strength of concrete, but if the ratio b/D is less than 0.04 that splitting tensile strength of concrete is not obvious; if b/D equals to 0.058, splitting tensile strength is almost the same with axial tensile strength of concrete.(3) Mortar-aggregate interface is the weak zone in concrete. The constitutive model of the interface has an important effect on the mechanical properties of concrete for the mesoscopic simulation. In this thesis, different tensile softening constitutive models and shear constitutive models for interface are used in the mesoscopic RSBM. Compared with test results, it is shown that the difference among different constitutive models is not to much when the fracture energy is kept constant; different shear constitutive models are all effective in mesoscopic simulation of concrete.(4) Based on the mesoscopic RBSM, and reinforcing bars are modeled as beam elements. Both the flexure and shear bearing capacity of reinforced concrete members are simulated. Compared with the experimental results, it is shown that RBSM on mesoscale can be sucessfully applied to the simulation of the failure mode, load-displacement response and the stress variation of reinforcement subjected to loading. In addition, the results from the failure progress of reinforced concrete beams under different sizes show that the nominal compressive strength goes lower with the growth of effect depth of beams, and the strength does not change if the effect depth of beam is larger than 240mm.