Mesoscopic Simulation Of Mechanical Properties For Lightweight Aggregate Concrete

Along with the development of computer-aided technology, during the past decades, the numerical simulation methold has become a significant tool for large-scale structural design, such as the hydraulic engineering structures, ocean platforms, long-span bridges, and so on. Due to the advantages on simulating the occurrence and propagation of cracks in concrete, as well as the prediction of crack width, the Rigid Body Spring Model (RBSM) destines to become a prospective numerical method on the structural design and durability analysis. In this thesis, the static mechanical properties of lightweight aggregate concrete (LWAC) are numerically simulated by using the mescocopic RBSM. Moreover, the numerical analysis results are compared with the available experimental findings. The major contents are summarized as follows:1. On meso scale, the LWAC is regarded as a three-phase composite, composing of lightweight coarse aggregates (lytag), mortar and interfacial transition zone around the coarse aggregates. The RBSM is introduced into the study of mechanical properties and cracks propagation of LWAC. The parameters, which fit for LWAC, are estimated and confirmed, i.e., the fineness of element meshing, Young's modulus, Poisson's ratio, tensile strength and particle size fraction of lightweight aggregate. The constitutive relationship and strength criterion are determined for different kinds of elements (mortar-mortar, mortar-aggregate, aggregate-aggregate) on meso scale.2. The effect of boundary conditions on carrying capacity and crack propagation of the prism specimen is simulated under uniaxial compression. The simulation results show good agreement with the test phenomena. Additionally, in order to investigate the size of specimen on the compressive strength, three types of cubic specimens, i.e., 100mm×100mm×100mm, 150mm×150mm×150mm, 200mm×200mm×200mm, are selected to conduct the numerical loading analysis. The predicted results agree well with the experimental facts.3. The behaviors of the prism specimen under uniaxial compression and tension are numerically simulated. The full compressive and tensive stress-strain curves of LWAC under the static condition are obtained, and the factors which affect cracks propagation and the relationship between stress and strain at the peak point are analyzed. The simulated stress-strain curves agree well with the previously proposed curves. And then, a simple formula for the full stress-strain curve under uniaxial compression and the ascending branch under uniaxial tension is proposed.4. The flextural failure modes and crack propagation characteristics for mortar and LWAC are studied by the single-point bending beams and the three-point bending beam. The effect of such influencing factors as loading mode, water-to-cement ratio and the depth of notch, on the the stress and strain at the peak point, is analyzed respectively.Though the analyses of mechanical properties of LWAC for different loading models, the results indicate that the static mechanical properties and failure of LWAC could be predicted by the mescocopic RBSM. So, it is concluded that the RBSM could be applied to the structural analysis of LWAC concrete structures.