Nonlocal Multiscale Method And Its Application In The Meso-level Analysis Of Concrete Gravity Dam

The macro-level behavior of concrete, one of the typical composites, is associated with the meso-level structure. Generally speaking, meso-level structure of concrete is composed of aggregate, mortar and interface transition zone. Lots of cracks and pores in the mortar and ITZ have been found existed before loading. The propagation, kink and converge of these initial defects have eminent influence on the macro-level behavior of concrete and cause concrete deterioration. Accordingly, the complicated behavior of the macro-level structure can be studied by the numerical model established on the meso-level. In this dissertation, the meso-level numerical model with brittle phases and the nonlocal multiscale method are developed and applied to the analysis of the failure behavior of prenotched gravity dam models. Based on the results, the size effect of dam models is discussed on the meso-level.According to the characteristic of meso-level structure, the meso-level structure including initial defects on the ITZ is recommended in the simulation of the macro-level behavior of concrete. By means of the relationship between stress concentration and stress intensity factor, an equivalent fracture criterion is proposed for checking the brittle failure. The simulation results for the cubic concrete specimen in the uniaxial tension and compression tests by using the proposed model conform to the physical tests. Moreover, the influence of different content of initial defects on the simulation is analyzed; the results show the nonlinear behavior simulated on the meso-level relies on existing of the initial defects.By means of multiscale analysis of bending tests, the relations between different behavior of material and the size of meso-level structure are discussed, and the size dependency is studied. On the basis of the nonlocal constitutive theory and couple volume multiscale model, the nonlocal multiscale method is developed. In simulation of the bending test, the results from the nonlocal multiscale analysis are in agreement with those from the direct meso-level analysis. Based on the modified Voigt-Reuss model, the simplified nonlocal multiscale method is proposed for the fracture analysis of concrete.Combined with the fracture tracking method in which the direction of fracture is assumed to be characterized by the maximum principal stress, the nonlocal multiscale analysis of the prenotched gravity dam model is in accordance with the tests. Contrast to the macro-level analysis, the nonlocal multiscale analysis can obtain more accurate results for the size effect of the dam models. Based on the virtual dam model conforming with Buckinghan's theorem on the meso-level, the size effect of dam models is explained via meso-structure.