1,721,091 research outputs found
Impact Behaviour of Concrete: a Computational Approach
No full textThe purpose of this study is to examine the numerical simulation of concrete specimens under high loading rates in tension. The data found in the literature are described: they show an increase in compressive and tensile strength as a function of the loading rate. To study this behavior, we focused our attention on the assessment of the consistency model through the simulation of many experimental results related to a wide range of strain rates. In particular, the tests on unnotched and notched specimens performed at Delft University in recent years are examined. The proposed model is able to describe the increase in strength due to a high loading rate by an appropriate choice of the viscosity parameter
Modelli Numerici per lo Studio dei Fenomeni Fessurativi nelle Dighe
No full textPolitecnico di Torino, PhD thesi
Fuzzy modelling of powder snow avalanches
Full text linkThis paper examines powder snow avalanches by introducing a predetermined degree of variation, or fuzziness, in model parameters. Given a value of vagueness in the parameters, fuzzy set theory makes it possible to evaluate the vagueness in the results. The use of a more complex stochastic analysis can be avoided. Six parameters of the model are taken to be affected by a certain amount of uncertainty; the response of the numerical model is calculated by solving the fuzzy equations. In this way, it is possible to evaluate how the results are affected by a given change in the model parameters. The paper first presents a well-known avalanche model and its solution considering the influence of friction. A brief introduction of the fuzzy set is given with regard to the avalanche model mentioned. Later, the fuzzy solution of the model in terms of velocity and average pressure is calculated for three different levels of imprecision in the data. At the end, the results are presented and commented
Subcritical crack propagation in concrete structure
No full textThe safety of cracked concrete dams is fundamentally affected by their mechanical behaviour under cyclic loading conditions. It is well known that concrete presents a diffused damage zone within which micro-cracking increases and stresses decrease as the overall deformation increases. This results in the softening of the material in the so-called fracture process zone (FPZ), whose size is comparable to that of a characteristic dimension of the structure. This dimension is not constant and may vary during the evolutionary process. In this context, a numerical method has to be used together with the cohesive or fictitious crack model, also known as Barenblatt, Dugdale and Hillerborg model. The proposed approach combines a micromechanical model for the static softening behaviour of cracked concrete in the fracture process zone (Huang & Li (1989)) with a local model along the FPZ for the hysteresis loop under unloading-reloading conditions (see Hordijk (1991)). The loading process analysed in this paper is based on a first monotonic step stopped before reaching the peak load. Afterwards, a series of cyclic loading phases is applied, at increasing load levels, until collapse occurs. The results of numerical analyses appear in good agreement with the experimental data obtained in the case of wedge splitting test
Hydromechanical coupling at dam-foundation joint
No full textWhen fracture occurs in a concrete dam, the crack mouth is typically exposed to water. Very often this phenomenon occurs at the dam-foundation joint and is driven also by the fluid pressure inside the crack. Since the joint is the weakest point in the structure, this evolutionary process determines the load bearing capacity of the dam. In this paper the cracked joint is analyzed through the cohesive model proposed by [Cocchetti et al., 2002], which takes into account the coupled degradation of normal and tangential strength. The water pressure inside the crack, which reduces fracture energy and increases the driving forces, is analyzed through the model proposed by [Reich et al., 1994], [Bruhwiler and Saouma, 1995] . Some numerical results are presented which refer to the benchmark problem proposed in 1999 by the International Commission On Large Dams (see [ICOLD, 1999]). The first crack is induced by tensile stress at the upstream edge. This propagation is stable in load control even when the water pressure is applied inside the crack. Initially the Mode I displacement discontinuity dominates. As the crack grows, the Mode II contributions become important. If the tensile strength of the rock is high, vertical branching of the crack is prevented and the next crisis occurs at the downstream edge. It is a sliding crack, under high compressive stresses in dry conditions. There is a phase in which both cracks grow in load control. Since in exceptional flood conditions the load cannot be reduced, the maximum load carrying capacity is achieved when the load control condition is los
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