پديد آورندگان :
فلاحي، رضا دانشگاه تهران , اميني مزرعه نو، مصطفي دانشگاه امام حسين (ع) - دانشكده پدافند غيرعامل , فياض، محمد دانشگاه امام حسين (ع) - دانشكده پدافند غيرعامل , امين الرعايا، محسن دانشگاه تربيت مدرس
چكيده فارسي :
مدل‌هاي عددي راهكاري مقرون به صرفه در مقايسه با تست هاي ميداني و آزمايشگاهي مي‌باشند كه در صورت لحاظ نمودن خصوصيات دقيق ماده توانايي پيش بيني رفتار مصالح را با دقت قابل قبولي دارند. مزيت ديگر مدل‌هاي عددي در مقياس مزو، قابليت ارائه رفتار اندركنش اجزاء مختلف مصالح غيرهمگن مانند بتن مي‌باشد كه اين ويژگي در پيش بيني رفتار بتن در مقابل بارهاي ديناميكي، كارآيي بالايي دارد. به منظور انجام مدلسازي بتن در مقياس مزو پلتفرمي براي ايجاد نمونه‌هاي بتني با درنظرگيري سنگدانه، ملات و الياف ايجاد گرديد. پلتفرم ايجاد شده در اين پژوهش قادر است سنگدانه‌هاي بيضوي مطابق با منحني دانه‌بندي دلخواه به صورت كاملا تصادفي توليد و با كنترل عدم تداخل سنگدانه‌ها در كنار يكديگر به صورت از پيش تعيين نشده درون مرزهاي قالب جايگذاري كند و پس از معين شدن هندسه نمونه و مش‌بندي آن، مدل ساخته‌شده تبديل به متن ورودي برنامه‌هاي تحليل عددي مي‌شود و بارگذاري فشاري و كششي بر روي آن انجام مي‌گيرد. در تحليل‌هاي انجام شده حداكثر مقاومت فشاري و ميزان شكل‌پذيري بتن و در مواردي مسير گسترش ترك مورد بررسي قرار گرفته است.
چكيده لاتين :
Numerical models are cost-effective solutions compared to field and laboratory tests that have the ability to
predict the behavior of materials with acceptable accuracy if the exact properties of the material are taken into
account. Another advantage of numerical models on the meso-scale is the ability to provide the interaction
behavior of different components of inhomogeneous materials such as concrete, which is highly effective in
predicting the behavior of concrete against dynamic loads. In order to model concrete at the meso-scale, a
platform was created to create concrete samples considering aggregates, mortars, and fibers. The platform
created in this research can produce elliptical aggregates according to the desired granulation curve in a
completely random manner. By controlling the non-interference of aggregates next to each other stochastically
placed within the mold boundaries and after determining the sample geometry and grid, The constructed model
is converted into input text of numerical analysis programs. Compression and tensile loading are performed
on it. Using numerical models, the effect of changes in these parameters was investigated: the volume ratio of
aggregates in the sample, the allowable elongation of elliptical aggregates, whether or not to consider the ITZ
element, and the use of fibers. In the performed analyzes, the maximum compressive strength and ductility of
concrete and, in some cases, the crack propagation path have been investigated. Results show that considering
both the maximum strength and the area under the stress-strain diagram; it can be concluded that among the
percentages of aggregate volume ratios to the sample equal to 65, 70, 75, and 80%, the volume ratio of 75%
to the optimal ratio to achieve the best compressive performance Concrete is closer.
Comparison of the shape of the elliptical aggregates in the modeling showed that the closer the aggregate form
is to the sphere, the maximum resistance increases, but the strength of the concrete decreases with a steeper
slope after the peak.although the analysis of concrete samples at the meso-scale requires much higher
computational costs than the macro analysis, this analysis can provide diagrams of tensile and compressive
strength of concrete more accurately and also to test new samples with changes in the main parameters
acceptable estimation of behavior. Provide concrete without the need to build a physical sample. Studies have
shown that unstructured tetrahedron meshing provides graphs closer to empirical results. In analyses with
unstructured mesh, mesh size has minimal effect on the results; In the case of models with a structured cubic
mesh, the mesh size severely overshadows the analysis results. Suppose the appropriate size for uniform
meshing is calibrated using the results of non-structured mesh samples. In that case, results close to the meshes
of non-structured samples can be obtained with much less computational time and cost. Although considering
the ITZ helps the stress-strain curve at the front of the peak to be closer to the laboratory graphs and also to
predict the location of the crack more accurately than without modeling without ITZ, it causes a decrease in
resistance at the rear of the peak and is predicted. This can be partially controlled by calibrating the ITZ
resistance reduction value.
