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Küp numunelerin yarmada-çekme dayanımında agrega granülometrisinin boyut değişimi üzerine etkisi

Effect of aggregate gradation on size effect in split-tension cubes

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Abstract (2. Language): 
In general, if geometrically similar specimens do not behave similarly for different sizes, this is called a size effect. It is known to structures become more brittle as their size increases, but the classical procedure uses working stresses which are the same in design. Size effects occur in concrete in any loading conditions like tensile or shear loading Kani was one of the first to demonstrate the size effect in concrete structures. He observed the shear strength of similar concrete beams decreases with increasing beam depth. Due to the fracture in a structural element being driven by stored elastic energy released from the whole structure, this size effect can be well interpreted by fracture mechanics. The fact that the strength of brittle materials is affected by the presence of imperfections is first suggested by Griffith, who is the founder of linear elastic fracture mechanics (LEFM). Due to his conclusion, it can be expected that the value of the ultimate strength will depend upon the size of specimens. As specimen size increases the strength is expected to be decreased since the probability of presence of weak links is increased. Traditionally, the size effect in fracture of concrete structural elements has been explained as Weibull’s theory. He showed that if tensile tests are performed on two geometrically similar specimens with different volumes, the corresponding ultimate strengths are different. Weibull’s approach has been widely used for estimating safety factor of materials. In the early 1980s, it is realized that neither LEFM nor Weibull’s approach were adequate for predicting size effect in cementitious materials. The experimental investigations on fracture mechanics of cement-based materials until 1970s indicated that classical linear elastic fracture mechanics (LEFM) is invalid for quasi-brittle materials such as concrete. This inapplicability of LEFM is due to existence of an inelastic zone with large scale and full cracks in front of the main crack tip in concrete. This so-called fracture process zone (FPZ) is ignored by LEFM. Consequently, several investigators have developed non-linear fracture mechanics approaches to describe failure of concrete/reinforced concrete structures. eterministic size effect laws among these non-linear approaches, for instance size effect law (SEL) by Bazant (1984), suggest that size effect on strength is primarily related to a relatively large FPZ in concrete. One of the main requirements in this law is the need to test samples, which are geometrically similar and made of the same material, and which must provide a minimum size range=1:4. The split-tension test has been used to indirectly test the tensile strength of quasi-brittle materials such as concrete and rock. Recently, concrete splitting specimens have been commonly used in concrete fracture because they have certain advantages, such as compactness and lightness, compared to beams. Additionally, cubical and cylindrical test specimens have the following advantages: a) These specimens are easy to handle, and there is no risk of breaking them during handling. b) The same molds can be used to cast specimens for both fracture and strength tests. c) In determining the fracture parameters of cementbased materials, the contribution of the weight of the specimen can be ignored, unlike notched beams. In experimental studies, it was determined that maximum aggregate diameter and aggregate type are effective in fracture behavior of concrete. In the samples without notch subjected to splitting tensile test, it has seen that as the sample diameter increases, the nominal strengths decreases and there is a very strong size effect. In addition, how it will behave in the actual structure size still remains uncertain theoretically. In size effect studies, β = (t/d) is the ratio of the distributed load width to specimen depth not taken into consideration up to now in splitting tensile test, although its importance has been emphasized several times in scientific studies in the literature. was taken as 0.10 and 0.16 in this study. When the test results of the cube sample without notch produced by gap-graded aggregate granulometry and analysis results produced by continuous aggregate granulometry taken from the literature were compared, it has been observed in this study that the mechanical behaviors of the mixtures prepared by gap-graded aggregate granulometry are better than continuous aggregate granulometry particularly in terms of ductility.
Abstract (Original Language): 
Beton ve betonarme yapılarda göçme analizi yapılırken birçok lineer ve lineer olmayan yaklaşımlar kullanılmaktadır. Betonarme bir yapıyı kırılma mekaniğine göre analiz edebilmek için ilk önce, kullanılan malzemenin kırılma parametrelerinin belirlenmesi gerekir. Betondaki neme ve zamana bağlı olarak mekanik sabitlerin değişmesi ve boyut etkisinden dolayı, Lineer Elastik Kırılma Mekaniği (LEKM), kırılma parametrelerinin tespitinde yetersiz kalmıştır. Bunun nedeni çatlağın ucunda yer alan diğer malzemelere göre daha büyük bir yer işgal eden kırılma süreci bölgesinin (KSB) var olmasıdır. Betonun kırılma parametrelerini belirlemek için şartnameler ve araştırmacılar tarafından birçok lineer olmayan kırılma mekaniği modelleri önerilmektedir. Bu lineer olmayan yaklaşımlardan Bazant (1984) boyutun dayanım üzerindeki etkisini inceleyerek betonda daha büyük bir KSB olduğunu öne sürmüş ve ‘Boyut Etkisi Kanunu’ geliştirmiştir. Betonun kırılma mekaniğinde kiriş numuneler yaygın olarak kullanılmakla birlikte, taşınabilirlik ve hafiflik açısından bazı avantajlara sahip olduğundan küp ve silindir numuneler son zamanlarda kullanılmaya başlanmıştır. Bununla birlikte karşılıklı basınç kuvveti uygulanan küp yarma testi ile ilgili deneysel ve teorik çalışmalar oldukça sınırlıdır. Sunulan bu çalışmada, su/çimento oranı 0.6 olan, maksimum agrega çapı 8 mm'lik kesikli ve sürekli granülometrili beton karışımları hazırlanmıştır. Aynı geometriye sahip farklı boyutlu (4:2:1) küp numuneler üzerinde boyut etkisi incelenmiştir. 50x50x50 mm3, 100x100x100 mm3, 200x200x200 mm3’lük küp numunelerin 28 günlük yarmada-çekme dayanımları belirlenmiş, elde edilen deney sonuçları Bazant’ın “Boyut Etkisi Kuralı”na göre analiz edilmiştir. Sonuç olarak kesikli granülometriye sahip betonların daha sünek davrandığı tespit edilmiştir.
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