Numerical investigation of bond test based on dynamic spallation
Başlık çevirisi mevcut değil.
- Tez No: 714672
- Danışmanlar: PROF. DR. E.H. MANFRED CURBACH, DR. MARİA PATRİCİA GARİBALDİ, DR. PETR MáCA
- Tez Türü: Yüksek Lisans
- Konular: İnşaat Mühendisliği, Civil Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2019
- Dil: İngilizce
- Üniversite: Technische Universität Dresden
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 91
Özet
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Özet (Çeviri)
This master's thesis focuses on the numerical investigation of the dynamic spallation test described by Wensauer [71]. Reinforced concrete structures which consist of reinforcement and concrete are subjected to extreme loading conditions such as impacts, earthquakes and explosions. Due to their composite behavior, it is very important to achieve a good bond between the rebar and concrete specially under these loadings. Investigations on the bond started in early 1900's. Since then many different techniques are developed to understand the interaction between these two materials. Many different test procedures are used throughout the years. Pull-out, push-in and direct tension tests are the most common ones. However, these test set-ups are mostly developed and used for quasi-static conditions. For impact loadings where the loading rates are much higher than the static ones, a new type of specimen based on dynamic spallation should be designed. The main purpose of this thesis is to investigate the bond for the dynamic spallation by using the finite element (FE) software LS-Dyna. During the modeling, the specimen which consists of two concrete segments and a reinforcing bar placed to the center of segments is subjected to impact loading by using the split-Hopkinson bar. Effects of Poisson's ratio (PS), the friction coefficient between the surfaces of two bodies, the material models defined for the concrete and impactor length are studied. Results showed that while the coefficient of friction is not affecting the generated stress wave, Poisson's ratio has a great impact on it. It is not just influencing the maximum stress state achieved but also elements at the same cross section experienced different stresses when a PS bigger than zero is defined to the material laws. Although different material laws did not affect the stress states much but the deformation (damage) of the concrete segments is highly influenced. After that, two different geometries are tested; a specimen with a cut and a specimen with a separation layer. The rib scale modeling (where the rebar is design with 3D solid elements) and bar scale modeling (where beam elements are used to define the rebar and a bond stress-slip law is defined to the system) are used for both geometries. Results of the tests conducted on the specimen with a cut when the bar scale modeling is used revealed that maximum impactor velocity of 1 m/s should be used otherwise the tensile stresses generated in concrete will be too high and will crack the body. Also, a maximum bond length of 10 mm (which corresponds to the diameter of the rebar) should be used to observe the failing of the bond. Two different material models are used in this thesis mainly, the Winfrith material model (MAT 084) and the Karagozian & Case Concrete (KCC) model (MAT 072R3). The results for the two were highly different in terms of the bond behavior and the damaging of concrete. For the specimen with a cut, while concrete with Winfrith model did not crack but at the same time the bond did not fail, when the KCC model is implemented, concrete material experienced radial and splitting cracks with breaking of bond. However, for the specimen with a separation layer, this time bond is failed for MAT 084 but not for MAT 072R3. Same cracking behavior is observed with the specimen with a cut; no damage when Winfrith model is used but radial and splitting cracks when KCC model is implemented. For the rib scale models, only the KCC model was used
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