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    A study on load-deflection behavior of two-span continuous concrete beams reinforced with GFRP and steel bars
    (Techno-Press, 2017) Unsal, Ismail; Tokgoz, Serkan; Cagatay, Ismail H.; Dundar, Cengiz
    Continuous concrete beams are commonly used as structural members in the reinforced concrete constructions. The use of fiber reinforced polymer (FRP) bars provide attractive solutions for these structures particularly for gaining corrosion resistance. This paper presents experimental results of eight two-span continuous concrete beams; two of them reinforced with pure glass fiber reinforced polymer (GFRP) bars and six of them reinforced with combinations of GFRP and steel bars. The continuous beams were tested under monotonically applied loading condition. The experimental load-deflection behavior and failure mode of the continuous beams were examined. In addition, the continuous beams were analyzed with a numerical method to predict the load-deflection curves and to compare them with the experimental results. Results show that there is a good agreement between the experimental and the theoretical load-deflection curves of continuous beams reinforced with pure GFRP bars and combinations of GFRP and steel bars.
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    Experimental and analytical research on geopolymer concrete beams reinforced with GFRP bars
    (Techno-Press, 2024) Adakli, Suleyman Anil; Tokgoz, Serkan; Karaahmetli, Sedat; Dundar, Cengiz
    This paper presents the behavior of geopolymer concrete beams reinforced with glass fiber reinforced polymer (GFRP) bars. In the study, ordinary Portland cement concrete and geopolymer concrete beams having GFRP bars were prepared and tested under four- point loading. The load- deflection diagrams and load capacities of the tested beams were obtained. It was observed that the tested beams exhibited good ductility and significant deflection capacity. The results showed that increasing the tension GFRP reinforcement ratio caused enhancement in the strength capacity of geopolymer concrete beams. In addition, the tested beams were analyzed to obtain the load capacity and the load- deflection responses. The theoretical load-deflection curves and load bearing capacities have been predicted well with the test results. Parametric study has been performed to determine the influences of concrete strength, shear span to depth ratio (a/d) and reinforcement ratio on the behavior of geopolymer concrete beams longitudinally reinforced with GFRP bars. It was concluded that increasing concrete strength led to an increase in load capacity. Besides, the ultimate load increased as the reinforcement ratio increased. On the other hand, increasing a/d ratio reduced the ultimate load value of GFRP reinforced geopolymer concrete beams.
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    Investigation of the behavior of carbon fiber reinforced polymer confined standard cylinder concrete specimens under axial load
    (Pamukkale Univ, 2017) Erturkmen, Duygu; Dundar, Cengiz; Tokgoz, Serkan
    The use of fiber reinforced polymer composites for strengthening in concrete structures has become quite prevalent in recent years. Especially, to provide ductile behavior from the structural elements that produced by using the high strength concrete under the load effects, the externally wrapping of these elements with using the fiber reinforced polymer materials comes into prominence as an alternative method for strengthening. These materials with high tensile strength can often be preferred due to their lightweight and easy to apply. In this study, cylinder-shaped concrete specimens with compressive strengths range between 53.13 similar to 74.87 MPa, are wrapped one or two layer with using bi-directional carbon fiber reinforced fabric (CFRP). These wrapped specimens were tested under the axial comprehensive loads and the effects of the CFRP wrapping on concrete strength and ductility was investigated. In addition, stress-strain relations obtained from the tested specimens were compared with the results of existing models for strengthened cylindrical specimen with CFRP in literature. As a result a significant increase was obtained in the compressive strength and deformation capacity of CFRP wrapped specimens. Especially, it was observed that the stress-strain values obtained from the two layers CFRP wrapped specimens show good agreement with the values obtained from the models.
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    Kentsel Peyzajlarda Geçirimli Beton Kullanımı ve Özelliklerinin Değerlendirilmesi
    (2022) Tokgöz, Gülay; Karaahmetlı, Sedat; Tokgoz, Serkan
    Artan dünya nüfusu ile birlikte su ihtiyacı, temini ve yönetimi çok önemli bir konu haline gelmiştir. Özellikle iklim değişikliği nedeniyle şiddetli yağışlar, sel vb. durumlarda suyun yer altı sularına kolay ve hızlı bir şekilde ulaştırılması gerekir. Kentin yeşil altyapı sistemlerini güçlendiren sürdürülebilir yağış suyu yönetimi uygulamalarından birisi geçirimli betondur. Otopark, bisiklet yolları, yürüyüş yolları vb. peyzaj yapılarında geçirimli beton kullanılarak su etkin bir şekilde yeraltına iletilebilir. Geçirimli betonda su geçirgenliğini sağlamak için özellikle karışımdaki su/çimento oranı ve agrega miktarının uygun oranlarda olması önemlidir. Geçirimli beton, az miktarda kum ve çok miktarda iri agregadan oluşur. Geçirimli betonun hazırlanmasında farklı tipte çimentolar kullanılabilir. Sunulan çalışmada, CEM V/A 32.5 R, CEM I 42.5 R ve CEM I 52.5 R çimentoları kullanılarak hazırlanan geçirimli betonun mekanik özellikleri incelenmiş ve kentsel peyzajlarda kullanımı araştırılmıştır. Beton karışımlarından alınan küp ve prizma örneklerinden beton basınç dayanımı ve eğilme dayanımı değerleri elde edilmiştir. Ayrıca, polipropilen lif içeren geçirimli beton hazırlanmış ve dayanım değerleri belirlenmiştir. Bu araştırma çalışmasından elde edilen sonuçlar, geçirimli betonun otopark, bisiklet yolları ve yürüyüş yolları gibi kentsel peyzajlarda uygulanabileceğini göstermiştir.
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    Research on concrete-filled stainless steel tubular composite columns
    (Elsevier Science Inc, 2021) Tokgoz, Serkan; Dundar, Cengiz; Karaahmetli, Sedat; Ozel, Ruken
    Concrete-filled stainless steel tubular composite columns are used in the structures. It is important to define the structural behaviour of this type of columns. This paper presents experimental and theoretical studies of eccentrically loaded concrete-filled stainless steel tubular composite columns. The column specimens were manufactured with high strength outer stainless steel tube, in-filled concrete and inner carbon structural steel. The tubular composite column specimens were designed with plain concrete and steel fiber reinforced concrete. The column specimens were tested and the experimental load-deflection curves of columns were presented in the study. In addition, the tested plain and steel fiber concrete-filled stainless steel tube composite columns were analysed based on a theoretical method for the prediction of strength and load-deflection behaviour. It was observed that the tested tubular column specimens behaved in a ductile manner. A good degree of agreement was obtained between the experimental and theoretical load-deflection curves of concrete-filled stainless steel tubular composite columns. In addition, a parametric study was carried out to examine the influences of loading eccentricity, slenderness, plate slenderness and the concrete compressive strength on concrete-filled stainless steel tubular composite column behaviour. It was concluded from the parametric study that the strength of columns increased by increasing stainless steel wall thickness and concrete compressive strength. However, column strength decreased when the eccentricity and column length were increased.
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    Test and analysis of concrete-filled double steel and double skin tubular columns having outer stainless steel tube
    (Techno-Press, 2022) Tokgoz, Serkan; Karaahmetli, Sedat; Dundar, Cengiz
    This paper presents experimental and analytical studies of eccentrically loaded concrete-filled double steel (CFDST) and concrete-filled double skin tube (DCFST) columns having outer stainless steel tube. Eighteen CFDST and DCFST column specimens were manufactured and tested to examine the strength and load-deflection responses. In the study, the main parameters were concrete strength, load eccentricity, cross section and slenderness. The strengths, load-deflection diagrams and failure patterns of the columns were observed. In addition, the tested CFDST and DCFST columns were analyzed to attain the capacity and load versus lateral deflection responses. The obtained theoretical results were compared with the test results. A parametric study was also performed to research the effects of the ratio of eccentricity (e/Ho) slenderness ratio (L/r), Ho/to ratio, Hi/ti ratio and the concrete compressive strength on the behavior of columns. In this work, the obtained results indicated that the ductility and capacity of columns were affected by cross section, concrete strength, steel strength, loading eccentricity and slenderness.