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Öğe Beton İçindeki Düz Yüzeyli ve Kum Kaplı Donatı Çubuğu Aderans Davranışının Eğilmede Aderans Yöntemiyle Deneysel ve Sayısal Olarak İncelenmesi(2024) Sakcalı, Gokhan Barıs; Yuksel, Isa; Sağıroğlu, SerkanBetonarme davranışın sergilenebilmesi çelik donatı çubuğu ve betonun birlikte hareket etmesiyle mümkündür. Bu durum, çelik donatı çubuklar ve beton ara yüzeyinde basit amprik denklemlerin kullanımı için tam aderans kabulünü beraberinde getirir. Ancak, daha gerçekçi ve kapsamlı modellemelerde aderans gerilmesi-donatı sıyrılması ilişkisi önemli olabilir. Bu durum, düz yüzeyli çubuklarda mekanik kenetlenmenin olmaması nedeniyle aderansı oluşturan diğer faktörlerin ön plana çıkmasına neden olmaktadır. Bu sebeple, bu tip donatı çubuklarının sayısal modeli oluşturulurken aderans gerilmesi-donatı sıyrılması ilişkilerinin sayısal modellere doğru bir şekilde tanımlanması önemlidir. Bu çalışmada, donatı yüzeyine uygulanan kum kaplamanın aderans dayanımına etkisini incelemek için donatı olarak düz yüzeyli çelik çubuk ve kum kaplı çelik çubuk kullanılmış, iki farklı eğilmede aderans deney numunesi hazırlanmıştır. Bu iki numune yük taşıma kapasitesi, düşey yer değiştirme kapasitesi, sıyrılma ve göçme mekanizması yönünden kıyaslamalı olarak irdelenmiştir. Bunun sonucunda CEB-FIP (2010) standardında önerilen BPE model için hem düz yüzeyli hem de kum kaplı çubuklarda kullanılmak üzere sınır durumlar önerilmiştir. Ayrıca deneyler ve önerilen BPE modeller ışığında farklı kenetlenme boyuna sahip sayısal modeller oluşturulmuştur. Bu modellerde kenetlenme boyunun kiriş nihai yük kapasitesini önemli derecede etkilediği sonucuna varılmıştır.Öğe Bond Behavior of Sand-Coated GFRP Rebar Embedded in Concrete(Springer International Publishing Ag, 2024) Sakcali, Gokhan B.; Sagiroglu, Serkan; Yuksel, IsaBond between rebar and the surrounding concrete is a vital property for the earthquake resistant reinforced concrete (RC) structures. It is required to provide sufficient force transfer between the concrete and rebars for the RC elements to exhibit composite behavior. In this study, it is aimed to examine the bond behavior of the sand-coated GFRP rebar embedded in the concrete. In this context, beam test specimens with three different embedment lengths were prepared in laboratory environment. The behavior of the specimens are investigated comparatively by utilizing the load-displacement relationships, the slippage of the rebar through the concrete, crack propagations, diagonal crack angles, failure modes, bond strength. As a result of the investigations, it was determined that the failure mode changed and accordingly load bearing capacity of the samples increased as the embedment length of the rebars increased. In addition, two different approaches were used to determine the bond stress and the results are discussed comparatively.Öğe Development of one-part geopolymer binder produced from alkali fused boron mine tailings(Elsevier, 2025) Kiziltepe, Cavit Cagatay; Yuksel, Isa; Aydin, Serdar; Sigindere, AysenurThe main purpose of this study is to investigate whether the boron mine tailings can be used as a raw material in producing one-part geopolymer binder by using the alkali fusion method. The boron mine tailings and alkali activator were calcined at 650 degrees C for 3h in a furnace. Both sodium hydroxide and sodium carbonate were used at different ratios as the alkali activator during the calcination process. The setting times, mechanical properties, sorptivity, and drying shrinkage of the one-part geopolymer mixtures based on alkali-fused boron mine tailings were investigated within the scope of this study. Furthermore, microstructural analyses were performed on one-part geopolymer paste samples to complement the obtained test results. The highest compressive strength value (24.2 MPa) was obtained from specimens activated with sodium hydroxide (4 % Na2O by binder weight), while the highest flexural strength value (4.3 MPa) was obtained from the specimens with 20 % sodium carbonate. New crystalline phases such as merwinite, monticellite, sodium peroxide, and magnesium oxide were identified in the alkali-fused boron mine tailings. Ultimately, the main reaction product contributing to specimens' compressive strength development was identified as the riversideite phase.Öğe Experimental investigation of flexural bond behavior of sand-coated GFRP rebar embedded in concrete(Elsevier, 2024) Sakcali, Gokhan B.; Yuksel, Isa; Sagiroglu, SerkanSteel rebars used in Reinforced Concrete (RC) elements may be subjected to corrosion due to aggressive environmental conditions. Rebar corrosion reduces the durability and the structural capacity of RC elements. On the other hand, since the steel rebars affect the magnetic fields, it is not preferred to be used in RC structures which is used to carry the equipment that propagate magnetic waves such as toll plazas on highways. For these reasons, the use of Fiber Reinforced Polymer (FRP) rebars is increasing, especially in RC infrastructure constructions. The objective of the present study is to investigate the bond behavior of Glass Fiber Reinforced Polymer (GFRP) rebar with a sand-coated outer surface in concrete using the arched beam test method. The concrete strength and the embedment length were chosen as variable parameters and 34 beam test specimens were tested in the laboratory. A comparative analysis of the crack patterns, the diagonal crack angles and the failure modes of the specimens is made. In addition, the experimentally determined bond -slip relationships were compared with different analytical models in the literature. Consequently, a bond -slip model, which takes into account CMR (Cosenza-Manfredi-Realfonzo) for the increasing part and mBPE (modified Bertero-Popov-Eligehausen) for the decreasing part, is proposed to be used in the numerical models of RC beams with sand-coated GFRP rebars. A prediction model for the bond strength is proposed, along with a recommendation for an upper bound value for the bond stress, which indirectly offers a minimum embedment length for a bond without slippage.Öğe Numerical Simulation of GFRP-reinforced Rectangular Concrete Beams and Proposed Design Expressions(Budapest Univ Technology Economics, 2025) Sakcali, Gokhan Baris; Yuksel, IsaRebar corrosion, which has emerged as a primary detrimental factor, significantly impacts the structural performance, durability, and overall serviceability of reinforced concrete (RC) structures. In response to this issue, the growing use of GFRP, which offers superior corrosion resistance compared to steel, highlights the need to compare its performance with traditional steel-reinforced beams. To address this need, this study aims to evaluate the flexural behavior of beams reinforced solely with GFRP rebar and assess their structural performance relative to steel-reinforced beams. To achieve this, finite element models of both steel-reinforced and GFRP-reinforced beams were developed using ANSYS software. The analysis focused on load-bearing capacities, displacement characteristics, and crack patterns, and included the calculation of strain energies corresponding to collapse prevention performance limits. Overall, the study concludes that these modifications enhance design guidelines for GFRP-reinforced beams, offering improved practical applications in structural design. Significant findings include the proposed modification to the minimum reinforcement ratio equation in ACI 440.1R-15 for GFRP-reinforced concrete, the introduction of a suggested strain reduction factor for GFRP rebar, and the revision of the effective moment of inertia equation with coefficients of 0.05 and 0.95. These revisions improved the general performance indicator to 1.17, yielding better results compared to other equations in the literature. The study concludes that these modifications enhance design guidelines for GFRP-reinforced beams, offering improved practical applications in structural design.Öğe One-Part Geopolymer Binder Based on Boron Wastes: Effects of Calcination Temperature and NaOH Dosage on Strength and Microstructure(2024) Kızıltepe, Cavit Çağatay; Yuksel, Isa; Aydın, SerdarBoron Enterprise Facilities are located in Kütahya-Emet, Eskişehir- Kırka and Balıkesir-Bigadiç regions in Türkiye. Waste materials containing a sum of boron (15-20%) occur during boron beneficiation with different mining procedures. Boron mine wastes are not evaluated completely in any sector. In the scope of this study, boron mine wastes from Kırka Boron Enterprise Facility were used as raw material in the production of one-part geopolymer binder by alkali fusion method. The effect of sodium hydroxide dosage (%4, %6, %8 and %10) and calcination temperature (600 °C, 650 °C and 700 °C for 4h) on compressive strength and microstructure was investigated. Test results showed that one-part geopolymer binder can be produced from boron wastes by using alkali fusion method. The highest compressive strength of 29,1 MPa was obtained by using 4% NH and calcination at 650 C for 4h. Furthermore, the formation of new crystalline phases in geopolymer binders at higher calcination temperature caused a decrease in compressive strength values. The main reaction product of the one-part geopolymer based on boron wastes is Mg and Na incorporated C-(Mg, Na)S-H structure.Öğe Serviceability assessment of a steel pile supported wharf structure: a case study(Springer Int Publ Ag, 2025) Yuksel, Isa; Avsar, TolgaThe objective of this case study is to ascertain whether an existing pile-supported wharf structure can withstand the service and seismic loads to which it may be subjected. Data pertaining to the materials and soil were collected in situ, and a mathematical model of the wharf was subsequently constructed. Initially, a series of capacity checks was conducted under service loads. Subsequently, a deformation-based assessment was conducted in accordance with the TCHSEC-2020 principles. Plastic hinges were then defined at the nodal points of the pile cap-beam connections by means of the lumped plasticity approach. The target displacement was calculated taking into account the free soil behaviour. The system was then subjected to a static pushover analysis for both of earthquake levels DD-1 and DD-3. In accordance with the TCHSEC-2020 code, performance evaluations must satisfy two distinct performance targets, which have been determined for two different earthquake levels, designated DD-1 and DD-3. The results showed that the wharf met the performance targets defined separately for DD-3 and DD-1 earthquake levels. It is concluded that the steel pile wharf meets the requirements of TCHSEC-2020 under operational and seismic loads as it meets the requirements of TCHSEC-2020.Öğe Shear Strength Evaluation of Concrete Beams with FRP Transverse Rebar(Budapest Univ Technology Economics, 2024) Sakcali, Gokhan Baris; Yuksel, IsaRebar corrosion in traditional reinforced concrete (RC) components may lead to a decrease in service life and carrying capacity. This condition is one of the reasons of the growing popularity of Fiber Reinforced Polymer (FRP) rebars as a corrosion-resistant alternative, particularly in RC infrastructure projects. Because the material properties and behavior of FRP rebar are very different from conventional steel rebar, the calculations used for reinforced concrete with conventional steel reinforcement should be updated for this material. The aim of this study is to propose a new shear strength prediction model for RC beams with transverse steel rebar in order to calculate the shear strength of RC beams with FRP transverse rebar according to TS-500, which is the Turkish Building Code. To achieve this goal, Finite Element Method (FEM) models were created for 27 RC beams with FRP transverse rebars and 9 RC beams without transverse rebars. Furthermore, for RC beams with FRP transverse rebars, a prediction model has been developed. Additionally, 13 prediction models obtained from regulations or scientific studies were compared to the proposed prediction model using a database of 105 tests obtained from previous experimental studies. It was observed that the proposed prediction model provides more consistent results with the test database from the literature compared to the models suggested by other regulations or studies. Therefore, by modifying the shear strength relations recommended in TS-500 for RC beams with transverse steel rebar, they can also be applied to RC beams with transverse FRP rebars.
