Browsing by Author "Altun, Fatih"

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Citation - WoS: 26
Citation - Scopus: 29
Determination of Stress-Strain Relationship Based on Alkali Activator Ratios in Geopolymer Concretes and Development of Empirical Formulations
(Elsevier Science Inc, 2023) Ozbayrak, Ahmet; Kucukgoncu, Hurmet; Atas, Oguzhan; Aslanbay, Huseyin Hilmi; Aslanbay, Yuksel Gul; Altun, Fatih
Fly ash-based geopolymer has recently gained attention of researchers due to its potential application, as well as being an alternative binder with low emissions compared to ordinary Portland cement (OPC) in concrete production. Studies which are conducted on the design and mechanical properties of structural members produced from fly ash geopolymer concrete (GPC) are very important in terms of increasing the use of this concrete. The aim of this study is to obtain experimental data on the effect of sodium silicate/sodium hydroxide (SS/SH) and alkali activators/fly ash (AA/FA) ratios on the mechanical properties of a low calcium heat-cured fly ash geopolymer. In addition, it is to reveal the similarities and differences of OPC and GPC by comparing the mathematical formulations in existing regulations and concrete models with experimental data. Thus, geopolymer cylinder concrete samples were produced using 15 different mixtures with SS/SH ratios of 1.5, 2.5 and 3.5, while AA/FA ratios of 0.4, 0.5, 0.6, 0.7 and 0.8. At the end of the study, the optimum SS/SH ratio was obtained as 2.5. A decrease in the AA/FA ratio increases the compressive and splitting tensile strength, while an increment increases the ductility and consuming energy. In addition, the relationship between the experimental data and the splitting tensile strength and modulus of elasticity formulations depending on the compressive strength given in other studies and regulations as a part of literature was investigated, and then, two alternative empirical formulations considering the ratios of alkali activators were proposed at the end of the regression analysis. When the stress-strain relationship of OPC concrete models and GPC mixtures were compared, the closest unconfined concrete model for GPC concrete was the Hognestad model.
Structure Health Monitoring Using Wireless Sensor Networks on Structural Elements (vol 82, pg 68, 2019)
(ELSEVIER, RADARWEG 29, 1043 NX AMSTERDAM, NETHERLANDS, 2020) Ayyildiz, Cem; Erdem, H. Emre; Dirikgil, Tamer; Dugenci, Oguz; Kocak, Taskin; Altun, Fatih; Gungor, V. Cagri
This paper presents a system that monitors the health of structural elements in Reinforced Concrete (RC), concrete elements and/or masonry buildings and warn the authorities in case of physical damage formation. Such rapid and reliable detection of impairments enables the development of better risk management strategies to prevent casualties in case of earthquake and floods. Piezoelectric (PZT) sensors with lead zirconate titanate material are the preferred sensor type for fracture detection. The developed sensor mote hardware triggers the PZT sensors and collects the responses they gather from the structural elements. It also sends the collected data to a data center for further processing and analysis in an energy-efficient manner utilizing low-power wireless communication technologies. The access and the analysis of the collected data can be remotely performed via a web interface. Performance results show that the fractures serious enough to cause structural problems can be successfully detected with the developed system.
Citation - WoS: 11
Citation - Scopus: 11
The Seismic Behaviour of RC Exterior Shear Walls Used for Strengthening of Intact and Damaged Frames
(Springer, 2020) Kucukgoncu, Hurmet; Altun, Fatih
Several strengthening techniques such as steel plate bonding, external post-tensioning, steel bracing, or addition of new structural elements have been widely used to improve the seismic behaviour of structures, which suffer from earthquakes. Especially, adding infill walls and shear walls to the structures are preferred because of the added increase in lateral strength and stiffness. Nevertheless, applications of these techniques have some difficulties in terms of labour, cost, usage, and comfort for occupants. Due to these difficulties, the exterior shear wall, instead of an infill wall, is applied to strengthen structures, especially for public buildings like schools, hospitals, etc. In this study, the seismic behaviours of the exterior shear walls used to strengthen intact and damaged frames were investigated experimentally. For this purpose, reinforced concrete shear walls were positioned in parallel to the exterior sides of the damaged and the intact three-dimensional frames. Both frames were tested under cyclic loads. After the investigation, the hysteresis curve, strength envelope, stiffness degradation, and the energy dissipation capacity were obtained to reveal the seismic behaviour of the strengthening exterior shear walls. In addition to these, the differences in behaviours of the shear walls applied to damaged and intact frames were identified.
Citation - WoS: 55
Citation - Scopus: 64
Structure Health Monitoring Using Wireless Sensor Networks on Structural Elements
(Elsevier Science Bv, 2019) Ayyildiz, Cem; Erdem, H. Emre; Dirikgil, Tamer; Dugenci, Oguz; Kocak, Taskin; Altun, Fatih; Gungor, V. Cagri
This paper presents a system that monitors the health of structural elements in Reinforced Concrete (RC), concrete elements and/or masonry buildings and warn the authorities in case of physical damage formation. Such rapid and reliable detection of impairments enables the development of better risk management strategies to prevent casualties in case of earthquake and floods. Piezoelectric (PZT) sensors with lead zirconate titanate material are the preferred sensor type for fracture detection. The developed sensor mote hardware triggers the PZT sensors and collects the responses they gather from the structural elements. It also sends the collected data to a data center for further processing and analysis in an energy-efficient manner utilizing low-power wireless communication technologies. The access and the analysis of the collected data can be remotely performed via a web interface. Performance results show that the fractures serious enough to cause structural problems can be successfully detected with the developed system. (C) 2018 Elsevier B.V. All rights reserved.
Citation - WoS: 1
Citation - Scopus: 2
Structure Health Monitoring Using Wireless Sensor Networks on Structural Elements (Vol 82, Pg 68, 2019)
(Elsevier, 2020) Ayyildiz, Cem; Erdem, H. Emre; Dirikgil, Tamer; Dugenci, Oguz; Kocak, Taskin; Altun, Fatih; Gungor, V. Cagri
Numerical Analysis and Experimental Comparison of Stress and Stiffness Parameters of Steel Reinforced Geopolymer Concrete Columns
(Elsevier Sci Ltd, 2026) Ozbayrak, Ahmet; Kucukgoncu, Hurmet; Aslanbay, Huseyin Hilmi; Aslanbay, Yuksel Gul; Altun, Fatih
Despite extensive research, Geopolymer concrete (GPC) lacks reinforced concrete construction and design specifications. Developing such specifications requires comprehensive studies to promote the use of GPC, which is known for its superior performance and environmental benefits compared to ordinary Portland cement concrete (OPC). This study numerically investigated and compared the behavior and strength of fly ash-based geopolymer-reinforced concrete columns with the experimental results. Comparisons with OPC were made based on existing specifications. Herein, FEM analyses were conducted on 16 GPC and 4 OPC columns under eccentric axial compressive loads. Parameters such as eccentricity, reinforcement ratio, curing method, and activation solution ratios were varied. According to average numerical results, the GPC columns have 7% more moment capacity and 30% more curvature values than OPC. Moreover, GPC columns absorbed more energy than OPC columns. Also, GPC columns have higher axial load and bending moment carrying capacities than OPC for numerical results. Error analysis between FEM and experimental data revealed a strong correlation, with MAPE values of 8.88% (axial load) and 7.20% (moment) for GPC columns, confirming the reliability of the numerical model. ACI 318 and Eurocode 2 specifications were deemed applicable for GPC columns, provided axial loads are limited per TEC 2018.
One-Story Three-Dimensional Frame Structures Behavior Strengthened With External Shear Wall Under Cyclic Loading: An Experimental Study
(Taylor & Francis Ltd, 2022) Kucukgoncu, Hurmet; Altun, Fatih
In this study, the seismic behaviors of strengthened three-dimensional frames, as in real-life structures, are presented. Three reinforced concrete (RC) frames, containing common structural deficiencies were constructed to represent existing older structures. The bare, damaged, and undamaged frames, strengthened by RC external shear walls with steel tie beams, were tested under a reversed cyclic load. The experimental results indicated that strengthening by external shear walls made significant contributions to the frames in lateral strength, stiffness, and energy dissipation capacity. This proposed method appears to be an efficient technique for strengthening structures in an effective, economical, and practical way.