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    Buckling of axially loaded shell structures made of stainless steel
    (Techno-Press, 2023) Zeybek, Ozer; Celik, Ali Ihsan; Ozkilic, Yasin Onuralp
    Stainless steels are commonly employed in engineering applications since they have superior properties such as low maintenance cost, and high temperature and corrosion resistance. These features allow them to be preferred in cylindrical shell structures as well. The behavior of a cylindrical shell structure made of stainless steel can be quite different from that made of carbon steel, as the material properties differ from each other. This paper deals with buckling behavior of axially loaded cylindrical shells made of stainless-steel. For this purpose, a combined experimental and numerical study was carried out. The experimental study comprised of testing of 18 cylindrical specimens. Following the experimental study, a numerical study was first conducted to validate test results. The comparisons show that finite element models provide good agreement with test results. Then, a numerical parametric study consisting of 450 models was performed to develop more generalized design recommendations for axially compressed cylindrical shell structures made of stainless steel. A simple formula was proposed for the practical design purposes. In other words, buckling strength curve equation is developed for three different fabrication quality.
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    Buckling of axially loaded shell structures made of stainless steel
    (Techno-Press, 2023) Zeybek, Ozer; Celik, Ali Ihsan; Ozkilic, Yasin Onuralp
    Stainless steels are commonly employed in engineering applications since they have superior properties such as low maintenance cost, and high temperature and corrosion resistance. These features allow them to be preferred in cylindrical shell structures as well. The behavior of a cylindrical shell structure made of stainless steel can be quite different from that made of carbon steel, as the material properties differ from each other. This paper deals with buckling behavior of axially loaded cylindrical shells made of stainless-steel. For this purpose, a combined experimental and numerical study was carried out. The experimental study comprised of testing of 18 cylindrical specimens. Following the experimental study, a numerical study was first conducted to validate test results. The comparisons show that finite element models provide good agreement with test results. Then, a numerical parametric study consisting of 450 models was performed to develop more generalized design recommendations for axially compressed cylindrical shell structures made of stainless steel. A simple formula was proposed for the practical design purposes. In other words, buckling strength curve equation is developed for three different fabrication quality.
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    Effects of reinforcing steel tanks with intermediate ring stiffeners on wind buckling during construction
    (Elsevier Sci Ltd, 2023) Zeybek, Ozer; Ozkilic, Yasin Onuralp
    Many tank structures may not be stable during the construction phase, and this may lead to their becoming vulnerable to buckling under environmental loading conditions such as wind. Installing intermediate ring stiffeners of the proper size at the mid-height of the cylindrical shell may be the most effective way to stabilize these structures, especially under the effects of wind action. In the study, analytical and numerical studies were conducted to identify the required strength and stiffness for the intermediate ring stiffener. First, a new cylin-drical shell -to-intermediate ring stiffness ratio was derived by considering curved beam and shell membrane theories. For strength criteria, the tributary height and the effect of shell-ring interaction on the internal forces and moments were examined by making use of Linear Analysis (LA) and Geometrically Nonlinear Analysis (GNA). The stress resultants developed in the intermediate ring stiffener were identified so that they could be used as strength criteria. For stiffness criteria, by considering the changes in the buckling resistance based on the developed stiffness ratio, an expression to compute the minumum intermediate ring stiffness was determined. In addition, Geometrically Nonlinear Analysis including Imperfections (GNIA) was also performed to examine the effect of the geometric imperfections on buckling strength of the steel tank with an intermediate ring stiffener, taking different imperfection amplitudes into account. The developed design equations in simple algebraic form can be utilized for the structural stability of cylindrical steel tanks during erection.
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    Influence of Replacing Cement with Waste Glass on Mechanical Properties of Concrete
    (Mdpi, 2022) Zeybek, Ozer; Ozkilic, Yasin Onuralp; Karalar, Memduh; Celik, Ali Ihsan; Qaidi, Shaker; Ahmad, Jawad; Burduhos-Nergis, Dumitru Doru
    In this study, the effect of waste glass on the mechanical properties of concrete was examined by conducting a series of compressive strength, splitting tensile strength and flexural strength tests. According to this aim, waste glass powder (WGP) was first used as a partial replacement for cement and six different ratios of WGP were utilized in concrete production: 0%, 10%, 20%, 30%, 40%, and 50%. To examine the combined effect of different ratios of WGP on concrete performance, mixed samples (10%, 20%, 30%) were then prepared by replacing cement, and fine and coarse aggregates with both WGP and crashed glass particles. Workability and slump values of concrete produced with different amounts of waste glass were determined on the fresh state of concrete, and these properties were compared with those of plain concrete. For the hardened concrete, 150 mm x 150 mm x 150 mm cubic specimens and cylindrical specimens with a diameter of 100 mm and a height of 200 mm were tested to identify the compressive strength and splitting tensile strength of the concrete produced with waste glass. Next, a three-point bending test was carried out on samples with dimensions of 100 x 100 x 400 mm, and a span length of 300 mm to obtain the flexure behavior of different mixtures. According to the results obtained, a 20% substitution of WGP as cement can be considered the optimum dose. On the other hand, for concrete produced with combined WGP and crashed glass particles, mechanical properties increased up to a certain limit and then decreased owing to poor workability. Thus, 10% can be considered the optimum replacement level, as combined waste glass shows considerably higher strength and better workability properties. Furthermore, scanning electron microscope (SEM) analysis was performed to investigate the microstructure of the composition. Good adhesion was observed between the waste glass and cementitious concrete. Lastly, practical empirical equations have been developed to determine the compressive strength, splitting tensile strength, and flexure strength of concrete with different amounts of waste glass. Instead of conducting an experiment, these strength values of the concrete produced with glass powder can be easily estimated at the design stage with the help of proposed expressions.
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    Mechanical Behavior of Crushed Waste Glass as Replacement of Aggregates
    (Mdpi, 2022) Celik, Ali Ihsan; Ozkilic, Yasin Onuralp; Zeybek, Ozer; Karalar, Memduh; Qaidi, Shaker; Ahmad, Jawad; Burduhos-Nergis, Dumitru Doru
    In this study, ground glass powder and crushed waste glass were used to replace coarse and fine aggregates. Within the scope of the study, fine aggregate (FA) and coarse aggregate (CA) were changed separately with proportions of 10%, 20%, 40%, and 50%. According to the mechanical test, including compression, splitting tensile, and flexural tests, the waste glass powder creates a better pozzolanic effect and increases the strength, while the glass particles tend to decrease the strength when they are swapped with aggregates. As observed in the splitting tensile test, noteworthy progress in the tensile strength of the concrete was achieved by 14%, while the waste glass used as a fractional replacement for the fine aggregate. In samples where glass particles were swapped with CA, the tensile strength tended to decrease. It was noticed that with the adding of waste glass at 10%, 20%, 40%, and 50% of FA swapped, the increase in flexural strength was 3.2%, 6.3%, 11.1%, and 4.8%, respectively, in amount to the reference one (6.3 MPa). Scanning electron microscope (SEM) analysis consequences also confirm the strength consequences obtained from the experimental study. While it is seen that glass powder provides better bonding with cement with its pozzolanic effect and this has a positive effect on strength consequences, it is seen that voids are formed in the samples where large glass pieces are swapped with aggregate and this affects the strength negatively. Furthermore, simple equations using existing data in the literature and the consequences obtained from the current study were also developed to predict mechanical properties of the concrete with recycled glass for practical applications. Based on findings obtained from our study, 20% replacement for FA and CA with waste glass is recommended.
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    Optimum usage of waste marble powder to reduce use of cement toward eco-friendly concrete
    (Elsevier, 2023) Ozkilic, Yasin Onuralp; Zeybek, Ozer; Bahrami, Alireza; Celik, Ali Ihsan; Mydin, Md Azree Othuman; Karalar, Memduh; Hakeem, Ibrahim Y.
    In this study, waste marble powder (WMP) was used to replace cement of concrete in specific amounts. To accomplish this aim, WMP was replaced at 10%, 20%, 30%, and 40% of the cement weight, and a reference concrete sample without WMP (REF) was created to compare the compressive strength, splitting tensile strength, and flexural strength. The replacement of WMP at 10%, 20%, 30%, and 40% of the cement weight resulted in 5.7%, 21.7%, 38.1%, and 43.6% decreases in the compressive strength compared with REF. Furthermore, the splitting tensile strength results commonly followed the same trend as the compressive strength. However, WMP at 10%, 20%, 30%, and 40% led to 5.3%, 8.6%, 19.4%, and 26.7% decreases in the flexural strength compared with REF. In addition, three different calculations, ranging from simple to complex, were proposed to compute me-chanical resistances of concrete with WMP. These proposed calculations for practical ap-plications were validated using values from the literature and the implications obtained from the current research. While the simple calculations were based on the strength of REF and the WMP percentages, the complex calculations were dependent on the design of the concrete mixture, age of the samples, and the WMP percentages. For the complex calcu-lations, the ANN approach was used with the help of the coefficient of determination (R2) for the K-fold cross validation method. All the proposed methods provided high accurate estimation to predict the properties of concrete with WMP. Based on the studies, utilizing 10% WMP as the replacement of cement is recommended to obtain the optimum benefits considering both mechanical and environmental aspects. Moreover, scanning electron microscope (SEM) and energy dispersive X-ray (EDX) analyses were then conducted to observe the interaction of WMP in concrete. According to the SEM analyses, some pores were detected and the interfacial transition zone was observed in the reaction zone. On the other hand, based on the EDX analyses, the presence of WMP in concrete was manifested by the presence of high levels of calcium.(c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
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    Performance Assessment of Fiber-Reinforced Concrete Produced with Waste Lathe Fibers
    (Mdpi, 2022) Celik, Ali Ihsan; Ozkilic, Yasin Onuralp; Zeybek, Ozer; Ozdoner, Nebi; Tayeh, Bassam A.
    The amount of steel waste produced is on the increase due to improvements in steel manufacturing industries. The increase in such wastes causes significant environmental problems and, furthermore, a large area is also required to store these waste products. Instead of disposing of these wastes, the reuse of them in different industries is an important success in terms of both reducing environmental pollution and providing low-cost products. From this motivation, the effect of lathe scrap fibers generated from Computer Numerical Control (CNC) lathe machine tools on concrete performance was investigated in this study. Pursuant to this aim and considering different fiber content, an experimental study was conducted on some test specimens. Workability and slump values of concrete produced with different lathe scrap fibers were determined, and these properties were compared with those of plain concrete. For the hardened concrete, 150 mm x 150 mm x 150 mm cubic specimens and cylindrical specimens with a diameter of 100 mm and a height of 200 mm were tested to identify compressive strength and splitting tensile strength of the concrete produced with different volume fracture of lathe waste scrap (0%, 1%, 2% and 3%). With the addition of the lathe scrap, the compressive and splitting tensile strength of fiber-reinforced concrete increases, but after a certain value of steel fiber content, there is a decrease in workability. Next, a three-point bending test was carried out on samples with dimensions of 100 x 100 x 400 mm and a span length of 300 mm to obtain the flexure behavior of different mixtures. It has been shown that the flexural strength of fiber-reinforced concrete increases with an increasing content of waste lathe. Furthermore, microstructural analysis was performed to observe the interaction between lathe scrap fiber and concrete. Good adhesion was observed between the steel fiber and cementitious concrete. According to the results obtained, waste lathe scrap fiber also worked as a good crack arrestor. Lastly, practical empirical equations were developed to calculate the compressive strength and splitting tensile strength of fiber-reinforced concrete produced with waste lathe scrap.
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    Stability of laterally unsupported shear links in eccentrically braced frames
    (Wiley, 2022) Ozkilic, Yasin Onuralp; Zeybek, Ozer; Topkaya, Cem
    I-shaped links in eccentrically braced frames (EBFs) are susceptible to lateral or lateral torsional buckling when subjected to cyclic link rotations. Lateral bracing should be provided at the ends of the I-shaped links in order to prevent these failures. Requirements for such braces are available in widely used design specifications such as the AISC Seismic Provisions for Structural Steel Buildings (AISC341-16) and EC8. These requirements limit the use of I-shaped links in bridge piers and elevator shafts. A combined experimental and numerical study was undertaken to investigate the behavior of laterally unsupported I-shaped links under cyclic loading. The experimental study consisted of testing of six nearly full-scale EBFs where the link length, link length ratio, and presence of lateral supports were considered as the prime variables. The test results demonstrated that short links with link length ratios less than 1.22 can experience inelastic link rotations greater than the codified limit of 0.08 rad even without lateral bracing. A numerical parametric study was conducted to develop more generalized design recommendations for laterally unsupported I-shaped shear links. Stability of one-story one-bay EBFs was studied using geometrically and materially nonlinear finite element analysis including imperfections. The numerical results showed that I-shaped links without lateral bracing can provide a stable response when the link length ratio is less than 1.15. In addition to this limit, the ratio of the elastic critical buckling capacity to the plastic shear capacity should be greater than 3.5 and 2.5 for links with and without axial force, respectively.