Sürdürülebilir Kalkınma Amaçları

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• MakaleYalnız künye2024/r/gumushane/11295
  Availability of sedimentary and volcanic rock deposits on Northeastern Turkey as concrete aggregates

  Çavdar, Ahmet; Çavdar, Özlem

  Turkey has large aggregate deposits; however, these deposits cannot be used effectively due to a lack of controls. This can lead to fatal errors, as in the 6 February 2023 Turkey-Syria earthquakes. The main motivation of this study is to investigate the availability of existing and new aggregate deposits as concrete aggregates in northeastern Turkey. Thus, the quality of aggregates in this region will be studied comparatively. This research was carried out with aggregate samples taken from 30 different rock quarries in 10 different provinces in this region of Turkey. First, the locations of 30 crushed rock aggregates were identified, and their petrographic, mineralogical, physical, geometric and durability properties were determined. Fifteen different test procedures were applied to 30 crushed rock samples. It was concluded that these rocks are generally sedimentary rock types and that 18 of these 30 samples are of limestone origin. To obtain high-strength concrete, in addition to quality cement, the aggregates used must also be of high quality. The use of aggregate resources mentioned in this study for building concrete will contribute to the production of high-strength concrete. These samples, which generally have sufficient physical, mechanical and durability properties, meet the limitations of the standards much better than concrete aggregates. High-statistical-performance regression equations were obtained for the physical and durability properties.

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• MakaleYalnız künye2018/r/gumushane/16684
  Earthquake Performance of Reinforced-Concrete Shear-Wall Structure Using Nonlinear Methods

  Çavdar, Ozlem; Çavdar, Ahmet; Bayraktar, Ender

  In earthquake engineering, the performance-based design method is used to determine the expected performance level of structures under an earthquake effect. The level of performance is related to the damage situation that could occur in the structure after the earthquake. In performance-based structural design, it is predicted that more than one damage level can emerge under one earthquake effect. In this study, the seismic behavior of a reinforced-concrete shear-wall building that collapsed during the 2003 Bingol earthquake was investigated by nonlinear static analysis and nonlinear dynamic analysis. The selected reinforced-concrete shear-wall structure is located in Bingol, Turkey. Local code was considered for assessing a seismic performance evaluation of the selected reinforced-concrete shear-wall building. The performance goals of the reinforced-concrete shear-wall structure were evaluated by applying the pushover (incremental equivalent earthquake load) method and procedures of the code and nonlinear dynamic analysis. According to the code, the reinforced-concrete shear-wall building was not expected to satisfy life safety performance levels under a design earthquake. In this study, one collapsed building was selected in order to test the reliability and usability of performance analysis methods under different earthquakes.

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• MakaleYalnız künye2018/r/gumushane/15340
  A New Nomogram Proposal to Determine Concrete Compressive Strength by Combined Nondestructive Testing Methods

  Bingöl, Şinasi; Çavdar, Ahmet

  Concrete is the most widely used construction material in contemporary construction technology. In particular, it holds an important place in the building industry in the world. Since concrete is a nonhomogeneous material, determining the strength of concrete accurately is quite difficult. In this respect, to check the mechanical properties of concrete in-situ, nondestructive test (NDT) methods can be used. They are useful as they do not damage concrete; however, these test results are sometimes deceptive. To reduce these deceptive results, destructive test methods were proposed to increase the accuracy of nondestructive methods. The objective of this study is to determine the strength of concrete with different characteristic strengths using destructive and NDT methods, and to establish new relationships between the compressive strength of concrete and Schmidt rebound values, and ultrasonic wave velocities. For this purpose, 101 concrete cube samples were prepared. After 7 and 28 days of curing, Schmidt rebound and ultrasonic wave velocity tests were applied as NDT methods. New formulations and graphs were established by carrying out a multiple regression analysis between the ultrasonic wave velocities, Schmidt rebound values, and compressive strengths. Thus, a new combined NDT method was developed with a nomogram. Furthermore, the applicability and accuracy of the formula and graph obtained were investigated by comparing the results of core samples from existing structures. The most important findings obtained from the study are summarized below. The concrete strength can be determined with nondestructive formulas obtained with an accuracy of 85%. High strength concrete cube samples are obtained in-house with 1.6% deviation, and core samples in-situ can be obtained with 7.3% deviation with the newly developed NDT nomogram. These test results show that the newly developed NDT formulas in this study are a very good alternative for determining concrete strength in-situ.

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• BildiriAçık Erişim2014/r/gumushane/15789
  Suggestion of new formulations for schmidt hammer and UPV test methods for concrete

  Cavdar, A.; Bingöl, S.

  The concrete is the most widely used building material in Turkey. Especially reinforced concrete dominates at building sector. Because of concrete is an non-homogeneous and non-isotropic material, the strength of concrete cannot be accurately achieved at the site. To control the mechanical properties of concrete in the site, non- -destructive test methods can be used. They are useful for having no damage on concrete, however these test results sometimes gives deceptive results. In this study, two of non-destructive test methods, Schmidt hammer testing and ultrasonic pulse velocity methods were used for determining concrete compressive strength. 101 samples were poured concrete cube dimensions 150×150×150 mm3. On 28th days, firstly, the samples were applied Schmidt hammer test and ultrasonic pulse velocity test and then the compressive strength of these samples was measured by breaking in the press, destructive method. Thus, the new formulations are obtained for Schmidt hammer test and ultrasonic pulse velocity test.

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• MakaleYalnız künye2014/r/gumushane/13272
  Investigation of freeze-thaw effects on mechanical properties of fiber reinforced cement mortars

  Çavdar, Ahmet

  Fibers are used for improving some properties of conventional concrete (which is a brittle material) such as tensile strength, abrasion resistance, absorption and crack control. This study investigates the usability of fibers against the harmful effects of freeze-thaw cycles on cement mortars. For this objective, five different types of fibers, i.e., Polypropylene (PP), Carbon (CF), Aramid (AR), Glass (GF) and Poly vinyl alcohol (PVA) in four different ratios (0.0%, 0.4%, 0.8% and 1.2%) were added to cement mortars along with an amount of air agent. These samples were then subjected to five different freeze-thaw cycles (0, 25, 50, 75 and 100). Thus, mechanical behaviors were investigated under freeze-thaw effects. The most important results of the study are summarized; the fibers increase flexural strength and deflection ability of the samples while decreasing compressive strength, dynamic modulus of elasticity and specific mass. The highest flexural strength was obtained with a 1.2% addition of CF fiber for the samples in normal conditions. The mechanical properties of the samples subjected to repetitive freeze-thaw cycles were also investigated; the best flexural strength was provided with 1.2% CF addition, while the highest dynamic modulus of elasticity was obtained with a 1.2% PP addition.

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• MakaleYalnız künye2013/r/gumushane/13182
  The effects of high temperature on mechanical properties of cementitious composites reinforced with polymeric fibers

  Çavdar, Ahmet

  Polymeric fibers are cheap and popular materials used in the concrete industry, and they may improve the mechanical properties of cementitious composites under high temperature. In this study, three different types of polymeric fibers - Copolymer Polypropylene/polyethylene (CPP), Homopolymer Polypropylene (HPP), and Aramid (AR) - are added to cement mortars with the aim to investigate their mechanical contributions to mortars under high temperature, comparatively. These fibers are added into mortars in five different ratios (0.0%, 0.3%, 0.6%, 0.9% and 1.2%) by volume. The mortars are subjected to following temperatures: 21 °C (normal conditions), 100 °C (oven dry), 450 °C, 650 °C and 850 °C. It is concluded that polymeric fibers used in this study contribute to the flexural strength of mortars under normal dry conditions (100 °C). This effect continues clearly up to 450 °C and polymeric fibers show effects on flexural strength especially at 450 °C. Each fiber shows the best performance different addition ratio when flexural and compressive strength are taken into consideration at the same time under high temperature. The highest increase in flexural strength and the lowest decrease in compressive strength are at 0.3-0.9% fiber addition ratio for HPP, at 0.3-0.6% fiber addition ratio for CPP and at 0.9% fiber addition ratio for AR for every temperature.

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• BildiriYalnız künye2012/r/gumushane/16628
  The Effects of Types and Content of Fibers on Mechanical Properties of Cementitious Composites

  Çavdar, Ahmet

  In this study, four different types of fibers are added to cement mortars and it is aimed to investigate their mechanical contributions to mortars, comparatively. Polypropylene (PP), carbon (CF), glass (GF) and polyvinyl alcohol (PVA) fibers are chosen as fibers to research. These fibers are added into mortars five different ratios (0.0%, 0.5%, 1.0%, 1.50% and 2.0%) by volume. The mechanical properties investigated are flexural strength, deflection and compressive strength of the cement mortars. These properties are determined under two conditions, one of two is saturated surface dry (SSD) and second one is oven dry (OD). It is concluded that each fibers contributes the mechanical properties of mortars in different addition ratios. PVA fibers show the best performance of the fibers investigated in this study. Fibers present best performance at OD condition.

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• MakaleYalnız künye2012/r/gumushane/15621
  A study on the effects of high temperature on mechanical properties of fiber reinforced cementitious composites

  Çavdar, Ahmet

  The flexural strength and ductility properties of cementitious composites (mortar) under high temperature may be significantly improved by incorporating different types of fibers. In this study, four different types of fibers are added to cement mortars with the aim to investigate their mechanical contributions to mortars under high temperature, comparatively. Polypropylene (PP), carbon (CF), glass (GF) and polyvinyl alcohol (PVA) fibers are chosen for research. These fibers are added into mortars in five different ratios (0.0%, 0.5%, 1.0%, 1.50% and 2.0%) by volume. The mortars are subjected to the following temperatures: 21°C (normal conditions), 100°C (oven dry), 450°C and 650°C. The mechanical properties investigated are flexural strength, deflection and compressive strength of the cement mortars. In addition, thin sections of mortars are investigated to obtain changes in mortar because of high temperature. It is concluded that all fiber types contribute to the flexural strengths of mortars under high temperature. However, this contribution decreases with an increase in temperature. The samples with PVA show the best flexural performance (75-150%) under high temperature. CF which does not melt under high temperature also gives high flexural strength (11-85%). The compressive strengths of the mortars reduce under high temperature or with fiber addition. The highest increase in flexural strength and the lowest decrease in compressive strength is at 0.5-1.5% for CF if all temperature conditions are taken into consideration. The optimum fiber addition ratios of the samples containing PP and GF are 0.5% by volume. And for PVA, it is between 0.5% and 1.5% by volume.

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• MakaleYalnız künye2011/r/gumushane/16575
  Abrasion Resistance of Cement Mortar with Different Pozzolanic Compositions and Matrices

  Yetgin, Sukru; Çavdar, Ahmet

  Abrasion of concrete occurs due to scraping, rubbing, skidding, or sliding of objects on its surface. The abrasion resistance of concrete is influenced by a number of factors, such as compressive strength, surfacing finish, aggregate properties, types of hardeners, and curing. The main objective of this study is to determine the effects of the pozzolanic compositions and matrix structure (or voids) on the abrasion resistance of cement mortars. In this study, the mortars produced with cement samples with seven different compositions and varied with an air-entraining agent were subjected to the abrasive effects. Several examples of mortars were evaluated using samples cured for six different periods throughout 1 year. This study is supported by thin section investigations, in addition to being subjected to the basic tests, such as compression, flexure, and abrasion. The Bohme apparatus was used during abrasion tests. To summarize the most important findings from this study, a compact cement matrix is more effective against abrasive effects than mineral additives.

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• MakaleYalnız künye2011/r/gumushane/15718
  Effects of random material and geometrical properties on structural safety of steel-concrete composite systems

  Çavdar, Özlem; Bayraktar, Alemdar; Çavdar, Ahmet

  A stochastic finite element-based algorithm for probabilistic analysis of structural systems made of composite sections with random material and geometrical properties under earthquake forces is proposed in this paper. Uncertainties in the structural parameters can be taken into account in this algorithm. For the perturbation-based stochastic finite element method, only the first two moments of random variables need to be known, and is numerically much more efficient and feasible than simulation techniques. The efficiency and accuracy of the proposed algorithm are validated by comparison with results of Monte Carlo simulation method. A summary of stiffness matrix formulation and perturbation-based stochastic finite element dynamic analysis formulation of structural systems made of composite sections is given. These are followed by suitable numerical examples, which indicate that employment of such a dynamic stochastic finite element method leads to significant economical, efficient and accurate solutions for the dynamic analysis of composite structures with stochastic parameters under earthquake forces.

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