Sürdürülebilir Kalkınma Amaçları
Yayınlar
- MakaleAçık Erişim2026Endüstriyel/Madensel Atıklardan Elde Edilen Geopolimer Bileşenler Üzerinde Taguchi Metodu Yardımıyla Farklı Üretim Parametrelerinin Etkisinin Belirlenmesi
Çavdar, Özlem; Aksüt, Yavuz Selim; Temizer, Hülya
Çimento üretimi kaynaklı CO2 sera gazının ve diğer kirleticilerin başta iklim değişikliği ve küresel ısınma olmak üzere, çevre ve insan sağlığını tehdit ettiği bilinmektedir. Bu çalışmada, geopolimer kompozit harçlar üzerinde farklı üretim parametrelerinin etkisi incelenmiştir. Ana bağlayıcılar olarak yüksek fırın cürufu ve uçucu kül içeren geopolimer yapılara ek olarak endüstriyel ve madensel katkı maddeleri ilave edilmiştir. Bağlayıcılar üzerinde kür sıcaklığı, kür süresi ve endüstriyel /madensel atıklar gibi birçok parametrenin etkisi araştırılmıştır. Bu kapsamda Taguchi metodu kullanılarak 3 farklı seviye ve 6 farklı parametre ile L27 (36) ortogonal matris oluşturulmuştur. Çalışmada, üç farklı molar oranı (8M,10M,12M) olmak üzere sodyum hidroksit çözeltisi ile sodyum silikat kullanılmıştır. 56 gün atmosferik kür uygulanan numunelere ANOVA analizleri de yapılmıştır. Taguchi ve ANOVA istatistiksel sonuçlarına göre, geopolimer numuneler üzerinde en etkili parametrenin kür sıcaklığı olduğu belirlenmiştir. ‘En büyük en iyidir’ kriteri sonuçlarına göre hazırlanan sinyal/gürültü (S/N) oranı verilerinden en etkin sıcaklığın 75⁰C olduğu anlaşılmaktadır.
- MakaleAçık Erişim2025Yapım Aşamaları Dikkate Alınarak Mevcut bir Köprünün Yapısal Performans Davranışının Belirlenmesi
Çavdar, Özlem; Sarıgün, Osman
Türkiye’de öngermeli kirişlerin hesap ve tasarım esaslarında uluslararası kabul gören American Association of State Highway and Transportation Officials (AASHTO) Köprü Tasarım Yönetmeliği, Türkiye Cumhuriyeti Karayolları Yol Köprüleri Teknik Şartnamesi ve TS 3233 (1979) yönetmeliği kullanılmaktadır. Çalışma kapsamında bu yönetmelikler çerçevesinde üstyapı tasarım esaslarınca model güvenirliliği belirlenen Gümüşhane İli Şiran İlçesi’nde yer alan üç açıklıklı, öngerme kirişli, betonarme yapıya sahip Çirmiş Köprüsü model olarak belirlenmiştir. Bu çalışmanın amacı, öngerme kiriş yöntemiyle inşa edilen karayolu köprüsünün yapısal davranışına yapım aşamalarının ve zamana bağlı malzeme deformasyonları etkisinin belirlenmesi için gerçekleştirilen sonlu eleman analizleriyle yapı elemanlarında ortaya çıkan kesit tesirlerinin karşılaştırmasını yapmaktır. Statik ve doğrusal olmayan yapım aşamalı analizler neticesinde köprü tabliye uzunluğu ve ayak yüksekliğince elde edilen normal kuvvet, kesme kuvveti, eğilme momenti ve yer değiştirme değerleri karşılaştırılarak zamana bağlı malzeme deformasyonlarının ve inşa süresinin önemi ele alınarak incelenmiştir. Çalışmanın sonucunda öngerme kiriş yöntemiyle inşa edilen köprü tasarımlarının sadece servis durumunu dikkate alacak şekilde değil yapım aşamalarının ve zamana bağlı malzeme deformasyonlarının da dikkate alınarak çözümlenmesi gerektiği belirlenmiştir.
- MakaleAçık Erişim2025Microstructural investigation of geopolymer composites obtained from recyclable waste materials
Çavdar, Özlem; Temizer, Hülya
Today, researchers are exploring materials that could replace cement and provide solutions for utilizing waste products. In this study, a binder was formulated using 85% blast furnace slag and 15% fly ash. Three different additives—marble powder, strontium mineral waste, and titanium dioxide—were incorporated as partial replacements for blast furnace slag at ratios of 5%, 5%, and 1%, respectively, to create geopolymer mortars. The impact of these additives on the flexural and compressive strength of the mortars was evaluated. Furthermore, SEM/EDX analysis was performed to assess the microstructural effects of the additives. The findings revealed that titanium dioxide resulted in the highest compressive strength, recorded at 65.7 MPa. The SEM/EDX analysis suggested that the samples demonstrated a homogeneous internal structure, indicating a robust bond among the components of the matrix.
- MakaleAçık Erişim2025Investigation of new mixtures based on natural rubber and nitrile-butadiene rubber for high damping base isolation systems
Çavdar, Özlem; Yıldız, Zeynep; Naghshineh, Ali Karimzadeh
High damping rubber isolators (HDRBs), which are popular in base isolation systems, extend the natural vibration periods of structures and increase the energy dissipation capacity of the systems. Thus, they can protect structures from damage that may occur in earthquakes. The difference between HDRBs and other elastomer bearings is the chemical formulation of the rubber used. The aim of this study is to prepare a new rubber mixture that is resistant to seismic loads and has good damping properties for HDRBs. In this direction, rubber mixtures were prepared with three different formulations. The mixture of ingredients used in this study is Natural Rubber (NR), Nitrile Butadiene Rubber (NBR), Carbon Black (CB), process oil, Zinc Oxide (ZnO), Stearic Acid (StA), coumaron resin, protective agent, sulfur and accelerators. Quadruple shear block specimens were produced with elastomers produced with mixtures. Dynamic tests were performed on these samples. Elastomer earthquake isolation bearings with a damping ratio of 6% or greater are classified as ‘highly damped’. In this study, values greater than 10% were obtained for damping ratio values at 100% shear stresses. Experimental and numerical analyses revealed that the damping values of the compounds developed with NBR-based formulations are at an acceptable level for highly damped isolators. In general, it was observed that the damping properties increased from 6% to 12%. Therefore, it is thought that the developed HDRB compounds can be used as elastomers in the construction of seismic isolators with high damping properties.
- MakaleYalnız künye2024INVESTIGATION OF THE EFFECTS OF VARIOUS OPERATING PARAMETERS ON GEOPOLYMER MORTARS MADE FROM NATURAL MINERALS AND INDUSTRIAL WASTE MATERIALS
Temizer, Hülya; Çavdar, Özlem
In this study, fly ash (FA) from Sivas/Kangal thermal power plant and blast furnace slag (BFS) from Bolu cement industry were used as the main binder materials. Based on both the literature and preliminary tests, samples were prepared with 85% blast furnace slag and 15% fly ash (85BFS15FA) as the main binder. In addition, the effect of geopolymer main binders and different additives such as mine waste, marble powder, and titanium dioxide were evaluated under various working conditions. The aim was to observe the effect of three different levels and 6 different parameters on the geopolymer samples using the Taguchi optimization method. Accordingly, the L27 orthogonal matrix was created. Three different molar ratios (8M, 10M, 12M) of sodium hydroxide (NaOH) solution and sodium silicate (Na2SiO3) solution were used as alkaline activators. Physical and some mechanical tests such as flexural strength, compressive strength, water absorption, and void ratio were performed on the 7, 28, 56, and 90-day samples, and Taguchi and ANOVA statistical analyses were performed on the 90-day samples. The highest compressive strength observed among 108 samples reached 65.75 MPa in the S20 samples (90-day). Taguchi and ANOVA statistical analyses identified curing temperature as the most significant parameter influencing the geopolymer samples. Additionally, the Signal to Noise ratio data indicated that the optimal curing temperature, determined to be the most effective based on the 'Larger is better' criterion, was found to be 75 ̊C.
- MakaleYalnız künye2024Availability 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.
- MakaleAçık Erişim2023Prekast öngerme kirişli köprünün yapım aşamaları dikkate alınarak zaman tanım alanında doğrusal olmayan analiz yöntemiyle performansının belirlenmesi
Çavdar, Özlem; Sunca, Gülfem Çisem Köse
Mühendislik yapılarının tasarımında gerekli olan yapısal çözümlemelerin gerçekçi sonuçlar verebilmesi için tasarım aşamasında yapının inşa aşaması, süresi ve yapıya esas beton, çelik gibi malzemelerin bu süre zarfında meydana gelecek değişimleri ile beraber dinamik etkilerin de dikkate alınması gerekmektedir. Çalışma kapsamında karayolu köprüsünün uygulama modeli üzerinde gerçekleştirilecek sonlu eleman analizleriyle yapı tasarımlarının sadece servis durumu ve yapım aşamalarını dikkate alacak şekilde değil, zaman tanım alanında gerçek ivme kayıtlarının da kullanılarak dinamik çözümlenmesi gerekliliği amaçlanmıştır. Model olarak seçilen Çirmiş Köprüsü üç eşit açıklığa sahip olup toplam 96 metre uzunluğundadır. Köprü üst yapısı, tabliye ve öngerme kirişlerden oluşmaktadır. Bu tip köprülerin tasarım esaslarında kullanılan AASHTO, TS 3233 Yönetmelikleri ve TCK Yol Köprüleri Teknik Şartnamesi dikkate alınarak köprü üst yapısının model güvenilirliği sağlanılıp çözümlemelere başlanılmıştır. Dinamik etkilerin tespiti amacıyla TBDY-2018 kapsamında belirtilen kurallar çerçevesinde gerçekleştirilen zaman tanım alanında doğrusal olmayan yapım aşamalı analiz ile doğrusal olmayan yapım aşamalı analiz sonuçları karşılaştırılmıştır. Zaman tanım alanında doğrusal olmayan yapım aşamalı analiz sonuçlarının yapı elemanlarında daha yüksek kesit tesirleri ve yer değiştirme değerleri verdiği gözlemlenmiştir. Ülkemizin aktif fay kuşağında yer almasından dolayı yapı tasarımlarının, zaman tanım alanında gerçek ivme kayıtlarının da kullanılarak dinamik çözümlenmesi gerekmektedir.
- MakaleAçık Erişim2022Yüksek bir binanın deprem performansına dış destek kirişlerin etkisinin doğrusal ve doğrusal olmayan yöntemlerle incelenmesi
Çavdar, Özlem; Çelik, Halil İbrahim
Bu çalışmada, Türkiye Bina Deprem Yönetmeliği 2019 (TBDY-2019) esas alınarak 29 katlı betonarme perde-çerçeveli bir yüksek binanın deprem yükleri altındaki davranışı incelenmiştir. TBDY-2019’da tavsiye niteliğinde dış destek kirişlerin yüksek binalarda dayanım fazlalıklarının sınırlandırılmasının gerekliliğine dikkat çeken maddesi dikkate alınarak incelenen 29 katlı binaya, bina yüksekliği H olmak üzere 0.33H ve 0.66H mesafelerinde dış destek kirişler ilave edilmiştir. Oluşturulan iki farklı sayısal model için öncelikle dayanıma göre tasarım kapsamında kullanılacak doğrusal hesap yöntemlerinden mod birleştirme yöntemine göre spektrum analizi gerçekleştirilmiştir. Yüksek binaların davranışını daha doğru tahmin edebilmek için diğer gelişmiş ülkelerdeki deprem yönetmeliklerinde olduğu gibi TBDY-2019’da doğrusal olmayan şekildeğiştirme esaslı tasarım yaklaşımı önerilmektedir. Çalışmanın sonucunda incelenen iki sayısal model için hedeflenen performans etkileri dahilinde kalınıp kalınmadığı tespit edilmiştir ve sonuçlar karşılaştırmalı olarak verilmiştir. Dış destek kiriş kullanılan modelde yapı rijitliği ve perdelerde kesme kuvvetlerinin arttığı görülürken, buna bağlı olarak; yerdeğiştirmeler, göreli kat ötelemeleri, plastik dönme değerleri ve perdeler için eğilme momenti değerlerinin azaldığı görülmüştür.
- MakaleAçık Erişim2022Seismic performance of a high-rise building by using linear and nonlinear methods
Çavdar, Özlem
In this paper, the seismic behavior of the existing reinforced concrete tall building is investigated by using the linear and nonlinear dynamic methods. The selected existing reinforced concrete structure was designed according to Turkey Seismic Code-2007. The performance analysis according to the Turkey Building Earthquake Code-2019 is realized in a 41-story reinforced concrete shear wall-framed structure in Istanbul where active fault lines are located. For high-rise building, firstly, spectrum analysis according to mode superposition methods of linear computational methods used within the scope of strength-based design is performed. Turkey Building Earthquake Code-2019 advises a nonlinear deformation-based design approach to determine more accurately the behavior of high-rise building, as in the earthquake regulations of other developed countries. In addition, the nonlinear time history analyses of building were performed. At the end of the study, torsional irregularity is seen on the normal floors and intermediate floor; stiffness irregularity was found on second floors. In addition, it has been observed in some of the oblique columns of the building that load bearing capacities were exceeded due to creep, axial compressive loads and severe damages occurred. According to the Turkey Building Earthquake Code-2019, the high-rise reinforced concrete shear wall building is not expected to satisfy life safety performance levels under design earthquake.
- MakaleYalnız künye2020Betonarme binaların deprem performanslarına dolgu duvarların etkisinin incelenmesi
Sunca, Fezayil; Çavdar, Özlem; Sunca, Gülfem Çisem Köse
Bu çalışmada, kat içinde farklı oran ve düzende yerleştirilen dolgu duvarların betonarme binaların sismik davranışlarına olan etkileri araştırılmıştır. Türkiye Bina Deprem Yönetmeliği (TBDY-2018)'ne uygun olarak tasarımı gerçekleştirilen binaların performansları zaman tanım alanında doğrusal olmayan analiz yöntemiyle tespit edilmiştir. Analizler için 11 adet deprem kaydı, yakın ve uzak fay etkileri, depremlerin büyüklüğü, zemin cinsi ve Ülkemizin faylanma mekanizması gibi parametreler dikkate alınarak seçilmiştir. Seçilen ivme kayıtları, basit ölçeklendirme yöntemi kullanılarak TBDY-2018'de verilen yatay elastik tasarım spektrumuyla uyumlu olacak şekilde ölçeklendirilmiştir. Analizlerde 5 farklı oranda dolgu duvar dikkate alınmıştır. Bu dolgu duvarlar diyagonal (eşdeğer) basınç çubuğu olarak analizlerde dikkate alınmıştır. Binanın sonlu eleman modelinde SAP2000, kesit analizlerinde ise RESPONSE2000 programı kullanılmıştır. Analizler sonucunda, her bir dolgu duvar oranı için binalardan elde edilen mod şekilleri, titreşim periyot değerleri, göreli kat ötelemesi oranları ve bina performans seviyeleri karşılaştırmalı olarak sunulmuştur.
- MakaleYalnız künye2015Stochastic seismic analysis of Kömürhan Highway Bridge with varying material properties
Çavdar, Özlem; Bayraktar, Alemdar; Altunışık, Ahmet Can
Stochastic seismic finite element analyses of the Kömürhan Bridge, the material properties of which are described by random fields, are presented in this paper. The stochastic perturbation technique and Monte Carlo simulation (MCS) method are used in the analyses. A summary of MCS and perturbation-based stochastic finite element dynamic analysis formulation of the structural system is given. The Kömürhan Bridge, located on the 51st km of Elazığ-Malatya highway in the east of Turkey, was chosen as a numerical example. The Erzincan earthquake in 1992 was considered a ground motion, since it took place in the vicinity of the bridge. The material properties were considered to be random variables. During the stochastic analysis, displacements and internal forces of the bridge under consideration were obtained using the perturbation-based stochastic finite element method (SFEM), as well as the MCS method. The selected random variables were elastic modulus and mass density. The efficiency and accuracy of the proposed SFEM algorithm were validated through comparison with results of the MCS method.
- MakaleYalnız künye2014Pushover and nonlinear time history analysis evaluation of a RC building collapsed during the Van (Turkey) earthquake on October 23, 2011
Çavdar, Özlem; Bayraktar, Alemdar
The nonlinear seismic behavior of a collapsed reinforced concrete (RC) residential building in the city of Van in Turkey is investigated by the static pushover and nonlinear time history analyses. The selected RC structure was designed according to the 1975 version of Turkish Earthquake Code (TEC-1975). The building had experienced heavy damage, and it was demolished in the Van earthquake on October 23, 2011. The 2007 version of Turkish Earthquake Code (TEC-2007) is considered for the assessing seismic performance evaluation of the selected RC building. The RC structure presents collapse performance level under the earthquake loads. Besides, the analytical solutions show that different performance levels for the sections are obtained from the pushover and nonlinear time history methods.
- MakaleYalnız künye2013Probabilistic sensitivity analysis of suspension bridges to near-fault ground motion
Çavdar, Özlem
The sensitivities of a structural response due to variation of its design parameters are prerequisite in the majority of the algorithms used for fundamental problems in engineering as system uncertainties, identification and probabilistic assessments etc. The paper presents the concept of probabilistic sensitivity of suspension bridges with respect to near-fault ground motion. In near field earthquake ground motions, large amplitude spectral accelerations can occur at long periods where many suspension bridges have significant structural response modes. Two different types of suspension bridges, which are Bosporus and Humber bridges, are selected to investigate the near-fault ground motion effects on suspension bridges random response sensitivity analysis. The modulus of elasticity is selected as random design variable. Strong ground motion records of Kocaeli, Northridge and Erzincan earthquakes are selected for the analyses. The stochastic sensitivity displacements and internal forces are determined by using the stochastic sensitivity finite element method and Monte Carlo simulation method. The stochastic sensitivity displacements and responses obtained from the two different suspension bridges subjected to these near-fault strong-ground motions are compared with each other. It is seen from the results that near-fault ground motions have different impacts stochastic sensitivity responses of suspension bridges. The stochastic sensitivity information provides a deeper insight into the structural design and it can be used as a basis for decision-making.
- MakaleYalnız künye2011Effects 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.
- MakaleYalnız künye2010Stochastic finite element analysis of long-span bridges with CFRP cables under earthquake ground motion
Çavdar, Özlem; Bayraktar, Alemdar; Adanur, Süleyman; Başaǧa, Hasan Basri
Stochastic seismic analysis of long-span bridges with Carbon fibre reinforced polymer (CFRP) cables are presented in this study through combination of the advantages of the perturbation based stochastic finite element method (SFEM) and Monte Carlo simulation (MCS) method. Jindo cable-stayed and Fatih Sultan Mehmet (Second Bosporus) suspension bridges are chosen as an example. Carbon fibre reinforced polymer cable (CFRP) and steel cables are used separately, in which the cable's cross sectional area is determined by the principle equivalent axial stiffness. Geometric nonlinear effects are considered in the analysis. Uncertainties in the material are taken into account and Kocaeli earthquake in 1999 is chosen as a ground motion. The efficiency and accuracy of the proposed algorithm are validated by comparing with results of MCS method. It can be stated that using of CFRP cables in long-span bridges subjected to earthquake forces is feasible.
- MakaleYalnız künye2010Stochastic finite element analysis of a cable-stayed bridge system with varying material properties
Çavdar, Özlem; Bayraktar, Alemdar; Adanur, Süleyman
Stochastic seismic finite element analysis of a cable-stayed bridge whose material properties are described by random fields is presented in this paper. The stochastic perturbation technique and Monte Carlo simulation (MCS) method are used in the analyses. A summary of MCS and perturbation based stochastic finite element dynamic analysis formulation of structural system is given. The Jindo Bridge, constructed in South Korea, is chosen as a numerical example. The Kocaeli earthquake in 1999 is considered as a ground motion. During the stochastic analysis, displacements and internal forces of the considered bridge are obtained from perturbation based stochastic finite element method (SFEM) and MCS method by changing elastic modulus and mass density as random variable. The efficiency and accuracy of the proposed SFEM algorithm are evaluated by comparison with results of MCS method. The results imply that perturbation based SFEM method gives close results to MCS method and it can be used instead of MCS method, especially, if computational cost is taken into consideration.
- MakaleYalnız künye2009Stochastic finite element analysis of structural systems with partially restrained connections subjected to seismic loads
Çavdar, Özlem; Bayraktar, Alemdar; Çavdar, Ahmet; Kartal, Murat Emre
The present paper investigates the stochastic seismic responses of steel structure systems with Partially Restrained (PR) connections by using Perturbation based Stochastic Finite Element (PSFEM) method. A stiffness matrix formulation of steel systems with PR connections and PSFEM and MCS formulations of structural systems are given. Based on the formulations, a computer program in FORTRAN language has been developed, and stochastic seismic analyses of steel frame and bridge systems have been performed for different types of connections. The connection parameters, material and geometrical properties are assumed to be random variables in the analyses. The Kocaeli earthquake occurred in 1999 is considered as a ground motion. The connection parameters, material and geometrical properties are considered to be random variables. The efficiency and accuracy of the proposed SFEM algorithm are validated by comparison with results of Monte Carlo simulation (MCS) method.