178
Archived Theses
5
DOIs Assigned
3%
DOI Rate
Archived Theses
Evaluation of a simple method for the preliminary design of low-to-medium rise reinforced concrete structures
A simple method is evaluated in this study for suitability to the preliminary design of low-to-medium rise reinforced concrete building-type structures without significant irregularity problems. The method discussed herein, originally proposed by Ersoy (2013) is based on essential rules and guidelines of earthquake engineering such as member ductility and global ductility. Two main classes of structures are considered: buildings consisting solely of frames and buildings with frames and shear walls (also referred to as dual systems). In frame systems, the seismic loads are resisted entirely by columns, whereas in dual systems it is assumed that the columns take 30% and the shear walls take 100% of the lateral loads. It is also assumed that the locations of the shear walls are well configured on the plan so that the lateral loads are distributed fairly throughout the entire frame and the concentration of forces around a specific region is prevented. In an effort to ensure flexural failure of the members, the dimensions of the vertical members are determined under the action of gravity loads and seismic loads. Simple expressions representing the demand are derived as a function of plan area of the stories, column tributary areas, dead loads and live loads. Once the demands and required capacities are specified, dimensions of the load bearing members are determined by taking into account restrictions regarding certain effects leading to brittle failure such as axial stress, shear stress and interstory drifts. For the flexural and shear reinforcements, certain ratios of minimum reinforcements are adopted for the analysis. The buildings are modeled as per ASCE 41-13 with the aforementioned criteria and nonlinear static pushover analyses are performed to validate the expected performance level.
Kazıklı temellere etki eden dinamik yüklerin statik yükler cinsinden uygulanabilirliğinin araştırılması
Bu çalışmada, sıvılaşan zeminde inşa edilen yüzen kazık gruplarına etki eden dinamik yüklerin statik yükler cinsinden uygulanabilirliği incelenmiştir. Tez çalışmasında, Plaxis paket programı dinamik modülü yardımı ile dinamik etki altında kazık grubu deformasyonları belirlenmiş, bu deformasyonlardan geri hesap yapmak sureti ile kazık grubuna aynı deformasyonları yaptıracak eşdeğer statik yükler bulunmuştur.Sonuç olarak, dinamik etkilerin de hesaba katıldığı programların kullanılamadığı durumlarda, üst yapıdan gelecek yüklere göre sıvılaşan zeminlerde kazık temel tasarımı için dinamik kuvvetler statik yük cinsinden uygulanabilirliği belirlenmiştir. 6,0 şiddetine kadar olan depremler için kazık temele etkiyen statik düşey yük %100 arttırılarak; şiddeti 6,0~8,0 arasında değişen depremler için kazık temele etkiyen düşey statik yük %200 arttırılarak dinamik etki statik yük cinsinden göz önüne alınmış olur.Anahtar Kelimeler: Kazık Temeller, Sürtünme Kazıkları, Deprem, Sıvılaşma, Plaxis
Uçucu kül esaslı geopolimer tuğla üretimi
Bu tez çalışması yapı malzemesi biliminin son zamanlarda ilgi gören konularından olan sürdürülebilir ve enerji tasarrufu sağlayan malzemelerin üretimi ile ilgilidir. Çalışma geopolimerizasyon yöntemini araştırarak, C ve F sınıfı uçucu kül yüksek dayanımlı yapı tuğlası üretiminde değerlendirilmesini amaçlamaktadır. Geopolimer 1970 yılında Prof. Dr. Joseph Davidovits'in geliştirdiği yeni nesil malzemedir. Geopolimer jeolojik kaynak malzemelerden alkalinasyon ve polikondensasyon ile sentezlenmektedir. Uçucu kül esaslı geopolimer malzemeler hammaddenin fırınlama işlemi gerektirmemesi yönüyle enerji tasarrufu sağlayan ürünlerdir. Çalışmanın başlangıcında Türkiye'deki termik santrallerin bir kısmından sağlanan uçucu küllerin mineral kompozisyonunun geopolimer sentezine uygunluğu araştırılmıştır. En uygunsuz kompozisyondaki C sınıfı uçucu kül ile en uygun kompozisyondaki F sınıfı uçucu kül deneysel çalışmanın devamında kullanılmıştır. 30 MPa basınçla şekillendirilen 40?60?80?100 ºC arasındaki sıcaklıklarda 2?4?6?24?48?72 saat aralığındaki ısıl işlemlerle üretilen, geopolimer tuğlaların basınç dayanımı, su içeriği, yoğunluk değerleri değerlendirilmiştir. F sınıfı uçucu külden üretilen geopolimer tuğlalar Si / Al molar oranının 2 olduğu 60 ºC sıcaklıkta etüvde 24 saat uygulanan ısıl işlem sonrasında optimum basınç dayanımı değerini 45 MPa düzeyinde vermiştir. Suda çözme kurutma ve öğütme işlemleri sonrasında C sınıfı uçucu küllerle üretilen geopolimer tuğlalar geleneksel tuğla malzeme standartlarına ulaşmaktadır.Anahtar Kelimeler:Geopolimer tuğla, alkalizasyon, su içeriği, yoğunluk, basınç dayanımı
indexedOpen AccessTRBeton dolgulu çift cidarlı oluklu çelik kolonların eksenel ve döngüsel yükleme altındakı davranışının sonlu elemanlar yöntemiyle incelenmesi
Bu tez çalışmasında, beton dolgulu çift cidarlı oluklu çelik kompozit kolonların döngüsel yükler altındaki yapısal davranışı sonlu elemanlar yöntemi kullanılarak incelenmiştir. Çalışmanın temel amacı, oluklu çelik cidar kullanımının kolonların taşıma kapasitesi, süneklik performansı ve enerji yutma kapasitesi üzerindeki etkilerini ortaya koymaktır. Bu kapsamda, farklı kesit geometrilerine sahip üç konfigürasyon ele alınarak kompozit kolon numuneleri modellenmiştir. Bu konfigürasyonlar, iç çelik cidarı oluklu ve dış çelik cidarı düz olan kolonlar, dış çelik cidarı oluklu ve iç çelik cidarı düz olan kolonlar ve iç ve dış çelik cidarları düz olan referans kolonlardan oluşmaktadır. Ayrıca çelik cidar kalınlığının ve kolon narinliğinin yapısal davranış üzerindeki etkisi incelenmiştir. Tüm modellerde malzeme özellikleri sabit tutulmuştur. Analiz sonuçlarına göre oluklu kesit geometrisine sahip kolonların, düz cidarlı kolonlara kıyasla daha yüksek taşıma kapasitesi ve daha kararlı bir yük–deplasman davranışı sergilediği belirlenmiştir. Ayrıca, dış oluklu tasarımın beton çekirdeğe daha iyi bir sargılama sağladığını, yerel burkulmayı geciktirdiğini ve böylece referans kolona göre ortalama üç kat, içten oluklu kolonlara göre ise bir buçuk kat daha fazla enerji yutma kapasitesi sağladığını göstermiştir. Çelik cidar kalınlığının artırılması hem nihai kapasitede hem de enerji dağıtımında önemli iyileştirmeler sağlamıştır. Genel olarak, bu çalışma, özellikle oluklu dış yüzeye sahip çift cidarlı çelik kesitlerin geometrisinin faydalı olduğunu ve deprem riski yüksek bölgelerdeki yapılar için avantajlı olabileceğini ortaya koymaktadır.
Assessing the efficiency of pre-soaked expanded perlite usage incorporation on the self-healing ability of cementitious composites
Usage of Pre-Soaked Expanded Perlite Aggregate (PS-EPA) as an internal curing material in the production of cementitious based composites has been shown to an influential method of counteracting autogenous shrinkage and therefore early-age cracking. These beneficial effects of PS-EPA usage evoke that the use of PS-EPA as internal water reservoirs may also promote the self-healing ability of cracks in cementitious composites. This study assesses the efficiency of the PS-EPA usage on the self-healing of cementitious composites. For this purpose, PS-EPA was replaced with the aggregate used in cementitious composites at different replacement rates. Cementitious composite specimens with or without PS-EPA were stored in water up to 28 days, and then mechanical loading was applied to generate deterioration on the specimens. At the age of 28 days, pre-loaded and sound specimens exposed to continuous air exposures for a month. The degree of deterioration as result of mechanical pre-loading and the degree of self-healing were determined by the characterization of crack numbers and widths, transport (chloride ion permeability) and mechanical properties (splitting tensile strength), and compared with the specimens without PS-EPA. Test results revealed that mechanical properties, crack widths and numbers, and chloride ion permeability of specimens were significantly improved with the increase of PS-EPA content while enhanced further hydration and healing capability of specimens under the continuous air exposure after pre-loading.
Design of crack free, durable and ductile concrete for sustainable highway rigid pavement overlays
The superior ductility with high strength and improved durability characteristics suggest that the Engineered Cementitious Composites (ECC) could be used as an alternative to conventional concrete overlay materials. In this thesis, the research program was divided into two phases. In the first phase, an experimental program was performed to understand the dependence of the composite properties on its mixture composition governed by mineral admixture types and maximum aggregate size and amount. In the second phase, two different ECC-overlay mixture designs were selected from the first phase: one with high strength and moderate ductility, and the other with moderate strength and high ductility. The performance of two selected ECC mixture as an overlay material was investigated by laboratory experiments. Micro-silica concrete (MSC) was also prepared as a reference mixture. The layered composite specimens? flexural strength, reflective cracking characteristics and bond properties were investigated as performance criteria. The test results show that, layered ECC beams have significantly increased both load carrying capacity and deformability and shows better crack width control in comparison with MSC composite beam. Also, ECC increases bond strength, eliminates the reflective cracking and delamination failure in repaired systems and ECC overlay with 35 mm thickness is superior to MSC overlay with 50 mm thickness for rehabilitating concrete pavements. The superior performance of ultra-thin ECC overlay system under mechanical loading will be expected to prolong the service life of the structure under traffic loading and to reduce the costs in the rehabilitation work.
Nonlinear pushover analysis of medium and high rise buildings with X-braces
This study aims to investigate the structural behavior of medium and high rise frame buildings with and without X-brace. The performance of the concentrically X-braced frame structures were examined using pushover analysis. For this purpose, steel moment resisting frame buildings having four to sixteen stories were considered. All buildings have the same plan and contain three bays on each direction. The existing steel frames had two different design properties and designated as flexible moment-resisting frames and rigid moment-resisting frames. Then, X-braces were introduced into the middle bay of each frame. The nonlinear analyses were performed using the finite element analysis program of SAP 2000. The parameters such as capacity curve, inter-storey drift index, global damage index, and base shear were evaluated for the frame systems. It was observed that the incorporation of concentric X-braces into the frame resulted in a significant enhancement in the structural behavior of the existing frames.
High early strength ductile cementitious composites with characteristics of low early age shrinkage
Reduced performance in concrete infrastructures is mainly caused by the formation of cracks, which may arise due to deteriorating mechanisms during service life. In most cases, reduced performance calls for urgent repairs to the degraded section. Therefore, it is highly desirable to develop dimensionally stable, ductile repair materials that can attain adequately high strength in a limited amount of time, compensate for significant deformation due to mechanical and environmental loadings, and prevent early-age shrinkage cracks. In this paper, the performance of such a material (High Early Strength Engineered Cementitious Composites ? HES-ECC with very low early-age shrinkage capacity) was investigated by studying mechanical properties and dimensional stability. Composites were produced with different water to cementitious materials and slag to Portland cement ratios. In order to rehabilitate composite properties in terms of ductility and early age shrinkage characteristics, saturated lightweight aggregates replaced sand in the mixtures. The experimental results show that the majority of HES-ECC mixtures developed in this study attained compressive strength values of more than 20.0 MPa and minimum flexural strength of 6.0 MPa within six hours. Moreover, the HES-ECC mixtures exhibited strain-hardening behavior with strain capacities comparable to normal strength ECC, as well as substantially reduced autogenous shrinkage strain capacity, both which are unlikely to trigger the formation of cracks in tension at early ages. The integration of these conflicting parameters suggests that HES-ECC can easily meet the need for fast and durable repairs.
Modeling of shear strength of rc beam without web reinforcement by stepwise regression
experimental studies has also been carried out regarding shear strength of RC beams without web reinforcement and a wide range of experimental database (398 tests) has been gathered from literature from 46 separate studies. New expressions are proposed based on the database taking into account the observed behavior for the design of normal-strength reinforced concrete beams without web reinforcement. The database is used for studying parameters that affect shear behavior/strength and for evaluating and comparing four national shear design provision (ACI 318-02, CSA A23.3 2004 edition (Collins, 2003), Euro code EC2 Part 1 (1994, 2003) and the German Code (DIN, 2001)) as well as for identifying research needs.
Ultimate load carrying capacity of thin-walled stiffened structures
To generate more robust designs to serve significant magnitude of compressive forces, plate assemblies are stiffened by specially designed stringers. The benefit of stiffening of a plate structure lies in achieving divided more efficient segments which use compression and bending performances of stringers. The characteristics of structure, expected loading type, used materials, expected performance and employed manufacturing technique are examples of parameters which governs the design and shape of stringers. Generally stiffened panels are constructed as built-up structures, where individual stringers are riveted or welded on thin skins. This way of assembling process has many advantages in conventional stiffened panel manufacturing such as reduction of material cost and production of individual elements with lower imperfection tolerances. In this thesis with the intent of delivering significant key findings, buckling-and post-buckling behaviour of stiffened panels are investigated. Towards this aim, various headings in the field of stiffened panel performance under compressive loadings are studied. Main focus is directed to aircraft stiffened panels. Metallic fuselage panels which comprise the significant components of aircrafts are the main research elements in this thesis. Studied panel configurations selected in such a way that would represent subcomponents of commercial aircrafts. This thesis links experimental and theoretical practices on metallic aircraft panels by laboratory tests and non-linear simulation techniques. Comparisons of the used techniques allowed undertaking some sensitivity and parametric studies on panels? static strength behaviour to deliver the key details. Outcomes of the present study have the potential to guide to build efficient advanced simulation models for compression loaded aircraft panels.