137
Arşivlenen Tez
5
DOI Atanmış
4%
DOI Oranı
Arşivlenen Tez
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.
indexliAçık ErişimTRBeton 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.
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.
Fracture behavior of high strength concretes containing silica fume and metakaolin
The study presented in this thesis reports the findings of an experimental study conducted on fracture behavior of high strength concretes incorporating metakaolin (MK) and silica fume (SF). The concrete mixtures with water-to-binder (w/b) ratio of 0.28 and 570 kg/m3 binder content were designed for the experimental study. MK or SF modification was achieved through replacing Portland cement (PC) with mineral admixture by 5% and 15% of the total binder content. Moreover, a plain concrete mixture was produced as control for comparison. The effectiveness of MK and SF incorporation on the compressive strength, splitting and flexural strengths, modulus of elasticity, fracture energy, and characteristic length of concrete were monitored at the end of 28 days of water curing. The results have revealed that the utilization of mineral admixtures provided improvement in fracture properties such as increased fracture energy. Moreover, the results obtained for SF concretes demonstrated a similar trend to the ones incorporating MK. Increasing the replacement level from 5% to 15% resulted in relatively better performance for the concretes including mineral admixture.
Flow field around hydrokinetic turbines
In the search for clean, renewable and sustainable energy, the hydrokinetic energy which is harnessed from moving water of rivers, streams and oceans is being studied as a predictable and environmentally benign source. Compare to conventional hydropower turbines, hydrokinetic turbines are new technology in electricity generation and need to be improved from efficiency point of view. In this study, a vertical axis cross-flow hydrokinetic turbine, namely, a modified form of Savonius turbine was investigated. The working principles of cross-flow hydrokinetic turbines are different from those of commonly used horizontal axis turbines. The advantages of this type of turbines are; independency from the current direction including reversibility, stacking and self-starting without complex pitching mechanisms. The turbine has been simulated in a three dimensional and fully developed rectangular open channel flow. Computational fluid dynamics (CFD) simulation of the hydrokinetic turbine was performed by computationally solving the Reynolds-Averaged Navier-Stokes Equations (RANS). In computational studies ANSYS FLUENT, which is commercially available software was employed. CFD can be used to support turbine design and performance over a wide range of parameters to minimize the number of prototypes which are used for optimization and experimental studies. CFD can also provide a cost-effective way of evaluating detailed full scale effects, such as mooring lines or local bottom bathymetry features, on both turbine performance and environmental assessment. Keywords: Computational Fluid Dynamics, Hydrokinetic Turbines, Kinetic Energy, Renewable Energy, ANSYS FLUENT
Determining the hydrological characteristics of the Greater Zap River basin by gis
Water resources management is closely linked to the concept of river basin characteristics. Basin is a dynamic and very complex system which has mainly two types of characteristics; geographic and hydrologic. In this study, the hydrologic characteristics of the Greater Zab River Basin were determined by employing Geographic Information System (GIS). GIS techniques are useful not only in obtaining data from a basin; they also provide valuable contribution in performing the spatial distribution of hydrological data in assessment of water resources projects. The Greater Zab River is approximately 460 km long, flowing through Turkey and Iraq with a total catchment area of about 26,325 square kilometres (km2). The headwater of the Greater Zab River originates in the mountainous area near Lake Van, Turkey, where it springs at an altitude of 4,168 m above sea level and joins the Tigris River in the south western of the city of Hewler (Erbil), Iraq. The terrain pre-processing models, namely, fill sinks, flow direction, flow accumulation, stream networks, watershed boundary have been acquired from digital elevation model (DEM) by using spatial analysis tools in ArcGIS. Hydrological processing such as, map of sub-catchments, characteristics of sub-catchments, river network map and river network characteristics have been determined by employing ArcHydro tools. On the other hand hydrological analysis such as, slope map, Thiessen polygon map, Thiessen polygon areas were defined by Arc Toolbox. The annual average discharge of the stream flow at five flow measurement stations (FMS) along the river and the annual total precipitations measured at twenty-four rainfall measurement stations in the basin were used here in order to perform the hydrological analysis of the basin. The annual average discharge values were obtained from monthly average discharge measurements while the annual total precipitations were acquired from monthly total precipitations. Based on the stream flow measurements, rainfall-runoff coefficients were estimated by rational method for five sub-basins. The rainfall-runoff coefficient for the whole basin was found to be 0.53. Keywords: Greater Zab, Basin Characteristics, GIS, ArcHydro, Rational Method