4,283
Archived Theses
21
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Investigation of climate change impact on large dam projects equipped with hydropower
Hydrological prediction is crucial for managing water resources, and innovations like machine learning present an opportunity to enhance predictive modeling capabilities. The aim of this study is to compare the usage of the new machine learning method, CatBoost, with traditional methods about investigating prediction streamflow in the future under climate change scenarios and determining the effect of predicted streamflows on hydropower energy production. The investigation found that CatBoost was superior to conventional models. After it was proven that the best-performing model is CatBoost, future projections according to the NorESM2-MM scenarios were calculated using this model. Climate projections are based on simulations from the Coupled Model Intercomparison Project Phase 6 model, utilizing shared socioeconomic pathway (SSP) scenarios. The results show that SSP3-7.0 and SSP5-8.5 scenarios indicate an increasing trend between 2015 and 2100, while SSP1-2.6 and SSP2-4.5 expect a balancing tendency. This suggests that climate change has little effect on the measuring station and its basin and that the flow is increasing positively. On the other hand, it is noted that the estimated energy amount in the SSP1-2.6 and SSP2-4.5 scenarios is lower, particularly in the 2015–2039 timeframe. The amount of energy computed under the SSP3-7.0 and SSP5-8.5 scenarios, however, shows a notable increase.
Kritik altı açık kanal akımının deneysel ve k- türbülans modelleri ile sayısal analizi
Yavaş değişen kritik altı açık kanal akımının (M1 profili) hız alanı iki farklı debi durumu için bir boyutlu Lazer Doppler Anemometresi (LDA) ile ölçülmüştür. Deneyler ile aynı koşullara sahip akımları idare eden temel denklemler Standard k-ε (SKE), Renormalization Group k-ε (RNG), ve Realizable k-ε (RKE) türbülans modelleri kullanılarak sonlu hacimler yöntemine dayalı ANSYS Fluent yazılımı ile sayısal olarak çözülmüştür. Su yüzü profilinin teorik olarak hesaplanmasında Akışkan Hacimleri Yöntemi (VOF) kullanılmıştır. Sayısal çözümde ağ yapısının sonuçlara olan etkisini belirlemek için Grid Convergence Index (GCI) ölçüt olarak kullanılmıştır. Sayısal hesaplardan elde edilen bulgular deneysel olarak elde edilen bulgularla karşılaştırılmıştır. Yapılan karşılaştırmalar sonucunda, Reliazable k-ε (RKE) türbülans modelinin hız alanının hesaplanmasında, bu çalışmada kullanılan diğer türbülans modellerine göre daha başarılı olduğu görülmüştür.
Investigation of residual shear strength of two-way slab panels exposed to high temperatures
Steel fiber reinforced concrete is an old concept, where first appearance of it was around a 100 years ago, although it's a successful material in improving the behavior of concrete especially when it combines with the conventional steel reinforcement, there's an absence of codes and standard that predict and estimate the real punching capacity of the panels containing steel fiber especially particularly when it is exposed to fire. The current work in this thesis is a twenty slab panels that is casted and tested to obtain the residual punching shear strength after exposing to different temperatures and comparing the results with slab panels in ambient condition, also it is compared with ACI (American concrete institute) predicted results. The recent research results indicate that the steel fiber has a significant improvement on the behavior of concrete in groups under the same conditions, also in general the residual punching shear strength improved after exposing to 150 °C and 300 °C when it compared to the panels containing the same mixture in ambient condition.
Rehabilitation of the damaged glass-fiber reinforced concrete corbels using steel threaded rods
The aim of this thesis is to investigate the efficiency of using threaded rods in a confinement system to rehabilitate damaged glass-fiber reinforced concrete corbels. Some of the specimens were treated with crack repair epoxy before confining for further enhancement. This study is the first experimental investigation that studies rehabilitating reinforced concrete corbels using threaded rods and confinement technique. A total of 19 double sided damaged corbels with different mechanical properties and test parameters were used in the investigation. Differences in specimens are shear span, fiber percentage, diameter of main reinforcement, and concrete strength. All corbels have the same dimensions. Four different rehabilitation styles were tried for the investigation. The rehabilitated specimens were loaded under vertical load until failure. Test results show that the proposed rehabilitation techniques enhanced the bearing capacity of the corbels and improved the ductility remarkably.
Properties of glass fiber reinforced scc and structural performance of short composite columns having such concrete core
Tüpler içerisine yerleştirilerek sargılanan cam fiber takviyeli kendiğinden yerleşen betonun (CFTKYB) yapısal davranışı üzerine yapılmış çalışmalar oldukça azdır. Benzer olarak, yapısal betonlarda cam fiber takviyesi de sınırlıdır. Bu tez kapsamında, iki bilimsel program detaylı olarak tanımlanmıştır. Birincisi, CFTKYB'un davranışını incelemek amacıyla deneysel çalışmalar yapılmıştır. Toplam 15 fiber takviyeli karışım farklı nano silika içeriğinde hazırlanmıştır. Bu karışımların taze ve mekanik performansları test edilmiştir. Tezin ikinci kısmında CFTKYB dolgulu çelik tüplerin yapısal performansları incelenmiştir. Kolonların mühendislik özellikleri, 3 farklı çap-cidar kalınlığı oranında ve çelik akma dayanımında kabul edilerek nümerik olarak değerlendirilmiştir. Beton çekirdek dayanımı üzerine yapılan deneysel çalışmalar, kolonların performansının Eurocode 4, ACI, AIJ ve DL/T standartlarına göre belirlenmesinde kulanılmıştır. Toplam 1080 farklı durum değerlendirilmiştir. Sonuç olarak, CFTKYB'nun tatmin edici mühendislik performansına sahip olduğu görülmüştür. Buna ek olarak, mevcut nümerik çalışma, tasarım yönetmeliklerinin bu yapısal betonlar ile entegre edilmiş kompozit kolonların kapasitelerini makul ölçüde tahmin ettiğini göstermiştir.
Mechanical characteristic of conventional and geopolymer modified uhpc and design code assessment of axially loaded composite members with such concrete
The need for developing new structural members having high performance has gained significant attention in the construction industry all over the world. This thesis covers the material aspects of ultra-high performance conventional and geopolymer concrete (UHPC/UHPGC) and the structural aspects of the composite columns in the case of UHPC/UHPGC used as an infill. For this, the experimental and numerical works were carried out. The experimental work included two phases aim to investigate the possibility of producing and developing UHPC/UHPGC. In the first, a total of 11 conventional UHPC mixes were designed with different binder type and content at fixed micro steel fiber volume fraction. Whereas in the second, a total of 10 UHPGC mixtures were produced with the same parameters used in the first, but with a constant material/alkaline solution ratio. Three curing methods were adopted for the specimens and then they were tested for identifying the material characterization. On the other hand, the numerical work included the structural behavior of the steel tubular columns infilled with conventional and geopolymer modified UHPC. For the composite columns, circular cross-section with fixed slenderness ratio and wall thickness were taken account. However, the diameter to wall thickness ratio and yield strength of the steel tubes varied. Furthermore, a special theoretical procedure was adopted to take the benefit of compressive strength results on the axial behavior of CFST column. Three international design codes of ACI-318R, Eurocode 4 and Chinese code DL/T were used to evaluate and discuss the performance of the composite compression members.
Experimental and numerical study on steel fiber reinforced scc and those filled circular structural steel tubes
The present study aims firstly to investigate experimentally material behavior of steel fiber reinforced self-compacting concrete (SFRSCC) and secondly to introduce a numerical investigation regarding the structural performance of circular structural steel tube columns infilled with SFRSCC. To this purpose, twelve different mixtures were designed. Hooked ends steel fiber was used to produce SFRSCC. Some engineering properties in terms of workability, compressive and flexural strength, fracture energy and steel-concrete bond strength were tested. Thereafter, to simulate the behavior of SFRSCC filled steel tubular short column under concentrically compression load, the experimental results obtained in the first part of the study were utilized in the evaluation of ultimate axial capacity of concrete filled steel tube column. In this context, different diameter to tube thickness ratio and steel grade were utilized. Based on the predicted column axial capacity, a comparative analysis was made by means of international design codes such as Eurocode 4, ACI, AIJ and DL/T. At each code, a total of 216 column capacity results were assessed and discussed herein. The results revealed that the experimental parameters significantly affected the fresh and mechanical performance. Furthermore, the analytical study presented in this thesis showed that the codes assessed a rational capacity for such special composite column.
Effects of steel cnc milling waste on some geotechnical properties of silty soil
The aim of this study is to investigate the properties of silty soil mixed with steel computer numerical control machine (CNC) milling waste (St-CNC-mw). In this study; laboratory experiments including compaction, California Bearing Ratio (CBR), Unconfined Compressive Strength (UCS), consolidation, swelling permeability and direct shear test have been conducted. Soil and St-CNC-mw mixtures at various rates (5%, 10%, 15%, 20% and 25% by dry weight) were tested at maximum dry density and optimum moisture content values of the mixtures. St-CNC-mw materials are coated by zinc to avoid high corrosion rate (electrogalvanisation) and corrosion rate of steel are reduced more than 100 times after coating. The results have shown that the optimum moisture content decreased and maximum dry density increased by increasing St-CNC-mw. Also the CBR increased and the swelling decreased by increasing St-CNC-mw. Soil with 15% St-CNC-mw has the highest UCS value. In addition, internal friction angle and cohesion increased while the coefficient of permeability (k) decreased by increasing St-CNC-mw. Furthermore, the consolidation tests demonstrated that the initial void ratio (eo), swelling index (cs) and the coefficient of consolidation (cv) of the soil decreased while compression index (cc) increased by adding the amount of St-CNC-mw content in the mixture.
Fiber reinforced uhpc and its effect on load carrying capacity of composite tube members according to current design codes
The main objective of using reinforced ultra-high performance concrete (UHPC) by different type and volume of fibers with concrete filled steel tube (CFST) structure is to minimize the size of the structural steel tube and to improve the mechanical, fracture, and shrinkage properties of concrete core. This provides high strength and performance for the composite elements. Accordingly, this thesis consists of two parts: First describes the experimental behavior of UHPC reinforced with various fiber types and concentrations. While the second part presents the research results of the structural behavior of axially loaded steel tube column filled with ultra-high performance fiber reinforced concrete (UHPFRC). For this, 19 UHPC mixtures containing micro-steel, hooked-steel, and micro glass fibers up to 2% volume fractions were produced. All designed mixtures were tested for the mechanical, fracture and physical performance. On the other hand, three outer diameters to wall thickness D/t ratios (30, 60, and 90) corresponded by 300, 450, and 600 MPa of yield strength (fy) of the steel tube were used to calculate the axial load capacity (Nu) of circular CFSTs infilled with mentioned UHPFRCs via design equations given by Eurocode 4 (EC4), American Concrete Institute (ACI), American Institute of Steel Construction (AISC), Architectural Institute of Japan (AIJ), and Chinese (DL/T) codes. The results of code comparison revealed that AIJ and DL/T were so near to EC4 followed by AISC then ACI.
Mechanical behavior of uhpc having various binder compositions and influence of such infilled concrete on the structural response of cfst columns
To enhance the sustainability of a structure, three pillars of the sustainability, namely, environmental, social, and economical factors are needed to be considered in the design. On this issue, the development of new structural composite systems with high performance plays a critical role. This study contained two parts: Firstly, the experimental results on the mechanical behavior of ultra high performance concrete (UHPC) mixed with various binder types and volumes were given. Whereas, the second part provided the numerical results on the structural behavior of steel tube column infilled with such UHPC. For this, single, binary, ternary and quarternary binder systems up to 75% replacement levels were used to develop 26 different UHPC mixtures with low cement content. All designed mixtures were tested for identifying the properties of core concrete. Moreover, three diameter to wall thickness D/t ratios (35, 65, and 95) matched by 300, 450, and 600 MPa of yield strength (fy) of the steel tube were used to calculate and examine the axial load capacity of circular concrete filled steel tube (CFST) with UHPCs through design equations given by Eurocode 4 (EC4), American Concrete Institute (ACI) and Chinese (DL/T) codes. The results of experimental and numerical study were given and discussed accordingly.
Experimental behavior of scc with nano-silica andnumerical analysis of cfst composite columns usingscc as an infill
Composite sections are being increasingly popular in constructionindustry. Among them, concrete lled steel tube (CSFT) members areprimarily suited for dierent structural applications. This compositesystem uses the compressive strength of the concrete core as well asthe strength, stiness and connement eect of the surrounding steeltube. In this thesis, rstly, an experimental study on the behavior ofself- compacting concrete (SCC) containing high volume of nano- silica(up to 6%) and 'y ash (up to 75%) was conducted. Secondly, anumerical investigation on short CFST columns made with SCCproduced in the rst part of study was carried out. The structuralresponse of the composite columns were evaluated under the eect ofcompression up to failure. Two design codes such as AmericanConcrete Institute (ACI) and Eurocode 4 (EC4) were used forcalculating the ultimate axial strength of CFST columns lled with SCC.The 16 SCC mixtures were studied and their concrete compressivestrength results at two dierent testing ages were used to get the code predicted ultimate axial strength of the composite columns. Theexperimental and numerical results were given and discussedcomparatively.
Experimental study for flexural behavior of high strength rc beams with hybrid fibers
An experimental program is achieved in this study to show the enhancement gained from addition of steel, basalt, and glass fibers to the concrete mix on the flexural performance of reinforced concrete beams. Ten different reinforced concrete beams are tested and results are compared. First one is a control beam, group A consist of three beams strengthened with different volumetric ratios (0.5, 1.0, and 1.5 %) of steel fibers. Group B consist of three beams (0.25-0.75, 0.5-0.5, and 0.75-0.25) % of steel and basalt hybrid fibers, and group C consist of three beams (0.25-0.75, 0.5-0.5, and 0.75-0.25) % of steel and glass hybrid fibers. Moreover, 30 standard concrete cubes are tested to show the effect of the fibers on concrete compressive strength, and 30 standard concrete cylinders are tested to show the difference in split strength. Test and comparison results show that group A beams give enhancement in first crack load values, which means enhancement in tension zone characteristic with maximum values of 60 % increase in cracking load for the beam with 1.0 % addition of steel fibers. Yield load is also, enhanced by (9.0 %, 0.4 %, and 5.0 %) increase for beam 1.0 % and 1.5 % volumetric ratios of steel fibers, and (0.5-0.5) % volumetric ratios of steel-glass hybrid fibers, respectively. Ultimate loads are enhanced by 0.6 %, and 2 % for beams with volumetric ratios of 1 % steel fibers and (0.5-0.5) % steel-glass hybrid fibers additives, respectively. Extending this experimental program to study different beam cross sections, deep beams, hybrid beams and creep-shrinkage effect are suggested as future work.
Optimum design of post-tensioned concrete flat slabs using finite element method
Post-tensioned slabs commonly used in building and bridge construction are grouped into two basic categories. These are the unbonded and bonded systems. This thesis investigates the structural behaviour of post-tensioned one-way concrete slabs. A nonlinear finite element model for the analysis of post- tensioned unbonded and bonded concrete slabs at elevated temperatures was developed. The numerical analysis was conducted by the finite element ANSYS software and was carried out on different one-way concrete slabs chosen from literature. A parametric study was conducted to investigate the effect of several selected parameters on the overall behavior of post-tensioned one-way concrete slab. These parameters include the effect of tendon bonding, thermal loading and tendon profile. The results showed that restrained post tensioned slab with bottom surface hotter has smaller failure load capacity. Optimization in its wide sense can be used to solve many engineering problems. A three-dimensional finite element model for the optimization of bonded and unbonded post-tensioned concrete one-way slab was also developed in this study. The total weight of post-tensioned tendons was considered as the objective function. It is concluded that the tendon area design variable of post- tensioned slab is very effective due to, it enables us to find the optimum design of post-tensioned tendon with low cost under suitable service conditions.
Experimental and numerical analysis of thermal behavior of composite bridge girders
Due to their permanent external exposure, bridge structures are under the continuous exposure to the temporal thermal loads. These loads are mainly due to the temporal fluctuation of solar radiation and air temperature. In this research, experimental and FE studies were directed to investigate the thermal behavior of composite girders under the variation of solar radiation and air temperature. This research is divided into four parts. In the first, an experimental work including two composite girder segments, T-Beam and I-Beam, was conducted. The segments were instrumented with thermocouples, strain gages and weather sensors. In the second part, a thermo-mechanical FE analysis was conducted using COMSOL for the two segments, which was verified using the experimental temperature records. Using the verified FE model, a parametric study was conducted in the third part to evaluate the effect of the girder's size. The fourth part was directed to evaluate the long-term temperature variations in Turkey. In this part, the verified FE model in addition to weather history records for more than 50 years of 10 Turkish cities were utilized. The experimental results showed that the temperature variation in concrete parts was higher than in steel for the two segments. Comparisons between the experimental and FE temperatures revealed that the FE models could capture the temperatures accurately. The parametric study disclosed that the thickness of the top concrete flange was the most effective geometrical parameter. The extreme temperature analysis showed that based on the vertical temperature gradients, Turkey can be divided into two regions.
Use of construction and demolition materials to improve geotechnical properties of a clay
A study was conducted to explore the various effects of construction and demolition materials (CDMs), which are considered to be solid waste materials (SWMs), on the geotechnical properties of clay. The properties of the mixed samples were investigated by adding crushed brick pieces (CBPs), dumped asphalt pieces (DAPs), and crushed concrete pieces (CCPs) into clay. The laboratory tests included the testing of consistency limits, California bearing ratio (CBR), unconfined compressive strength (UCS), swelling, consolidation, and direct shear. A series of plate loading tests on clay with 10% CDMs was also carried out in a specially-designed model box made of reinforced concrete with a dimension of 2.0m diameter and depth of 1.5m to gain a deep understanding of the samples. The results show that when the CDMs percentages were 20%, there were decreases of about 15% and 25% in liquid limit and plasticity index of clay, respectively. Small increases of about 3% in γdrymax for the clay were noticed when the DAPs and CCPs content was increased from 5% to 20%. A reduction of about 35% of wopt for clay was shown by increasing the DAP percentage to 20%. The CBR and UCS strength values of the clay were increases by around 25% by increasing the CDMs percentage from 5% to 20%. In the direct shear test, 10% of all CDMs additions gave out the maximum angle of internal friction. In the plate load test, the addition of 10% CDMs increased the ultimate bearing capacity of clay by about 50% to 75%. The oedometer characteristics, including the swelling and consolidation of CDMs-clay mixtures, were controlled mainly by the type and content of CDMs in the clay. Using Plaxis 2D for the program, a remarkable matching of the results of the numerical simulation and the plate load test was observed (R2=0.97).
Investigation of replacement of stirrups with steel fibers in self-compacting reinforced concrete haunched beams
Reinforced Concrete Haunched Beams (RCHBs) are important structural members in the construction sector. Usage of steel fiber reinforced concrete (SFRC) can be considered as a possible replacement to use of traditional shear in RCHBs. Usually one of the disadvantages related to the use steel fiber is that adding fiber to a regular concrete mixture can occur large problems in workability of concrete. Therefore, the use of self-compacting concrete (SCC) is a suitable solution to such a problem and can enhance the workability of fresh concrete. This thesis presents the experimental study for one type of RCHBs. The experimental work consists of 9 self-compacting fiber reinforced concrete (SCSFRC) beams, which is classified into 6 RCHBs and 3 prismatic beams which examined under four-point loading. One type of steel fiber that has a hooked end was used in this study. The studied variables included inclination angle, beam type, and steel fiber percentage. These variables have been significantly influential on the shear behavior of RCHBs. The results show that the higher inclination angle of SCSFRC haunched beams has a negative influence on shear load capacity due to increase in shear stress. Also, the results indicated that the combination of the use SCC and steel fibers in RC beams can significantly improve shear strength, post-cracking behavior, and ductility. Steel fibers both reduced the crack width and converted the failure mode from brittle and sudden to ductile. Furthermore, the results showed that the use of 1% volumetric ratio can be a substitute for minimum shear reinforcement in RCHBs
Ultimate load carrying capacity of steel fiber reinforced self-compacting concrete haunched beams with stirrups
This thesis includes a comprehensive experimental study regarding mechanical behavior of steel fiber reinforced concrete haunched beams. The experimental study was conducted on 12 reinforced concrete beams, 8 of them are RCHBs and 4 are prismatic beams. Different parameters have been adopted by steel fiber ratio, flexural reinforcement, and inclination angle. All the beams were classified into three modes depending on the angle of inclination. The beams were divided into two main groups, each contains 6 RC beams, each group has the same ratio as the steel fiber (SF) and main steel reinforcement and differs from the other group while all the RC beams have been used as stirrups. The results have shown that as the steel reinforcement ratio increases, the load capacity of the RCHBS with an inclination angle of 10o increases as the amount of 40%. Moreover, the effect of increasing the ratio of steel fiber was clear to increase the failure load as compared to the capacity of the beams without steel fiber. Load capacities of these beams are greater than the capacity of prismatic beams with the same parameters. Increasing of steel reinforcement ratio increases the load capacity of the RCHBS with the inclination angle of 15o as an amount of 26%. However, the addition of steel fiber has slightly affected the increase in load failure. It is also noticeable that the increment the angle of inclination decreases the load capacity. The addition of SF has led to an increase in the ductility of the concrete and collapse load, as well as reducing the thickness of cracks compared with specimens that do not contain steel fiber.
Sustainable design of commercial buildings through embodied energy optimization
Nowadays, buildings industry consumes large amounts of energy. The current procedures, which have been used for years, are really lack to be improved, and very important insurances and inventions are required to reduce the energy consumption. In this study, a life cycle energy (LCEA) and carbon dioxide releases ( LCCO2A ) analysis of two commercial buildings has been performed. The study involves the literature review, the records used for such an overall procedure, and approach and offers an application of the method that studies two real commercial buildings built in Gaziantep, Turkey. The intended pattern concentrated on building construction, operating and destruction stages in order to evaluate gross energy consumption and carbon dioxide throughout 50-year lifetime. Energy efficiency and emissions factors are expressed for the buildings per square meter base. The results expressed that the operating stage is prevailing in both commercial buildings and share in86- 90% of the primary energy necessities and 77–86% of CO 2 releases, respectively. The embodied energy (EE) of the buildings calculated for 10–14% of the total life- cycle energy consumption.
Size effect on punching shear behavior of slab-column assembly made from engineering cementitious composite materials (ECC)
Bu çalışmada iki farklı tip (polivinil alkol 6-12 mm ve polipropilen 12 mm) sentetik elyaf eklenerek üretilen çimento bazlı kompozit malzemeden (ECC) oluşan düz plaka kolon bağlantısının zımbalama kesme davranışı araştırılmıştır. Toplam on iki adet döşeme üretilerek test edilmiştir. Deneyler dört gruptan oluşmaktadır. Bunlar PVA 6, PVA 12 ve PP 12 sentetik elyaf kullanılarak üretilen üç grup ile karşılaştırma amacıyla üretilen normal betondan olan dördüncü gruptur. Her bir gruptaki levhaların kalınlığı 50, 60 ve 80 mm olarak değişirken diğer boyutlar sabit (500 × 500 mm) tutulmuştur. Tüm plakalarda aynı donatı oranı 0.12 kullanılmıştır. Test sonuçları, ECC'den yapılan döşemelerin normal betona göre daha az deformasyon verdiğini göstermiştir. Bu, ECC'nin çatlak büyümesini önleme ve genişlemesini engelleme özelliğinden kaynaklanmaktadır. Elyafın eklenmesi tüm yükleme aşamalarında ve özellikle ilk çatlaktan sonra deformasyonlarda bir azalmaya yol açmaktadır. Ayrıca düz döşeme ile taşınan nihai yükün artması, elyafların, yalnızca diyagonal çatlakların ve deformasyon oluşumunu ertelemekle kalmayarak, aynı zamanda zımbalama etkisinin kırılgan davranıştan sünek davranışa doğru değişmesinden olmaktadır. Ayrıca, döşeme kalınlığı arttıkça kesme gerilmesinde azalma görülmüştür. Ancak döşeme kalınlığı arttıkça nominal kesme kuvveti artmaktadır. PVA 6 sentetik elyaf, normal beton göre % 25-43 daha fazla nominal kayma mukavemeti artışı ile diğer elyaf çeşitlerine göre en büyük artışı göstermektedir. Anaktar Kelimeler: Kolon kiriş birleşimi, PVA ve PP elyaf takviyeli beton, , zımbalama kesme.
Investigation of flexural behavior of fibers reinforced geopolymer concrete hallow beams
This study is focused influence of steel and glass fibers on mechanical and structural properties for geopolymer concrete. Furthermore, the effect of hybrid fiber of steel and glass fibers on same these properties was studied also. Where test specimens were manufactured from the geopolymer concrete composites contain of alkaline liquids, 50% fly ash and 50% ground granulated blast furnace slag. The mixtures were designed for 14M molarity and the proportion of sodium silicate equivalent 2.5 than sodium hydroxide and used for producing geopolymer concrete. With this mixture, fibers were added (1%) steel, (0.5%) glass to the full volume of concrete and obtained hybrid fiber by mixing half of amount from both types. The material tests were done for workability, compressive strength (fc') and tensile strength (fsp) for 7, 28 and 56 days. For structural parameters were casted 12 beams (4 solid, 4 circular-hollow and 4 square-hollow) and tested under 3-points monotonic test, for investigation and comparison in terms of Flexural strength, ductility and failure patterns. The experimental test results indicated that there were improved compressive and tensile strength of geopolymer concrete due to use the steel, glass and hybrid fibers. Also these fibers led to improvements in resistance the first crack and ultimate load, ductility increasing, best control on crack patterns and an appropriate converge in the behavior of solid and hollow beams. Key words: Fly ash, Glass fiber, Geopolymer concrete, Hybrid fibers, Steel fiber.
Mechanical behavior of self-compacting fiber reinforced concrete at elevated temperatures
It is worth mentioning that the dense microstructure of the self-compacting concrete (SCC) makes it more brittle and thus less resistant to high temperatures. Therefore, it tends to fail due to spalling and development of cracks are rapid at elevated temperatures. In the present study, the influence of steel fibers on the mechanical properties of SCC after exposure to elevated temperatures are investigated. The effect of steel fiber (SF) on the mechanical properties including compressive and tensile strengths of SCC has been studied. Also, the characteristics of stress-strain curves for fiber reinforced SCC (FR-SCC) were discussed in detail. Experimental results have shown that the addition of SF leads to significant improvement in mechanical properties of SCC, particularly after elevated temperatures. The findings revealed that the polypropylene (PP) fibers were able to prevent the risk of spalling in SCC during heating processes. None of the respective previous studies have investigated the mechanical behavior of fiber-reinforced concrete corbels subjected to elevated temperatures. For this reason, the other aim of the present thesis is a novel experimental attempt to understand the behavior of FR-SCC corbels after exposure to temperatures. This study accounts for the ability of SFs to improve ductility and enhance mechanical behavior of RC-corbels after exposure to elevated temperatures. The results were presented in terms of load-deflection curves, crack patterns and failure modes. Experimental results showed that the SFs have a positive effect on load-carrying capacity and ductility of RC-corbels before and after exposure to elevated temperatures.
An experimental investigation on the effect of water/cement ratio on the compressive strength of ready mixed concrete designed by chemical admixture and different cements
In this study, an experimental investigation was conducted to investigate effect of water/cement ratio on the compressive strength of ready mixed concrete designed by using a chemical admixture and 3 different cements. For each cement type, 5 mixtures were designed with different water/cement (w/c) ratios varying from 0.3 to 0.7 without using admixture and 3 mixtures were designed with different w/c ratios varying from 0.5 to 0.3 by adding admixture. Compressive strength tests were carried out on the 50 mm cubic specimens at the ages of 7 and 28 days. Tests results revealed that when w/c ratio decreased from 0.7 to 0.5, compressive strength increased about 168.2%, 181.9% and 148.0% for each cement type. Compressive strength reduced with decrease in w/c between 0.5 and 0.3. It was attributed to the influence of insufficient mixing and placing of concrete due to lower workability. Superplasticizer was used to improve workability without changing the w/c ratio and significant increases in compressive strength values were observed for w/c of 0.3 about 228.2%, 272.5% and 144.8%. Results showed that cement type has an important role on the compressive strength irrespective of w/c ratio. Compressive strength values of the samples having w/c ratio of 0.5 at the age of 28 days were found to be 26.2, 44.4 and 48.7 MPa for CEMIV, CEMII and CEMI respectively.
Bitümlü ılık karışımların mekanik etüdü
Bitümlü sıcak karışımların karışım ve sıkıştırma sıcaklıklarının yüksek olması enerjinin daha fazla kullanılmasına ve çevrenin olumsuz etkilenmesine sebep olmaktadır. Bu da ülke ekonomisini ve emisyonun artmasıyla çevreyi olumsuz etkilemektedir.Bitümlü karışımların içine katkı maddeleri katılarak, karışımın sıcaklığı normal bitümlü sıcak karışımlara göre 25 ? 55 C daha düşük sıcaklıklara sahip bitümlü karışımlar üretilebilmekte ve sıkıştırılmaktadır. Bu tür bitümlü karışımlar, bitümlü ılık karışımlar olarak adlandırılmaktadır. Katkı maddeleri katılarak üretilen bitümlü ılık karışım, klasik bitümlü sıcak karışım ile aynı ve hatta daha iyi özelliklere sahip olabilmektedir.Bu çalışmada, 160/220 penetrasyon dereceli bitümlü bağlayıcı iki farklı vaks türü FT ? parafin - sasobit (S) ve polietilen vaks (PW), ile modifiye edilmiştir. Hazırlanan numunelerin üzerinde Marshall stabilite ve dolaylı çekme deneyleri yapılarak, karışımın performansı incelenmiştir.
Çelik tel içeren betonarme kirişlerin mekanik davranışı
Bu çalışma çelik tellerin 20 kg/m3, 40 kg/m3, 60 kg/m3, 80 kg/m3 ve 100 kg/m3 miktarlarda betona ve geleneksel betonarme kirişlere katılmasıyla elde edilen numunelerin mekanik özelliklerinin araştırılmasını içermektedir. Bu amaçla üretilen çelik tel takviyeli betonlar üzerinde basınç dayanımı, elastisite modülü ve eğilme dayanımı tayini deneyleri yapıldı. Ayrıca, eğilme deneyinden elde edilen yük-sehim eğrilerinden çelik tel donatılı betonların toklukları elde edildi. Bunun yanı sıra, çelik tellerin betonarme kirişlerin eğilme altında kırılma yüküne ve tokluklarına etkisini belirlendi.Yapılan deneysel çalışma sonunda, çelik tellerin betonların eğilme dayanımı ve tokluğunu belirgin şekilde arttırdığı belirlendi. Ayrıca, çelik tellerin geleneksel donatılı betonarme kirişlerin eğilme altında kırılma yüklerini ve tokluklarında kayda değer iyileştirmeler yaptığı sonucuna varıldı.
Genleştirilmiş vermikülit kullanılarak üretilen çelik tel takviyeli-çimento esaslı kompozitlerin yüksek sıcaklık dirençleri
Bu çalışma, yüksek sıcaklığın genleştirilmiş vermikülit içeren çelik tel takviyeli çimento esaslı kompozitlerin fiziksel ve mekanik özelliklerinin deneysel olarak araştırılmasını kapsamaktadır. Bu amaçla, vermikülit/çimento hacimsel oranı 4, 6 ve 8 olan harçlara hacimce %0, %0,5, %1 ve %1,5 çelik tel ilave edilmiş, 40x40x160 mm boyutlarında numuneler üretilmiştir. Üretilen numuneler, 20°C, 300°C, 600°C ve 900°C sıcaklıklara maruz bırakıldıktan sonra ortam sıcaklığına kadar soğutulmuş, eğilme ve basınç dayanımları ile ultrases geçiş hızları araştırılmıştır.Deneysel çalışmadan elde edilen sonuçlara bağlı olarak, genleştirilmiş vermikülit ile üretilen çelik tel takviyeli çimento esaslı kompozitlerin sıcaklık altındaki mekanik dayanımlarına vermikülit/çimento oranı ve çelik tel miktarının etkisi ortaya konmuştur. Kuru birim hacim ağırlıkları 795-1295 kg/m3 arasında değişen, 20°C sıcaklıktaki basınç dayanımları 6,0-15,0 MPa ve eğilme dayanımları 2,5-6,2 MPa arasında değişen çimento esaslı hafif kompozitler üretilmiştir. Çelik tel içeriğinin sıcaklığa altında numunelerin dirençlerini çelik tel içermeyen numunelere kıyasla artırtığı görülmüştür. Sıcaklığa maruz bırakılan numunelerin basınç ve eğilme dayanımlarında, ultrases geçiş hızlarında azalmalar tespit edilmiştir.
Genleştirilmiş vermikülit kullanılarak üretilen silis dumanı katkılı-çimento esaslı kompozitlerin yüksek sıcaklık dirençleri
Bu tez çalışmasında genleştirilmiş vermikülit ile üretilen, farklı oranlarda silis dumanı içeren çimento esaslı harçların yüksek sıcaklık etkisindeki mekanik dayanımları araştırılmıştır. Bu amaçla, üç değişik vermikülit/çimento hacimsel oranına sahip karışımlar içerisine, çimento ağırlığının %5, %10 ve %15'i oranında silis dumanı ilave edilerek, 40 mm× 40mm ×160 mm boyutlarında dikdörtgen prizma numuneler üretilmiştir. Üretilen numuneler; yüksek sıcaklık fırınında, 300 ºC, 600 ºC ve 900 ºC sıcaklık etkisinde bırakıldıktan sonra eğilme ve basınç dayanımı ile ultrases geçiş hızı testlerine tabi tutulmuşlardır. Elde edilen sonuçlar, oda sıcaklığı etkisindeki numunelerin mekanik dayanımları ve ultrases geçiş hızları ile karşılaştırılmıştır.Yüksek sıcaklığa dirençli harç üretmek amacıyla yapılmış olan bu çalışma sonucunda, deney sonuçları değerlendirilmiştir. Yüksek sıcaklık etkisinde silis dumanı içeren numunelerin, silis dumanı içermeyen numunelere göre, basınç dayanımlarının yüksek, eğilme dayanımlarının ve ultrases geçiş hızlarının düşük olduğu gözlenmiştir.
Bitümlü ılık karışımların neme karşı hassasiyetlerinin belirlenmesi
Avrupa ve ABD'de sera gazı salınımı ve enerji tüketimini azaltmak, çevreye ve ekonomiyekatkı sağlamak amacıyla araştırmalar yapılmakta olup, bitümlü karışım endüstrisi özellikleBitümlü Ilık Karışım (Warm Mix Asphalt - WMA) teknolojisi üzerinde yoğunlaşmaktadır.Yüksek sıcaklıklarda, bitümlü ılık karışım katkı maddeleri ile modifiye edilmiş bitümlübağlayıcıların viskoziteleri, katkısız bitümlü bağlayıcılara göre daha düşük olmaktadır. Bunedenle bitümlü karışımın, karıştırma ve sıkıştırma sıcaklıkları daha düşük olabilmektedolayısıyla da enerji tüketimini ve çevreye salınan emisyon miktarını azaltmaktadır.
Çelik tel ve silis dumanı katkılı betonların sodyum klorürlü ortamda mekanik davranışı
Bu çalışma % 10, % 20 silis dumanı, % 0,4, % 0,8 çelik tel katkılı betonların 0 g/L, 15 g/L ve 30 g/L sodyum klorürlü (NaCl) ortamda mekanik özeliklerinin araştırılmasını içermektedir. Bu amaçla üretilen taze betonlar üzerinde birim ağırlık ve işlenebilme (VeBe)deneyleri yapılmıştır. Ayrıca 28. ve 91. günlerde sertleşmiş beton numuneler üzerinde çelik teltakviyeli ve silis dumanı katkılı betonlar üzerinde basınç dayanımı, yarmada çekme dayanımı ve eğilme dayanımı tayini deneyleri yapılmıştır.Bu çalışmada elde edilen deney sonuçlarına bağlı olarak, çelik telin ve silis dumanının tuzluortama maruz betonların performansına belirgin etkisi olmadığı söylenebilir.
Improving some of geo technical properties of an organic soil using crushed waste concrete
Many urban areas are now struggling with the high volume of solid wastes, especially the construction and demolition materials. In this study, the crushed waste concrete (CWC), which is considered as one of the biggest components of solid waste, was used to improve some geotechnical properties of an organic soil. The CWC at the ratios of 5%, 10%, 15%, and 20% were added to organic soil in order to conduct an intensive series of experimental tests. The laboratory tests included the consistency limits by fall cone, modified compaction, unconfined compressive strength (UCS), and swelling percentage. The results show that when the CWC percentages were increased to 50%, there were decreases of about 30% and 60% in liquid limit and plasticity index of clay, respectively. Increase of about 35% in γdrymax for the organic soil was noticed when the CWC content was increased from 10% to 50%. A reduction of about 50% of wopt for organic soil was shown by increasing the CWC percentage to 50%. The UCS values of the organic silt increases by around 25% by increasing the CWC percentage up to 50%. The swelling percentage increased by adding CWC up to 30%, and then decreased with the addition of CWC up to 50%.and increasing the CWC proportions has a positive effect on the consolidation features of organic soil. CWC decreased the consolidation of organic soil by decreasing the compression index (Cc) and the time of consolidation for organic soil was decreased due to the increasing of the coefficient of consolidation (Cv) and coefficient of conductivity (k) for organic-CWC mixtures
Concrete-filled steel tube columns and the confinement effect
Concrete-filled steel tube (CFST) columns are one of the pioneering types of composite columns and are increasingly used in applications that require the support of large loads such as tall buildings, bridges, and offshore structures. CFST columns are used due to their high strength, high stiffness, high ductility, and high energy absorption capacities besides high speed of construction, relatively low economic cost, and compatibility with different types of connections. These advantages result due to the composite action between the steel and the concrete where the concrete and the steel act together to combine the best features of both the steel tube and concrete to yield efficient performance. The steel tube confines the infilled concrete and serves as a perpetual formwork. Also, it works as longitudinal and transverse reinforcement. The circular cross-section offers enhanced confinement to the concrete compared to other shapes. This thesis examines the conduct of circular CFST columns and the confinement effect with different types of strengths of concrete. In addition to classical CFST columns, a new configuration, concrete-filled double circular steel tube (CFDCST) stub columns were also studied, which provides an effective improvement in compression, ductility, and stiffness capacities relative to classical CFST columns of the corresponding size. Furthermore, the possibility of the CFDCST column concept for repairing deformed CFST columns was examined and gave good results. For assessment, test results were compared with the estimates of the AISC360-16, EC4, AS5100.6, and AIJ2001 design specifications.
Concrete filled steel tube composite beams and improvement of flexural performance
Concrete-filled steel tube (CFST) beams represent one of the most promising composite members within the CFST family. CFST beams are widely utilized in different structural applications including, bridges of several typologies, offshore structures, and high-rise buildings. CFST beams display several advantages over the conventional tubular steel or reinforced concrete members, including high flexural capacity, high stiffness, significant ductility, and energy absorption ability. The superior performance of CFST beams is thanks to the composite action between the steel profile and the concrete core. The concrete core delays and even precludes local buckling of the confining steel tube, and this significantly increases strength and ductility. On the other hand, the steel section provides continuous longitudinal and lateral reinforcement for the concrete core in addition to effective confinement. The essential goal of this thesis is to experimentally investigate the flexural performance of concrete-filled steel tube beams subjected to a pure bending load. To achieve this aim three different typologies of CFST beams have been studied comprising lightweight-concrete filled steel tube (LWCFST) beams, self-compacting-concrete filled steel tube (SCCFST) beams, and finally, SCCFST beams retrofitted using external bolted steel plates, all with various parameters and configurations. Five international pioneering design codes have been adopted to assess the flexural capacities of the tested CFST beams, involving the AISC 360-16, EC4-2004, DBJ/T13-51-2010, AS 5100.6-2004, and AIJ-2001. Furthermore, a theoretical model was developed to predict the moment resistance of the retrofitted SCCFST beams.
Çelik tel kanca tipinin betonların mekanik özelliklerine etkisi
Betonların mekanik özeliklerinin arttırılması amacıyla lif kullanımı uzun zamandır yapılan yaygın bir uygulamadır. Lif olarak çeşitli malzemeler kullanılabilmekle beraber üstün mekanik özelikleri dolayısıyla çelik teller daha yüksek performans istenilen uygulamalarda tercih edilmektedir. Çelik tellerin uzunluğunun, narinliğinin, miktarının, dayanımının betonlar üzerindeki etkileri birçok araştırmacı tarafından incelenmiştir. Son yıllarda yapılan araştırma sonuçları ve teknolojinin gelişmesiyle çelik tel çeşitleri artmış ve farklı kanca tipine sahip çelik teller üretilmiştir. Tez kapsamında, çelik tel özelikleri ve miktarı farklı olan betonlar üzerinde bir deneysel çalışma yapılmıştır. Deneysel çalışmada, 3 faklı kanca tipi ve dayanıma sahip çelik teller (3D, 4D ve 5D) 4 farklı miktarda (15, 30, 45, 60 kg/m3) 3 farklı basınç dayanımdaki (C40/50, C50/60 ve C80/95) betonlara katılmıştır. Elde edilen betonlar üzerinde basınç dayanımı, elastisite modülü ölçümü, yarmada çekme dayanımı ve eğilme dayanımı deneyleri yapılmış ve betonlara ait mekanik özellikler belirlenmiştir. Çalışma sonucunda elde edilen verilerle çelik tel kanca tipinin betonların mekanik özellikleri üzerine etkisi ortaya konmuştur. Ayrıca beton numunelerden alınan kesitler üzerinde yapılan görüntü analizleri ile mekanik özellikler arasında ilişkiler incelenmiştir. Anahtar Kelimeler: Beton, çelik tel, kanca tipi, mekanik özelikler, görüntü analizi.
Design of the optimum ogee spillway toe for a maximum energy dissipation
Hydraulic design of a spillway has been one of the most studied subjects in hydraulic engineering. Properly designed, flow condition dependent spillways will be able to release water efficiently and safely from a dam reservoir to the downstream. This study aims to investigate the energy dissipation at the toe of ogee spillway by making an ogee spillway with different end sill models at the downstream by using a commercially available Flow-3D. The case A model was an ogee spillway with rectangular end sill, the case B, C, D and E with a curved end sill with radius of 0.10, 0.15, 0.18 and 0.20 meters, respectively, and the case F which has an inclined end sill. The major amount of energy dissipation occurs at the toe in the region where the hydraulic jump takes place. The hydraulic jump is used to dissipate energy at the downstream. These models were compared to one another to see the corresponding energy loss respectively. To simulate the turbulent flow, the "𝑘−𝜀" turbulence model is done in the numerical modelling. The numerical result shows that the model with curved end sill dissipates more energy than others. In the case F model with inclined end sill, it can be concluded that the hydraulic jump did not occur, the velocity remained high for all cases of discharge and the energy loss is insignificant regarding its form. Therefore, energy loss changes in relation to discharge, most loss occurs at low discharge while in the case of high discharges energy loss decreases. Results indicated numerical methods as convenient and time-saving, with least errors.
Yapay sinir ağları modeliyle betonarme taşıyıcı sistem maliyetinin tahmin edilmesi
Bu çalışmada, brüt toplam kat alanı, brüt zemin kat alanı, brüt normal kat alanı, toplam kat yüksekliği, fonksiyonel mekân sayıları, toplam brüt çevre uzunluğu, temel tipi, bodrum tipi gibi farklı değişken parametrelere ve mimari özelliklere sahip konut tipi yapı projelerinin betonarme taşıyıcı sistem maliyet tahminlemesi yapay sinir ağları modeli kullanılarak yapılmıştır. Elde edilen sonuçlar, istatistiksel regresyon analizi yöntemi ile hesaplanan değerlerle karşılaştırılmış ve yapay sinir ağları yönteminin performansı ortaya konulmuştur. Anahtar Kelimeler: Yapay Sinir Ağları, Regresyon Analizi, Betonarme Taşıyıcı Sistem, Maliyet Tahmini
Baraj yıkılması akımının deneysel ve interpolasyonlu parçacık hidrodinamiği (SPH) yöntemi ile incelenmesi
Yapılan çalışmada baraj yıkılması akım problemi farklı yoğunluklu akışkanların davranışlarını ele alabilmek amacı ile deneysel ve nümerik yöntemlerle incelenmiştir. Yatay bir düzlem üzerinde dikdörtgen yapıdaki bir kanalda mansabın kuru olduğu durum ile birlikte iki ayrı durgun haldeki akışkanları birbirinden ayıran düşey bir kapak mekanizmasının aniden kaldırılması ile oluşan şok dalgasının mansapta oluşturduğu etkiler irdelenmiştir. Deneyler sonucu elde edilen görüntüler görüntü işleme teknikleri kullanılarak sayısallaştırılmıştır. Farklı yoğunluklu akışkan olarak su, yağ ve tuzlu su tercih edilmiştir. Modellemelerde ağ yapısına dayanan Flow-3D ve parçacık esaslı İnterpolasyonlu Parçacık Hidrodinamiği (SPH) yöntemi uygulanmıştır. Akışkanların mansapta yayılımı sırasında belirli anlardaki görüntüleri ve kanal boyunca noktasal akışkan serbest yüzey derinlik değişimleri incelenen fiziksel özelliklerdir. Ayrıca Kocaman (2007)'nin çalışmasında elde ettiği deney ve nümerik model sonuçları SPH yönteminde incelenerek, bu yöntemin akışkan davranışlarını ölçmedeki hassasiyeti test edilmeye çalışılmıştır. Çalışma sonucunda tüm yöntemler için elde edilen sonuçların birbirleriyle oldukça uyumlu olduğu gözlemlenmekte, özellikle baraj yıkılması başlangıç safhalarında parçacık tabanlı Lagrange yöntemi olan SPH'ın değişken açık kanal akım problemlerini çözme konusunda gelişen yazılım ve bilgisayar teknolojileri desteği ile iyi bir alternatif olabileceği öngörülmektedir.
Investigation of concrete slab crack when placed directly on clay
In this study, investigation of concrete slab cracks when placed directly on clay, types of cracks in seam zone, cracks depth and width, modulus of elasticity and compressive strength were studied. Also the effects of the cracks on the physical properties of concrete due to dry shrinkage. A total of eight concrete mixtures were produced with 500 kg/m3 of total cementitious materials content and with a constant water/binder ratio of (0.55). each mixture were casted over clay layer, Each layer of clay had various water content ratio from 0% to liquid limit , concrete samples were either cured by spraying at 23℃ or maximum temperature of 28 days curing period. Test results revealed that 28-days compressive strength enhanced while leading to reduce in ultrasonic pulse velocity, it was found that the concrete mixtures that placed over high clay water content had higher compressive strength and lower dry shrinkage values compared to the samples that casted over low water content clay. However e-modulus of elasticity increased due to dry shrinkage.
Şiddetli çevrelere maruz kalmış sargılı ve sargısız geopolimer betonun mekani̇k performansı ve durabilitesi
This study reports the mechanical properties and durability of unconfined/confined sustainable geopolymer concrete (GPC) exposed to chemical attack under static and cyclic loadings. A low calcium (Class F) fly ash incorporating nano-silica was activated by a combination of sodium silicate and sodium hydroxide solutions to make the GPC. Unconfined/confined ordinary Portland cement concrete (NC) counterparts were also made for comparison purposes. The confined GPC/NC specimens were wrapped by one/three layers of basalt/carbon fiber-reinforced polymers (BFRP/CFRP). Effects of type and number of wrapping layers, along with wrapping and testing ages on the mechanical properties and durability of confined GPC/NC were investigated. In addition, microstructure of the unconfined/confined GPC specimens was compared with that of the unconfined NC counterparts. The results showed confinement of the GPC with BFRP/CFRP fabrics enhanced the strength, ductility and durability of the GPC specimens exposed to chemical attack. The GPC specimens confined with CFRP fabric were found more ductile and durable than specimens confined by BFRP fabric. In addition, the GPC specimens confined with three layers of FRP fabrics were found more ductile and durable than that of the specimens confined with only one-layer. Further, the unconfined/confined GPC specimens were more durable than the corresponding unconfined/confined NC.
Mechanical behavior and durability of confined and unconfined engineered cementitious composite exposed to chemical attack
In this thesis, the mechanical performance and the durability of Engineered Cementitious Composites (ECC) specimens under chemical attacks were investigated. Static and cyclic loading tests were carried out for confined and unconfined ECC specimens in order to research the performance after chemical attack. Carbon fiber reinforced polymer (CFRP) and basalt fiber reinforced polymer (BFRP) fabrics were used to achieve the confinement of the specimens. In addition, the use of CFRP/BFRP fabrics as a rehabilitation technique was also studied for the specimens exposed to the chemical environments. Unconfined ECC specimens were also produced as a reference specimens and all specimens were continuously immersed in chemical solutions. The mechanical performance and the durability of specimens were evaluated by means of the visual inspection, weight change, static and cyclic loading tests, failure mode and microscale analysis by scanning electron microscopy (SEM). Results indicated that ECC specimens produced with low lime fly ash (LCFA) showed superior performance than the specimens produced with high lime fly ash (HCFA) in the chemical environments. In addition, confinement of ECC specimens with BFRP/CFRP fabrics significantly improved compressive strength, ductility, and durability of the specimens. Both fiber reinforced polymer (FRP) can be used as a rehabilitation material in the chemical environment.
Pull-out capacity of double-helix screw pile in organic soil
The organic soil used in this study was obtained from Sakarya region, Turkey. According to the system of classification (USCS), the present soil is classified as an organic silt soil with high plasticity (OH). Standard and modified compaction, sieve analysis, specific gravity and organic content tests were done to obtain the engineering properties of organic soil. An experimental investigations on single helical piles were conducted in organic soil. In this work, the effect of spacing ratio of double-helix pile and soil density on the pile performance under vertical pull-out static load were investigated. Double-helix piles were installed and loaded axially in two soil densities: soft and stiff organic soil. Up lift performance was predicted using the axial load versus displacement readings. The pull-out load was applied vertically with the axis of the pile. Test results showed that the ultimate pull-out load capacities of double-helix pile are controlled by the spacing of helical plates. An increase in spacing ratios causing a decrease in ultimate pull-out capacity of helical pile in organic soil. Also, increasing the soil density increasing the ultimate pull-out load capacity. The study showed that the capacity of double-helix pile is greater when the spacing ratios 1 and 2 than 3 and 4. In general, the capacity of double-helix piles with a spacing ratios of 1 and 2 is ranged from 1.25 to 1.77 times the capacity of double-helix pile with spacing ratios of 3 and 4 in both stiff and soft soil respectively. Keywords: Organic soil, helical pile, pull-out, soil classification, pile installation.
Reliability analysis of concrete filled steel tube for quadrilateral and circular cross sections
Concrete filled steel tube beams is a structural composition that brings the advantages of the combination of the surrounding steel with the core concrete, this structural member had been investigated under different conditions but still, there is a significant difference among the well-known design codes provisions and limitations. Assessing the limit states of the codes can be conducted based on structural reliability analysis. Bending capacity of the beams can be characterized by the reliability index in terms that can be readily understood by structural engineers with only a basic knowledge of probability theory. In this study, First-order Reliability Method was used in assessing the selected tested specimens. More than 2000 concrete filled steel tube members of different shapes cross-section had been collected from recently introduced literature (from 2000 up to 2018); moreover, the selected specimens were compared with the provisions of many codes. The judgment was based on the convergences between the calculated beams load capacity in term of bending strength according to mentioned codes and the recorded load capacity that obtained from the experimental work. Different parameters were evaluated from the selected beams, while the geometry of the beams were the main parameters, the tube thickness is ranging between, the width of the members. The material properties are also altered in order to evaluate its effect on the beam strength, where the concrete compressive strength was ranging between 10 to 154 MPa, and the steel yield strength was less than 762 MPa. The results show that both codes (EC4-2004 and AISC360-10) have percentages of error within the unsafe zone, and EC4 is less conservative than the AISC.
Effects of size and shape of sand grains on some engineering properties of a clayey soil
This thesis presents an experimental research studying in the effect of shape and size of sand grains on some geotechnical properties of a clayey soil using unconfined compression and triaxial compression machines equipped with a pair of bender elements. The materials used in this study were low plasticity clay, Narli Sand and Crushed Stone Sand. Three different gradations of the sands (0.6-0.3, 1.0-0.6, and 2.0-1.0) mm were chosen. Five contents of clay-sand (90-10, 80-20, 70-30, 60-40 and 50-50) by dry weight were investigated. Series of bender elements (BE) tests were carried out on clay-sand mixtures to measure small strain shear modulus (Gmax). Unconfined compression (UC) tests were conducted on these mixtures to have a correlation between Gmax and unconfined compressive strength (qu). Gmax and qu increased with increasing roundness and sphericity of sand grains. The qu values decreased, and the Gmax values increased when sand content in the mixture increased. As size of sand grains increased, Gmax and qu values increased. For the results that obtained from triaxial compression machine equipped with bender elements tests, the deviatoric stress increased with increasing content, size, roundness and sphericity of sand grains. The pore water pressure decreased as sand content increased and it is increased as size, roundness and sphericity decreased. The effective cohesion (c') decreased and effective angle of friction (ϕ΄) increased as sand content increased. A correlation between Gmax, voids ratio and effective stress were developed for rounded and angular sand of clay-sand mixtures.
Farklı beton türü ve lif oranları kullanılarak oluşturulmuş numuneler için dinamik ve statik elastisite modülünün karşılaştırılması
Günümüz yapı teknolojisinde, en çok kullanılan yapı malzemelerinden birisi betondur. Özellikle ülkemizde yapı sektöründe oldukça yaygın kullanım alanına sahiptir. Betonun homojen olmayan yapısı nedeniyle dayanımının ve kalitesinin yerinde kontrol edilmesi oldukça zordur. Bu nedenle, betonun mekanik özelliklerinin kontrol altında tutulabilmesi için tahribatsız yöntemler geliştirilmiştir. Ancak bu yöntemler de kullanılabilirliğinin yanında yanıltıcı sonuçlar verebilmektedir. Bu yanıltıcı sonuçları azaltabilmek için tahribatlı ve gerçeğe yakın sonuçlar veren yöntemlerle desteklenmesi ve böylece tahribatsız yöntemlerin doğruluğunun artırılması gerekmektedir. Yapı standartları ve literatür de betonun elastisite modülüyle ilgili hesap yöntemleri genellikle normal dayanımlı beton karışımlarını kapsamaktadır. Bu tez çalışmasında farklı lif oranlarındaki Normal Beton (NB) ve Kendinden Yerleşen Betonların (KYB) basınç dayanımı ve elastisite modülü değerleriyle ilgili araştırma sonuçları verilmiştir. Yapılan bu çalışmada hacimsel olarak %0,5 ve %1 lif oranlarında 15 tane NB ve 17 tane KYB olmak üzere toplam 32 numune üzerinde deneyler yapılmış ve bu numunelerin Dinamik (Ed) ve Statik Elastisite (Ec) modülleri belirlenmiştir. Elde edilen sonuçlar farklı ülkelerin konuyla ilgili standartları tarafından ortaya konulan bağıntılarla karşılaştırılmıştır. Sonuçlar arasındaki en iyi ilişkiyi CEB-FIB 90 (İsviçre) standardının verdiği görülmüştür. Elde edilen sonuçlar, Statik Elastisite modülünün, karot numune ile belirlenemediği durumlarda, Ultra ses cihazı kullanılarak belirlenebileceğini ve Ultra ses cihazıyla belirlenen Dinamik Elastisite Modülünün yapı analizi hesaplarında kabul edilebilir bir doğrulukla Statik Elastisite Modülü yerine kullanılabileceğini göstermiştir.
Effects of imperfections on the flexural behaviour of concrete filled steel tubes beams with circular sections
Bending tests of the Concrete Filled Steel Tube (CFST) beams with artificial notches in the steel tubes were conducted in this thesis to investigate the effects of the material imperfections of steel tubes on beam flexural. This study presents the results of an experimental program the bending behaviors of CFST beams with notches in the steel tube circular two different thickness (2mm, 4mm) involve of 26 specimens which consist of 24 with notch CFST beams, two (control) without notch CFST beams were investigated in the present work. Investigating the flexural performance of Self-Compacting Concrete (SCC) filled steel tube beams The CFST with notches from the top, bottom and sidewall with two different thicknesses and two different lengths of the notch (long and short). The moment carrying capacities, ductility, failure modes, moment - mid span deflection relations, bending moment capacities were presented. The results also show that the notched CFST specimens had lower mechanical performances than the intact CFST specimens. Furthermore, the investigating notch in the bottom more effect and danger to the structures when compared with the notch top and sidewall for (2 mm, 4 mm), in addition to the notch in the bottom had less than ductility from top and sidewall. Keywords: Self compacted concrete (SCC), Concrete Filled Steel Tube (CFST) beams, notches, flexural strength, ductility.
Experimental investigation and finite element modeling of rehabilitated and steel fiber rc members
This thesis consists of four essential parts which investigate the mechanical behavior of rehabilitated reinforced concrete haunched beams (RCHBs) and rehabilitated reinforced concrete corbels (RCCs) in addition to the behavior of steel fiber reinforced concrete haunched beams (SF RCHBs). The main objective of the first and second part are to investigate the behavior of reinforced concrete haunched beams after being rehabilitated by Basalt Fiber Fabric (BFF) and Carbon Fiber Reinforced Polymer (CFRP) Fabric. These parts consist of two studies; experimental and the finite element (FE) modeling studies. The experimental study consists of loading tests of 24 different rehabilitated RCHBs which had failed in shear and flexural mode beforehand. In the second study, a new FE based technique is proposed to form a zone that exhibits all possible load capacities of rehabilitated RCHBs. The results show that there is a nearly perfect agreement between tested RCHBs and the maximum limit of strengthened RCHBs regarding ultimate load capacity. The main objective of the third part of this thesis is to investigate the effectiveness of the steel fiber, which is used to resist shear loads instead of stirrups, on the mechanical behavior of RCHBs. Moreover, effects of main steel reinforcement, compressive strength, and the inclination angle of RCHBs on the behavior of steel fiber reinforced concrete haunched beams (SF RCHBs) are researched in this part. 81 FE models were prepared for this purpose. The parametric study was carried out to clarify the effect of each parameter on the behavior of SF RCHBs. Parametric results show that the effective inclination angle of the haunched beam is 10º regarding shear load capacity. The last part of this thesis investigates the behavior of normal and self-compacted steel fiber reinforced concrete corbels (SF RCCs) rehabilitated by Basalt Fiber Mesh (BFM) and Basalt Fiber Fabric (BFF). The experimental program includes totally 60 corbels. Test results show that there is no any increase in load capacity of the RC corbels rehabilitated by BFM without crack repair. Moreover, it can be concluded that the use of BFF is an effective and powerful technique for the rehabilitation of damaged RC corbels.
Yanal deformasyonları karbon elyaf kumaş ve cam elyaf kumaş ile sınırlandırılmış betonların eksenel yük altındaki davranışlarının incelenmesi
Bu çalışmada yanal deformasyonları FRP ile sınırlandırılmış betonların deneysel davranışı incelenmiştir. C20, C50 ve C75 olmak üzere üç farklı beton sınıfı, tek kat ve iki kat olmak üzere iki farklı sargı kalınlığı ve CFRP (Karbon Lifleriyle Güçlendirilmiş Polimer) ve GFRP (Cam Lifleriyle Güçlendirilmiş Polimer) olmak üzere iki farklı sargı malzemesi kullanılmıştır. FRP ile sınırlandırılmış betonların mekanik davranışını belirlemek için deneysel bir çalışma yürütülmüştür. Test sonucu olarak gerilme – şekil değiştirme ilişkisi grafik olarak sunulmuştur. Deneyler sonucunda sargılı betonun dayanım ve düktilitesi önemli ölçüde artmıştır. Bu artış beton dayanımının azalmasıyla artmıştır. Deneysel sonuçlar sargılı beton için kullanılan bazı modeller ile karşılaştırılmış ve grafik olarak sunulmuştur. Anahtar Kelimeler: FRP, GFRP, Sargı, Beton, Eksenel Basınç Dayanımı.
Yanal deformasyonları cam elyaf ve aramid elyaf kumaş ile sınırlandırılmış betonların eksenel basınç altında davranışı
Bu çalışmada yanal deformasyonları FRP ile sınırlandırılmış betonların eksenel basınç altında davranışı incelenmiştir. C20, C50, C75 olmak üzere üç farklı beton sınıfı, tek kat ve iki kat olmak üzere iki farklı sargı kalınlığı ve AFRP (Aramid Lifleriyle Güçlendirilmiş Polimer) ve GFRP (Cam Lifleriyle Güçlendirilmiş Polimer) olmak üzere iki farklı sargı malzemesi kullanılmıştır. FRP ile sınırlandırılmış betonların mekanik davranışını belirlemek için deneysel bir çalışma yürütülmüştür. Test sonucu olarak gerilme şekil değiştirme ilişkisi grafik olarak sunulmuştur. Deneyler sonucunda sargılı Betonun dayanım ve düktilitesi önemli ölçüde artmıştır. Bu artış beton dayanımının azalmasıyla artmıştır. Anahtar Kelimeler: Aramid, Güçlendirme, Cam
Gövdesinde delikler açılarak hafifleştirilen çelik kiriş ve eklerinin eğilmede davranışı
Dünyadaki ve ülkemizdeki kentlerin hızlı bir şekilde gelişmesine paralel olarak endüstrinin ve sanayinin hızlı bir şekilde geliştiği, zamanın paranın önüne geçtiği günümüz koşullarında bu ihtiyaçlara cevap verebilecek sanayi yapılarının inşası giderek yaygınlaşmakta ve gelişmektedir. Ayrıca kentlerin sosyal ihtiyaçlarına cevap verebilecek ekonomik, sportif, kültürel ve ticaret amaçları ile inşa edilen yapıların gereksinimi giderek artmaktadır. Bu tür yapıların daha hızlı ve ekonomik inşa edilebilme talebi çelik taşıyıcı elemanların kullanılmasına olan gereksinimi ortaya koymaktadır. Bu tür yapı elamanlarının kullanılması hem ülke ekonomisine hem de hızlı inşaat tekniklerine katkısı büyük olanak sağlayabilir. Günümüz gelişmiş ülkelerinde çeşitli şekillerle oluşturulan boşluklu kirişler üretilmekte ve kullanılmaktadır. Boşluklu kiriş kullanımı I şekilli profillerden daha mukavemetli ve daha ekonomik yapı elemanları elde edilmesine imkân vermektedir. Tez çalışmasının amacı hali hazırda bulunan I şekilli profillerin gövdesin de farklı geometrilerde delikler açarak ve ek bağlantı elemanlarını oluşturarak eğilme davranışının incelenmesinin yapılması ve hızlı üretim ve ekonomik yapı elamanları oluşturulabilmesidir. Bu çalışmanın gerçekleştirebilmesi için, standart üretimi yapılan I en kesitli profiller temin edilerek daha önceden hazırlanan kesit ölçülerinde biçimlendirilerek eğilme deneyi ve kritik noktalar belirlenmiştir. Bu kritik noktaların nasıl davrandığı analiz edilip nasıl teşkil edileceği ele alınmıştır. Aynı I şekilli Profillerin farklı şekil ve boyutlardaki hesaplama sonuçları tez çalışmasında yer almaktadır. Tez çalışması 4 Bölüm, sonuçlar ve öneriler kısmından oluşmaktadır. Tezde I şekilli profillerin gerekli ödenekleri üniversitemiz bünyesinde bulunan BAP koordinasyon merkezi tarafından karşılanmıştır.
Enerji kırıcı yapı üzerindeki akımın sayısal ve deneysel analizi
Farklı eğimlere sahip dolusavak şüt kanalının mansabındaki enerji kırıcı üzerinde oluşan hidrolik sıçramanın karakteristik özellikleri farklı Froude sayıları ve eşik yükseklikleri için deneysel ve sayısal olarak incelenmiştir. Akım bölgesindeki hızlar Lazer Doppler Anenometre (LDA) kullanılarak ölçülmüştür. Ölçülen hız ve akım profilleri, aynı koşullar altındaki akımın sayısal model bulgularının doğrulanması için kullanılmıştır. Akımın hareketini idare eden temel denklemler sonlu hacimler yöntemine dayalı Ansys-Fluent programı yardımıyla, Standard k-e, Renormalization group k-e, Realizable k-e, Modified k-w, Shear Stress Transport k-w ve Reynolds Stress Model türbülans modelleri kullanılarak sayısal olarak çözülmüştür. Akım profillerinin sayısal hesaplamaları, Akışkan Hacimleri Yöntemi (VOF) ile gerçekleştirilmiştir. Hesaplama ağının sayısal sonuçlar üzerindeki etkisinin test edilmesi için Ağ Yakınsama İndeksi (GCI) yöntemi kullanılmıştır. LDA ile yapılan ölçümlerden elde edilen deneysel bulgulara göre hidrolik sıçramanın geometrik ve kinematik özellikleri belirlenmiş, farklı yapı ve akım koşullarının hidrolik sıçrama ve enerji sönümlenmesi üzerindeki etkileri sunulmuştur. Deneysel ölçümlerle yapılan karşılaştırmalardan, Reynolds Stress Modelinin diğer türbülans modellerine göre hız alanının ve akım profilinin belirlenmesinde daha başarılı olduğu görülmüştür.
Taş kolon tasarım parametrelerinin incelenmesi
Bu çalışmada, taş kolon uygulaması için kritik önem arz eden bazı tasarım parametrelerinin etkisi analitik ve sayısal yöntemler yardımı ile araştırılmıştır. Yapılan sayısal analizlerde, sonlu elemanlar yöntemine dayalı PLAXIS bilgisayar yazılımı kullanılmıştır. Analizlerde taş kolon çapı, boyu, içsel sürtünme açısı, rijitliği, drenajsız kayma mukavemeti ve kolonlar arası mesafe gibi parametrelerin etkisi araştırılmıştır. Ayrıca tez kapsamında, 2010-2013 tarihleri arasında arazide gerçekleştirilmiş tam ölçekli grup taş kolon yükleme deneyi de detaylı olarak incelenmiştir. Söz konusu grup taş kolonlar, TÜBİTAK projesi kapsamında arazide inşa edilmiş ve davranışı aletsel ölçüm sistemleri yardımıyla izlenmiştir. Arazide inşa edilen grup taş kolonlar literatürde önerilen analitik yöntemler ve PLAXIS bilgisayar programı yardımıyla 2 ve 3 boyutlu olarak analiz edilmiştir. Analitik yöntemler ve sayısal analiz sonuçları araziden elde edilen ölçüm sonuçları ile karşılaştırılarak grup taş kolon davranışı için önerilen analitik ve sayısal yöntemlerin doğruluğu ve güvenirliği araştırılmıştır.
Akışkan,yapı,zemin etkileşimine göre ham petrol boru hatlarının tasarımı
Sıvı taşımacılığında en çok kullanılan yöntem boru hattı ile taşımasıdır. Özellikle ham petrol ve akaryakıt gibi enerji üretilen sıvıların taşınması için oldukça yaygın olarak boru hatları ile taşıma yapılmaktadır. Boru hattıyla taşımanın üstünlükleri olarak ekonomik taşımacılık, işletmesi kolaylığı, otomasyona elverişlilik, gömülü hat olması nedeniyle çevre dostu olması, gömülü hattın sabotaja karşı güvenlikli olması, tankerle petrol taşımacılığını sona erdirmesi, hat kapasitesini artırmanın mümkün olması, gömülü hattın trafik ve benzer servisleri engellememesi, rota seçmenin karayolu ve demiryolundan daha kolay olması, kaza oranının düşük olması, araçların geçemeyeceği yerden geçmesinin mümkün olması gibi faktörlerden söz etmek mümkündür. Boru hattının yapımı ise ön etüt, keşif ve fizibilite çalışmaları, güzergâh seçimi, harita çalışmaları, basınçlı iletim hidroliği, gerilme analizi, geoteknik analiz, birleşim detayları ve imalat-inşaa maliyetinin belirlenmesidir. Bu tez çalışmasının amacı; enerji koridoru olan Türkiye'de petrol boruhattı taşımacılığının artan kapasitesinin doğuracağı boruhattlarının yapımı için Hidrolik-Geoteknik-Yapı Etkileşimli tasarım ve projelendirme kriterlerini ortaya koymak, bir uygulama ile tasarımı daha belirgin ve uygulanabilir kılmak, hidrolik olarak basınçlı iletim hattı olan boruhatlarıyla taşımacılık maliyetini diğer taşımacılığı maliyetleri ile karşılaştırmak olarak ifade edilebilir.