Research on Engineering Structures and Materials

164-175

Authors: İsmet Çalık, Alemdar Bayraktar, Temel Türker, Ali Osman Ayan

The effects of restoration on the experimental dynamic characteristics of historical masonry Molla Siyah Mosque in Trabzon, Turkey, are investigated in this paper. Firstly, the initial situation and the implemented restoration works of the mosque are mentioned in detail. Then, the experimental dynamic behaviors of the mosque before and after the restoration are obtained by using the Ambient Vibration Tests. High sensitivity seismic accelerometers with cables are used during the tests. The collected signals are evaluated by Enhanced Frequency Domain Decomposition Technique, and experimental natural frequencies, mode shapes and damping ratios of the mosque are determined for the initial and restoration cases. The obtained results are compared with each other and restoration effects on the dynamic behavior of the mosque are discussed in detail.

186-191

Authors: Derya Yesim Hopa, Alime Yilmaz, Tuba Aksoy Bahtli

One of the major enviromental problems around the world is disposal of waste tyres without any purpose. Disposal of waste tyres is an increasing enviromental problem. Also because of high content of valuable chemicals and other compounds hidden in the waste tyres, disposal of them is an economical problem as well. Pyrolysis is a thermochemical process that can be used for recovery of the valuable chemicals in the waste tyre. Pyrolysis is a recycling process in which, liquid product can be used as a fuel directly or can be mixed with petroleum refined oils. Derived gaseous product can also be used as a fuel and solid product can be considered as a fuel and low grade carbon black. In this work, granulated waste tyres have been pyrolyzed in a fixed bed reactor under different conditions of temperature, heating rate and inert purging gas (N2) flow rate. The purpose of the study was to optimize the pyrolysis parameters in order to produce the highest amount of oil. 400°C, 450°C and 500°C were selected and the maximum yield of liquid product was observed at 450°C. Among the heating rates of 10°C/min, 15°C/ min and 20°C/min; 10°C/min was the parameter that gave maximum oil yield. And while working at 450°C and 10°C/min; N2(g) flow rate was examined by using 0.5 L/min, 1 L/min and 1.5 L/min. The maximum oil yield was observed at 1 L N2(g) /min. According to the results of the study; at 450°C, with a heating rate of 10°C/min and 1 L N2(g)/min gave the maximum yield of oil, which is 53.33 wt.%. The pyrolytic oil from waste tyre had the Gross Calorific Value of 42.6 MJ/kg which is very close to that of commercial diesel no 2 (around 42-46 MJ/kg). The pyrolytic oil produced is a promising fuel and can be used as a source of energy after some future work for make it suitable for use in vehicles or in other areas like factories or houses etc.

202-209

Authors: Erdem Çiftçi, Adnan Sözen

Heat wheel is a heat exchanger in which the working fluid is air and it has parallel and counter current flow layout. These type heat exchangers are used for enthalpy recovery and/or air dehumidification processes. By means of numerous micro channels they have, it is enable for the heat wheels to transfer the heat so quickly and in a short span of time, which makes them superior. In this paper, performance of the heat wheel used for enthalpy recovery has been numerically determined. Utilizing Computational Fluid Dynamics (CFD) algorithm, the alteration of the wheel efficiency with time has been investigated for optimum rotation speed. With the help of ANSYS Fluent™ software in which calculations have been made, the temperature distributions by location have been presented graphically. Consequently, it is found that maximum efficiency of the heat wheel is 52.62 %.

228-236

Authors: George Kollaros, Antonia Athanasopoulou

Road pavement serviceability is primarily governed by the type of vehicles anticipated to use the facility. Along with the size of traffic loads, climatic conditions affect the behavior of the materials in a pavement structure. The relative strength loss in a layer due to its drainage characteristics and the total time it is exposed to near-saturation moisture conditions is represented by drainage coefficients. There is a need for computerized methodologies for thickness design of flexible asphalt pavements (granular base course) for a wide variety of pavement uses providing users the capability to conduct structural analysis of special pavement structures. An algorithm for a computer-based procedure towards the calculation of the layer thickness of flexible pavements has been developed. The design equation used is that described by the American Association of State Highway and Transportation Officials. The present work deals with the effect of drainage on the total thickness of the structure as it directly influences the cost of large infrastructure projects like roads. The output of different cases solved is presented in table and schematic form. Changes in technology related to pavement design and construction practices will necessitate revisions to currently used computing techniques. Improvements in computing times which will affect the cost of computerized methods available to engineers are to be suggested in the near future. Empirically supported pavement designs used nowadays in Greece require modifications based on regional experience and on a better assessment of the drainage conditions prevailing in each area crossed by a roadway project. Since design considerations constantly change, it is obligatory to shift towards more sophisticated design methods.

89-97

Authors: Filiz Ugur Nigiz, Nilufer Durmaz Hilmioglu

The production of new generation fuels from sustainable resource is prominent issue of the current world. A wide range of feedstock can be used to produce first generation liquid fuel from starch to corn. Besides the first one, second generation fuel is considered as fuel additive for increasing the calorific value of gasoline and limiting the hazardous gas emission. Only small amount usage of lignocellulosic based additives such as ethyl valerate (EV) increases the energy density of fuel. Due to the non-hazardous and less irritant properties of ethyl valerate it is defined as “green fuel”. It was reported that the 10-20% blend ratio of EV with gasoline causes a significant improvement for engine performance. EV is chemically produced by esterification reaction between ethanol and valeric acid. Reaction can be carried out by means of heterogeneous, homogeneous acid catalyst, lipase and ionic liquids and reactive polymers. In this study, a reactive poly (styrene sulfonic acid) (PSSA) catalyst was prepared and used for ethyl valerate synthesis at different temperature conditions. Effect of alcohol:acid feed molar ratio was also investigated as a function of acid conversion. Better results were obtained as 77.9 % acid conversion at 343 K when alcohol:acid feed molar ratio was 4:1.

113-121

Authors: Ioanna Papayianni, Vasiliki Pachta

Earth structures constitute a great part of European Monumental Heritage and are closely related to the wider historic, socio-economic and environmental aspects of each region. In this paper, a methodology is presented regarding the analysis of the constructional materials and techniques of historic earth block structures situated in Northern Greece, as well as the design and testing of compatible repair materials for their restoration. A series of laboratory tests were performed, in order to define the physico-mechanical and chemical characteristics of the historic materials (earth blocks, structural mortars, renders-plasters). After the evaluation of the results compatible repair materials based on earth were designed, manufactured and tested.

135-146

Authors: Erion Bukaçi, Thoma Korini, Erion Periku, Skënder Allkja, Paulin Sheperi

Convergence - confinement method can be used to analyze rock support systems in interaction with rock mass in order to select the appropriate supports system for tunnels in rock. This method enables calculation of the charge applied to the support system and the factor of safety for the tunnel supports. The factor of safety calculated from traditional deterministic analysis methods cannot fully represent tunnel stability. There are many uncertainties in parameters used to calculate the factor of safety, and these uncertainties are not integrated in a deterministic analysis, but can be taken into account using a reliability analysis. Reliability analyses, used to calculate probability of failure for tunnel support system, is a complement of the factor of safety calculated by using deterministic analyses. In this paper, Monte Carlo Simulation is used to calculate probability of failure for tunnel support system. This article shows that significant error may be introduced by accepting a distribution for the performance function, which is obligatory for methods like FOSM, FORM, PEM. It is concluded that in cases when the distribution for the performance factor is not fully known, Monte Carlo analysis may give better results.

155-162

Authors: Müslüm Arıcı, Çağatay Kaptan, Hasan Karabay

In this study, the enhancement introduced by nanoparticles is investigated. Nanosized copper particles are dispersed into water which is confined in a cavity with a trapezoidal cross-section. The bottom and top walls of the cavity are adiabatic while the inclined lateral walls are kept at different constant temperatures. The cavity contains an adiabatic block at its center. The top wall of the cavity slides horizontally with a uniform constant velocity. The effect of adiabatic block size and particle volume fraction on the fluid flow and heat transfer is examined. Grashof number is set to 105 whereas Reynolds number is varied to examine the flow and heat transfer for Richardson numbers of 0.1, 1 and 10. The computational results show that heat transfer rate enhances as Richardson number decreases. It is also observed that large size of adiabatic block impedes the fluid circulation which reduces heat transfer rate.

1-10

Authors: Mustafa Ekici, Fatma Ayaz

In this paper we investigate the natural convection which exists under the Boussinesq approximation and completely passive boundary conditions. This phenomenon is applicable to the cooling of a heated body and heating and cooling of rooms and buildings and etc. The model equations of momentum and energy are solved by using improved differential transform method. This method is an iterative way for obtaining Taylor series coefficients. The convergence of the Taylor series is obtained by combining the method with the Least Square method for the problem first time here. The combination of these two powerful methods yields semi analytical solutions in the form of a polynomial through a straightforward manner. The efficiency and applicability of the algorithm are assessed and tested and error calculations have been presented.

27-44

Authors: Diogo Miguel Silva Costa, Maria Amélia Ramos Loja

continuous varying distribution of the micro and nano inclusion reinforcement particles through the matrix material. This continuity guarantees a smooth transition of material properties through the spatial domain of the composite and provides a great suitability to achieve specified structural responses. From the manufacturing point of view as well as from the computational perspective, these materials can be thought as effectively having a continuous variation of their properties, or as being constituted by a stacking of different layers, each having constant properties although following the continuous trend variation profile. Due to this ability to tailor the material to be used, and thus to obtain different structural responses, it is important to characterize the relative influence of material and geometrical parameters. These influences are investigated through a detailed parametric study.

55-64

Authors: Seun Samuel Owoeye, Yinusa Daniel Lamidi, Olusola Joseph Ajayi

The disposal of industrial wastes comprises one of the major worldwide environmental problems as these wastes render the environment unfriendly. The growing demand for waste utilization has made solid wastes- like materials from granite processing industry, and sand to be absorbed into the ceramic composition of bricks. The possibility of reduction in production costs provides a strong logic for use of these wastes. In this work, attempt was made to develop acid resistant bricks from quarry fine waste residues (stone dust, kaolin and sand). In order to investigate the possibility of producing acid resistant bricks, nine suggested batches, namely, A1, A2, A3, A4, A5, B1, B2, B3 and B4, were composed for this present study. These mixtures were composed of 40 wt% of Kaolin fine residue with 10-50 wt% of stone dust and silica sand; and 50 wt% of Kaolin fine residue with 10-40 wt% of stone dust and silica sand respectively. The bodies made with the variation of raw materials were sintered at 9700C and their behaviors with respect to apparent porosity, water absorption, bulk density, firing volume changes, compressive strength and acid resistance as a function of temperature, stone dust and sand was studied. It was observed that most of the developed brick samples showed excellent results in both HCl and H2SO4 media in accordance with IS: 4860-1968 and ESS:41-1986.

77-87

Authors: Hüseyin İpek, Hamdullah Çuvalcı

In this study, randomly oriented discontinuous chopped glass fiber (E-glass) reinforced cast polyamide (PA6G or castamide) composites were produced by pressure molding method. Two different sample groups were produced with different method. First group was produced under constant pressure at different molding temperature, second one was produced under constant temperature with different pressure. Produced samples friction tests were performed by using a pin-on-disc type friction test machine under dry sliding condition. The performance of the friction tests was carried out different distances and loads. Wear loss of the samples were detected and worn surfaces were investigated with scanning electron microscope (SEM) for determination of the wear mechanism. It was concluded that maximum wear loss was observed at the 300 oC molding temperature in the first group. On the other hand, total wear in second group was decreased with increasing molding pressure according to first group.

51-57

Authors: Alp Karakoç

Fiber networks, in which the natural or artificial fibers are randomly or directionally aligned and bonded together through a chemical, mechanical and/or thermal processes, form the structural foundations for fibrous materials such as nonwoven fabrics, paper and paperboards. Fiber network deformation plays critical role in determining the mechanical properties of such materials. Therefore, there have been extensive efforts to generate fiber network models in two and three dimensional space. As a contribution to the modelling efforts, a fiber network model is introduced in the present study. The main goal is to understand the microstructural parameters including fiber length and cross-section affecting the fiber network deformation and compute the mechanical properties of the aggregate. The present numerical advancement is believed to guide researchers and designers to analyze fiber network characteristics more efficiently and in shorter time spans.

67-74

Authors: Gözde F. Çelebi Efe, Mediha İpek, Sakin Zeytin, Cuma Bindal

Pure Cu matrix composite reinforced with MgO were successfully produced by powder metallurgy method. Nano sized MgO particles with 0.5, 1, 2 and 3 wt.% were mixed with copper powder in size of 40 µm mechanically and compacted by applying 220 MPa pressure and sintered at 700°C for 2 hours in an open atmospheric furnace followed by hot pressing with the pressure of 590 MPa. SEM studies revealed that MgO particles were dispersed homogenously in copper matrix and any oxides of copper matrix were not detected which confirmed by EDS and XRD analyses. With the addition of 3wt.% MgO particles, hardness of composites increased from 89 HVN to 122 HVN while, relative density decreased from 94.2% to 84.1% and electrical conductivity from 90.15 to 43.5 IACS (International Annealed Copper Standard). As a result, optimum electrical conductivity and hardness balance for promising contact material was obtained with the addition of max. 2wt.% of MgO.

89-104

Authors: Raif Sakin

This study had two fundamental purposes: fatigue-life estimation by statistical analysis of fatigue test data of cold-rolled commercial-purity aluminum sheets and material selection in HCF and LCF regions. Aluminum alloys 1100 and 1050 were cut in the rolling direction and long transverse direction. The specimens were subjected to cantilever-type plane bending fatigue tests using a fully reversed stress rate at room temperature. A two-parameter Weibull distribution was used for statistical analysis. S–N curves with 12 different reliability levels between 0.01 and 0.99 and empirical formulas were obtained for fatigue-life estimation. The reliability graphs were obtained for material selection.

1-18

Authors: Oktay Demirdag, Bulent Yildirim

In this study, two approaches having different characteristics, one being Transfer Matrix Method (TMM) that reduces computational effort and time by reducing the dimension of the considered matrix to four for all problems and the other being The Adaptive Network based Fuzzy Inference System (ANFIS) used in The Fuzzy Logic Toolbox of Matlab software that again needs less computational effort and time are compared in the free vibration analysis of Timoshenko columns with attached masses having rotary inertia. The governing equation of the column elements is solved by applying the separation of variables method in the TMM algorithm. The same problems are solved, also, by fuzzy-neural approach in which ANFIS model is used by establishing Neuro Fuzzy Frequency Estimation (NFFE) models. Natural frequencies for the first three modes of an elastically supported Timoshenko column with 1, 5 and 10 attached masses are computed using NFFE models, and the results are compared with the ones of TMM. The comparison graphs are presented in numerical analysis to show the effectiveness of the considered methods, and it is resulted that neuro-fuzzy approach may give encouraging results for these kinds of models having great number of attached masses.

29-37

Authors: Serdar Carbas, Mehmet Polat Saka

Sustainable development in construction industry is emerging as a major issue among cities and communities in the current century. As global climate change becomes an increasingly serious concern for the future and construction industry dependence on fossil fuels for energy creates greater adverse influence on human health and natural environment, an interest in high-efficient, low environmental impact buildings has begun to transform the notion of building design, construction, and operation. As it stands, the most of the standard buildings in the world consume an extraordinary amount of resources while taking an enormous toll on the environment. The utilization of cold-formed thin-walled open steel sections in structural sites supplies green structural opportunities demanding less material and cost while providing high strength. The developed algorithm for this study obtains the optimum geometric dimensions of cold-formed thin-walled open steel sections under various external loading. Moreover, this design algorithm takes into account of the effect of geometric nonlinearity as well as effect of warping. Also the displacement and stress constraints are included in the formulation of the design problem. The optimum design problem obtained turn out to be mixed integer and discrete programming problem. Artificial Bee Colony (ABC) algorithm is used to obtain its solution. This technique is a recent numerical optimization technique which mimics the intelligent behavior of honey bee swarm. The recent studies with the ABC method have shown its effectiveness and robustness in finding the optimum solution of combinatorial optimization problems. A design example is included to demonstrate the efficiency of the optimum design algorithm developed.

49-59

Authors: M. Evren Toygar, Onur Sayman, Uğur Kemiklioğlu, Hasan Öztürk, Zeki Kıral, Farshid Khosravi Maleki

In this study, a stress analysis and free vibration analysis were carried out for a curved sandwich composite beam. The curved composite beam was manufactured using glass fibers and vinylester resin. The polyvinylchloride (PVC) foam was preferred in the manufacturing of the sandwich composite beam for obtaining desired structure. The effect of the root and vertical cracks on the stress distribution and critical buckling loads for a curved composite sandwich beam were investigated numerically. The vibration analysis was performed experimentally and numerically. Experimental and numerical results were in a good agreement for the in-plane vibrations. It was seen that, the critical buckling forces changed not uniformly for the transverse crack and also, buckling loads decreased with increasing root crack length.