Challenge Journal of Structural Mechanics
http://www.challengejournal.com/index.php/cjsmec
<a href="http://cjsmec.challengejournal.com"><img src="/public/journals/1/images/CJSMEC_small.png" alt="" width="200" height="181" align="left" hspace="10" /></a><p><em style="font-style: normal;"><a href="http://cjsmec.challengejournal.com"> <strong>cjsmec.challengejournal.com</strong></a></em></p><p><em>Challenge Journal of Structural Mechanics</em> is an international, quarterly published and open access scholarly journal that publishes original research articles as well as review articles, case studies, short communications, discussions, book reviews, letters to the editor and a diary on international events related to any aspect of structural engineering.</p><p>Primary aim of <em>CJSMEC</em> is to encourage academic challenges in structural mechanics and materials disciplines to seek for the global truth. Therefore, the Journal intends to publish at least a review or discussion as a challenge to previously published papers at each issue. A double blind peer-review policy is followed in order to increase the scientific quality of the published papers.</p>TULPAR Academic Publishingen-USChallenge Journal of Structural Mechanics2149-8024Optimum design of purlin systems used in steel roofs
http://www.challengejournal.com/index.php/cjsmec/article/view/309
<div><p class="CJ-Abstracttext">In this study, one existing purlin system which is used in steel roof is optimized by taking into account less cost and bearing maximum load via developed software. This software runs with firefly algorithm which is one of the recent stochastic search techniques. One of the metaheuristic techniques, so-called firefly algorithm imitates behaviors of natural phenomena. Behaviors and communications of firefly are inspired by this algorithm. In optimization algorithm, steel sections, distance between purlins, tensional diagonal braces are determined as design variables. Design loads are taken into account by considering TS498-1997 (Turkish Code) in point of place where structure will be built, outside factors and used materials. Profile list in TS910 is used in selection stage of cross sections of profile. Constraints of optimization are identified in accordance with bending stress, deformation and shear stress in TS648. Design variables of optimization are selected as discrete variables so as to obtain applicable results. Developed software is tested on existing real sample so; it is evaluated with regard to design and performance of algorithm.</p></div>İbrahim AydoğduMukaddes Merve KubarDahi ŞenOsman TuncaSerdar Çarbaş
Copyright (c) 2018 TULPAR Academic Publishing
2018-06-122018-06-1242Re-examination of steel frame office buildings in preventing collapse when subject to intense fires
http://www.challengejournal.com/index.php/cjsmec/article/view/304
<div><p class="CJ-Abstracttext">The purpose of the paper is to investigate the extent to which present-day design of steel framed buildings is susceptible to total collapse when subjected to extreme fire events. We select a 50 storey structure in which 2 and 4 adjacent storeys located at different above-ground heights are, in separate scenarios engulfed in raging fires. A total of 8 scenarios are analyzed, employing Newtonian mechanics and realistic energy dissipating properties of H-shaped columns and normal concrete floor slabs possessing secondary (shrinkage and temperature) reinforcement alone. While the present Canadian building code is the basis for our column designs, other standards provide very similar specifications. Although fire proofing is required in virtually all high rise building construction, we are excluding such materials in order to simplify the analyses, but clearly do not advocate its omission – quite the opposite in fact. As well, attributes such as floor beams, partitions and furnishings of every description, all of which would in practice participate in absorbing the kinetic energy of a crush-down upper block are excluded. Despite such a vast array of conservative assumptions, it is shown that partial collapse may occur during crush-down, however, in no case will total collapse be the consequence. These results should provide some comfort to code writers that their requirements should indeed prevent the most catastrophic of failures due to fires.</p></div>Robert Mathews KorolKen S. SivakumaranPaul Heerema
Copyright (c) 2018 TULPAR Academic Publishing
2018-06-112018-06-1142Analyzing pre-stressed steel arch beams
http://www.challengejournal.com/index.php/cjsmec/article/view/302
<div><p class="CJ-Abstracttext">Techniques are being developed day-by-day to make it possible to pass through larger openings using smaller beam-column sections. Parallel to this trend, there is another necessity to produce not only smaller but also more economical and architecturally attractive beams. The aim of this study is to explain the structural behavior of steel arch beams reinforced using post-tension cables. Due to the effect of these, the arch beam load carrying capacity increases and a smaller sized optimized section can be obtained with a better architectural view. Moreover, it also allows better mechanical and applicable solutions for buildings. For a better understanding of the behavior of the reinforced beam, a steel beam and a steel arch beam with post-tensioned cables were modeled and analyzed using the SAP2000 finite element analysis computer program and compared with each other. In addition, full-scale specimens were prepared for testing to determine the structural behavior and compare the results with those from the computer modeling, the outcome of which was very promising. The similarity between the results inferred that no extra engineering knowledge and effort are needed to design such beams. The predicted (and proved by the testing) beam bearing capacity was 35% higher than that of the unreinforced beam. With just three full-scale tests completed, it was evident that the ratio (35%) could be increased by adjusting the cable post-tension force on much smaller sized beams.</p></div>Erkan PolatBarlas Özden Çağlayan
Copyright (c) 2018 TULPAR Academic Publishing
2018-06-112018-06-1142Performance based study on the seismic safety of buildings
http://www.challengejournal.com/index.php/cjsmec/article/view/296
<div><p class="CJ-Abstracttext">In the scope of this study, information has been provided on the Static Pushover Analysis which is a nonlinear deformation controlled analysis method and the Capacity Spectrum Method used to determine the performance point. In this study, static pushover analysis was made on a six-storey building with reinforcement concrete frame system by changing the materials, steel rebars and soil characteristics. The building’s capacity curves were drawn and decided according to different concrete and reinforcement groups. Furthermore the performance points of different classes of concrete were studied according to three seismic effect levels. In the case of a decrease in the reinforcement strength, a decrease of approximately 30% occurs in the base shear force. If the concrete strength is increased, an increase of 11% occurred in the base shear force. Consequently, in the comparisons made with five different concrete groups and two different reinforcement groups, rather than the increase in the strength of the concrete, an increase in the reinforcement strength was observed to be more effective on the structural capacity. Furthermore, local soil classifications were observed to be the most significant point regarding peak displacement.</p></div>Zinnur ÇelikAhmet Budak
Copyright (c) 2018 TULPAR Academic Publishing
2018-06-092018-06-0942455310.20528/cjsmec.2018.02.002Use of geosynthetics to reduce the required right-of-way for roadways and railways
http://www.challengejournal.com/index.php/cjsmec/article/view/299
<div><p class="CJ-Abstracttext">Roadway and railway routes require a right-of-way (ROW) to provide the necessary width for the required travelled way, drainage and earthwork. Correct understanding of ROW along a route is necessary in order to establish a correct width for the intended transportation corridor. Availability of land becomes scarce and cost of land increases in urban zones. Therefore, the costs of establishing a ROW in rural areas and in urban areas are not the same. Earthworks are an important component of route establishment. The required excavations and fills necessitate the use of proper side slopes for the stability of the excavation or the fill. These side slopes directly relate to the mechanical properties of the soil and the depth of the earthwork. This study provides a quantitative and a qualitative understanding of the ROW requirements of roadways and railways and the influence of the earthworks on the determined values of the ROW. The study further investigates the benefits of using geogrids to reduce the necessary ROW for a transportation route through finite element analysis.</p></div>Niyazi Özgür Bezgin
Copyright (c) 2018 TULPAR Academic Publishing
2018-06-092018-06-0942546010.20528/cjsmec.2018.02.003Structural features of cold-formed steel profiles
http://www.challengejournal.com/index.php/cjsmec/article/view/310
<div><p class="CJ-Abstracttext">Using capacity of cold-formed steel sections increases thanks to the opportunities which are offered by the developing technology. Low production cost and variety of profiles that can be produce easy, fast, high quality provide to improve its popularity as a structural material. In production, Sulphur and Phosphorous accumulation region occurs at intersection region of flanges and web of hot rolled steel profile. This causes to decrease strength of profile. Other difference between cold-formed and hot rolled steel sections is that mechanical properties of steel material homogeneously distributes throughout the profile. Both in frame and truss systems, cold-formed steel profiles develop both as main and secondary bearing element. These present variety options to the designers with pure, galvanized, aluminized applications. As with many building materials, mechanical behavior of cold-formed steel profile is quite complex due to the nature of thin walled steel sections. Design and analysis methods of cold-formed steel profile are rapidly shaped day by day. The general theory of beams investigated in past studies make possible analyses of cold-formed steel profile. Moreover, in structural systems, using of cold-formed steel profile provide height strength besides sustainable, environmentalist, green building because it requires less material and cost. Although these profiles have many advantages, use of cold-formed steel profiles in our country structures is rather limited unfortunately. New steel construction regulations in Turkey also do not mention cold-formed thin walled steel structure. Main purpose of this study reviews structural specifications of cold-formed steel profiles which are applied world-wide.</p></div>Osman TuncaFerhat ErdalArif Emre SağsözSerdar Çarbaş
Copyright (c) 2018 TULPAR Academic Publishing
2018-06-092018-06-0942778110.20528/cjsmec.2018.02.005Eigenvector and eigenvalue analysis of thick plates resting on elastic foundation with first order finite element
http://www.challengejournal.com/index.php/cjsmec/article/view/331
<div><p class="CJ-Abstracttext">The purpose of this paper is to study free vibration analysis of thick plates resting on Winkler foundation using Mindlin’s theory with first order finite element, to determine the effects of the thickness/span ratio, the aspect ratio, subgrade reaction modulus and the boundary conditions on the frequency parameters of thick plates subjected to free vibration. In the analysis, finite element method is used for spatial integration. Finite element formulation of the equations of the thick plate theory is derived by using first order displacement shape functions. A computer program using finite element method is coded in C++ to analyze the plates free, clamped or simply supported along all four edges. In the analysis, 4-noded finite element is used. Graphs are presented that should help engineers in the design of thick plates subjected to earthquake excitations. It is concluded that 4-noded finite element can be effectively used in the free vibration analysis of thick plates. It is also concluded that, in general, the changes in the thickness/span ratio are more effective on the maximum responses considered in this study than the changes in the aspect ratio.</p></div>Yaprak Itır Özdemir
Copyright (c) 2018 TULPAR Academic Publishing
2018-06-092018-06-0942617610.20528/cjsmec.2018.02.004Cover & Contents Vol.4 No.2
http://www.challengejournal.com/index.php/cjsmec/article/view/350
Journal Management CJSMEC
Copyright (c) 2018 TULPAR Academic Publishing
2018-06-092018-06-0942Effects of structural irregularities on low and mid-rise RC building response
http://www.challengejournal.com/index.php/cjsmec/article/view/288
<div><p class="CJ-Abstracttext">During the recent earthquakes, it has been observed that structural irregularities are one of the main reasons of the building damage. Irregularities are weak points in a building which may cause failure of one element or total collapse of the building during an earthquake. Since Albania is a country with moderate seismicity which has been hit by earthquakes of different magnitudes many times establishes the need to study the effect of irregularities is well-founded. The main structural irregularities encountered in Albanian construction practice consist of short column, large and heavy overhangs and soft story. In this study, these types of irregularities are considered in two different types of buildings, low and mid-rise reinforced concrete frame buildings represented by 3- and 6- story respectively. Pushover analyses are deployed to get the effect of structural irregularities on RC building response. A building set is chosen to represent the existing construction practice in the region; regular framed building and buildings with irregularities such as soft stories, short columns, heavy overhangs and the presence of soft story with heavy overhangs. The analyses have been conducted by using ETABS and Seismosoft software. Pushover curves of building set are determined by nonlinear static analysis in two orthogonal directions. Comparative performance evaluations are done by considering EC8 and Albanian Seismic codes (KTP-N2-89). From the obtained results, it is observed that low and mid-rise structures with soft story- two sided overhangs and short column are more vulnerable during earthquakes.</p></div>Hüseyin BilginRezarta Uruçi
Copyright (c) 2018 TULPAR Academic Publishing
2018-06-092018-06-0942334410.20528/cjsmec.2018.02.001Investigating the effect of infill walls on steel frame structures
http://www.challengejournal.com/index.php/cjsmec/article/view/308
<div><p class="CJ-Abstracttext">Infill walls consisting of materials such as hollow concrete, hollow clay and autoclaved aerated concrete bricks are not only preferred in reinforced concrete buildings but also in steel frame structures. It is a well-known fact that infill walls limit the displacement of frames under horizontal loads. However, they may also bring about certain problems due to being placed randomly in horizontal and discontinuously in vertical directions for some architectural reasons. Moreover, cracks in frame-wall joints are observed in steel frame structures in which ductile behaving steel and brittle behaving infill walls are used together. In this study, the effect of infill walls on steel frames has been investigated. In the steel frame structure chosen for the study, four different situations consisting of different combinations of infill walls have been modeled by using ETABS Software. Later, the pushover analyses have been performed for all the models and their results have been compared. As a result of the analyses done by using the equivalent diagonal strut model, it has been found out that infill walls limit the displacement of steel frames and increase the performance of a structure. However, it has been also determined that in the steel frame structure in which the infill walls have been placed discontinuously in vertical and asymmetrically in horizontal, infill walls may lead to torsional and soft story irregularities. As a result, it is possible to observe cracks in the joints of infill walls and steel frame, the deformation properties of which differ, unless necessary precautions are taken.</p></div>Osman Fatih BayrakSeda YedekMuhammet Musab ErdemMurat Bikce
Copyright (c) 2018 TULPAR Academic Publishing
2018-03-032018-03-0342273210.20528/cjsmec.2018.01.005Seismic assessment of a curved multi-span simply supported truss steel railway bridge
http://www.challengejournal.com/index.php/cjsmec/article/view/295
<div><p class="CJ-Abstracttext">Fragility curve is an effective method to determine the seismic performance of a structural and nonstructural member. Fragility curves are derived for Highway Bridges for many studies. In Turkish railway lines, there are lots of historic bridges, and it is obvious that in order to sustain the safety of the railway lines, earthquake performance of these bridges needs to be determined. In this study, a multi-span steel truss railway bridge with a span length of 25.7m is considered. Main steel truss girders are supported on the abutments and 6 masonry piers. Also, the bridge has a 300m curve radius. Sap 2000 finite element software is used to model the 3D nonlinear modeling of the bridge. Finite element model is updating according to field test recordings. 60 real earthquake data selected from three different soil conditions are considered to determine the seismic performance of the bridge. Nonlinear time history analysis is conducted, and maximum displacements are recorded. Probabilistic seismic demand model (PSDMs) is used to determine the relationship between the Engineering Demand Parameter (EDP) and Intensity Measure (IMs). Fragility curve of the bridge is derived by considering the serviceability limit state, and results are discussed in detail.</p></div>Mehmet Fatih YılmazBarlas Özden ÇağlayanKadir Özakgül
Copyright (c) 2018 TULPAR Academic Publishing
2018-03-032018-03-0342131710.20528/cjsmec.2018.01.003Forced vibration analysis of Mindlin plates resting on Winkler foundation
http://www.challengejournal.com/index.php/cjsmec/article/view/313
<div><p class="CJ-Abstracttext">The purpose of this paper is to study shear locking-free parametric earthquake analysis of thick and thin plates resting on Winkler foundation using Mindlin’s theory, to determine the effects of the thickness/span ratio, the aspect ratio and the boundary conditions on the linear responses of thick and thin plates subjected to earthquake excitations. In the analysis, finite element method is used for spatial integration and the Newmark-β method is used for the time integration. Finite element formulation of the equations of the thick plate theory is derived by using higher order displacement shape functions. A computer program using finite element method is coded in C++ to analyze the plates clamped or simply supported along all four edges. In the analysis, 8-noded finite element is used. Graphs are presented that should help engineers in the design of thick plates subjected to earthquake excitations. It is concluded that 8-noded finite element can be effectively used in the earthquake analysis of thick plates. It is also concluded that, in general, the changes in the thickness/span ratio are more effective on the maximum responses considered in this study than the changes in the aspect ratio.</p></div>Yaprak Itır Özdemir
Copyright (c) 2018 TULPAR Academic Publishing
2018-03-032018-03-0342182610.20528/cjsmec.2018.01.004Mechanical performance comparison of glass and mono fibers added gypsum composites
http://www.challengejournal.com/index.php/cjsmec/article/view/290
<div><div><div><p class="CJ-Abstracttext">Gypsum and gypsum based composite are widely preferred in construction industry for various purposes. Mechanical performances of gypsum composite have been enhanced by researchers in order to increase its area of usage. In this research, gypsum composites containing expanded glass were reinforced by glass fibers (GF) and mono polypropylene fibers (MPF). GF and MPF were used up to 1.5 %. The flexural strength, compressive strength, and shrinkage behavior of the composites were examined within the scope of this study. 50 x 50 x 50 mm and 40 x 40 x 160 sized specimens were prepared for the mechanical performance tests. It was obtained that flexural and shrinkage behavior of the composite were enhanced with the addition of MPF compared to GF added mixes; however, compressive strength values were not as high as GF reinforced composites.</p></div></div></div>Sadık Alper YıldızelSerdar Çarbaş
Copyright (c) 2018 TULPAR Academic Publishing
2018-03-032018-03-034291210.20528/cjsmec.2018.01.002Cover & Contents Vol.4 No.1
http://www.challengejournal.com/index.php/cjsmec/article/view/332
Journal Management CJSMEC
Copyright (c) 2018 TULPAR Academic Publishing
2018-03-032018-03-0342Influencing factors on effective width of compressed zone in joint column - cylindrical shell of steel silo
http://www.challengejournal.com/index.php/cjsmec/article/view/251
<div><p class="CJ-Abstracttext">In order to ensure unloading of whole amount of stored product by gravity, steel silos are often placed on supporting structure. The simplest way to design these complicated facilities is to divide cylindrical shell on two parts in our minds - discretely supported ring beam and continuously supported shell above it. Obviously, to ensure continuously support of shell, bending stiffness of ring beam should be high. In European standard EN 1993-4-1, that concept is recognized but it keeps silence about recommended stiffness of ring beam. Another way to design is to know law of distribution of compressive axial stresses due to discrete column reactions <em>R</em>, by height of shell. Knowing it, we could calculate the effective width <em>l</em><sub>eff</sub> of distribution of compressive stresses on every level. Where effective width is equal to distance between discrete supports, there critical height of shell ends and above it cylindrical body is continuously supported. Unfortunately the above quoted standard EN 1993-4-1 does not give an information how to calculate <em>l</em><sub>eff</sub>. The questions here are; should we accept linear distribution of compressive forces by height? In addition, could we use directly the results of Whitmore (1952), where angle of distribution <em>α </em>= 30°? Or, even to accept a far more brave opinion that <em>α </em>= 45°, used by many of the elder designers? Moreover, is value of angle <em>α</em> constant or does it depend on various influencing factors?</p></div>Lyubomir Zdravkov
Copyright (c) 2018 TULPAR Academic Publishing
2018-03-032018-03-03421810.20528/cjsmec.2018.01.001Structural behaviour of concrete filled hollow steel sections exposed to parametric fire
http://www.challengejournal.com/index.php/cjsmec/article/view/214
<p>This article analyzes steel-concrete composite columns subjected to natural fire scenarios in order to verify that the possibility of structural collapse during or after the cooling phase is real. The main objectives of this study are: first, to highlight the phenomenon of delayed collapse of this type of columns during or after the cooling phase of a fire, and then analyze the influence of some determinant parameters, such as section size, tube thickness, reinforcement (ratio), concrete cover and column length. The results show that critical conditions with respect to delayed failure arise for massive sections, small values of the steel tube thickness and for columns with massive section.</p>Mohammed Salah DimiaSoumia SekkiouMohamed BaghdadiMohamed Guenfoud
Copyright (c) 2017 TULPAR Academic Publishing
2017-12-182017-12-184216016510.20528/cjsmec.2017.02.004Mechanical and thermal behaviors comparison of basalt and glass fibers reinforced concrete with two different fiber length distributions
http://www.challengejournal.com/index.php/cjsmec/article/view/291
<div><p class="CJ-Abstracttext">This paper deals with the mechanical and thermal behavior of glass and basalt fiber reinforced concrete. Two different composites were studied containing either basalt or glass fibers. Fiber ratios were selected as 1%, 1.25% and 1.5% for glass fiber; 0.3%, 0.4% and 0.5% for basalt fibers. Fiber length was preferred as 12 mm and 24 mm. The addition of basalt fiber had very limited effect on the compressive, flexure and thermal conductivity properties compared to the glass fiber reinforced composite. The results also showed that composites having fibers with the length of 12 mm had better mechanical properties. Heat transfer simulation of the composites were also conducted. It was obtained that both fibers with the length of 12 mm had very close results on the heat transfer studies.</p></div>Sadık Alper Yıldızel
Copyright (c) 2017 TULPAR Academic Publishing
2017-12-182017-12-184215515910.20528/cjsmec.2017.12.017Estimating bearing capacity of shallow foundations by artificial neural networks
http://www.challengejournal.com/index.php/cjsmec/article/view/256
<div><div><p class="CJ-Abstracttext">In this study, the Artificial Neural Network, ANN is applied to data extracted from a large set of random data created by using Terzaghi and Meyerhof formulae. By using MS Excel, 3750 sets of data for Terzaghi's equation, 4000 for Meyerhof's equation were generated. A simulated ANN was trained on a subset of bearing capacity data, and the performance was tested on the remaining data. The performances of the ANN models were compared to Terzaghi and Meyerhof results. ANN models were as accurate as the other techniques in estimating the ultimate bearing capacity. The models estimated the ultimate bearing capacity with an average error of around 1% of the value obtained from Terzaghi and Meyerhof equations, and the coefficient of determination (<em>r</em><sup>2</sup>) was almost equal to 1. Their sensitivity and specificity is dependent on the function and the algorithm used in the training process. Validation subset is crucial in preventing the over-fitting of the ANN models to the training data. ANN models are potentially useful technique for estimating the bearing capacity of the soil. Large training data sets are needed to improve the performance of data-derived algorithms, in particular ANN models.</p></div></div>Mustafa Aytekin
Copyright (c) 2017 TULPAR Academic Publishing
2017-12-182017-12-184215115410.20528/cjsmec.2017.11.016A hybrid multi-objective algorithm to predict the characteristics of soil profiles from seismic ground motion records
http://www.challengejournal.com/index.php/cjsmec/article/view/261
<div><div><p class="CJ-Abstracttext">The underlying goal of this study is to present an efficient algorithm to identify soil parameters such as thicknesses, shear wave velocities, damping and others parameters of subsurface layers, and site amplification characteristics (natural frequencies, peak amplitudes) from a given pair of seismic records. It is a hybrid procedure combining the stochastic genetic algorithms (GAs) optimization method, to find a point close to the global optimum in the global search phase, and a gradient based local determinist method (Levenberg-Marquardt: LM), to refine the solution. To improve the performance of the global search phase, a multi-objective optimization algorithm is used to minimize the errors between some characteristics of the theoretical amplification function and the experimental one of vertical array records. The weighted sum method which combines the weighted objectives into a single objective function is used to solve the optimization problem. The efficiency of the present algorithm is proven by several examples. Results show that the scheme works well and the curve fitting was always satisfying. Also, the proposed procedure leads to good approximations, requiring a lower computational effort, yet with good rates of convergence. Moreover, neither the growing number of parameters nor the vastness of the search space reduces the efficiency of the algorithm in predicting the characteristics of soil profiles and site amplification commonly required in seismic risk mitigation.</p></div></div>Zamila HarichaneMourad A. KhellafiAmina Sadouki
Copyright (c) 2017 TULPAR Academic Publishing
2017-12-182017-12-184213815010.20528/cjsmec.2017.09.015Cover & Contents Vol.3 No.4
http://www.challengejournal.com/index.php/cjsmec/article/view/307
Journal Management CJSMEC
Copyright (c) 2017 TULPAR Academic Publishing
2017-12-182017-12-1842The strain sensitivity of brass fiber reinforced concrete
http://www.challengejournal.com/index.php/cjsmec/article/view/239
<p>The structures are challenged by earthquakes and other environmental factors. Structural health monitoring is crucial to protect the lives. The strain gages used in structural health monitoring have low durability and can get point wise measurements which limit their use. In this study, five different concrete mixtures with different brass fiber volume fractions were designed. Along with the control mixture which does not have brass fiber, six mixtures were designed and three cube samples from each mixture were cast and cured. Compression test was conducted with simultaneous measurement of electrical resistance. The brass fiber reinforced concrete has strong linear relationship between the electrical resistance change and strain. Important progress was achieved in development of “Smart Concrete” which can sense its strain and damage.</p>Egemen TeometeErman DemircilioğluSerap Kahraman
Copyright (c) 2017 TULPAR Academic Publishing
2017-09-182017-09-184213413710.20528/cjsmec.2017.02.008Total potential energy minimization method in structural analysis considering material nonlinearity
http://www.challengejournal.com/index.php/cjsmec/article/view/216
<p>Minimum potential energy principle is the basis of the most of the well-known traditional techniques used in the structural analysis. This principle determines the equilibrium conditions of systems with reference to minimization of the sum of the total potential energy of the structure. In traditional applications, this methodology is formulized by using matrix operations. A methodology has been proposed in the last decades for structural analyses based on the idea of using metaheuristic algorithms to obtain minimum potential energy of the structural system instead of following this classical approach. This new method, called “Total Potential Optimization using Metaheuristic Algorithms (TPO/MA)”, has been applied in this paper to truss structures considering linear and nonlinear behavior of the structural material. The metaheuristic method used in this process is teaching-learning based optimization (TLBO) algorithm. The proposed technique is applied on numerical examples and results are compared with other techniques in order to test the efficiency of the proposed method. According to results obtained, TPO/MA method with TLBO algorithm is a feasible technique for the investigated problem.</p>Rasim TemürGebrail BekdaşYusuf Cengiz Toklu
Copyright (c) 2017 TULPAR Academic Publishing
2017-09-182017-09-184212913310.20528/cjsmec.2017.02.005The influence of elevated temperatures on the mechanical properties of polypropylene fiber reinforced concrete
http://www.challengejournal.com/index.php/cjsmec/article/view/262
This paper describes the strength of Polypropylene Fiber Reinforced Concrete (PFRC) exposed to the elevated temperatures. In the study, control specimens without any fibers and the concrete specimens with the ratios of 0.30, 0.60, 0.90 and 1.20 kg/m³ polypropylene fibers both in woolen and bar shape fiber have been produced. The specimens have been kept in the laboratory conditions for 28 days. Shortly after the curing period was completed, every group was heated at 23, 150, 300, 450, 600 and 750°C for two hours then the compressive strengths of them were determined. The maximum compressive strength was obtained by the specimens including 0.30 kg/m³ woolen polypropylene. For this group, the compressive strength increase was 8% according to the control specimens. The compressive strengths of bar polypropylene fiber concrete were higher than the wool fibers under elevated temperatures. On the other hand, more compressive strength values are obtained from the control specimens than fiber groups at 600°C temperature. Melting the polypropylene fiber at 500°C formed some pore spaces in concrete and caused reduction of the compressive strength.Majid AtashafrazehAhmet Ferhat BingölMurat Caf
Copyright (c) 2017 TULPAR Academic Publishing
2017-09-182017-09-184211612210.20528/cjsmec.2017.08.013Vertical stiffeners and internal pressure - influencing factors on distribution of meridional stresses in steel silos on discrete supports
http://www.challengejournal.com/index.php/cjsmec/article/view/257
<p class="JIASSAbstract">Steel silos are interesting, complicated facilities. In order to ensure unloading of whole amount of stored product by gravity, they are often placed on supporting structure. Values of stresses in joints between thin sheets and supporting frame elements are very high, which could cause local loss of stability in thin shells. Many researchers have worked on values and distribution of the meridional stresses in that joints. Their traditional approach is to divide in their minds cylindrical shell on two parts - discretely supported ring beam and continuously supported shell above it. As a result of their efforts critical height of shell <em>H</em><sub>cr</sub> and ideal position of intermediate stiffening ring on shell are determined. The scientific results are based on semi-membrane theory of Vlasov, in which influence of vertical stiffeners and internal pressure is not accounted. On other hand all steel silos are loaded with an internal pressure and majority of them have vertical stiffeners above supports. Is it possible the obtained scientific results to be applied to these silos? In a present article the author will show that stiffeners and pressure should not be ignored in an analysis.</p>Lyubomir A. Zdravkov
Copyright (c) 2017 TULPAR Academic Publishing
2017-09-182017-09-184212312810.20528/cjsmec.2017.08.014Modal identification of a reduced-scale masonry arch bridge with experimental measurements and finite element method
http://www.challengejournal.com/index.php/cjsmec/article/view/241
This study aims to investigate modal parameters such as mode shapes, natural frequencies and damping ratios of a reduced scale one-span historical masonry arch bridge constructed in laboratory conditions by performing numerical and experimental analysis. Sarp Dere historical masonry bridge, in Ordu, Ulubey, has 15.5m in length and 4.75m in width was chosen as a prototype model. The reduced-scale bridge model and structural details were carried out in the scale of 1:12.5. Operational Modal Analysis (OMA) technique was used for experimental study. The experimental modal parameters of the bridge model were figured out by using Enhanced Frequency Domain Decomposition (EFDD). ANSYS software was used to create 3D finite element (FE) model and to expose the analytical modal parameters of the reduced-scaled bridge model. Moreover, FE model of the reduced-scale bridge model was calibrated based on the experimental results by using the Response Surface based FE model calibration technique to obtain more accurate results. The analysis results of experimental, initial and calibrated FE model were compared. It is noted that there are significant differences between the modal parameters obtained from experimental and initial FE model. Model calibration techniques are beneficial to get a more reasonable FE model.Emre AlpaslanBurcu DinçKemal HacıefendioğluGökhan DemirOlgun Köksal
Copyright (c) 2017 TULPAR Academic Publishing
2017-09-182017-09-184210811510.20528/cjsmec.2017.06.012Cover & Contents Vol.3 No.3
http://www.challengejournal.com/index.php/cjsmec/article/view/274
Journal Management CJSMEC
Copyright (c) 2017 TULPAR Academic Publishing
2017-09-182017-09-1842Elastic foundation effects on arch dams
http://www.challengejournal.com/index.php/cjsmec/article/view/236
<div><p class="CJ-Abstracttext">Earthquake response of an arch dam should be calculated under ground motion effects. This study presents three-dimensional linear earthquake response of an arch dam. Thereby, we considered different ground motion effects and also foundation conditions in the finite element analyses. For this purpose, the Type 3 double curvature arch dam was selected for application. All numerical analyses are carried out by SAP2000 program for empty reservoir cases. In the scope of this study, linear modal time-history analyses are performed using three dimensional finite element model of the arch dam and arch dam-foundation interaction systems. According to numerical analyses, maximum horizontal displacements and maximum normal stresses are presented by dam height in the largest section. These results are evaluated for rigid and various elastic foundation conditions. Furthermore, near-fault and far-field ground motion effects on the selected arch dam are taken into account by different accelerograms obtained from the Loma Prieta earthquake at various distances.</p></div>Muhammet KarabulutMurat Emre KartalOmer Faruk CaparMurat Cavusli
Copyright (c) 2017 TULPAR Academic Publishing
2017-06-132017-06-134210210710.20528/cjsmec.2017.02.006The strain sensitivity of copper powder reinforced concrete
http://www.challengejournal.com/index.php/cjsmec/article/view/238
<div><p class="CJ-Abstracttext">Earthquakes, material deteriorations and other environmental factors challenge the structural safety. In order to protect the lives, structural health monitoring is crucial. The metal foil strain gages have low durability, low sensitivity and can get point wise measurements which are disadvantages. In this study six different concrete mixtures were designed; one without any copper powder, the rest five having different copper powder volume fractions. Three cube samples from each mixture were cast and cured. Simultaneous measurement of electrical resistance and strain were conducted during the compression tests. A strong linear relationship between strain and electrical resistance change was obtained for copper powder reinforced concrete. The results are contribution to the development of “Smart Concrete” which can sense its strain and damage.</p></div>Egemen TeometeÖzkan Ayberk KolatarErman DemircilioğluSerap Kahraman
Copyright (c) 2017 TULPAR Academic Publishing
2017-06-132017-06-13429610110.20528/cjsmec.2017.02.007Teaching-learning based optimization for parameter estimation of double tuned mass dampers
http://www.challengejournal.com/index.php/cjsmec/article/view/85
<div><p class="CJ-Abstracttext">The classical methods for parameter estimation of tuned mass dampers are well known simple formulations, but these formulations are only suitable for multiple degree of freedom structures by considering a single mode. If special range limitation of tuned mass dampers and inherent damping of the main structure are considered, the best way to estimate the parameters is to use a numerical method. The numerical method must have a good convergence and computation time. In that case, metaheuristic methods are effective on the problem. Generally, metaheuristic method is inspired from a process of life and it is formulated for several steps in order to reach an optimal goal. Differently from the single tuned mass dampers, double tuned mass dampers can be also used for the reduction of vibrations. In civil structures, earthquake excitation is a major source of vibrations. In this study, optimum double tuned mass dampers are investigated for seismic structures by using a wide range of earthquake records for global optimum. As an optimization algorithm, teaching learning based optimization is employed. In this algorithm, the teaching and learning phases of a class are modified for optimization problems. The optimization of double tuned mass damper is more challenging than the single ones since the number of design variable is doubled and the design constraint about the stroke of the both masses must be considered. The proposed method is compared with the existing approaches and the methodology is feasible for parameter estimation of double tuned mass dampers.</p></div>Sinan Melih NiğdeliGebrail Bekdaş
Copyright (c) 2017 TULPAR Academic Publishing
2017-06-132017-06-1342909510.20528/cjsmec.2016.11.032Flexural behavior of sustainable reactive powder concrete bubbled slab flooring elements
http://www.challengejournal.com/index.php/cjsmec/article/view/181
<div><p class="CJ-Abstracttext">Voided slabs are reinforced concrete slabs in which voids allow to reduce the amount of concrete. The bubbled deck slab is a new and sustainable biaxial floor system to be used as a self-supporting concrete floor. The use of voided slabs leads to decrease the consumption of materials and improve the insulation properties for enhancing the objectives of sustainability. This study presents an investigation into the flexural behavior of sustainable Reactive Powder Concrete RPC bubbled slab flooring elements. Six one-way slabs were cast and tested up to the failure. The adopted variables in this study are: the volumetric ratio of steel fibers, type of slab; bubbled or solid, placing of reinforcement and thickness of slab. The effect of each variable on the ultimate load, deflection and strain has been discussed. The results show that increasing the percent of steel fibers from 1% to 2% in solid and bubbled slabs decreases the deflection by (18.75%) and (50%) respectively. As well as, the deflection increases by (41%) for bubbled slab compared to the solid slab. The slabs reinforced with top and bottom steel meshes show less deflection than slabs reinforced by only bottom steel mesh.</p></div>Ashraf Abdulhadi AlfeehanHassan Issa AbdulkareemShahad Hameed Mutashar
Copyright (c) 2017 TULPAR Academic Publishing
2017-06-132017-06-1342818910.20528/cjsmec.2017.04.010Cover & Contents Vol.3 No.2
http://www.challengejournal.com/index.php/cjsmec/article/view/255
Journal Management CJSMEC
Copyright (c) 2017 TULPAR Academic Publishing
2017-06-132017-06-1342Modelling of non-linear seismic ground response using elasto-plastic constitutive framework within a finite element soil column model
http://www.challengejournal.com/index.php/cjsmec/article/view/235
<div><p class="CJ-Abstracttext">The prediction of seismic ground response is conditioned by the knowledge of each material behavior of soil deposits. The recourse to plasticity criterion to simulate cyclic behavior of soils under seismic loading is becoming more realistic. In this study, an elasto-plastic constitutive equation is cast within the framework of one dimensional finite element (FE) soil column model to account for the spatial and material nonlinearity of the secant shear modulus. To account of the spatial non linearity, shear modulus is written in terms of rigid base shear modulus and height of the soil column, while for material nonlinearity, the shear modulus degradation is deducted by the application of the isotropic evolution of the Von Misès criterion. Obtained results proved the efficiency of the proposed methodology and the predictive capability of the elaborated elastoplastic model which captures both small- and large-strain behaviors. They likewise highlight the important roles that play the spatial and material shear modulus variation in the prediction of the seismic soil responses.</p></div>Azeddine ChehatZamila HarichaneAmina Sadouki
Copyright (c) 2017 TULPAR Academic Publishing
2017-06-132017-06-1342728010.20528/cjsmec.2017.05.011Modal response identification of a highway bridge under traffic loads using frequency domain decomposition (FDD)
http://www.challengejournal.com/index.php/cjsmec/article/view/237
<div><p class="CJ-Abstracttext">In this study, a four-span, 224m long, post-tensioned concrete box girder bridge supported on single column piers was subject to a series of controlled vehicle tests. Bridge acceleration response datasets were used to study the effect of truck speed and a sudden stop, on the modal identification of the bridge structure. Natural frequencies and mode shapes of the bridge were determined using the frequency domain decomposition technique for all datasets. The passing of the truck rendered difficult to identify the first bridge frequency. Conversely, the vehicle tests improved the identification of higher vibration modes. This is because the truck preferentially excites the bridge vertical response, which is associated with higher modes of vibrations, especially when a sudden stop of the vehicle occurs. Thus, carefully conducted vehicle-crossing tests provide detailed information about the bridge structure dynamics in the vertical direction. However, to identify lower modes, no vehicle on the bridge is preferred.</p></div>Mehmet AkköseHugo C. GomezMaria Q. Feng
Copyright (c) 2017 TULPAR Academic Publishing
2017-06-132017-06-1342637110.20528/cjsmec.2017.03.009Effect of time step size on stress relaxation
http://www.challengejournal.com/index.php/cjsmec/article/view/82
<div><div><p class="CJ-Abstracttext">Many materials used in industry show time and temperature dependant stress strain relationship. While essentially most of the materials exhibit stress relaxation or in general viscoelastic material properties, some of them are assumed as linear elastic to be able to make their stress calculations simpler. On the contrary, there are some materials showing intense viscoelastic stress strain relationship even at lower temperatures and short time periods. Most of these materials are employed in construction industry as pavements on roads or bridges and needed a better understanding of their viscoelastic material properties and calculation methods for their design. For a better understanding and comparison between several material products in industry, their stress strain behavior shall be evaluated. Stress relaxation of materials, which shows time and temperature dependant properties, is investigated in this paper. For that reason first, relaxation test results existed in the literature are used to verify the numerical stress relaxation calculation of commercial FEM program, ANSYS. Second, the determination of Prony series parameters and the commands to be entered in ANSYS to perform stress relaxation are given. Finally, the amount of error in the numerical calculation depending on time step sizes at different temperatures is presented.</p></div></div>Abdullah Fettahoğlu
Copyright (c) 2017 TULPAR Academic Publishing
2017-03-102017-03-1042586210.20528/cjsmec.2016.11.029Non-linear behaviour modelling of the reinforced concrete structures by multi-layer beam elements
http://www.challengejournal.com/index.php/cjsmec/article/view/87
<div><p class="CJ-Abstracttext">A two-dimensional multi-layered finite elements modeling of reinforced concrete structures at non-linear behaviour under monotonic and cyclical loading is presented. The non-linearity material is characterized by several phenomena such as: the physical non-linearity of the concrete and steels materials, the behaviour of cracked concrete and the interaction effect between materials represented by the post-cracking field. These parameters are taken into consideration in this paper to examine the response of the reinforced concrete structures at the non-linear behaviour. Two examples of application are presented. The numerical results obtained, are in a very good agreement with available experimental data and other numerical models of the literature.</p></div>Mourad KhebiziHamza GuenfoudMohamed Guenfoud
Copyright (c) 2017 TULPAR Academic Publishing
2017-03-102017-03-1042525710.20528/cjsmec.2016.11.034Universal size effect of concrete specimens and effect of notch depth
http://www.challengejournal.com/index.php/cjsmec/article/view/215
<div><p class="CJ-Abstracttext">The universal size effect law of concrete is a law that describes the dependence of nominal strength of specimens or structure on both its size and the crack (or notch) length, over the entire of interest, and exhibits the correct small and large size asymptotic properties as required. The main difficulty has been the transition of crack length from 0, in which case the size effect mode is Type 1, to deep cracks (or notches), in which case the size effect mode is Type 2 and fundamentally different from Type 1. The current study is based on recently obtained comprehensive fracture test data from three-point bending beams tested under identical conditions. In this test, the experimental program consisted of 80 three-point bend beams with 4 different depths 40, 93, 215 and 500mm, corresponding to a size range of 1:12.5. Five different relative notch lengths, <em>a</em>/<em>D</em> = 0, 0.02, 0.075, 0.15, 0.30 were cut into the beams. A total of 20 different geometries (family of beams) were tested. The present paper will use these data to analyze the effects of size, crack length. This paper presents a studying to improve the existing universal size effect law, named by Bazant, using the experimentally obtained beam strengths for various different specimen sizes and all notch depths. The updated universal size effect law is shown to fit the comprehensive data quite well.</p></div>Sıddık ŞenerKadir Can Şener
Copyright (c) 2017 TULPAR Academic Publishing
2017-03-102017-03-1042475110.20528/cjsmec.2017.02.003HVAC systems: measurements of airflows in small duct length
http://www.challengejournal.com/index.php/cjsmec/article/view/80
<div><p class="CJ-Abstracttext">One of the most feasible ways to measure duct airflows is by tracer gas techniques, especially for complex situations when the duct lengths are short as well as their access, which makes extremely difficult or impossible other methods to be implemented. One problem associated with the implementation of tracer gas technique when the ducts lengths are short is due to the impossibility of achieving complete mixing of the tracer with airflow and its sampling. In this work, the development of a new device for the injection of tracer gas in ducts is discussed as well as a new tracer-sampling device. The developed injection device has a compact tubular shape, with magnetic fixation to be easy to apply in duct walls. An array of sonic micro jets in counter current direction, with the possibility of angular movement according to its main axle ensures a complete mixing of the tracer in very short distances. The tracer-sampling device, with a very effective integration function, feeds the sampling system for analysis. Both devices were tested in a wind tunnel of approximately 21m total length. The tests distances between injection and integration device considered were:<em> X</em>/<em>Dh</em>=22; <em>X</em>/<em>Dh</em>=4; <em>X</em>/<em>Dh</em>=2; and <em>X</em>/<em>Dh</em>=1. For very short distances of <em>X</em>/<em>Dh</em>=2 and <em>X</em>/<em>Dh</em>=1, semi empirical expressions were needed. A good reproducibility of airflow rate values was obtained. These preliminary tests showed that the practical implementation of tracer gas techniques in HVAC systems for measuring airflow rates with a very short mixing distance is possible with the devices developed.</p></div>Clito Félix Alves Afonso
Copyright (c) 2017 TULPAR Academic Publishing
2017-03-102017-03-1042384610.20528/cjsmec.2016.11.027Influence of blast-induced ground motion on dynamic response of masonry minaret of Yörgüç Paşa Mosque
http://www.challengejournal.com/index.php/cjsmec/article/view/89
<div><p class="CJ-Abstracttext">This paper focuses on the dynamic response analysis of masonry minaret of Yörgüç Paşa Mosque subjected to artificially generated surface blast-induced ground motion by using a three-dimensional finite element model. The mosque is located in the town of Kavak of Samsun, in Turkey. This study intended to determine the ground motion acceleration values due to blast-induced ground motions (air-induced and direct-induced) calculated by a random method. In order to model blast-induced ground motion, firstly, peak acceleration and the time envelope curve function of ground motion acceleration were obtained from the distance of the explosion center and the explosion charge weight and then blast-induced acceleration time history were established by using these factors. Non-stationary random process is presented as an appropriate method to be produced by the blast-induced ground motion model. As a representative of blast-induced ground motion, the software named BlastGM (Artificial Generation of Blast-induced Ground Motion) was developed by authors to predict ground motion acceleration values. Artificial acceleration values generated from the software depend on the charge weight and distance from the center of the explosion. According to the examination of synthetically generated acceleration values, it can be concluded that the explosions cause significant effective ground movements. In the paper, three-dimensional finite element model of the minaret was designed by ANSYS. Moreover, the maximum stresses and displacements of the minaret were investigated. The results of this study indicate that the masonry minaret has been affected substantially by effects of blast-induced ground motion.</p></div>Olgun KöksalKemal HacıefendioğluEmre AlpaslanFahri Birinci
Copyright (c) 2017 TULPAR Academic Publishing
2017-03-102017-03-1042313710.20528/cjsmec.2016.12.036Metaheuristic approaches for optimum design of cantilever reinforced concrete retaining walls
http://www.challengejournal.com/index.php/cjsmec/article/view/84
<div><div><p class="CJ-Abstracttext">An approach is presented for optimum design of cantilever reinforced concrete (RC) retaining wall via teaching-learning based optimization (TLBO) algorithm. The objective function of the optimization is to minimize total material cost including concrete and reinforcing steel bars of the cantilever retaining wall by considering overturning, sliding and bearing stabilities, bending moment and shear capacities and requirements for design and construction of reinforced concrete structures (TS 500/2000). TLBO algorithm is a simple algorithm without any special algorithm parameters. This innovative approach is providing an advantage to TLBO in terms of easily applying to the problem. The proposed method has been performed on numerical examples and the results are compared with previous approaches. Results show that, the methodology is feasible for obtaining the optimum design of RC cantilever retaining walls.</p></div></div>Gebrail BekdaşRasim Temür
Copyright (c) 2017 TULPAR Academic Publishing
2017-03-102017-03-1042233010.20528/cjsmec.2016.11.031Research on relation between natural frequency and axial stress of round bar with intermediate-supported ends
http://www.challengejournal.com/index.php/cjsmec/article/view/133
<div><p class="CJ-Abstracttext">In order to make a method be useful to measure an axial stress of a member by a natural frequency, we investigated a relation between a natural frequency and an axial stress of a round bar with intermediate-supported ends, the boundary condition of which was one between a fix-supported end and a simply-supported end. To define an intermediate-supported end condition, we adopted a parameter, a ratio of a moment of a force to a deflection angle at the end. It was shown theoretically that the parameter of an intermediate-supported end could be evaluated by one at a support on a continuous beam consisted of 3 spans. The 3-spanned beam has same vibration characteristics of a beam with intermediate-supported ends. We manufactured a test device of a 3-spanned beam by which we could simulate a vibration under various intermediate-supported end conditions. The theoretical relation and experimental results between a natural frequency and an axial stress agreed for the most part.</p></div>Tsutomu YoshidaTakeshi WatanabeKunihiko Sakurada
Copyright (c) 2017 TULPAR Academic Publishing
2017-03-102017-03-1042172210.20528/cjsmec.2017.02.002Analytical solution for bending and buckling response of laminated non-homogeneous plates using a simplified-higher order theory
http://www.challengejournal.com/index.php/cjsmec/article/view/224
In this study, analytical solutions for the bending and buckling analysis of simply supported laminated non-homogeneous composite plates based on first and simplified-higher order theory are presented. The simplified-higher order theory assumes that the in-plane rotation tensor is constant through the thickness. The constitutive equations of these theories were obtained by using principle of virtual work. Numerical results for the bending response and critical buckling loads of cross-ply laminates are presented. The effect of non-homogeneity, lamination schemes, aspect ratio, side-to-thickness ratio and in-plane orthotropy ratio on the bending and buckling response were analysed. The obtained results are compared with available elasticity and higher order solutions in the literature. The comparison studies show that simplified-higher order theory can achieve the same accuracy of the existing higher order theory for non-homogeneous thin plate.Ferruh TuranMuhammed Fatih BaşoğluZihni Zerin
Copyright (c) 2017 TULPAR Academic Publishing
2017-03-102017-03-104211610.20528/cjsmec.2017.02.001Cover & Contents Vol.3 No.1
http://www.challengejournal.com/index.php/cjsmec/article/view/245
Journal Management CJSMEC
Copyright (c) 2017 TULPAR Academic Publishing
2017-03-102017-03-1042Thermoelastic stress analysis for detecting wrinkles and associated resin pockets in polymer composites
http://www.challengejournal.com/index.php/cjsmec/article/view/78
<div><p class="CJ-Abstracttext">A thermos elastic stress analysis method is proposed consisting of an array of infrared measurement sensors used for evaluation the wrinkling defects and associated resin pockets in a fiber reinforced polymer (FRP) composite structure. Wrinkling or fiber waviness defects results when out of plane distortions occur in some or all of the composite layers of the laminate. The wrinkles result in significant reductions of mechanical properties in the composite structure. The method involves instrumentation and device for application of internal energy in the material such as transient or cyclic mechanical excitations. These external excitations are induced in a prescribed or measurable cyclic or transient function of time. Infrared measurements from the surface of the composite are synchronized with the applied excitation energy. The results are used to provide for a map detailing the inner wrinkle defects and associated resin pockets in the laminated composite structure.</p></div>Rani ElhajjarRami Haj-Ali
Copyright (c) 2016 TULPAR Academic Publishing
2016-12-262016-12-264224624710.20528/cjsmec.2016.11.025Soft-story effects on the behaviour of seismically isolated buildings under near and far-fault earthquakes
http://www.challengejournal.com/index.php/cjsmec/article/view/212
<div><p class="CJ-Abstracttext">In this study, the effects of soft-story on the seismic behaviour of 3-story and 8-story isolated buildings under near and far-fault earthquakes were investigated. Four different structural models with two different 1<sup>st</sup> story height were designed: One with 1<sup>st</sup> story height of 3m and 2<sup>nd</sup> with 1<sup>st</sup> story height of 4.5m to capture soft story effect. The prototype fixed base buildings were converted to seismically isolated buildings by introducing rubber isolators at base level. Analyses were conducted by using two different isolation systems (QW7.5Tb3 and QW7.5Tb4). The modelling of conventional fixed base prototype seismically isolated buildings and their modal analyses were conducted on finite-element program SAP2000, whereas, modelling of seismically isolated buildings and nonlinear time-history analyses were conducted using 3D-BASIS program. The four accelerations records has been used for the time-history analysis. Floor accelerations, story shears and inter-story drift ratios were the key structural responses considered. The analysis results showed seismic isolations can be used as a viable mitigation method for the buildings with soft-stories under near and far-fault earthquakes. Based on the results obtained, it is interesting to note that all types of buildings whether with soft story or with typical story height show the same acceleration trend and close values (except top floor) for all types of isolation systems and earthquakes considered. In addition, both 3 and 8-story buildings suffered increase in interstory drifts beyond the limits defined UBC 97 under earthquakes containing long period pulses.</p></div>Savaş ErdemKhalid Saifullah
Copyright (c) 2016 TULPAR Academic Publishing
2016-12-262016-12-264223424510.20528/cjsmec.2016.12.038Nonlinear finite element analysis of cold-formed steel plain angle columns
http://www.challengejournal.com/index.php/cjsmec/article/view/86
<div><p class="CJ-Abstracttext">The main objective of this paper is to provide an efficient and accurate finite element model to understand the behavior of cold-formed steel plain angle columns. The effects of initial local and overall geometric imperfections have been taken into consideration in the analysis. The material nonlinearities of flat and corner portions of the angle sections were incorporated in the model. Failure loads and buckling modes as well as load-shortening curves of plain angle columns were investigated in this study. The nonlinear finite element model was verified against experimental results. The finite element analysis was performed on plain angles compressed between fixed ends over different column lengths, and column curves were obtained.</p></div>Mustafa DurmazAyşe Daloğlu
Copyright (c) 2016 TULPAR Academic Publishing
2016-12-262016-12-264222022510.20528/cjsmec.2016.11.033Wind loads for stadium lighting towers according to Eurocode 1
http://www.challengejournal.com/index.php/cjsmec/article/view/88
<div><p class="CJ-Abstracttext">The determination of actions on structures is an important step of in the design process. In nature, so many outer and inner actions are acting on structures continuously. The two most important ones of those actions are the earthquake and wind actions. For some structures, i.e. towers, high chimneys or lighting towers, the priority of these two severe actions can change. Wind forces can become a governing force on the design of these structures. Therefore, the determination of wind forces for these tall, slender and wind-sensitive structures becomes very important. Also, these tall and slender structures have a high ratio of height to least diameter that makes them more slender and wind-sensitive than any other structures. In this study, the determination of wind loads for a selected and modeled stadium lighting tower was given according to Eurocode 1 which is an international well-known standard. This study showed that it is difficult to calculate wind loads of stadium lighting towers according to Eurocode 1 because of the complexity of the document, insufficient explanation of some formulas like resonant response factor and unclear graph sections for the reader. This study is believed to enlighten the way of the users of Eurocode 1.</p></div>Zeki KaracaHasan Tahsin ÖztürkErdem Türkeli
Copyright (c) 2016 TULPAR Academic Publishing
2016-12-262016-12-264222623310.20528/cjsmec.2016.12.035Optimum design of reinforced concrete columns employing teaching-learning based optimization
http://www.challengejournal.com/index.php/cjsmec/article/view/83
<div><p class="CJ-Abstracttext">In structural engineering, the design of reinforced concrete (RC) structures needs an initial de-sign for cross sectional dimensions. After these dimensions are defined, the design constraints and the required reinforcement bars are calculated. But the required reinforcement area is not exactly provided since the size of rebars are fixed. At the end of the design, the security measures are provided, but the designer has no idea for the optimization of the design in mean of economy. For that reason, a powerful search methodology can be programed by using metaheuristic algorithms. In this study, optimum design of reinforced concrete columns was investigated by using an education based metaheuristic algorithm called teaching-learning based optimization (TLBO). In the methodology, the slenderness of the columns is also taken into consideration by using a simple approach given in the ACI 318 design code. In this approach, the factored design flexural moments are defined according to the buckling load and axial load of columns. The design variables of the problem include cross section dimension of the column and the detailed reinforcement design and the optimization objective is the minimization the maximum material cost of the column. Differently from the other metaheuristic algorithms, the decision of the optimization type (global or local search) is not defined by using a probability parameter in TLBO. In optimization, two phases of TLBO; teacher (global search) and learner (local search) phases are consequently applied in search of best design variables. The proposed approach is effective for the structural optimization problem.</p></div>Gebrail BekdaşSinan Melih Niğdeli
Copyright (c) 2016 TULPAR Academic Publishing
2016-12-262016-12-264221621910.20528/cjsmec.2016.11.030Bonded particles models of rock plates with circular cavities in uniaxial and biaxial compression
http://www.challengejournal.com/index.php/cjsmec/article/view/79
<div><p class="CJ-Abstracttext">In this paper, a distinct elements code is used to perform a numerical investigation for the size and stress gradient effects on the fracture initiation and propagation around single or pairs of pre-existing cavities in brittle rock. To investigate the rock fracture around cavities and to assess the potential of the numerical model to simulate this behavior, published laboratory physical model on granite is simulated numerically with a Bonded Particles Model (BPM). The numerical model is presented and the calibration of the BPM micro-parameters is described. Then, the calibrated BPMs are used to investigate the effect of the size of the cavity on the primary, secondary and side wall fracturing, as well as on the fracturing modes. Moreover, BPMs with two circular cavities were used to study the interaction of these holes of the same diameter and to investigate the importance of their relative distance. Finally, the simulated material was studied by biaxial tests on BPMs with a pre-existing hole.</p></div>Michail A. LotidisPavlos P. NomikosAlexandros I. Sofianos
Copyright (c) 2016 TULPAR Academic Publishing
2016-12-262016-12-264220521110.20528/cjsmec.2016.11.026High strain rate and quasi-static compression behavior and energy absorption characteristic of PVC foam
http://www.challengejournal.com/index.php/cjsmec/article/view/81
<div><p class="CJ-Abstracttext">The mechanical properties at room temperature of two densities PVC foams have been experimentally evaluated in both quasi-static and dynamic compression loading conditions. The strain rate effect have been evaluated by comparing the constant strength during plateau region. Energy absorption efficiency of PVC foam is investigated, and it shows that in certain density range, the efficiency of lighter PVC foam is larger than that of heavier PVC foam, but the efficiency stress of lighter PVC foam is smaller than that of heavier PVC foam. While the lighter PVC foam has been compressed more than heavier PVC foam when they reach their peak efficiency. Therefore, for a certain density of PVC foam itself, when the loading rates increase, the PVC foam will absorb more energy more efficiently.</p></div>Zhang WeiYe Nan
Copyright (c) 2016 TULPAR Academic Publishing
2016-12-262016-12-264221221510.20528/cjsmec.2016.11.028Assessment of aerodynamic response of the Nissibi cable-stayed bridge using three-dimensional computational fluid dynamics
http://www.challengejournal.com/index.php/cjsmec/article/view/91
<div><p class="CJ-Abstracttext">Aerodynamic behavior has the greatest impact on long-span bridges and is the most important factor in the design of cable stayed bridges, which should not be overlooked. CFD (Computational Fluid Dynamics) is the most widely used technique, among bridge engineers, to predict wind speed, direction and vortex-shedding form before conducting wind tunnel tests. In this study, a bi-directional CFD analysis with the wind flow parallel and perpendicular to Nissibi Bridge's, which has a main span of 400 m and claimed the spot of Turkey’s 3<sup>rd</sup> largest bridge, deck cross-section has been performed by approximate modelling of the bridge and the surrounding structures. The study is done by using CFD++ software/computer program. The results showed that the effect of wind acting on <em>x</em> direction of impact with 30 m/s has caused turbulence and vortex on conjugation area of the tower and it is observed that the upside down Y shape of the tower breaks down the balance of wind flow. However, bridge deck is not exposed to serious amount of vortex influence due to the wind on <em>y</em> direction. In addition, the analysis revealed that maximum pressure distribution occurred on vertical surface of the tower and it increases in direct proportion to the height of the tower.</p></div>Savaş Erdemİrem YağmuroğluKhalid Saifullah
Copyright (c) 2016 TULPAR Academic Publishing
2016-12-262016-12-264219620410.20528/cjsmec.2016.12.037