Civil Engineering / İnşaat Mühendisliği
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Article Art and Construction Related Qualities of 14th‒15th Century Monuments in a Rural Landscape on the Western Coast of Türkiye(KeAi Communications Co., 2024) Hamamcıoğlu Turan, Mine; Aktaş, Engin; Toköz, Özge DenizThis study aims to contribute to the understanding of the evolution of art and construction in the early settlements established by Turkish communities on the far west Asian coast by focusing on two developed examples in Urla Peninsula. Conventional surveying and evaluation techniques of architectural restoration and civil engineering were utilized. Key findings include the understanding of the hierarchy of rural settlements in the studied landscape: old Çesme the most developed village of peninsula in the 16th century. It was positioned along a valley in distance to coast, but in control of harbor that played significant role in commerce between Europe and Asia. Its mosque and tomb, dated to late 14th – early 15th centuries, used to crown it. Cylindrical minaret tower of mosque, domed tomb tower on a cubical base and squinch in the transition zone of mosque are evidences for Central Asian roots. Usage of local lime stone, re-usage of andesite blocks, framing of the stone blocks with bricks, and pendentive in tomb refer to Roman-Byzantine constructions. The study presents the development of Turkish art and construction on the far west Asian coast in the 14th‒15th centuries. Findings will be a guide for related conservation management in similar contexts. © 2024 The Author(s)Article Citation - Scopus: 2Application of Endurance Time Method in Seismic Assessment of Rc Frames Designed by Direct Displacement-Based Procedure(Turkish Chamber of Civil Engineers, 2024) Karımzada, Nisar Ahmad; Shırkhanı, Amir; Aktaş, EnginThis paper addresses the Direct Displacement-Based Design (DDBD) approach of multi-story RC frame structures consistent with changes to design criteria between Turkish earthquake codes of TSC-2007 and TBEC-2018. The corresponding response modification factor (R) of structures designed based on the DDBD approach is also estimated in this research. The design base shear forces of both codes are compared considering different R factors and also with that of the DDBD approach. The results showed that the DDBD approach, as per TBEC-2018, provides RC frame structures with higher R values compared to the similar approach in accordance with TSC-2007. The Endurance Time (ET) method is a time history-based procedure for seismic assessment of structures under intensifying dynamic excitations aided to judge their performance at various intensity levels. Since, up to now, the ET method has not been considered to evaluate the performance of the structures designed by the DDBD approach, this paper addresses this issue. The ET performance curves of RC frames show that structures designed by the DDBD approach in accordance with TBEC-2018 exhibit higher Interstory Drift Ratios (IDRs) values than TSC-2007 at various hazard levels.Conference Object The Challenges and Advantages of Macro Modeling in Ansys Software for Seismic Vulnerability Assessment of Historic Masonry Structures(National Technical University of Athens, 2023) Demir, Hatice Ayşegül; Yücetürk, Kutay; Aktaş, Engin; Hamamcıoğlu Turan, MineThis study aims at creating an advancement guideline for a software which can be used for seismic vulnerability assessment of historic masonry structures by revealing the results of an experience related to the macro modeling of a historic masonry building. The case study structure is Bergama Bedesten (15th-16th centuries) located in Bergama, Izmir, Turkey. ANSYS software is used for the Finite Element Modeling of the structure. The seismicity at its location is determined and the structural response under lateral loads is obtained together with the dynamic characteristics. Mesh design, component creation according to the used material change in structural elements, contact surface identification, the arrangement of the stress scales, and result interpretation are realized. For these stages, the challenges are discussed with the solutions. The advantageous aspects of the software are explained. For the challenges, in mesh design, the ineffectiveness of cartesian method for some elements was detected and tetrahedrons method was chosen. In contact surface identification, the overlapping portions of structural components could not be detected by the software exactly, so the manual surface separation was realized. In the stress level interpretation, the lack of assignment for material limit strength values to the analysis scale was experienced and the addition of limit values was carried out. The scale also needs manual arrangement for the increase of interval numbers of stress values to emphasize vulnerable zones. This flexibility of scale to be arranged can be seen as an advantage, as well. The 3d section and axonometric view creation provide the presentation of stress changes at inner and outer surfaces of the structure which is another positive side. © 2023 COMPDYN Proceedings. All rights reservedArticle Citation - WoS: 7Citation - Scopus: 7Investigating the Effects of Pa66 Electrospun Nanofibers Layered Within an Adhesive Composite Joint Fabricated Under Autoclave Curing(American Chemical Society, 2023) Esenoğlu, Gözde; Tanoğlu, Metin; Barışık, Murat; İplikçi, Hande; Yeke, Melisa; Nuhoğlu, Kaan; Türkdoğan, Ceren; Martin, Seçkin; Aktaş, Engin; Dehneliler, Serkan; Gürbüz, Ahmet Ayberk; İriş, Mehmet ErdemEnhancing the performance of adhesively joined composite components is crucial for various industrial applications. In this study, polyamide 66 (PA66) nanofibers produced by electrospinning were coated on unidirectional carbon/epoxy prepregs to increase the bond strength of the composites. Carbon/epoxy prepregs with/without PA66 nanofiber coating on the bonding region were fabricated using the autoclave, which is often used in the aerospace industry. The single lap shear Charpy impact energy and Mode-I fracture toughness tests were employed to examine the effects of PA66 nanofibers on the mechanical properties of the joint region. Scanning electron microscopy (SEM) was used to investigate the nanofiber morphology and fracture modes. The thermal characteristics of Polyamide 66 nanofibers were explored by using differential scanning calorimetry (DSC). We observed that the electrospun PA66 nanofiber coating on the prepreg surfaces substantially improves the joint strength. Results revealed that the single lap shear and Charpy impact strength values of the composite joint are increased by about 79 and 24%, respectively, by coating PA66 nanofibers onto the joining region. The results also showed that by coating PA66 nanofibers, the Mode-I fracture toughness value was improved by about 107% while the glass transition temperature remained constant.Article Citation - WoS: 9Citation - Scopus: 13Analysis of Adhesively Bonded Joints of Laser Surface Treated Composite Primary Components of Aircraft Structures(Elsevier, 2023) Martin, Seçkin; Nuhoğlu, Kaan; Aktaş, Engin; Tanoğlu, Metin; İplikçi, Hande; Barışık, Murat; Yeke, Melisa; Türkdoğan, Ceren; Esenoğlu, Gözde; Dehneliler, SerkanThe performance of the adhesively bonded aerospace structures highly depends on the adhesion strength between the adhesive and adherents, which is affected by, in particular, the condition of the bonding surface. Among the various surface treatment methods, as state of the art, laser surface treatment is a suitable option for the CFRP composite structures to enhance the adhesion performance, adjusting the roughness and surface free energy with relatively minimizing the damage to the fibers. The aim of this study is the validation and evaluation of the adhesive bonding behavior of the laser surface-treated CFRP composite structures, using the finite element technique to perform a conservative prediction of the failure load and damage growth. Such objectives were achieved by executing both experimental and numerical analyses of the secondary bonded CFRP parts using a structural adhesive. In this regard, to complement physical experiments by means of numerical simulation, macro-scale 3D FEA of adhesively bonded Single Lap Joint and Skin-Spar Joint specimens has been developed employing the Cohesive Zone Model (CZM) technique in order to simulate bonding behavior in composite structures especially skin-spar relation in the aircraft wing-box.Article Citation - WoS: 15Citation - Scopus: 17Effects of Nanosecond Laser Ablation Parameters on Surface Modification of Carbon Fiber Reinforced Polymer Composites(SAGE Publications, 2023) Martin, Seçkin; İplikçi, Hande; Barışık, Murat; Türkdoğan, Ceren; Yeke, Melisa; Nuhoğlu, Kaan; Esenoğlu, Gözde; Tanoğlu, Metin; Aktaş, Engin; Dehneliler, Serkan; İriş, Mehmet ErdemRemoval of contaminants and top polymer layer from the surface of carbon-fiber-reinforced polymer (CFRP) composites is critical for high-quality adhesive-joining with direct bonding to the reinforcing fiber constituents. Surface treatment with a laser beam provides selective removal of the polymer matrix without damaging the fibers and increasing the wettability. However, inhomogeneous thermal properties of CFRP make control of laser ablation difficult as the laser energy absorbed by the carbon fibers is converted into heat and transmitted through the fiber structures during the laser operation. In this study, the effect of scanning speed and laser power on nanosecond laser surface treatment was characterized by scanning electron microscope images and wetting angle measurements. Low scanning speeds allowed laser energy to be conducted as thermal energy through the fibers, which resulted in less epoxy matrix removal and substantial thermal damage. Low laser power partially degraded the epoxy the surface while the high power damaged the carbon fibers. For the studied CFRP specimens consisting of unidirectional [45/0/?45/90]2s stacking of carbon/epoxy prepregs (HexPly®-M91), 100 mJ/mm2 generated by 10 m/s scanning speed and 30 W power appeared as optimum processing parameters for the complete removal of epoxy matrix from the top surface with mostly undamaged carbon fibers and super hydrophilic surface condition. © The Author(s) 2023.Research Project Tarihi yığma yapıların yapısal davranışlarının incelenmesinde izlenecek esasların belirlenmesi; Örnek çalışma: Urla Kamanlı camii(TÜBİTAK - Türkiye Bilimsel ve Teknolojik Araştırma Kurumu, 2004) Aktaş, Engin; Teomete, EgemenTarihi yapılar, binlerce yıllık kültürel birikimimizin en değerli parçalarmdandır. Onlarca medeniyete ev sahipliği yapmış Anadolu toprakları, bünyesinde sayısız tarihi yapı bulundurmaktadır. Bu yapıların yokolmasmı engellemek ve gelecek nesillere ulaşmasını sağlamak önemli bir insanlık vazifesidir. Yıllar tarihi yapılara oldukça hoyrat davranmış ve çoğunun üzerinde derin izler bırakmıştır. Bu yapıların bir kısmı restorasyon ve güçlendirmeye ihtiyaç duymaktadırlar. Hassas bir şekilde yaklaşılması gereken tarihi yapılar, herhangi bir müdahale öncesinde etraflıca gözlenip, analiz edilmelidir. Yapının problemleri iyi tanımlanmalıdır; yapının özgün durumu göz önüne alınarak, araştırma metodları planlanmalı ve uygulanmalıdır. Yapının tarihçe araştırması, röleve çıkartılması, malzeme ve yapısal testler, zemin analizi, uzun dönem gözlemler ve yapı analizi yapıya uygulanacak araştırma metodları arasında sayılabilir. Bu çalışmada örnek olarak seçilen, tarihi yığma yapı Urla Kamanlı Camii üzerinde araştırma metodlarmm uygulanması gösterilmiştir. Yapı analizleri için modellemede Sonlu Elemanlar Metodu seçilmiş, yapının test ve gözlemler sonucu elde edilen geometrik ve malzeme verileri bu modelde kullanılmıştır. Yığma yapıların sonlu elemanlar metodu ile modellenmesinde sıkça kullanılan mikro ve makro modellemeden, yapının büyüklüğü gözönüne alınarak makro modelleme tercih edilmiştir. Makro modellemede yığma sistem öğeleri, homojenize edilerek yığma davranışın modellenmesine gidilir. Toplanan verilerle, yapının sonlu elemanlar analizi, LUSAS adlı ticari bir program ile gerçekleştirilmiştir. Yapıya öz yük, sismik yükler ve olası oturma senaryoları için elastik lineer analizler uygulanmış ve yapıdaki sorunlu bölgeler irdelenmiştir. Ayrıca doğrusal olmayan analizler sayesinde ise yapının öz yük ve oturma senaryolarının beraberce etkittirilmesi ile yapıdaki mevcut durum açıklanmaya çalışılmıştır.Research Project Modal deney yöntemi ile betonarme yapılarda taşıyıcı çerçeve bölme duvar etkileşiminin incelenmesi(2010) Dönmez, Cemalettin; Altınkaya, Mustafa Aziz; Aktaş, Engin; Özen, SerdarBu çalışmada ana amaç betonarme çerçeve dolgu duvarlı sistemlerde çerçeve dolgu duvar etkileşimiyle sistemin dinamik değişkenlerinin nasıl değiştiğini ortaya koymaktır. Bu amaçla modal analiz yöntemleri kullanılmıştır. Ülkemizdeki mevcut yapı stokunun çok büyük bir kısmı betonarme çerçeve ve delikli kil tuğladan yapılmış dolgu duvarlara sahip yapılardan oluşmaktadır. Günümüze kadar olan depremler bu yapıların tipik olarak deprem yükleri altında yetersiz olduklarını göstermiştir. Bu sebeple mevcut yapıların nasıl güçlendirileceği konusunda yoğun çalışmalar yapılmaktadır. Son yıllarda bu yapıları mevcut dolgu duvarları kullanarak güçlendirme konusunda artan bir ilgi oluşmuş ve bir grup yöntem şartnameye kadar girmiştir. Konu hakkında alternatif yöntemler geliştirme çabaları sürmektedir. Sunulan çalışmada ilk olarak modal analiz yöntemlerine hakimiyet sağlamak amacıyla bir grup modal analiz yöntemi üzerine çalışılmıştır. Akabinde modal deney tasarımı ve uygulaması konusunda tecrübe elde etmek için dört farklı basit sistemin ilk kısımda çalışılan modal analiz yöntemlerini kullanarak dinamik değişkenleri belirlenmiştir. Asıl hedef olan betonarme çerçeve dinamik değişkenlerinin izlenmesi amacıyla dört adet tek açıklıklı, dört katlı, 1/5 ölçekli çerçeve imal edilmiştir. Çerçeveler kat sevilerinde uygulanan yükler vasıtasıyla ters üçgen yüklemeye maruz tutulmuş ve kademeli olarak önceden hedeflenen ötelenme seviyelerinde hasarlar verilmiştir. Her hasar seviyesinde modal deneyler yapılmış ve sistem dinamik değişkenlerinin kestirilmesi için gerekli veriler alınmıştır. Verilerin işlenmesi sonucu dolgu duvarların çerçevelerin hakim frekanslarını çok yükseltmekle kalmayıp hasar sonrası davranışı da ciddi şekilde değiştirdiği gözlenmiştir. Dolgu duvarlı sistemlerde artan hasarla birlikte ötelenmeler ilk kata yoğunlaşmakta ve bu katta ağır hasara sebep olmaktadır. Çerçevelerin frekanslarının artan hasar ile birlikte düştüğü fakat özellikle moment çerçevelerinde modal şekillerin ciddi bir değişikliğe uğramadığı gözlenmiştir. Dolgulu çerçevelerde birinci mod harici görece ciddi bir değişim gözlenmiştir. Çalışmada ayrıca modal yöntemleri kullanarak mevcut bir yapının dinamik değişkenleri belirlenmiştir.Article Citation - WoS: 8Citation - Scopus: 8Improving Adhesive Behavior of Fiber Reinforced Composites by Incorporating Electrospun Polyamide-6,6 Nanofibers in Joining Region(SAGE Publications, 2022) Esenoğlu, Gözde; Barışık, Murat; Tanoğlu, Metin; Yeke, Melisa; Türkdoğan, Ceren; İplikçi, Hande; Martin, Seçkin; Nuhoğlu, Kaan; Aktaş, Engin; Dehneliler, Serkan; İriş, Mehmet ErdemAdhesive joining of fiber reinforced polymer (CFRP) composite components is demanded in various industrial applications. However, the joining locations frequently suffer from adhesive bond failure between adhesive and adherent. The aim of the present study is improving bonding behavior of adhesive joints by electrospun nanofiber coatings on the prepreg surfaces that have been used for composite manufacturing. Secondary bonding of woven and unidirectional CFRP parts was selected since this configuration is preferred commonly in aerospace practices. The optimum nanofiber coating with a low average fiber diameter and areal weight density is succeed by studying various solution concentrations and spinning durations of the polyamide-6.6 (PA 66) electrospinning. We obtained homogeneous and beadles nanofiber productions. As a result, an average diameter of 36.50 +/- 12 nm electrospun nanofibers were obtained and coated onto the prepreg surfaces. Prepreg systems with/without PA 66 nanofibers were hot pressed to fabricate the CFRP composite laminates. The single-lap shear test coupons were prepared from the fabricated laminates to examine the effects of PA 66 nanofibers on the mechanical properties of the joint region of the composites. The single-lap shear test results showed that the bonding strength is improved by about 40% with minimal adhesive use due to the presence of the electrospun nanofibers within the joint region. The optical and SEM images of fractured surfaces showed that nanofiber-coated joints exhibited a coherent failure while the bare surfaces underwent adhesive failure. The PA66 nanofibers created better coupling between the adhesive and the composite surface by increasing the surface area and roughness. As a result, electrospun nanofibers turned adhesive failure into cohesive and enhanced the adhesion performance composite joints substantially.Article Citation - WoS: 4Citation - Scopus: 4Seismic Vulnerability Assessment of an Unanchored Circular Storage Tank Against Elephant's Foot Buckling(Springer, 2022) Bektaş, Nurullah; Aktaş, EnginPurpose Seismic vulnerability assessment of liquid containing storage tanks is the most vital relevance for industrial plants and society safety to endure damage during impending earthquakes. Because such systems also play an essential role in the public lifeline and also ensure continued use in emergencies. Furthermore, considering that the material contained in individual plants could be hazardous, requisite precautions have paramount importance against undesired leakage. The high internal pressure and axial forces exerted by the liquid in the steel tanks near the tank wall bottom produce elastic-plastic buckling, also known as Elephant's Foot Buckling (EFB). As far as the authors are aware, no study has been carried out that involves a critical assessment and comparison of IDA and truncated IDA-based EFB failure criterion. This study provides insight into incremental dynamic analysis (IDA) and truncated IDA-based seismic evaluation of cylindrical unanchored steel storage tanks by employing a developed pressure-based surrogate modeling approach. For this purpose, probability-based seismic assessment of a representative sample is considered based on IDA and truncated IDA approaches to identify the potential of the EFB failure and to explore potential enhancements in the sophisticated structural analysis model to prevent the hazardous effects of impending earthquakes. Methods Due to the significance of industrial plants for public safety and benefit, the structural response evaluation methods for different types of storage tanks have been widely reported. In the literature, the most comprehensive analytical assessment methodology is the IDA approach, in which nonlinear time-history analyses are considered in the finite element analysis model to assess the structural model's seismic performance. Results To generate fragility curves, both IDA approaches are employed, taking into consideration and ignoring uncertainty of material properties. The values of the two methods-based fragility curves approach each other as the magnitude of dispersion increases. Conclusion The two fragility curves give the probability of failures close to each other as the dispersion amount increases while considering the uncertainty of the material properties. In addition, fragility curves generated based on the truncated IDA have been found to give a higher probability of failure, up to 32.5 percent. When compared to the IDA-based fragility curves, the truncated IDA-based fragility curves were found to be on the conservative side.