Browsing by Author "Korkut, Fuat"

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Çelik ve Sentetik Liflerin Kendiliğinden Yerleşen Betonların Taze ve Mekanik Özellikleri Üzerine Etkisi
(2017) Taymuş, Refik Burak; Korkut, Fuat; Türkmenoğlu, Zehra Funda; Güler, Soner
Kendiliğinden yerleşen beton (KYB), kendi ağırlığı ile herhangi bir vibrasyon gerektirmeksizin, ayrışmaya uğramadan kalıbı doldurabilen özel bir beton türüdür. Bu çalışmada, beton içerisine katılan çelik ve sentetik liflerin kendiliğinden yerleşen betonların taze ve sertleşmiş özellikleri üzerindeki etkileri incelenmiştir. Bu amaçla, biri kontrol olmak üzere toplam 13 farklı beton karışımı hazırlanmıştır. Beton karışımlarının tamamında su/bağlayıcı oranı 0,40 olarak alınmıştır. Çelik ve sentetik lifler beton karışımına hacimce %0,25, 0,50 ve 0,75 oranlarında katılmışlardır. Kontrol betonunun hedef basınç dayanımı 40 MPa olarak belirlenmiştir. Lif katkısının taze beton özelliklerine etkisini belirlemek amacıyla çökme yayılma, V hunisi ve L kutusu deneyleri yapılmıştır. Sertleşmiş beton özelliklerini belirlemek için ise, basınç, yarmada çekme ve eğilme dayanımı deneyleri gerçekleştirilmiştir. Elde edilen sonuçlara göre, lif oranı arttıkça KYB'lerin işlenebilme özelliklerinin oldukça olumsuz yönde etkilendiği belirlenmiştir. Buna ilave olarak, betonun basınç dayanımında sınırlı artışlar olmasına rağmen, betonun yarmada çekme ve eğilme dayanımlarında önemli artışlar meydana gelmiştir.
Determination of Rigidity Center by Experimental Studies in Buildings
(2023) Aksoy, Enes; Korkut, Fuat; Erdil, Barış
Binaya gelen deprem yükü kütle merkezine etkir ve binayı rijitlik merkezi etrafında döndürür. Bu olaya burulma adı verilmektedir. Burulma etkisi düşey taşıyıcı sistem elemanlarında ikinci bir kesme kuvveti oluşturur. Bu durum binada hasarlara hatta yıkıma yol açabilmektedir. Rijitlik merkezi konumu burulmayı oluşturan ve etkisini artıran önemli bir faktördür. Bu çalışma kapsamında 14 adet gerçek boyuttaki betonarme bina ve 20 adet ölçekli ahşap malzemeden yapılmış bina üzerinde çalışma yapılmıştır. Gerçek boyuttaki binalar üzerinde yapılan araştırma analitik olarak yapılırken ölçekli binalar için deneysel çalışma yapılmıştır. Analitik çalışmada 2 adet simetrik bina, 7 adet düşey taşıyıcı sistemi değiştirilen örnek bina ve 5 adet burulmadan dolayı hasar aldığı düşünülen bina kullanılmıştır. Rijitlik merkezi hesap yöntemleri araştırılan yapısal analiz programlarında (Sta4CAD, İdeCAD, ProtaStructure ve ETABS) modellenen bu binalar için 2 farklı elle hesap yöntemiyle de hesap yapılmıştır. Her bina için hesaplanan 6 farklı rijitlik merkezi konumu test edilmiştir. SAP 2000 programında modellenen binalara noktasal olarak tanımlanmıştır. Tanımlanan noktalara deprem yükleri yüklenmiş ve çıkan dönmeler karşılaştırılmıştır. Elde edilen sonuçlardaki farklılıklardan dolayı deneysel çalışma yapılmıştır. Deneysel çalışma için 20 adet kat planı belirlenmiştir. Bu planlar belirlenirken bazı binalarda (12 plan) aşama aşama değişiklik yapılırken geriye kalan planlar analitik çalışmadan alınmıştır (8 plan). Döşemeler MDF'den düşey taşıyıcı sistem elemanları ise balsa malzemeden imal edilmiştir. Ölçekli binalar için tasarlanan deney masasında binalar yan çevrilerek yerleştirilmesiyle deneyler yapılmıştır. Deney sonucu elde edilen kat deplasmanları kaydedilmiştir. Deplasmanlar ile düşey taşıyıcı sistem elemanlarındaki kesme kuvvetleri elde edilmiştir. Her ölçekli bina için yapılan 2 deneyle kesme kuvvetlerinin ağırlık merkezleri alınarak rijitlik merkezleri hesaplanmıştır. Aynı binalar mevcut özellikleriyle ETABS programında modellenip analizi yapılmıştır. ETABS programında bulunan rijitlik merkezleri ile deney sonucu bulunan rijitlik merkezleri karşılaştırılmıştır.
Effects of Structural Parameters on Seismic Behaviour of Historical Masonry Minaret
(Budapest Univ Technology Economics, 2018) Erdil, Baris; Tapan, Mucip; Akkaya, Ismail; Korkut, Fuat
The October 23, 2011 (M-w = 7.2) and November 9, 2011 (M-w = 5.6) earthquakes increased the damage in the minaret of Van Ulu Mosque, an important historical masonry structure built with solid bricks in Eastern Turkey, resulting in significant shear cracks. It was found that since the door and window openings are not symmetrically placed, they result in unsymmetrical stiffness distribution. The contribution of staircase and the core on stiffness is ignorable but its effect on the mass is significant. The pulpit with chamfered corner results in unsymmetrical transverse displacements. Brace wall improves the stiffness however contributes to the unsymmetrical behaviour considerably. The reason for the diagonal cracks can be attributed to the unsymmetrical brace wall and the chamfered pulpit but the effect of brace wall is more pronounced. After introducing the cracks, a new model was created and calibrated according to the results of Operational Modal Analysis. Diagonal cracks were found to be likely to develop under earthquake loading. Drifts are observed to increase significantly upon the introduction of the cracks.
Experimental and Numerical Investigation of the Flexural Behavior of Reinforced-Concrete Beams Utilizing Waste Andesite Dust
(Mdpi, 2024) Korkut, Fuat; Karalar, Memduh; Motameni, Ali; Althaqafi, Essam; Ozdoner, Nebi; Ozkilic, Yasin Onuralp
During the process of cutting andesite stones, the waste mud is kept in powder form once fully dried. It is difficult to store the waste that is produced as a consequence of the extensive utilization area and consumption of andesite. Thus, eliminating waste storage challenges and incorporating these wastes into the economy are crucial. For this reason, this study examined the effects of waste andesite dust (WAD) on the flexural behavior of reinforced-concrete beams (RCBs) using experimental testing and 3D finite-element modeling (FEM) via ANSYS. Thus, different rates of WAD up to 40% were used to investigate the influence of the WAD rate on the fracture and bending behavior of RCBs. While the RCB with 10% WAD had a slightly lower load-bearing and ductility capacities, ductility capacities significantly drop after 10% WAD. At 40% WAD, both the load-bearing capacity and ductility significantly reduced. Based on the experimental findings, using 10% WAD as a replacement for cement is a reasonable choice to obtain eco-friendly concrete. Moreover, the outcomes of 3D FEM were also compared with those of experiments conducted using ANSYS v19 software. The displacement values between the test and FEM findings are quite similar.
Experimental Evaluation of Rigidity Center
(Mdpi, 2023) Korkut, Fuat; Aksoy, Enes; Erdil, Baris
It is known that when a reinforced concrete building exposed to a horizontal load is subjected to torsional moments around its center of rigidity, additional shear stresses occur in the vertical load-carrying elements, such as the columns and shear walls. Therefore, in order to estimate the additional stresses caused by the torsion, the rigidity center should be calculated precisely. It is known that there are several analytical approaches to calculating the rigidity center location. These approaches do not calculate the rigidity centers close to each other in asymmetric buildings. As significant differences were observed in the calculation of the rigidity center using analytical methods, it was decided to seek verification by conducting an experimental study. In order to calculate and verify the location of the rigidity center, an extensive experimental study was planned. A total of 20 scaled and revised buildings were built, and they were tested in the specially designed test setup. The tested buildings had square, rectangular and irregular floor plans. In addition, vertical load-carrying members were either symmetrically placed on the floor plan or kept asymmetrical to see the effect of their location on the rigidity center. All the buildings were tested under their self-weight, and the corresponding displacements were recorded. Additionally, all the buildings were modeled using ETABS to verify the theoretical background of the rigidity center. From the test results, it was found that the resultant shear force can be calculated by multiplying the displacements of each member of a given story found from the tests on its bending stiffness, and this will give the location of the rigidity center. The rigidity center was found to be identical to the results obtained from the 3D model analysis using ETABS, although it uses a different procedure. As the results from the experiment and 3D model are close to each other, it can be said that the rigidity center of reinforced concrete buildings can be found from simple tests using any material that has almost uniform mechanical properties.
A Gfdm Based Computational Model for the Analysis of Tunnels Under Gravitational Loadings
(Pergamon-elsevier Science Ltd, 2024) Mengi, Yalcin; Korkut, Fuat
Based on an impedance relation, a new computational model is developed for the analysis of tunnels under gravitational loading. The shape of tunnel is arbitrary. The impedance matrix, representing the soil resistance, is evaluated through integration of the equations of elasticity by generalized finite difference method (GFDM). The rigidity matrix of tunnel ring is constructed by using two types of elements: plate and shell elements. The equations of these elements are evaluated through integration of the equations of higher order plate and shell theories again by GFDM. These element equations accommodate not only axial and bending deformations, but, also shear deformations in the ring. In the study, the rotational joint deformation is simulated through the use of rotational spring model and the slippage is considered by modifying the impedance matrix so that the tangential soil resistance force between the ring and soil medium vanishes. Some numerical results are presented, in nondimensional forms, for circular and square tunnels where the following three cases are considered for circular tunnels: a) the soil medium is infinite, the change in sigma v (vertical (in situ) compressional stress) in the vicinity of tunnel is disregarded b) the soil medium is infinite, the change in sigma v is taken into account c) the soil medium is halfspace (HS). In connection with the case of (a), a comparison is presented for the ring flexibility curves of radial displacement and section forces of circular ring with those reported in literature. In view of the interpretations of the results and comparisons, we think, the proposed model may be used reliably in the analysis of tunnels.
Interaction Analysis Revisited by Generalized Finite Difference Method With Perfectly Matched Layer
(Elsevier Sci Ltd, 2023) Mengi, Yalcin; Korkut, Fuat
A unified formulation is given for solid-solid interaction problems. For the description of the formulation, the embedded foundation problem is considered with interaction interface being taken as either flexible or rigid. Introducing a transfer function relating free field displacements at interaction interface to seismic excitation, a formula is established for the evaluation of all the elements of input matrix at a single step without using complicated scattering analysis. Some sample problems are considered in the study for the assessment of the formulation. In the in-plane problem, involving an infinitely long rigid embedded foundation under the influence of inclined P-SV or Rayleigh waves, it is found that the behavior of input motion functions for OvOcr for the reasons discussed in the study, where Ov and Ocr are respectively the inclination and critical angles for SV waves. The computations in the work are carried out by generalized finite difference method (GFDM) together with perfectly matched layer (PML).
Investigational and Numerical Examination on Bending Response of Reinforced Rubberized Concrete Beams Including Plastic Waste
(Mdpi, 2023) Korkut, Fuat; Karalar, Memduh
In this investigational study, the fracture and bending performance of reinforced concrete beams (R-C-Bs) with varying proportions of plastic waste (PW), considered as fine aggregate (FA), were assessed via experimental and numerical examination. To achieve this aim, altered concrete series were designed, with the aggregate sizes changed within the range of 0 to 25 mm. To enhance the concrete, PW was selected to be used in combination with aggregate material measuring 0 to 5 mm in particle size, as an alternative FA, with proportions of 0%, 5%, 15%, 30%, and 45%. Experiments were performed to examine the performance of the R-C-Bs. It was found that a 30% PW proportion offered the optimum results in terms of displacement capability. Furthermore, ANSYS v.19 software was chosen to form 3D finite element models (F-E-Ms) of R-C-Bs to be compared with the experimental data. The experimental and 3D F-E-M investigations offered remarkably close-fitting bending and rupture performances. Then, a structure was modeled using SAP2000, and the strength of the R-C-Bs was then used in an RC structural model. The results show that the forces on the construction caused reductions while also increasing the PW proportion. Moreover, it was realized that the F-E-M simulations and experiments produced tiny cracks with highly matched formations.
On the Use of Complex Stretching Coordinates in Generalized Finite Difference Method With Applications in Inhomogeneous Visco-Elasto Dynamics
(Elsevier Sci Ltd, 2022) Korkut, Fuat; Mengi, Yalcin; Tokdemir, Turgut
In the study, in conjunction with perfectly matched layer (PML) analysis, an approach is proposed for the evaluation of complex derivatives directly in terms of complex stretching coordinates of points in PML. For doing this within the framework of generalized finite difference method (GFDM), a difference equation is formulated and presented, where both the function values and coordinates of data points might be complex. The use of the proposed approach is considered in the analysis of inhomogeneous visco-elasto-dynamic system and assessed through three example problems analyzed in Fourier space: the composite and inhomogeneous tube, layer and impedance problems. The GFDM results obtained for the tube and layer problems compare very closely and coincide almost exactly with the exact solution. In the impedance problems, rigid surface or embedded footings resting on a composite inhomogeneous half-space are considered. The influences of various types of inhomogeneities, as well as, of various geometric shapes of PML-(physical region) interfaces on impedance curves are examined.
Rijitlik Merkezinin Analitik, Deneysel ve Gözlemsel Değerlendirilmesi
(2023) Erdil, Barış; Korkut, Fuat; Aksoy, Enes
Bu çalışma kapsamında mimar ve inşaat mühendislerine dört adet betonarme bina kat planı verilerek kütle ve rijitlik merkezinin konumunu gözlemsel olarak belirlemeleri istenmiştir. Daha sonra bu binaların tamamı mevcutta sıklıkla kullanılan dört adet yapısal analiz programı ile 3 boyutlu olarak modellenmiş ve kütle ile rijitlik merkezleri belirlenmiştir. Son olarak 3 adet bina ölçekli olarak laboratuvar ortamında test edilmiş ve rijitlik merkezi deneysel olarak belirlenmiştir. Yapılan analizler ve değerlendirmeler gözlemsel olarak kütle merkezi konumunun tahmin edilebileceği, mimarların ve inşaat mühendislerinin rijitlik merkezi tahminlerinin deneysel çalışmalar sonucu elde edilen rijitlik merkezi konumundan çok farklı olduğu, yapısal analiz programlarından ETABS, Sta4CAD ve ProtaStructure’ın birbirine benzer konumları rijitlik merkezi olarak belirlemesine karşın, İdeCAD programından elde edilen sonuçların farklı olduğu görülmüştür.
Strength Prediction Models for Steel, Synthetic, and Hybrid Fiber Reinforced Concretes
(Ernst & Sohn, 2019) Guler, Soner; Yavuz, Demet; Korkut, Fuat; Ashour, Ashraf
This paper proposes new strength models to predict compressive, splitting tensile and flexural strengths of steel, synthetic and hybrid fiber reinforced concretes. The strength models depending on fiber reinforcing index, concrete compressive strength, and fiber volume fraction have been developed by multiple regression analyses of the experimental results obtained from a comprehensive experimental program. Twenty-five concrete batches, one control and 24 fiber reinforced concrete with target compressive strength of 40MPa were produced. Steel and synthetic fibers, namely hooked-end steel (HF) and polyamide (PA) synthetic fibers of total volume of 0.25, 0.5, and 0.75% were added in single and hybrid forms to concrete mixes. Moreover, the predictions of the proposed strength models have been compared with the existing strength models in the literature. The test results clearly showed that the predictions of the proposed strength models are more accurate than the existing strength models for compressive, splitting tensile and flexural strengths of all the fiber types. Although the existing strength models may be applicable to the prediction of compressive strength of steel, synthetic, hybrid fiber reinforced concrete (FRC), they may not be safely used for splitting tensile and flexural strength of steel, synthetic and hybrid FRC.
Structural Performance of Masonry Buildings Under Harsh Climate and Seismic Loads
(Springer int Publ Ag, 2022) Erdil, Baris; Korkut, Fuat; Aydin, Mahsum; Yaltay, Namik
Masonry buildings in Van which is a city located at the eastern border of Turkey exposed to several earthquakes in 2020 while continuously being subjected to harsh weather conditions. Two earthquakes with Mw = 5.9 occurred on the same day and four months after another one hit the region. Besides the earthquakes 124 freeze-thaw cycles occur annually and the region has snow and rain approximately 103 days. Both continuously and periodically applied environmental exposures due to harsh weather conditions and earthquakes that is significant in a short period, affects the structural performance of the masonry buildings adversely. During the field investigations after the earthquakes, it was realized that none of the buildings comply with the available codes, foundations, and walls damaged due to the environmental exposures and those damages either increased or end up with total collapse due to the seismic loading. Besides the damaged buildings, it was observed that some buildings were strengthened locally at the corners. L shaped reinforced concrete columns were added to the cracked corners to increase the lateral capacity of the walls. That strengthening seemed to be adequate for low seismicity because no significant damage was seen.
The Use of Fft Algorithm for Circumferential Coordinate in Axisymmetric Analysis of Solids by Generalized Finite Difference Method
(Elsevier Sci Ltd, 2023) Korkut, Fuat; Mengi, Yalcin
A formulation is presented for GFDM analysis of axisymmetric viscoelastic bodies under general loading conditions. The proposed formulation reduces the dimension of analysis by one by using complex Fourier series for circumferential coordinate ((0) dependency) of field variables. For 0 (Fourier) transform computations, the discrete Fourier transform formulas with FFT algorithm are employed. Radiational effects are accounted for through the use of perfectly matched layer (PML) with the equation being modified in accordance with the proposed formulation. For the assessment of the formulation, several sample problems are presented. The results indicate its capability in estimating the response even for that requiring sensitive analysis, such as, those in wave propagation analysis.
The Use of Generalized Finite Difference Method in Perfectly Matched Layer Analysis
(Elsevier Science inc, 2018) Korkut, Fuat; Tokdemir, Turgut; Mengi, Yalcin
This study deals with the use of Generalized Finite Difference Method (GFDM) in Perfectly Matched layer (PML) analysis. There are two options for performing PML analysis. First option is to express PML equations in terms of real coordinates of the points in actual (real) PML region; the second is to use governing equations (expressed in terms of complex stretching coordinates) as they are in complex PML region. The first option is implemented in this study; the implementation of the second option is under way and will be reported in another study. For the integration of PML equations, the use of GFDM is proposed. Finally, the suggested procedure is assessed computationally by considering the compliance functions of surface and embedded rigid strip foundations. GFDM with PML results are compared to those obtained by using Finite Element Method (FEM) with PML and Boundary Element Method (BEM). Excellent matches in results showed the reliability of the proposed procedure in PML analysis. (C) 2018 Elsevier Inc. All rights reserved.
Viscoelastic Rod Using the Generalized Finite Difference Method
(2023) Tokdemir, Turgut; Korkut, Fuat
The finite difference method is quite extensively used to obtain the approximate solutions of many equations of mathematical physics. In this study, the precise algorithm in the time domain is combined with the generalized finite difference method to solve dynamic viscoelasticity problems. The numerical results obtained are satisfactory, and they are presented together with finite difference and finite element solutions.