Civil Engineering / İnşaat Mühendisliği
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Article Citation - WoS: 53Citation - Scopus: 63Effective Stress Principle for Saturated Fractured Porous Media(Wiley-Blackwell, 1995) Tuncay, Kağan; Çorapçıoğlu, M. YavuzAn effective stress principle for saturated fractured porous media is proposed based On the double-porosity representation. Both the solid grains and the fractured porous medium are assumed to be linearly elastic materials. The derivation employs volume averaging technique to obtain macroscopic scale expressions. Two parameters, the bulk modulus of the fractured medium and bulk modulus of the porous matrix, are introduced in the formulation. The final expression reduces to the one obtained by Blot and Willis [1957], Skempton [1960], Nur and Byeerle [1971], and Verruijt [1984] when the volume fraction of the fractures vanishes, that is, for a nonfractured porous medium.Article Citation - WoS: 22Citation - Scopus: 29Inter-Granular Cracking Through Strain Gradient Crystal Plasticity and Cohesive Zone Modeling Approaches(Elsevier, 2019) Yalçınkaya, Tuncay; Özdemir, İzzet; Fırat, Ali OsmanEven though intergranular fracture is generally regarded as a macroscopically brittle mechanism, there are various cases where the fracture occurs at the grain boundaries with considerable plastic deformation at the macroscopic scale. There exists several microstructural reasons for grain boundaries to host crack initiation. They can interact with impurities and defects, can provide preferential location for precipitation, can behave as a source of dislocations and can impede the movement of dislocations as well. The understanding of the crack initiation and propagation at the grain boundaries requires the analysis of the grain boundary orientation and the orientation mismatch between the neighboring grains and the related the stress concentration, which is only possible through the combination of micro-mechanical plasticity and fracture mechanics. For this reason the current work studies the evolution of plasticity in three dimensional Voronoi based microstructures through a strain gradient crystal plasticity framework (see e.g. Yalcinkaya et al., 2011; Yalcinkaya et al., 2012; Yalcinkaya, 2016) and incorporates a potential based cohesive zone model (see Park et al., 2009; Cerrone et al., 2014) at the grain boundaries for the crack initiation and propagation. The numerical examples considers the effect of the orientation distribution, the grain boundary conditions, the specimen size and the fracture energy parameter on the intergranular fracture behavior of micron-sized specimens. The study presents important conclusions for the modeling of fracture at this length scale.Article Citation - WoS: 8Citation - Scopus: 9Dynamic Behavior Predictions of Fiber-Metal Laminate/Aluminum Foam Sandwiches Under Various Explosive Weights(SAGE Publications, 2016) Baştürk, Suat Bahar; Tanoğlu, Metin; Çankaya, Mehmet Alper; Eğilmez, Oğuz ÖzgürApplication of blast tests causes some problems to characterize the performance of panels due to the drastic conditions of explosive medium. Real test has high safety concerns and is not easily accessible because of its extra budget. Some approaches are needed for the preliminary predictions of dynamic characteristics of panels under blast loading conditions. In this study, the response of sandwiches under blast effect was evaluated by combining quasi-static experiments and computational blast test data. The primary aim is to relate the quasi-static panel analysis to dynamic blast load. Based on this idea, lightweight sandwich composites were subjected to quasi-static compression loading with a special test apparatus and the samples were assumed as single degree-of-freedom mass-spring systems to include dynamic effect. This approach provides a simpler way to simulate the blast loading over the surface of the panels and reveals the possible failure mechanisms without applying any explosives. Therefore the design of the panels can be revised by considering quasi-static test results. In this work, the peak deflections and survivabilities of sandwiches for various explosive weights were predicted based on the formulations reported in the literature. Major failure types were also identified and evaluated with respect to their thicknesses.Article Citation - WoS: 56Citation - Scopus: 67Characterization of Concrete Matrix/Steel Fiber De-Bonding in an Sfrc Beam: Principal Component Analysis and K-Mean Algorithm for Clustering Ae Data(Elsevier, 2018) Tayfur, Sena; Alver, Ninel; Abdi, Saeed; Saatçi, Selçuk; Ghiami, AmirSteel fibers have been used in concrete structures to increase the tensile strength and ductility of concrete. Fibers bridging cracks reduce micro cracking and improve post-cracking strength in concrete. Propagation of damage in a fiber reinforced concrete member occurs by concrete matrix cracking and widening of these cracks, which is accompanied by de-bonding of steel fibers from the concrete matrix. Fiber de-bonding is the main factor affecting the post-peak behavior of these members. Therefore, distinguishing the matrix cracking and fiber de-bonding mechanisms is important in nondestructive structural health monitoring methods. This study is focused on characterizing steel fiber/matrix de-bonding events apart from concrete matrix cracking sources in acoustic emission (AE) method. Two reinforced concrete beams, one of which included steel fibers within the concrete matrix, were tested under three point bending and monitored by AE. Afterwards, Principal Component Analysis (PCA) was applied to AE data and the failure mechanisms were clustered for characterization of steel fiber/matrix de-bonding. Finally, different AE features of these clusters were evaluated and applicable AE parameter distributions, which are useful to clarify steel fiber de-bonding mechanisms, were revealed.Article Citation - WoS: 4Citation - Scopus: 6An Alternative Implementation of the Incremental Energy/Dissipation Based Arc-Length Control Method(Elsevier Ltd., 2019) Özdemir, İzzetA robust solution algorithm is essential to trace the arduous equilibrium paths typically confronted with in cohesive fracture and continuum damage mechanics of quasi-brittle materials. Although robust arc-length type solvers exist suitable for such problems, the use of these methods is hindered by their non-standard implementation requirements. Departing from this fact, in this paper, the recently proposed arc-length solver presented in reference May et al. (2016) is reconsidered within the limitations/capabilities of the commercial software packages and recast in a form which is suitable for implementation through user element formalism. The constraint equation is re-expressed and appended to the system of equations through the internal force column and tangent stiffness matrix of a user element. The effectiveness of the proposed alternative implementation is illustrated by means of two cohesive fracture problems.Article Citation - WoS: 39Citation - Scopus: 40Mode-I Fracture Toughness of Carbon Fiber/Epoxy Composites Interleaved by Aramid Nonwoven Veils(Techno Press, 2019) Beylergil, Bertan; Tanoğlu, Metin; Aktaş, EnginIn this study, carbon fiber/epoxy (CF/EP) composites were interleaved with aramid nonwoven veils with an areal weight density of 8.5 g/m(2) to improve their Mode-I fracture toughness. The control and aramid interleaved CF/EP composite laminates were manufactured by VARTM in a [0]4 configuration. Tensile, three-point bending, compression, interlaminar shear, Charpy impact and Mode-I (DCB) fracture toughness values were determined to evaluate the effects of aramid nonwoven fabrics on the mechanical performance of the CF/EP composites. Thermomechanical behavior of the specimens was investigated by Dynamic Mechanical Analysis (DMA). The results showed that the propagation Mode-I fracture toughness values of CF/EP composites can be significantly improved (by about 72%) using aramid nonwoven fabrics. It was found that the main extrinsic toughening mechanism is aramid microfiber bridging acting behind the crack-tip. The incorporation of these nonwovens also increased interlaminar shear and Charpy impact strength by 10 and 16.5%, respectively. Moreover, it was revealed that the damping ability of the composites increased with the incorporation of aramid nonwoven fabrics in the interlaminar region of composites. On the other hand, they caused a reduction in in-plane mechanical properties due to the reduced carbon fiber volume fraction, increased thickness and void formation in the composites.Article Citation - WoS: 31Citation - Scopus: 34Data Pre-Post Processing Methods in Ai-Based Modeling of Seepage Through Earthen Dams(Elsevier Ltd., 2019) Sharghi, Elnaz; Nourani, Vahid; Behfar, Nazanin; Tayfur, GökmenIn this paper, seepage of Sattarkhan earthen dam in northwest Iran was simulated using various artificial intelligence (AI) models (e.g., Feed forward neural network, Adaptive neural fuzzy inference system and Support vector regression) and linear ARIMA model based on different input combinations. Both jittering pre-processing and ensembling post-processing methods were also used in order to enhance the performance of the used AI-based data driven methods. For this purpose, various jittered datasets were produced by imposing noises (at different levels) to the original time series to enlarge the training data sample space. Further, three techniques of simple linear, weighted linear and nonlinear neural averaging were considered for pre-post processing purpose. The obtained results indicated that using both jittering and ensembling (especially neural ensemble) enhanced the modeling performance by almost 30% in the testing phase. (C) 2019 Elsevier Ltd. All rights reserved.Article Citation - WoS: 2Citation - Scopus: 3A New Method To Quantify the Robustness of Self-Consolidating Grouts(Elsevier, 2019) Erdem, Tahir Kemal; Bilgiç, Esra; Kanpara Cıvaş, ZüleyhaThere are different methods in literature to evaluate the robustness of highly fluid cementitious mixtures. However, no one of them gained widely acceptance due to the relative advantages and disadvantages involved in each of them. Therefore, there is still need for further research on this topic. This study proposes a new and relatively easy method for quantifying the robustness of self-consolidating grouts by calculating so-called robustness indices. Due to the more difficulty to produce robust mixtures for highly fluid mixtures obtained by very powerful chemicals, the method is based on the variations in the superplasticizer (SP) type and amount. Mineral admixture (fly ash or limestone powder) usage and water-to-binder ratio (w/b) were other parameters investigated in this study. It was found that SP type was the most important factor affecting the robustness. The effect of w/b was less when compared to SP type. The mixtures containing naphthalene-based SP were more robust than those containing polycarboxylate-based SP. Mineral admixture type and amount had the least effect on robustness. (C) 2019 Elsevier Ltd. All rights reserved.Article Citation - WoS: 15Citation - Scopus: 16A Mode Shape Assembly Algorithm by Using Two Stage Bayesian Fast Fourier Transform Approach(Academic Press Inc., 2019) Hızal, Çağlayan; Turan, Gürsoy; Aktaş, Engin; Ceylan, HasanOperational modal analysis may require identifying global modal shapes by using multiple setup measurements. For this purpose, various algorithms have been developed which make use of the Bayesian approach to estimate the global mode shapes. The main motivation of the available Bayesian approaches is based on the estimation of the optimal global mode shape vector directly from Fast Fourier Transform data or assembling the local mode shapes that are identified in the individual setups by using Gaussian approximation. In this study, the two-stage Bayesian Fast Fourier Transform Approach which is originally applied to single setups is implemented to multiple setup problems for well separated modes. Analytically it is shown that the resulting formulation is the same for the mode shape assembly by using the Gaussian approximation. In addition, the weights of individual setups in the global mode shape vector is analytically calculated which depend on the Hessian matrix for local mode shapes. To validate the proposed methodology, a numerical example that considers setup-to-setup variability of modal signal-noise ratios is presented. For comparison purposes a ten-story shear frame model is experimentally investigated, and the measurements of a benchmark bridge structure are considered in the verification of the current procedure. (C) 2019 Elsevier Ltd. All rights reserved.Article Citation - WoS: 1Citation - Scopus: 3Effect of the Armor Crest Freeboard Relative To the Crown Wall Freeboard on Wave Overtopping for Simple Rubble Mound Slopes(Elsevier Ltd., 2018) Özbahçeci, Bergüzar; Bilyay, EnginSeveral studies have been carried out to investigate the effect of crest parameters on the wave overtopping for armored slopes with crown walls. However, the effect of the armor crest freeboard is still under question. In this study, for the first time, a series of hydraulic model experiments are conducted specifically to investigate how the armor crest freeboard relative to the crown wall freeboard affects the wave overtopping rate. Experimental results indicate that while the armor crest freeboard lower than the crown wall freeboard is giving larger overtopping, higher armor crest freeboard is reducing the overtopping. However, this reduction is not same as the reduction due to the increase in the crown wall freeboard. The reason may be the porosity of the armor crest. For the first time, a new correction factor is proposed to describe the change in the wave overtopping due to the armor crest freeboard by using experimental results. The correction factor C Ac is applied to cover the effect of armor crest freeboard in the predictions of EurOtop (2016). The verification study present that overtopping rate predictions of corrected EurOtop (2016) are more consistent with the measured rate results compared to the predictions of the original formula, if the armor crest freeboard is not equal to the crown wall freeboard.