Civil Engineering / İnşaat Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/13
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Article Citation - WoS: 13Citation - Scopus: 14Soil Erosion Model Tested on Experimental Data of a Laboratory Flume With a Pre-Existing Rill(Elsevier Ltd., 2020) Aksoy, Hafzullah; Gedikli, Abdullah; Yılmaz, Murat; Eriş, Ebru; Ünal, N. Erdem; Yoon, Jaeyoung; Tayfur, GökmenPrediction of sediment discharge transported within flow is strongly needed in order to provide measures for a well-established erosion control and water quality management practice. Initiated by runoff generation and erosion processes sediment transport is influenced by microtopography over hillslopes of hydrological watersheds. Consideration of microtopography provides more accurate results. In this study, a process-based two-dimensional rainfall-runoff mathematical model is coupled with erosion and sediment transport component. Both the rainfall-runoff and sediment transport components make simulations in rills and over interrill areas of a bare hillslope. Models at such fine resolution are rarely verified due to the complexity of rills and interrill areas. The model was applied on a data set compiled from laboratory experiments. Erosion flume was filled with granular sand to replace a bare soil. A longitudinal rill and an interrill area were pre-formed over the soil in the flume before the simulated rainfall exerted on. The flume was given both longitudinal and lateral slopes. The simulated rainfall was changed between 45 mm/h and 105 mm/h and exerted on granular uniform fine and medium sand in the erosion flume with longitudinal and lateral slopes both changing from 5% to 20%. Calibration of the model shows that it is able to produce good results in terms of sedigraphs, which suggest also that the model might be considered an important step to verify and improve watershed scale erosion and sediment transport models.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: 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: 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.Article Citation - WoS: 2Citation - Scopus: 2Effect of Seismic Wave Velocity on the Dynamic Response of Multi-Story Structures on Elastic Foundation(Elsevier Ltd., 2018) Hızal, Çağlayan; Turan, GürsoyTraveling wave effects are generally considered with three main cases: (i) Wave passage effect that results with time delay in earthquake motion. (ii) incoherence effect which is defined as loss of coherency in the ground motion due to the reflection and refraction of waves, and (iii) local site effects. For multi-story structures whose supports are close to each other, the incoherence and local site effect may be omitted. In this case, traveling waves result only in a pure time delay in the earthquake motion (wave passage effect). Due to the wave passage effect of vertical and/or horizontal ground motion, the superstructure needs to be analyzed by multi-support excitation. Raft foundations cannot constrain vertical deformations and/or rotations, but they cause a diaphragm effect in the horizontal direction which results in uniform excitation. In this study, the effect of vertical earthquake motions onto multi-story buildings on elastic soil is investigated. Multi support excitation is considered by using displacement loading, which defines the equivalent seismic loads in terms of the ground displacement. According to the performed simulations of the selected structures, it is shown that structural height has a direct influence that results in member force magnifications with slow traveling wave effect. Among these, the ground floor column axial forces are most affected.Article Citation - WoS: 97Citation - Scopus: 110Effect of Polyamide-6,6 (pa 66) Nonwoven Veils on the Mechanical Performance of Carbon Fiber/Epoxy Composites(Elsevier Ltd., 2018) Beylergil, Bertan; Tanoğlu, Metin; Aktaş, EnginIn this study, carbon fiber/epoxy (CF/EP) composites were interleaved with polyamide-6,6 (PA 66) nonwoven veils at two different areal weight densities (17 and 50 gsm) to improve their delamination resistance against Mode-I loading. Mode-I fracture toughness (DCB), tensile, open hole tensile (OHT), flexural, compression, short beam shear (ILSS) and Charpy-impact tests were performed on the reference and PA 66 interleaved composite specimens. The DCB test results showed that the initiation and propagation Mode-I fracture toughness values of the composites were significantly improved by 84 and 171% using PA 66-17 gsm veils respectively, as compared to reference laminates. The use of denser PA 66-50 gsm veils in the interlaminar region led to higher improvement in fracture toughness values (349% for initiation and 718% for propagation) due to the higher amount of veil fibers involved in fiber bridging toughening mechanism. The incorporation of PA 66-50 gsm nonwoven veils also increased the ILSS and Charpy impact strength of the composites by 25 and 15%, respectively. On the other hand, the PA 66 veils reduced in-plane mechanical properties of CF/EP composites due to lower carbon fiber volume fraction and increased thickness.Article Citation - WoS: 19Citation - Scopus: 22Influence of Thixotropy Determined by Different Test Methods on Formwork Pressure of Self-Consolidating Concrete(Elsevier Ltd., 2018) Tuyan, Murat; Ahari, Reza Saleh; Erdem, Tahir Kemal; Andiç Çakır, Özge; Ramyar, KambizIn this experimental study, the influence of thixotropy determined by different test methods on the formwork pressure of self-consolidating concrete (SCC) with varying compositions was investigated. In order to determine the effect of water/binder (w/b) ratio, slump flow diameter and coarse aggregate/total aggregate (CA/TA) ratio on thixotropy and formwork pressure of SCC, fifteen concrete mixtures were prepared. Four different test methods i.e., “structural break-down area” (SBDA), “break-down percentage” (BDP), “drop in apparent viscosity” (DAV) and “yield value at rest” (YVR) were performed to determine the thixotropy of the SCC mixtures. Test results showed that the SBDA, DAV and YVR methods were more appropriate to evaluate the thixotropy of SCC than the BDP method. A strong correlation between thixotropy and formwork pressure was found using SBDA, DAV and YVR methods in SCC mixtures having low w/b ratio. There was a strong relationship between thixotropy determined by SBDA, BDP and DAV methods and formwork pressure in low slump flow SCC mixtures, while thixotropy determined by the YVR method showed good correlation with the formwork pressure in SCC mixtures having high slump flow values. Finally, new models were developed to estimate the formwork pressure of all kinds of mixtures as a function of thixotropy and time. The models were found to be successful for each of the thixotropy measurement method.Annotation Citation - WoS: 1Citation - Scopus: 1Reply To Comment on “evaluation of a Physically Based Quasi-Linear and a Conceptually Based Nonlinear Muskingum Methods” by Reza Barati(Elsevier Ltd., 2017) Perumal, Muthiah; Tayfur, Gökmen; Rao, C. Madhusudana; Gürarslan, GürhanThe writers thank the discusser for his interest in the study of Perumal et al. (2017) and welcome the opportunity to address the issues raised by the discusser. The discusser has mainly raised four issues on the comparative study carried out by Perumal et al. (2017) in evaluating the performances of the VPMM model and the NLM based models, which was initiated by Gill (1977, 1978). These four issues are addressed by these writers in the following pages: As a first issue, the discusser has raised a question about the appropriateness of using the VPMM model (Perumal and Price, 2013), which he considers as the much improved routing model of the Muskingum-Cunge family approach, and the original nonlinear Muskingum model of Gill (1978), which he, perhaps, considers as a initial version of the NLM models. These writers perceive that the discusser intends to convey that the performance evaluation study presented by Perumal et al. (2017) based on a latest improved model and a initial version of the NLM models is inappropriate. Before discussing straightaway on this issue, the writer would like to clarify on the misconception of the discusser in categorizing the VPMM method and the Muskingum-Cunge method under one family approach.Article Citation - WoS: 23Citation - Scopus: 29Evaluation of a Physically Based Quasi-Linear and a Conceptually Based Nonlinear Muskingum Methods(Elsevier Ltd., 2017) Perumal, Muthiah; Tayfur, Gökmen; Rao, C. Madhusudana; Gürarslan, GürhanTwo variants of the Muskingum flood routing method formulated for accounting nonlinearity of the channel routing process are investigated in this study. These variant methods are: (1) The three-parameter conceptual Nonlinear Muskingum (NLM) method advocated by Gillin 1978, and (2) The Variable Parameter McCarthy-Muskingum (VPMM) method recently proposed by Perumal and Price in 2013. The VPMM method does not require rigorous calibration and validation procedures as required in the case of NLM method due to established relationships of its parameters with flow and channel characteristics based on hydrodynamic principles. The parameters of the conceptual nonlinear storage equation used in the NLM method were calibrated using the Artificial Intelligence Application (AIA) techniques, such as the Genetic Algorithm (GA), the Differential Evolution (DE), the Particle Swarm Optimization (PSO) and the Harmony Search (HS). The calibration was carried out on a given set of hypothetical flood events obtained by routing a given inflow hydrograph in a set of 40 km length prismatic channel reaches using the Saint-Venant (SV) equations. The validation of the calibrated NLM method was investigated using a different set of hypothetical flood hydrographs obtained in the same set of channel reaches used for calibration studies. Both the sets of solutions obtained in the calibration and validation cases using the NLM method were compared with the corresponding solutions of the VPMM method based on some pertinent evaluation measures. The results of the study reveal that the physically based VPMM method is capable of accounting for nonlinear characteristics of flood wave movement better than the conceptually based NLM method which requires the use of tedious calibration and validation procedures.Article Citation - WoS: 123Citation - Scopus: 140Effect of Various Supplementary Cementitious Materials on Rheological Properties of Self-Consolidating Concrete(Elsevier Ltd., 2015) Saleh Ahari, Reza; Erdem, Tahir Kemal; Ramyar, KambizIn design of self-consolidating concrete (SCC) for a given application, the mixture's rheological parameters should be adjusted to achieve a given profile of yield stress and plastic viscosity. Supplementary cementitious materials (SCM) can be useful for this adjustment in addition to their other advantages. In this study, the rheological properties of 57 SCC mixtures with various SCM were investigated for a constant slump flow value. For this aim, various amounts of silica fume (SF), metakaolin (MK), Class F fly ash (FAF), Class C fly ash (FAC) and granulated blast-furnace slag (BFS) were utilized in binary, ternary, and quaternary cementitious blends in three water/binder ratios. Results showed that SF and BFS decreased plastic viscosity and V-funnel time values in comparison with mixtures containing only Portland cement (PC). However the opposite tendency was observed when MK, FAC and FAF were incorporated with PC. Substitution of PC with SF, MK and FAC increased high range water reducer (HRWR) demand in the SCC mixtures having constant slump flow. Use of SCM in SCC mixtures increased yield stress values. Good correlations were established between plastic viscosity and V-funnel flow time values for all w/b ratios.
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