Civil Engineering / İnşaat Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/13
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Article Citation - WoS: 72Citation - Scopus: 79Artificial Neural Networks for Estimating Daily Total Suspended Sediment in Natural Streams(IWA Publishing, 2006) Tayfur, Gökmen; Güldal, VeyselEstimates of sediment loads in natural streams are required for a wide spectrum of water resources engineering problems from optimal reservoir design to water quality in lakes. Suspended sediment constitutes 75-95% of the total load. The nonlinear problem of suspended sediment estimation requires a nonlinear model. An artificial neural network (ANN) model has been developed to predict daily total suspended sediment (TSS) in rivers. The model is constructed as a three-layer feedforward network using the back-propagation algorithm as a training tool. The model predicts TSS rates using precipitation (P) data as input. For network training and testing 240 sets of data sets were used. The model successfully predicted daily TSS loads using the present and past 4 days precipitation data in the input vector with R2 = 0.91 and MAE = 34.22 mg/L. The performance of the model was also tested against the most recently developed non-linear black box model based upon two-dimensional unit sediment graph theory (2D-USGT). The comparison of results revealed that the ANN has a significantly better performance than the 2D-USGT. Investigation results revealed that the ANN model requires a period of more than 75 d of measured P-TSS data for training the model for satisfactory TSS estimation. The statistical parameter range (xmin - xmax) plays a major role for optimal partitioning of data into training and testing sets. Both sets should have comparable values for the range parameter.Article Citation - WoS: 277Citation - Scopus: 345Effects of Shear Mechanisms on Impact Behavior of Reinforced Concrete Beams(American Concrete Institute, 2009) Saatçi, Selçuk; Vecchio, Frank J.A well-instrumented experimental program was undertaken to contribute to our understanding of the effects of shear mechanisms on the behavior of reinforced concrete (RC) structures under impact loads and to provide data for verification of methods developed for the impact analysis of such structures. Eight RC beam specimens, four pairs, were tested under free-falling drop-weights, impacting the specimens at the midspan. All specimens had identical longitudinal reinforcement, but varying shear reinforcement ratios, intended to investigate the effects of shear capacity on the impact behavior. A total of 20 impact tests were conducted, including multiple tests on each specimen. The test program was successful in providing a substantial amount of high-quality impact test data. The test results showed that the shear characteristics of the specimens played an important role in their overall behavior. All specimens, regardless of their shear capacity, developed severe diagonal shear cracks, forming a shear-plug under the impact point. © 2009, American Concrete Institute.Article Citation - WoS: 20Citation - Scopus: 23Estimation of Suspended Sediment Concentration in Rivers Using Acoustic Methods(Springer Verlag, 2009) Elçi, Şebnem; Aydın, Ramazan; Work, Paul A.Acoustic Doppler current meters (ADV, ADCP, and ADP) are widely used in water systems to measure flow velocities and velocity profiles. Although these meters are designed for flow velocity measurements, they can also provide information defining the quantity of particulate matter in the water, after appropriate calibration. When an acoustic instrument is calibrated for a water system, no additional sensor is needed to measure suspended sediment concentration (SSC). This provides the simultaneous measurements of velocity and concentration required for most sediment transport studies. The performance of acoustic Doppler current meters for measuring SSC was investigated in different studies where signal-to-noise ratio (SNR) and suspended sediment concentration were related using different formulations. However, these studies were each limited to a single study site where neither the effect of particle size nor the effect of temperature was investigated. In this study, different parameters that affect the performance of an ADV for the prediction of SSC are investigated. In order to investigate the reliability of an ADV for SSC measurements in different environments, flow and SSC measurements were made in different streams located in the Aegean region of Turkey having different soil types. Soil samples were collected from all measuring stations and particle size analysis was conducted by mechanical means. Multivariate analysis was utilized to investigate the effect of soil type and water temperature on the measurements. Statistical analysis indicates that SNR readings ob tained from the ADV are affected by water temperature and particle size distribution of the soil, as expected, and a prediction model is presented relating SNR readings to SSC mea surements where both water temperature and sediment characteristics type are incorporated into the model. The coefficients of the suggested model were obtained using the multivariate anal ysis. Effect of high turbidity conditions on ADV performance was also investigated during and after rain events.Article Citation - WoS: 24Citation - Scopus: 24GA-optimized model predicts dispersion coefficient in natural channels(IWA Publishing, 2009) Tayfur, GökmenModels whose parameters were optimized by genetic algorithm (GA) were developed to predict the longitudinal dispersion coefficient in natural channels. Following the existing equations in the literature, ten different linear and nonlinear models were first constructed. The models relate the dispersion coefficient to flow and channel characteristics. The GA model was then employed to find the optimal values of the constructed model parameters by minimizing the mean absolute error function (objective function). The GA model utilized an 80% cross-over rate and 4% mutation rate. It started each computation with a population of 100 chromosomes in the gene pool. For each model, while minimizing the objective function, the values of the model parameters were constrained between [-10, +10] at each iteration. The optimal values of the model parameters were obtained using a calibration set of 54 out of 80 sets of measured data. The minimum error was obtained for the case where the model was a linear equation relating dispersion coefficient to flow discharge. The model performance was then satisfactorily tested against the remaining 26 measured validation datasets. It performed better than the existing equations. it yielded minimum errors of MAE = 21.4m2/s (mean absolute error) and RMSE = 28.5m2/s (root mean-squares error) and a maximum accuracy rate of 81%. © IWA Publishing 2009.Article Citation - WoS: 48Citation - Scopus: 51Laminar Box System for 1-G Physical Modeling of Liquefaction and Lateral Spreading(American Society for Testing and Materials, 2009) Thevanayagam, S.; Kanagalingam, T.; Reinhorn, A.; Tharmendhira, R.; Dobry, R.; Abdoun, T.; Elgamal, A.; Zeghal, M.; Ecemiş, Nurhan; El Shamy, U.Details of a large scale modular 1-g laminar box system capable of simulating seismic induced liquefaction and lateral spreading response of level or gently sloping loose deposits of up to 6 m depth are presented. The internal dimensions of the largest module are 5 m in length and 2.75 m in width. The system includes a two dimensional laminar box made of 24 laminates stacked on top of each other supported by ball bearings, a base shaker resting on a strong floor, two computer controlled high speed actuators mounted on a strong wall, a dense array advanced instrumentation, and a novel system for laboratory hydraulic placement of loose sand deposit, which mimics underwater deposition in a narrow density range. The stacks of laminates slide on each other using a low-friction high-load capacity ball bearing system placed between each laminate. It could also be reconfigured into two smaller modules that are 2.5 m wide, 2.75 m long, and up to 3 m high. The maximum shear strain achievable in this system is 15 %. A limited set of instrumentation data is presented to highlight the capabilities of this equipment system. The reliability of the dense array sensor data is illustrated using cross comparison of accelerations and displacements measured by different types of sensors. Copyright © 2009 by ASTM International.Article Citation - WoS: 28Citation - Scopus: 30Hydrochemical and Isotopic Composition of Tuzla Geothermal Field (canakkale-Turkey) and Its Environmental Impacts(Taylor and Francis Ltd., 2009) Baba, Alper; Yüce, Galip; Deniz, Ozan; Yasin, DidemTuzla is an active geothermal area located in northwestern Turkey, 80 km south of the city of Canakkale and 5 km from the Aegean Coast. Geothermal brine, deriving from this area, contains an abundance of NaCl and a water temperature of 173°C (T1 well at 814 m depth) is typically encountered. The aim of this study was to determine the hydrogeochemical properties of the geothermal brine using both chemical and isotopic data, and to investigate the origin of the geothermal brine in the Tuzla area and the environmental impacts of Tuzla Geothermal Field (TGF). Both geothermal brine and shallow groundwater in the area are of meteoric origin. Isotope results indicate that the hot saline waters (brine) in the Tuzla geothermal field originate from connate water along faults. As the saline water rises to the surface, it mixes with shallow groundwaters in various ratios. In addition, the high sodium (Na) and chloride (Cl) content in the Tuzla Stream, fed from the Tuzla geothermal brine during the dry season, cause an increase in sodium and chloride concentrations in the shallow groundwaters by infiltration into the aquifer. Moreover, salt accumulation on the surface is observed due to the uncontrolled artesian flow of geothermal brine, which adversely affects the salinity of shallow groundwater.Article Citation - WoS: 2Citation - Scopus: 5The Influence of Low Energy Impacts on the Static and Dynamic Response of a Foam Core Composite Wing(SAGE Publications Inc., 2009) Aktaş, Engin; Seaver, Mark; Nichols, Jonathan M.; Trickey, Stephen T.; Davis, W. R.This work describes damage detection efforts on a composite wing subject to a series of low-energy (ĝ̂1/47 J) impacts. Two airfoils with fundamentally different damage scenarios were considered. The first damage scenario produced no visible signs of damage on the wing surface following eight impacts. A duplicate wing, subjected to a similar series of impacts, was investigated using flash thermography and subsequently autopsied. The flash thermography showed small, localized damage in the skin, but gave no information about core damage. The autopsy showed core/skin disbonding at both interfaces that varied with the number of impacts, core crushing, and a through the core shear crack. No clear changes to the static or dynamic wing response were observed for this scenario. The second damage scenario involved cracking of the wing skin. While damage quantification was not undertaken for this scenario, both static and dynamic changes in wing response were observed. An analytical model of the wing is presented which helps explain the observed behaviors of the two damage scenarios.Article Citation - WoS: 78Citation - Scopus: 88Nonlinear Finite Element Modeling of Reinforced Concrete Structures Under Impact Loads(American Concrete Institute, 2009) Saatçi, Selçuk; Vecchio, Frank J.The methods available in the literature for the analysis of reinforced concrete (RC) structures subjected to impact loads generally exhibit some deficiencies in aspects relating to applicability, practicality, and accuracy. The shear-dominant behavior of RC members under impact loads creates another significant shortcoming, because modeling the shear behavior of RC has long been a challenging issue. This study aims to present and verify a nonlinear finite element analysis procedure employing the Disturbed Stress Field Model, based on a smeared rotating crack approach, as an advanced method of modeling shear behavior under impact conditions. The proposed methodology has a wide range of applicability, and displays fast solution time while providing extensive and accurate information on structural behavior. The methodology was tested by analyzing a set of RC beams subjected to impact loads. A high level of accuracy was demonstrated in various comparisons between test and analysis results, including peak and residual displacements, crack profiles, and reinforcement strains.Article Citation - WoS: 19Citation - Scopus: 19Using Numerical Models and Acoustic Methods To Predict Reservoir Sedimentation(Taylor and Francis Ltd., 2009) Elçi, Şebnem; Bor, Aslı; Çalışkan, AnılThis study draws on drainage basin hydrography, numerical modeling and geographic information system (GIS) techniques in concert with dual frequency echo sounder data to estimate sediment thickness when initial surveys are unavailable or inaccurate. Tahtali Reservoir (Turkey), which provides 40% of water supply to the city of Izmir, was selected as the study site. Deposition patterns within the whole lake were estimated with a 3-D hydrodynamic and sediment transport model applied to Tahtali Reservoir. The numerical model simulated lake response to wind forcing and inflows and/or outflows and was used to describe sediment deposition patterns resulting from the erosion of soils quantified by the implementation of Universal Soil Loss Equation (USLE) to the whole watershed. Surveying of the lake via dual frequency (28/200 kHz) echo sounder system revealed the current bathymetry, and sediment thickness was estimated from the difference of depths measured by the dual frequency sounder along surveyed transects. These results were compared to the modeled sedimentation thicknesses and to preliminary estimates of watershed sediment yield estimated by USLE. Results of this study can be used for further water quality studies and for long term management plans.Article Citation - WoS: 26Citation - Scopus: 31Groundwater Quality and Hydrogeochemical Properties of Torbali Region, Izmir, Turkey(Springer Verlag, 2008) Tayfur, Gökmen; Kırer, Tuğba; Baba, AlperThe large demand for drinking, irrigation and industrial water in the region of Torbalö (Izmir, Turkey) is supplied from groundwater sources. Almost every factory and farm has private wells that are drilled without permission. These cause the depletion of groundwater and limiting the usage of groundwater. This study investigates spatial and temporal change in groundwater quality, relationships between quality parameters, and sources of contamination in Torbali region. For this purpose, samples were collected from 10 different sampling points chosen according to their geological and hydrogeological properties and location relative to factories, between October 2001 and July 2002. Various physical (pH, temperature, EC), chemical (calcium, magnesium, potassium, sodium, chloride, alkalinity, copper, chromium, cadmium, lead, zinc) and organic (nitrate, nitrite, ammonia, COD and cyanide) parameters were monitored. It was observed that the groundwater has bicarbonate alkalinity. Agricultural contamination was determined in the region, especially during the summer. Nitrite and ammonia concentrations were found to be above drinking water standard. Organic matter contamination was also investigated in the study area. COD concentrations were higher than the permissible limits during the summer months of the monitoring period.