Civil Engineering / İnşaat Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/13
Browse
12 results
Search Results
Now showing 1 - 10 of 12
Article Citation - WoS: 27Citation - Scopus: 32Distribution of Strong Earthquake Input Energy in Tall Buildings Equipped With Damped Outriggers(John Wiley and Sons Inc., 2018) Morales-Beltran, Mauricio; Turan, Gürsoy; Yıldırım, U.; Paul, JoopThe seismic design of optimal damped outrigger structures relies on the assumption that most of the input energy will be absorbed by the dampers, whilst the rest of the structure remains elastic. When subjected to strong earthquakes, nevertheless, the building structure may exhibit plastic hinges before the dampers begin to work. In order to determine to which extent the use of viscously damped outriggers would avoid damage, both the host structure's hysteretic behaviour and the dampers' performance need to be evaluated in parallel. This article provides a parametric study on the factors that influence the distribution of seismic energy in tall buildings equipped with damped outriggers: First, the influence of outrigger's location, damping coefficients, and rigidity ratios core-to-outrigger and core-to-column in the seismic performance of a 60-story building with conventional and with damped outriggers is studied. In parallel, nonlinear behaviour of the outrigger with and without viscous dampers is examined under small, moderate, strong, and severe long-period earthquakes to assess the hysteretic energy distribution through the core and outriggers. The results show that, as the ground motion becomes stronger, viscous dampers effectively reduce the potential of damage in the structure if compared to conventional outriggers. However, the use of dampers cannot entirely prevent damage under critical excitations.Article Citation - WoS: 24Citation - Scopus: 30Energy Dissipation and Performance Assessment of Double Damped Outriggers in Tall Buildings Under Strong Earthquakes(John Wiley and Sons Inc., 2019) Morales-Beltran, Mauricio; Turan, Gürsoy; Dursun, Onur; Nijsse, RobThe use of a single set of outriggers equipped with oil viscous dampers increases the damping ratio of tall buildings in about 6–10%, depending on the loading conditions. However, could this ratio be further increased by the addition of another set of outriggers? Should this additional set include dampers too? To answer these questions, several double damped outrigger configurations for tall buildings are investigated and compared with an optimally designed single damped outrigger, located at elevation 0.7 of the total building's height (h). Using free vibration, double outrigger configurations increasing damping up to a ratio equal to the single-based optimal are identified. Next, selected configurations are subjected to several levels of eight ground motions to compare their capability for avoiding damage under critical excitations. Last, a simplified economic analysis highlights the advantages of each optimal configuration in terms of cost savings. The results show that, within the boundaries of this study, combining a damped outrigger at 0.5h with a conventional outrigger at 0.7h is more effective in reducing hysteretic energy ratios and economically viable if compared with a single damped outrigger solution. Moreover, double damped outrigger configurations for tall buildings exhibit broader display of optimal combinations, which offer flexibility of design to the high-rise architecture.Article Citation - WoS: 108Citation - Scopus: 117Enhancement of Interlaminar Fracture Toughness of Carbon Fiber–epoxy Composites Using Polyamide-6,6 Electrospun Nanofibers(John Wiley and Sons Inc., 2017) Beylergil, Bertan; Tanoğlu, Metin; Aktaş, EnginIn this study, carbon fiber–epoxy composites are interleaved with electrospun polyamide-6,6 (PA 66) nanofibers to improve their Mode-I fracture toughness. These nanofibers are directly deposited onto carbon fabrics before composite manufacturing via vacuum infusion. Three-point bending, tensile, compression, interlaminar shear strength, Charpy impact, and double cantilever beam tests are performed on the reference and PA 66 interleaved specimens to evaluate the effects of PA 66 nanofibers on the mechanical properties of composites. To investigate the effect of nanofiber areal weight density (AWD), nanointerlayers with various AWD are prepared by changing the electrospinning duration. It is found that the electrospun PA 66 nanofibers are very effective in improving Mode-I toughness and impact resistance, compressive strength, flexural modulus, and strength of the composites. However, these nanofibers cause a decrease in the tensile strength of the composites. The glass-transition temperature of the composites is not affected by the addition of PA 66 nanofibers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45244.Article Citation - WoS: 18Citation - Scopus: 24Empirical Sediment Transport Models Based on Indoor Rainfall Simulator and Erosion Flume Experimental Data(John Wiley and Sons Inc., 2017) Aksoy, Hafzullah; Eriş, Ebru; Tayfur, GökmenLand degradation processes start with accelerated runoff and sediment delivery. In this study, rainfall-runoff induced sediment transport is investigated using data from an indoor laboratory experimental setup consisting of a rainfall simulator and an erosion flume. The data are analysed to develop empirical models using sediment discharge, slope, flow discharge, rainfall intensity and sediment size. Fine and medium sands are considered as bare soil in experiments. Four rainfall intensities (45, 65, 85 and 105 mm h−1) are applied with combinations of lateral and longitudinal slopes of 5%, 10%, 15% and 20%. Eighty experiments are conducted. Flow is measured, and sediment within flow is separated and weighted. Experimental data are used for developing empirical models through multiple regression with parameters optimized by genetic algorithm. Results show that slope is the main contributing variable to the sediment transport over hillslopes. Accommodating variables among slope, rainfall intensity, flow discharge and median diameter of sediment as independent variables, one-variable, two-variable and four-variable models are developed considering also that higher number of parameters increases the performance of the model with higher cost of parameterization.Article Citation - WoS: 47Citation - Scopus: 49Downscaling of Monthly Precipitation Using Cmip5 Climate Models Operated Under Rcps(John Wiley and Sons Inc., 2016) Okkan, Umut; Kırdemir, UmutDownscaling of general circulation model (GCM) outputs extracted from CMIP5 datasets to monthly precipitation for the Gediz Basin, Turkey, under Representative Concentration Pathways (RCPs) was performed by statistical downscaling models, multi-GCM ensemble and bias correction. The output databases from 12 GCMs were used for the projections. To determine explanatory predictor variables, the correlation analysis was applied between precipitation observed at 39 meteorological stations located over the Basin and potential predictors of ERA-Interim reanalysis data. After setting both artificial neural networks and least-squares support vector machine-based statistical downscaling models calibrated with determined predictor variables, downscaling models producing the most suitable results were chosen for each meteorological station. The selected downscaling model structure for each station was then operated with historical and future scenarios RCP4.5, RCP6.0 and RCP8.5. Afterwards, the monthly precipitation forecasts were obtained from a multi-GCM ensemble based on Bayesian model averaging and bias correction applications. The statistical significance of the foreseen changes for the future period 2015–2050 was investigated using Student's t test. The projected decrease trend in precipitation is significant for the RCP8.5 scenario, whereas it is less significant for the RCP4.5 and RCP6.0 scenarios.Article Citation - WoS: 4Citation - Scopus: 5A Modified Fiber-Reinforced Plastics Concrete Interface Bond-Slip Law for Shear-Strengthened Rc Elements Under Cyclic Loading(John Wiley and Sons Inc., 2016) Selman, Efe; Alver, NinelThe objective of this article is to realistically analyze fiber-reinforced plastics (FRP) retrofitted reinforced concrete structures under cyclic loading taking into account FRP–concrete bond-slip law with cyclic bond degradation. In literature, even though numerous studies have been conducted in FRP–concrete interface bond-slip modeling under cyclic loads, a small number of them consider the influence of cyclic degradation on FRP–concrete interface bond behavior. Within this framework, the bond-slip law for carbon fiber-reinforced plastics–concrete interface is revised by utilizing Harajli's and Ko-Sato's approaches. The procedure is distinct from others because it develops existing deficiencies of these approaches, whereas a more reliable modeling process is proposed for use in practice. Conventional bond-slip law of Lu et al. is compared with this interface relationship stated in this investigation and the difference is clearly shown in terms of structural parameters. Experimental tests are conducted at the same time for verification. It is proved that cyclic bond degradation affects the interface behavior; thus, the structural response cannot be omitted in structural evaluations. Structural performance measures are obtained in good agreement for each level of cycles. The technique proposed clearly exhibits structural response difference between monotonic and cyclic loadings while good agreement is reached with experimental results. POLYM. COMPOS., 37:3373–3383, 2016. © 2015 Society of Plastics Engineers.Article Citation - WoS: 2Citation - Scopus: 3Numerical Model for Biaxial Earthquake Response of Reinforced Concrete(John Wiley and Sons Inc., 2007) Dönmez, Cemalettin; Sözen, Mete A.A numerical constitutive model is developed to simulate the biaxial nonlinear flexural response of slender reinforced concrete members subjected to earthquake excitation. The model is tested using data from two types of experiments with reinforced concrete elements: (1) elements subjected to varying pseudo-static biaxial lateral loads and (2) elements that responded biaxially to simulated earthquake motions. The goal for the model was not only to help determine the absolute maxima for earthquake response but also to enable calculation of the entire waveform, including the ranges of low- and moderate-amplitude response. The comparisons of measured and calculated results and sensitivity of the proposed model to variations in the input parameters are discussed. The output was found to be insensitive to the changes in input parameters related to concrete and sensitive to input parameters related to reinforcing steel. The results of the calculations were tested using experimental data.Article Citation - WoS: 16Citation - Scopus: 18Kinematic Wave Model of Bed Profiles in Alluvial Channels(John Wiley and Sons Inc., 2006) Tayfur, Gökmen; Singh, Vijay P.A mathematical model, based on the kinematic wave (KW) theory, is developed for describing the evolution and movement of bed profiles in alluvial channels. The model employs a functional relation between sediment transport rate and concentration, a relation between flow velocity and depth and Velikanov's formula relating suspended sediment concentration to flow variables. Laboratory flume and field data are used to test the model. Transient bed profiles in alluvial channels are also simulated for several hypothetical cases involving different water flow and sediment concentration characteristics. The model-simulated bed profiles are found to be in good agreement with what is observed in the laboratory, and they seem theoretically reasonable for hypothetical cases. The model results reveal that the mean particle velocity and maximum concentration (maximum bed form elevation) strongly affect transient bed profiles.Article Citation - WoS: 46Citation - Scopus: 49Predicting and Forecasting Flow Discharge at Sites Receiving Significant Lateral Inflow(John Wiley and Sons Inc., 2007) Tayfur, Gökmen; Moramarco, Tommaso; Singh, Vijay P.Two models, one linear and one non-linear, were employed for the prediction of flow discharge hydrographs at sites receiving significant lateral inflow. The linear model is based on a rating curve and permits a quick estimation of flow at a downstream site. The non-linear model is based on a multilayer feed-forward back propagation (FFBP) artificial neural network (ANN) and uses flow-stage data measured at the upstream and downstream stations. ANN predicted the real-time storm hydrographs satisfactorily and better than did the linear model. The results of sensitivity analysis indicated that when the lateral inflow contribution to the channel reach was insignificant, ANN, using only the flow-stage data at the upstream station, satisfactorily predicted the hydrograph at the downstream station. The prediction error of ANN increases exponentially with the difference between the peak discharge used in training and that used in testing. ANN was also employed for flood forecasting and was compared with the modified Muskingum model (MMM). For a 4-h lead time, MMM forecasts the floods reliably but could not be applied to reaches for lead times greater than the wave travel time. Although ANN and MMM had comparable performances for an 8-h lead time, ANN is capable of forecasting floods with lead times longer than the wave travel time.Article Citation - WoS: 17Citation - Scopus: 19Kinematic Wave Model for Transient Bed Profiles in Alluvial Channels Under Nonequilibrium Conditions(John Wiley and Sons Inc., 2007) Tayfur, Gökmen; Singh, Vijay P.Transient bed profiles in alluvial channels are generally modeled using diffusion (or dynamic) waves and assuming equilibrium between detachment and deposition rates. Equilibrium sediment transport can be considerably affected by an excess (or deficiency) of sediment supply due to mostly flows during flash floods or floods resulting from dam break or dike failure. In such situations the sediment transport process occurs under nonequilibrium conditions, and extensive changes in alluvial river morphology can take place over a relatively short period of time. Therefore the study and prediction of these changes are important for sustainable development and use of river water. This study hence developed a mathematical model based on the kinematic wave theory to model transient bed profiles in alluvial channels under nonequilibrium conditions. The kinematic wave theory employs a functional relation between sediment transport rate and concentration, the shear-stress approach for flow transport capacity, and a relation between flow velocity and depth. The model satisfactorily simulated transient bed forms observed in laboratory experiments.