Civil Engineering / İnşaat Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/13
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Article Sonlu Eleman Modellerinin Maksimum Olasılık Tahmini ile Güncellenmesi(Turkish Chamber of Civil Engineers, 2021) Hızal, ÇağlayanMatematiksel yapı modellerinin titreşim verileri kullanılarak güncellenmesi konusu, son yıllarda giderek artan bir şekilde araştırmacıların ilgisini çekmektedir. Bu hususta literatüre sunulan yöntemler genel olarak deterministik ve olasılıksal olarak sınıflandırılmaktadır. Bu bağlamda hem deterministik hem de olasılıksal model güncelleme yöntemlerinin birçok varyasyonu yer almaktadır. Bu çalışmada ise maksimum olasılık tahminine dayalı alternatif bir yaklaşım sunulmaktadır. Önerilen yöntemde, modal tanılama sırasında öngörülen ölçüm hatalarının yanı sıra model hatası da boyutsuz bir Rayleigh oranı üzerinden dikkate alınmaktadır. Sisteme ait model parametreler, ölçüm ve modelleme hatalarının normal dağılım göstereceği kabulüyle oluşturulan bir olasılık yoğunluk fonksiyonu üzerinden hesaplanmaktadır. Sunulan yöntemin güvenirliği bir sayısal ve bir deneysel uygulama üzerinden değerlendirilmiştir. Elde edilen verilere göre önerilen yöntemin oldukça makul sonuçlar verdiği gözlemlenmektedir.Article Mesnetlerinden Farklı Yer Hareketlerine Maruz Çok Katlı Çerçevelerin Deplasman Yüklemesine Göre Analizi(Turkish Chamber of Civil Engineers, 2019) Hızal, Çağlayan; Turan, GürsoyIn seismic analysis of structures, generally it is assumed that all supports are subjected to identical ground motions. This approach is assumed to be realistic when the foundation of the structure is formed as a rigid plate, but it cannot consider the dynamic effects of the earthquake wave propagation if the supports are able to move independently. In this study, the multi-support excitation analysis of multi-story, multi bay frames is performed by using displacement loading which defines the seismic load depending on the ground displacement. The modal analysis procedure of the structures subjected to multi-support excitations is given in detail and the effect of pseudo-static displacement on the dynamic response of the structure is highlighted. A static correction approach is implemented with a numerical example to reflect the higher mode effects which are a natural result of displacement loading.Article Citation - WoS: 7Citation - Scopus: 9Frequency Domain Data Merging in Operational Modal Analysis Based on Least Squares Approach(Elsevier, 2020) Hızal, ÇağlayanAssembling of multi-setup measurements emerges as a challenging problem in the structural health monitoring applications and may cause some important issues in the estimation of global modal parameters such as frequency, damping ratio and modal shape vector. To overcome this problem, a novel frequency domain pre-identification data merging method is proposed in this study. In the proposed methodology, to obtain a single measurement set, a least squares approach is employed resulting in a global response that is scaled from the multi-setup data. For the verification of the proposed merging procedure, one numerical, two experimental studies and one real data application have been conducted. The results obtained from the numerical, experimental and real data analysis indicate that the presented methodology provides rather high-quality estimations for multi-setup measurement problems. © 2020 Elsevier LtdArticle Citation - WoS: 2Citation - Scopus: 3Rotary Inertia and Higher Modes Effect on the Dynamic Response of Timoshenko Beams on Two-Parameter Elastic Foundation(Turkish Chamber of Civil Engineers, 2019) Hızal, Çağlayan; Çatal, Hikmet HüseyinThis study investigates the effects of rotary inertia and higher modes on the dynamic response of the axially loaded Timoshenko beams on two-parameter foundation with generalized elastic end conditions. A simplified modal analysis procedure is presented by using the conventional separation of variables method. The effect of rotary inertia on the solution of free vibration differential equation is discussed. A numerical example is presented to investigate the coupled effect of rotary inertia and higher modes on the bending moment and shear force responses.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: 29Citation - Scopus: 29A Two-Stage Bayesian Algorithm for Finite Element Model Updating by Using Ambient Response Data From Multiple Measurement Setups(Academic Press, 2020) Hızal, Çağlayan; Turan, GürsoyThis study presents a two-stage Bayesian finite element model updating procedure by using acceleration response measurements obtained from multiple setups. In the presented methodology, parametric uncertainties for the modal parameters are estimated by using the Bayesian Fast Fourier Transform Approach (BFFTA). Different from the previous Bayesian methods, a block diagonal covariance matrix is modeled for prior estimation of measured modal parameters. In addition, the modelling error in the eigenvalue equations is considered as soft constraints to be updated. Numerical and experimental studies are presented to validate the proposed method. The effect of soft constraints on the identification results as well as their posterior uncertainties are investigated. According to the results, it is shown that the proposed methodology can identify the most probable finite element model parameters with high level of accuracy. In addition, the posterior uncertainties obtained by the proposed procedure are significantly small when compared to the methods that consider rigid constraints for prediction and/or modelling error. (C) 2019 Elsevier Ltd. All rights reserved.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: 4Citation - Scopus: 5Importance of Static Correction and Damping in the Analysis of a Cable-Stayed Bridge Subjected To Displacement Loading(American Society of Civil Engineers (ASCE), 2017) Hızal, Çağlayan; Turan, GürsoyCable-stayed bridges with long spans are excited by different support vibrations on both sides of the main span. Therefore, a realistic seismic structural analysis of the bridge must involve multiple-support excitation. The dynamic equation of motion, in which all degrees of freedom are solved at once, can be solved directly. A modal analysis might also be possible, but care must be taken with the number of modes used in the analysis. If the ground motion is described in terms of displacement and velocity, which is referred to as displacement loading, then a static correction that will account for the unconsidered higher modes must be performed. In this study, the procedure of multiple-support excitation through the use of modal transformation is explained in detail. The effects of changes in damping levels that affect the analysis results are investigated by using the static correction method in displacement loading. An example is given to illustrate the mentioned problem by using a finite-element model of the cable-stayed Bill Emerson Memorial Bridge.Article Citation - WoS: 5Citation - Scopus: 8Comparative Dynamic Analysis of Axially Loaded Beams on Modified Vlasov Foundation(Techno Press, 2016) Hızal, Çağlayan; Çatal, Hikmet HüseyinVibration analysis of the beams on elastic foundation has gained the great interest of many researchers. In the literature, there are many studies that focus on the free vibration analysis of the beams on one or two parameter elastic foundations. On the other hand, there are no sufficient studies especially focus on the comparison of dynamic response including the bending moment and shear force of the beams resting on Winkler and two parameter foundations. In this study, dynamic response of the axially loaded Timoshenko beams resting on modified Vlasov type elastic soil was investigated by using the separation of variables method. Governing equations were obtained by assuming that the material had linear elastic behaviour and mass of the beam was distributed along its length. Numerical analysis were provided and presented in figures to find out the differences between the modified Vlasov model and conventional Winkler type foundation. Furthermore, the effect of shear deformation of elastic soil on the dynamic response of the beam was investigated.