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Öğe Döndürülmüş yer hareketleri için hesaplanacak ortalama sönüm azaltma katsayısının kestirimi için yeni bir yaklaşım(2019) Özdemir, Gökhan; Bayhan, BeyhanBu çalışma, sönüm azaltma katsayısının, yer hareketinin yönüne bağlı değişimini incelemektedir. Bu amaçla, seçilen orijinal yer hareketlerinin, birbirine dik yatay bileşenleri, maksimum yer hızlarına göre gruplandırılmış ve bu yatay bileşenler, 0°’den 180°’ye kadar, 10°’lik artımlarla döndürülmüştür. Orijinal ve döndürülmüş kayıtlara ait sönüm azaltma katsayıları, %10, %20 ve %30 sönüm oranları için hesaplanmıştır. Daha sonra, sönüm azaltma katsayısındaki değişimi, yer hareketinin yönüne bağlı olarak hesap etmek amacıyla, basitleştirilmiş yeni bir yöntem önerilmiştir. Sonuçlar, yer hareketi yönünün, sönüm azaltma katsayısının hesabında önemli bir parametre olduğunu ve bu çalışmada önerilen yöntemin, periyot ve sönüm oranından bağımsız olarak, sönüm azaltma katsayısını ortalama bazda hesaplanması bakımından oldukça başarılı olduğunu göstermiştir.Öğe Effective flexural rigidities for ordinary reinforced concrete columns and beams(Wiley-Blackwell, 2014) Avsar, O.; Bayhan, Beyhan; Yakut, A.Current effective flexural rigidities proposed for use in design and analyses of reinforced concrete structures have been examined. The level of accuracy in the estimation of section rigidity plays a very important role in determining realistic values for the structural stiffness and hence the seismic forces imposed. The most significant parameters influencing the effective rigidity, which reflects the effect of cracking as well as the theoretical yielding of reinforced concrete sections, have been determined through comprehensive moment-curvature analyses of various reinforced concrete sections. The geometry, axial load level, concrete strength and the amount of compression and tension reinforcements have been identified as the most important factors affecting the effective rigidity. New relationships that are believed to represent the effective stiffness of reinforced concrete members have been adequately developed. Efficiency of the code-specified and proposed values has been investigated through experimental data and parametric studies. It has been observed that the relationships developed herein have provided the most accurate results in prediction of the effective rigidity of older-type structural elements with low-strength and longitudinal reinforcement ratio. They can be used for assessment of ordinary buildings. Copyright (c) 2012 John Wiley & Sons, Ltd.Öğe Impact of Joint Modeling Approach on Performance Estimates of Older-Type RC Buildings(Earthquake Engineering Research Inst, 2017) Bayhan, Beyhan; Ozdemir, Gokhan; Gulkan, PolatThe behavior of beam-column connections has usually been ignored in the modeling process due to its complexity and relatively recent awareness of its possible impact on response. This study presents the features of modeling unrein-forced beam-column joints in estimating seismic demands. A representative RC frame is subjected to strong ground motions. Through nonlinear dynamic analyses, base shear, roof displacement, inter-story drift and joint rotation are noted. The dynamic analyses are performed comparatively through two analytical models with rigid and flexible joint assumptions. In the flexible joint model, shear deformation at the beam-column joint and bond-slip deformation at the beam-column interface are simulated through a previously verified analytical representation. Results indicate that introducing unreinforced beam-column joint behavior to the model may lead to almost two times larger seismic demands compared to those obtained from rigid connection assumption. Thus, the performance assessment of such buildings may conclude erroneously with underestimated seismic demands and damage levels when inelastic actions in the joints are ignored. However, in some cases, lower seismic demands can also be obtained for the flexible joint model.Öğe Numerical simulation of shaking table tests on 3D reinforced concrete structures(Techno-Press, 2013) Bayhan, BeyhanThe current paper presents the numerical blind prediction of nonlinear seismic response of two full-scale, three dimensional, one-story reinforced concrete structures subjected to bidirectional earthquake simulations on shaking table. Simulations were carried out at the laboratories of LNEC (Laboratorio Nacional de Engenharia Civil) in Lisbon, Portugal. The study was motivated by participation in the blind prediction contest of shaking table tests, organized by the challenge committee of the 15th World Conference on Earthquake Engineering. The test specimens, geometrically identical, designed for low and high ductility levels, were subjected to subsequent earthquake motions of increasing intensity. Three dimensional nonlinear analytical models were implemented and subjected to the input base motions. Reasonably accurate reproduction of the measured displacement response was obtained through appropriate modeling. The goodness of fit between analytical and measured results depended on the details of the analytical models.Öğe Persisting challenges for performance-based building assessment(Springer, 2014) Bayhan, Beyhan; Kazaz, I.; Gulkan, P.Intense research and refinement of the tools used in performance-based seismic engineering have been made, but the maturity and accuracy of these methods have not been adequately confirmed with actual data from the field. The gap between the assumed characteristics of actual building systems and their idealized counterparts used for analysis is wide. When the randomly distributed flaws in buildings as they exist in urban areas and the extreme variability of ground motion patterns combine, the conventional procedures used for pushover or dynamic response history analyses seem to fall short of reconciling the differences between calculated and observed damage. For emergency planning and loss modeling purposes, such discrepancies are factors that must be borne in mind. Two relevant examples are provided herein. These examples demonstrate that consensus-based analytical guidelines also require well-idealized building models that do not lend themselves to reasonably manageable representations from field data. As a corollary, loss modeling techniques, e.g., used for insurance purposes, must undergo further development and improvement.Öğe Seismic Response of a Concrete Frame with Weak Beam-Column Joints(Earthquake Engineering Research Inst, 2015) Bayhan, Beyhan; Moehle, J. P.; Yavari, S.; Elwood, K. J.; Lin, S. H.; Wu, C. L.A reduced-scale, planar, two-story by two-bay reinforced concrete frame with weak beam-column joints was subjected to earthquake simulations on a shaking table. The beam-column joints did not contain transverse reinforcement, as is typical in older construction designed without attention to detail for ductile response. A series of linear and nonlinear analytical models of the frame were developed in accordance with American Society of Civil Engineers standards and subjected to the input base motions. The goodness of fit between analytical and measured results depended on the details of the analytical model. Reasonably accurate reproduction of the measured response was obtained only by modeling the inelastic responses of both columns and beam-column joints. The results confirm the importance of modeling nonlinear joint behavior in older concrete buildings with deficient beam-column joints.Öğe Significance of Ground Motion Scaling Parameters on Amplitude of Scale Factors and Seismic Response of Short- and Long-Period Structures(Earthquake Engineering Research Inst, 2019) Cavdar, Esengul; Ozdemir, Gokhan; Bayhan, BeyhanIn this study, an ensemble of ground motions is selected and scaled in order to perform code-compliant bidirectional Nonlinear Response History Analysis for the design purpose of both short- and long-period structures. The followed scaling method provides both the requirements of the Turkish Earthquake Code regarding the scaling of ground motions and compatibility of response spectra of selected ground motion pairs with the target spectrum. The effects of four parameters, involved in the followed scaling method, on both the amplitude of scale factors and seismic response of structures are investigated. These parameters are the number of ground motion records, period range, number of periods used in the related period range, and distribution of weight factors at the selected periods. In the analyses, ground motion excitations were applied to both fixed-base and seismically isolated structure models representative of short- and long-period structures, respectively. Results revealed that both the amplitudes of scale factors and seismic response of short-period structures are more prone to variation of investigated parameters compared to those of long-period structures.Öğe Variations in the hysteretic behavior of LRBs as a function of applied loading(Techno-Press, 2018) Ozdemir, Gokhan; Bayhan, Beyhan; Gulkan, PolatThe study presented herein focused on the change in hysteretic force-deformation behavior of lead rubber bearings (LRBs). The material model used to idealize response of LRBs under cyclic motion is capable of representing the gradual attrition in strength of isolator unit on account of lead core heating. To identify the effect of loading history on the hysteretic response of LRBs, a typical isolator unit is subjected to cyclic motions with different velocity, amplitude and number of cycles. Furthermore, performance of an LRB isolated single degree of freedom system is studied under different seismic input levels. Finally, the significance of lead core heating effect on LRBs is discussed by considering the current design approach for base isolated structures. Results of this study show that the response of an LRB is governed strongly by the amplitude and number of cycles of the motion and the considered seismicity level.
