Quasi-Static Nonlinear Seismic Assessment of a Fourth Century A.D. Roman Aqueduct in Istanbul, Turkey

The majority of architectural heritage consists of load-bearing masonry components made up of stone units and relatively weak mortar joints, yielding potential weak planes for masonry structures where tension and shear failures are expected to occur. Advanced nonlinear analyses are required to simulate these phenomena and predict the corresponding nonlinear structural behavior of historic masonry constructions. In this context, this paper presents a model of a stone masonry Roman aqueduct (the Valens Aqueduct), constructed in the fourth century A.D. in Istanbul, Turkey, to explore the seismic capacity and behavior using the discrete element method (DEM). The employed modeling approach comprises distinct rigid blocks interacting along their boundaries based on the point-contact hypothesis. Thus, the discontinuous stone skeleton of the masonry aqueduct is represented explicitly in the computational model. First, a validation study was conducted on the laboratory experiment to demonstrate the capabilities of the adopted modeling approach. Then, a discontinuum model representing the Valens Aqueduct was used to assess the seismic capacity of the structure under gradually increasing lateral forces. The numerical simulations gave insight into the structural response of the aqueduct from the elastic range to total collapse. Additionally, parametric research was performed considering joint properties, namely the joint tensile strength, contact stiffness, joint friction angle, and compressive strength of the masonry, to quantify the effects of contact parameters on the displacement response of the DEM model. Further inferences were made regarding the modeling parameters, and practical conclusions were derived

Wave propagation in random elastic media.

Ph.D. - Doctoral Progra

Dynamics of embedded structures in solid medium in the presence of cavitation

This paper presents a probabilistic approach for predicting the existence of cavitation in a solid medium. The cavitation is assumed to be generated by the diffraction of a propogating random stress wave from an embedded structure. The analysis is based on one dimensional linear plane wave approximation and the stress wave is assumed to be stationary Gaussian, white random process. For the embedded structure lumped mass model approximation is used. Transitional probability is obtained by Caughy's method and relevant characteristics of the cavitation process such as mean square displacement for cavitation and expected time for crossing the displacement at cavitation are derived. Comparison of the cavitation behaviour is made between the existing deterministic solutions in the literature and the present probabilistic approach via numerical results. The principal conclusion of the study is that the phenomenon of cavitation must be at least explored by simple mathematical models in the design and analysis phases of embedded structures subjected to seismic and/or explosive loads

CHAOTIC DYNAMIC ANALYSIS OF VISCOELASTIC SHALLOW SPHERICAL-SHELLS

This paper investigates the dynamic behaviour of a shallow, viscoelastic, spherical shell under a harmonic excitation. The time evolutions of the response of the corresponding nonlinear dynamical system are described by the phase portraits and the bifurcation of the parameter dependent system is studied numerically so as to identify qualitative changes in the phase portrait. The viscoelastic shell, having more than one equilibrium configuration for some problem parameters, shows periodic and/or random-like chaotic oscillations under the given excitation according to the dimensions of the attracting set. The occurrence and nature of the chaotic attractors are verified by evaluating Lyapunov exponents

Quasi-static nonlinear seismic assessment of a fourth century A.D. Roman Aqueduct in Istanbul, Turkey

© 2021 by the authors. Licensee MDPI, Basel, Switzerland.The majority of architectural heritage consists of load-bearing masonry components made up of stone units and relatively weak mortar joints, yielding potential weak planes for masonry structures where tension and shear failures are expected to occur. Advanced nonlinear analyses are required to simulate these phenomena and predict the corresponding nonlinear structural behavior of historic masonry constructions. In this context, this paper presents a model of a stone masonry Roman aqueduct (the Valens Aqueduct), constructed in the fourth century A.D. in Istanbul, Turkey, to explore the seismic capacity and behavior using the discrete element method (DEM). The employed modeling approach comprises distinct rigid blocks interacting along their boundaries based on the point-contact hypothesis. Thus, the discontinuous stone skeleton of the masonry aqueduct is represented explicitly in the computational model. First, a validation study was conducted on the laboratory experiment to demonstrate the capabilities of the adopted modeling approach. Then, a discontinuum model representing the Valens Aqueduct was used to assess the seismic capacity of the structure under gradually increasing lateral forces. The numerical simulations gave insight into the structural response of the aqueduct from the elastic range to total collapse. Additionally, parametric research was performed considering joint properties, namely the joint tensile strength, contact stiffness, joint friction angle, and compressive strength of the masonry, to quantify the effects of contact parameters on the displacement response of the DEM model. Further inferences were made regarding the modeling parameters, and practical conclusions were derived

A Quantitative Study for Evaluation of Coastal Scenery

Scenery is a resource that has to be evaluated in an objective and quantitative manner to provide a means of comparison against other resource considerations and environmental impact assessments. This article presents the results of a quantitative evaluation of coastal scenery, enhancing the previous public survey questionnaires for Turkey, the U.K., Malta, and Croatia. The technique developed to evaluate coastal scenery uses 26 scenic parameters (of both physical and perceptual characteristics) for the four countries listed above and also for Australia, Ireland, the United States, New Zealand, and Japan, assembled via consultations with coastal users and experts. The weights of the scenic parameters are estimated and, together with a checklist that uses a fuzzy mathematics approach, an evaluation index (D) for each site is estimated for 86 worldwide coastal regions. These sites are further classified into five categories according to the D values they achieved. The results show that human impacts may adversely affect the coastal scenic value of a site. Comparison between assessment grades from experts and those from the public showed good agreement, specifically for human parameters. The results could be quite useful as a guideline for assessing, designing, and managing coastal areas when decisions must be made regarding intensive urban and industrial developments

Kıyı Alanlarının Bulanık Mantık Yöntemiyle Değerlendirilmesi için Açık Kaynak Kodlu Hesaplama Aracı Geliştirilmesi

“Kıyı Alanları Doğal Yapı ve İnsan Kullanımı Değerlendirilmesi, KADYİKD” (Coastal Scenic Evaluation System, CSES) kıyı alanlarının bilimsel olarak nitel değerlendilmesinde bulanık mantık yönteminin dünyada ilk kez kullanıldığı bir matematiksel modeldir (Ergin vd., 2004; Ergin, 2018). Kıyı alanlarında doğal yapı ve insan kullanımının bu model kullanılarak değerlendirilmesi için Türkiye, İngiltere, Malta, Avustralya, İrlanda, ABD, Yeni Zelanda ve Japonya kıyı-deniz mühendisliği anabilim dalı akademisyenleri ve uzmanlarının ortak çalışması ile 26 kıyı parametresi seçilmiştir. Parametreleri değerlendirmek üzere gene bir ilk olarak Türkiye, İngiltere, Malta ve Hırvatistan’da yapılan halk algılama anketleri uygulanmıştır. KADYİKD modelinde, kıyı alanlarına ilişkin görsel bulgular 26 kıyı parametre için puanlanmakta, parametrelerin ağırlıklı ortalamaları kullanılarak bulanık mantık yöntemi (BMY) ile değerlendirilmekte ve çalışma yapılan kıyı alanı için bir ‘Değerlendirme Katsayısı (D)’ hesaplanmaktadır. ‘Değerlendirme Katsayısı (D)’ ise kıyı alanlarının beş ayrı sınıfa göre sınıflandırılmasında sayısal bir ölçüt olarak kullanılabilmektedir. Bu çalışmada, KADYİKD matematik modeli MATLAB ortamında tekrar yazılarak “açık kaynak kodlu” olarak bir websitesi aracılığıyla kullanıma açılmış ve Çıralı, Olimpos’ta yapılan örnek bir çalışmayla test edilmiştir