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Öğe Advantages of infinite elements over prespecified boundary conditions in unbounded problems(Asce-Amer Soc Civil Engineers, 2015) Erkal, Aykut; Laefer, Debra F.; Tezcan, SemihThis paper promotes the further development and adoption of infinite elements for unbounded problems. This is done by demonstrating the ease of application and computational efficiency of infinite elements. Specifically, this paper introduces a comprehensive set of coordinate and field variable mapping functions for one-dimensional and two-dimensional infinite elements and the computational steps for the solution of the affiliated combined finite-infinite element models. Performance is then benchmarked against various parametric models for deflections and stresses in two examples of solid, unbounded problems: (1) a circular, uniformly-distributed load, and (2) a point load on a semiinfinite, axisymmetrical medium. The results are compared with those from the respective closed-form solution. As an example, when the vertical deflections in Example 2 are compared with the closed form solution, the 45% error level generated with fixed boundaries and 14% generated with spring-supported boundaries is reduced to only 1% with infinite elements, even with a coarse mesh. Furthermore, this increased accuracy is achieved with lower computational costs. (C) 2014 American Society of Civil Engineers.Öğe Climate threats to the earth-built heritage of Scotland(Ice Publishing, 2015) Parkin, Simon J.; Adderley, W. Paul; Kennedy, Craig J.; Aktaş, Yasemin Didem; D'Ayala, Dina; Erkal, AykutThe most significant concentration of surviving vernacular mudwall structures in Scotland is found in and around the town of Errol in the Carse of Gowrie. Mudwall, or cob, is particularly susceptible to climate-related impacts such as water ingress and freeze-thaw cycles. A lack of recognition can exacerbate the effects of these factors significantly. Using two sites as representative case studies, this paper considers the issues typically encountered. The procedures used in monitoring the performance of each building within a regional climate context are outlined. Using climate models and current weather data, the local climatic context within which these structures exist is considered. Climate-related impacts can then be considered for future scenarios. Temperature and humidity data were collected concurrently from targeted areas within the walls of both structures for over a year from April 2012, a period that exhibited a range of extreme weather events in the Carse of Gowrie. The system of datalogging at each structure is discussed and results considered against external weather conditions using decomposed time series statistical analysis. Recommendations are offered considering how an integrated approach to the analysis of historic mudwall structures can be achieved.Öğe Effective expressions for the estimation of the first and third natural periods of minarets based on extensive and comprehensive parametric modal analyses(Elsevier Ltd, 2025) Erkal, Aykut; Hilmi, Zahraa Husham IbrahimThis paper investigates the modal behaviour of minarets by conducting parametric modal analyses with a comprehensive set of geometric and material properties and critically proposes effective expressions to estimate the first and third natural periods of minarets. To make this unprecedented attempt, firstly, previously studied 52 minarets were examined to systematically select the geometric and material properties of 189 representative minarets. Subsequently, numerical models of these 189 minarets were created and assigned with the selected values for height, cross-sectional area, moment of inertia, modulus of elasticity, and mass density. Then, modal analysis was applied to each representative minaret to obtain modal characteristics to see the effect of each variable. Next, an iterative optimization algorithm was used to establish four effective expressions for the first and third natural periods, considering the effect of five and three variables. Finally, the performance of the proposed expressions was checked with 35 of the previously studied minarets whose dynamic characteristics are available. The results demonstrated a satisfactory level of accuracy. For example, the expression for the fundamental period with 5 variables presented discrepancies mostly far less than 19 % for 28 minarets of a total of 35 minarets. © 2025 Institution of Structural EngineersÖğe Environmental performance assessment using monitoring and DVS testing(Ice Publishing, 2015) Aktaş, Yasemin Didem; D'Ayala, Dina; Erkal, Aykut; Stephenson, VictoriaIt is now widely accepted that the adverse effects of climate change have become more visible over recent last decades, and current climatic trends suggest that more severe conditions are to follow. In relation to extreme weather events due to climate change, various material degradation phenomena and loss of structural integrity, due mostly to moisture-related deteriorating agents, have been observed on the existing building stock, especially historic buildings. The identification and quantification of such adverse effects is therefore of utmost importance, and environmental monitoring is one of the strongest tools to achieve this aim. This paper provides detailed information regarding on-site environmental monitoring work carried out on a sixteenth century timber frame cottage in Tewkesbury, Gloucestershire, England, along with hygroscopic characterisation using the dynamic vapour sorption (DVS) technique. The results obtained from monitoring and DVS testing are discussed to give detailed insight into hygrothermal damage mechanisms and the resulting loss of strength/physical integrity due to adverse environmental impacts on historic building envelopes.Öğe Evaluation of environmental impact on historical stone masonry through on-site monitoring appraisal(Geological Soc Publ House, 2013) Erkal, Aykut; D'Ayala, Dina; Stephenson, VictoriaThis paper presents the design and application of an environmental monitoring system on the historical site of Odda's Chapel in Deerhurst, Gloucestershire, UK, and the determination of hygroscopic behaviour of the original building materials to obtain long-term moisture content variation. The monitoring system provides a comprehensive profile of hygrothermal conditions in the walls at the locations where moisture conditions are potentially causing decay and damage. The system makes use of temperature and relative humidity sensing technology placed on the wall construction, providing continuous data including rainfall, wind-driven rain and runoff rain measurements. The relative merits and results of the designed system are evaluated and discussed, as well as the implications of its application in the conservation of historical structures. The environmental monitoring results show general deterioration in the shell of the building. Internal wall surface measurements are essential for the documentation of wall interior response and should be conducted across the wall section at several locations. The fact that 91% of in-wall recorded relative humidity (RH) values are greater than 75% RH throughout the monitoring period demonstrates the need for measures to conserve this historical stone masonry.Öğe Impact of traffic-induced vibrations on residential buildings and their occupants in metropolitan cities(Svenciliste U Zagrebu, Fakultet Prometnih Znanosti, 2019) Erkal, AykutThis paper evaluates and quantifies the adverse impact of traffic-induced vibrations on the structural systems of residential buildings and their occupants. To do this, istan-bul, one of the world's most populous and traffic-congested cities, was selected as a case study. Firstly, a survey was conducted on 100 occupants of six neighbourhoods to understand human perception of vibrations and the physical condition of typical buildings. Then, train-induced ground vibrations were measured near a busy railway. Using the survey data and the measured train vibrations, time-history analyses were applied to five typical residential buildings. The results showed that there is a considerable contribution of higher modes to overall building response. Peak particle velocities calculated on the buildings are predominantly intolerable. Critically, 95% of the occupants would like authorities to reorganize traffic regulations to reduce the effects of this global problem. Therefore, human response to traffic-induced vibrations should be consideration of serviceability limit state and site-specific analysis should be incorporated into the codes of practice.Öğe Interaction of vibrations of road and rail traffic with buildings and surrounding environment(Asce-Amer Soc Civil Engineers, 2020) Erkal, Aykut; Kocagöz, Muhammed ŞerifThis paper analyzes measured triaxial vibrations of road and rail traffic on and around a typical residential masonry building in Istanbul and its response to adjacent ground-born vibrations through numerical modeling. Therefore, to determine the dynamic behavior and resultant internal forces within the building, which stands between a road and a railway line, a numerical model was created, updated, and validated through the measured vibrations. The results show that train-induced vibrations caused the walls of the building to experience tensile stresses up to 23% of the masonry tensile strength. Additionally, the measured maximum vibration level on the building is well above the limit for complaints in residential environments and very close to the damage limit for historic and sensitive structures. Furthermore, a nearby vibration amplification zone on the ground surface suggests potential amplified loadings. Therefore, human responses to these prolonged vibrations should be the controlling factor, entailing site-specific analyses by the codes of practice in cities with dense traffic.Öğe Internal erosion and permeability of Na CMC-treated and PAM-treated geosynthetic clay liners(2023) Özhan, Hakkı O.; Erkal, AykutThis paper investigates the occurrence of internal erosion and the variation of the permeability of geosynthetic clay liner (GCL) with respect to its geotextile component, polymer type and polymer amount added to its bentonite component, hydraulic head, and subgrade material by performing extensive triaxial permeability tests on the GCL specimens. To do this, Na carboxymethyl cellulose (CMC) and polyacrylamide (PAM) were treated with the bentonite component of the GCLs. Then, the GCLs were placed over poorly graded gravel (GP) and poorly graded sand (SP). Consequently, they were tested with two different woven geotextile components under the hydraulics heads of 0.3 m and 10 m. Results showed that only GCLs tested with woven geotextile, having lower tensile strength, lower mass/area and lower thickness over the gravel at a hydraulic head of 10 m, experienced internal erosion. Critically, Na CMC and PAM treatment caused 2-2.5 orders of magnitude decrease in the permeability. Actually, 2% Na CMC and 1% PAM treatment by dry mass were found to be the optimum polymer contents. Both the environmentally friendly biopolymer Na CMC and the synthetic polymer PAM can effectively be treated with Ca bentonite to enhance the hydraulic performance of the GCLs.Öğe Laboratory testing of non-standard original historic building materials and related implications for conservation(Geological Soc Publ House, 2015) Erkal, Aykut; D'Ayala, DinaFor an assessment or an analysis of a historic building, determination of the material properties is always crucial. However, this is usually a challenging issue because material extraction from a historic building for standard laboratory testing is usually not allowed or the amount of material available for testing is very limited. Lack of comprehensive standards for testing irregularly shaped and non-standard-size specimens, taken from historic buildings, unfortunately compounds the uncertainty. This paper offers a discussion of such issues by using the case study of Odda's Chapel in Gloucestershire, UK, and describing the systematic examination of a total of six lime mortar and Blue Lias stone samples extracted from this Grade I listed building. The programme of testing and the results obtained are compared with the latest European standards relating to sampling and testing of material of cultural properties. Internal microstructure, hygroscopic sorption and water absorption characteristics, and the density and mechanical properties of the materials are documented and alternative testing techniques are compared. Identification of some of the above-mentioned material properties shows that the agreement between results obtained from the various test methods is considered satisfactory, depending on the testing approach and material heterogeneity.Öğe Selection, production, and testing of scaled reinforced concrete models and their components(Elsevier Sci Ltd, 2016) Laefer, Debra F.; Erkal, AykutThis paper presents considerations and procedures for the selection, production, and testing of small-scale, reinforced concrete frames to maintain geometric and kinematic similitude. To verify the proposed solutions, 1/10th scaled models were subjected to adjacent excavation-induced settlements in 1-gravity, soil-structure experiments. Material scaling strategies were verified by comparing the resultant surface soil settlements with published studies and by comparing the model building response with numerical simulation, as well as the extent of the damage with previously established thresholds. (C) 2016 Published by Elsevier Ltd.Öğe Transmission of traffic-induced vibrations on and around the minaret of little Hagia Sophia(Taylor & Francis Inc, 2017) Erkal, AykutWorldwide urbanization has caused heritage buildings to be in ever-closer proximity to heavily travelled roadways and railways. As an example of this, the minaret of Little Hagia Sophia was analyzed due to its historic prominence and close proximity to heavy rail traffic. A vibration measurement program was performed on and around the minaret. After material properties were determined, three-dimensional numerical model of the minaret was constructed and validated based on frequency analyses of measured vibrations and modal analysis. Self-weight analysis and linear time-history analyses were applied to the model using ground motions measured at the minaret's base. The results showed that stresses reached 32% of material strength and, critically, measured peak particle velocities of vibrations at times approached previously established damage thresholds. Therefore, construction and operation of traffic lines adjacent to heritage buildings in city centers should be analyzed carefully to prevent unintentional impacts on cultural heritage structures.Öğe Tren geçişlerinin Küçük Ayasofya Cami üzerinde ve yanındaki serbest zemin yüzeyinde oluşturduğu titreşimlerin deneysel olarak incelenmesi(2017) Erkal, AykutKentleşmenin dünya çapında hızlı artışına paralel olarak, karayolu ve demiryolu trafiği de artmaktadır. Bunun sonucunda, özellikle şehir merkezlerinde yaygınlaşan demiryolu ağları, kültürel miras yapılarına son derece yakın inşa edilebilmektedir. Tren geçişlerinin oluşturduğu dinamik yükler, bu hassas yapılara hasar verebileceği gibi, yapı sakinlerini de rahatsız edebilmektedir. Demiryolu hattına yakınlığı, tarihi zenginliği ve toplumsal değerinden dolayı Küçük Ayasofya Cami bu çalışmada örnek yapı olarak seçilmiştir. Öncelikle, yapı üzerinde ve bahçesinde, tren titreşimleri kaydedilmiş ve frekans ortamında incelenmiştir. Demiryolundan uzaklaştıkça zemin yüzeyindeki titreşimlerin yayılımı deneysel ve teorik olarak belirlenmiştir. Ayrıca, titreşimlerin genlikleri, yapısal hasar potansiyeli ve insan tepkisi bakımından değerlendirilmiştir. Geniş bir frekans aralığına yayılan zemin titreşimleri, demiryolundan yaklaşık 35-45m uzaklıkta, zemin büyütmesi göstermiştir. Yapı üzerinde ise tarihi yapılarda hasara sebep olabilecek, sınır titreşim seviyeleri, bazı durumlarda aşılmıştır. Sonuç olarak, kültürel miras yapıları üzerinde ve çevresinde titreşim ölçümleri yapılması, bu yapıların durum değerlendirmesi ve olası hasarların önlenmesi acısından oldukça önemlidirÖğe Value and vulnerability assessment of a historic tomb for conservation(Hindawi Ltd, 2014) Erkal, Aykut; Özhan, Hakkı O.Monumental tombs reflect various social, cultural, architectural, religious, economic, and engineering features of a community. However, environmental weathering, natural disasters, poor maintenance, vandalism, and misuse unfortunately pose serious threats to these cultural assets. Historic monuments are often exposed to the highest risk due to their vulnerability. The Ottoman-style Nis, anci Hamza Pas, a tomb located in Karacaahmet Cemetery, Istanbul, the largest and oldest public cemetery in Turkey, is a case in point. The tomb consisting of six granite columns and a brick dome supported by six arches was constructed in 1605. Cracks, material loss, and decay as a result of adverse environmental effects and past earthquakes are evident. Therefore, this paper analyses the overall value of the tomb with respect to its historical, communal, evidential, and aesthetic aspects. Using the finite element approach and data on the tomb's material properties, a structural analysis under the self-weight and a time history analysis based on the earthquake ground motion data recorded in Duzce, Turkey, in November 1999 were conducted to encourage the conservation of this tomb and similar cultural heritage assets all over the world. The damage observed in the structure is congruent with the analysis results.
