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Estimation of groundwater storage change and recharge using grace and gldas data, Firat basin, Turkey case
Groundwater plays an important role in the hydrologic cycle and it is one of sources of drinking water for about half the world's population. Groundwater is one of the main sources of water supply used for irrigation in agriculture and human consumption in Fırat basin. The groundwater water storage in Fırat Basin is mostly influenced by soil moisture, groundwater, snow water equivalent and plant surface water. In this research, the GRACE and GLDAS data sets are used, for 11 year period to estimate Terrestrial water storage and change over the Fırat basin on the Turkish side. Subsequently, the estimates are used to derive groundwater storage and to further estimate the groundwater recharge on the entire basin. The groundwater storage anomaly is obtained by subtracting the sum of the state variables of GLDAS from the Terrestrial water storage anomaly of GRACE. The groundwater recharge is estimated from time series of groundwater storage using water table fluctuation method. According to the estimated groundwater storage, the time series shows decreases in the groundwater at rate of -12.40 mm year-1 in the entire basin. The averaged annual groundwater recharge in 11 year period over the entire Fırat basin was 279.26 mm year-1. The annual recharge varies from 174 to 351 mm/year and 33 % can be explained by the variability in precipitation. And the correlation coefficient of annual recharge and precipitation is 0.33. Understanding the groundwater storage changes and groundwater recharge estimation are important in hydrological fields because this can lead to sustainable use of groundwater resources. Keywords: GRACE, GLDAS, groundwater storage, water table fluctuation, groundwater recharge, Fırat Basin
Yoğun kentsel ağlarda kaydedilen kuvvetli yer hareketi verilerine göre azalım ilişkilerinin yerelleştirilmesi
The regional dependency of ground motions underlines the necessity of adopting a more localized approach in the estimation of ground motion parameters (GMPs). This thesis kicks off with a consistency assessment of the five most suitable regional or global ground motion prediction equations (GMPEs) for the interested area and our local database including 6,534 individual horizontal-component ground motions recorded by the İstanbul Earthquake Rapid Response and Early Warning System (IERREWS) network during 78 small-to-moderate earthquakes. The examination uncovers a systematic overestimation tendency in GMPEs. Using the same database, an analysis is conducted to ascertain whether there are any regional azimuth-dependent effects on ground motions. Due to the vagueness of azimuthal effects, the ground motion recording axes are converted to their principal axes, indirectly introducing the azimuthal influence into the analyses. This thesis suggests a station-specific methodology to refine GMP estimations by isolating regional variations. Evaluation of regression outcomes, distance scalings, and residuals guide the selection of the most appropriate functional forms for the empirical equation. Comparisons of the spatial distribution of peak ground acceleration (PGA) for hypothetical and actual earthquakes serve as the basis for the evaluation of the result consistency. Local variations between GMPEs' estimates and station-specific approximations provide insight into the impact of regional effects on ground motions. The assertion is substantiated by the finding that PGAs calculated from actual earthquake records demonstrate a closer match with station-specific methodology's predictions, especially in regions with observed local differences.
Makine öğrenmesi siniflandirma algoritmalari ile yapay veri seti kullanilarak deprem hasari tahmin modeli geliştirilmesi
Assessing the potential damage to buildings due to a possible earthquake in a region and taking measures, such as strengthening or reconstruction of vulnerable structures, is critically important to minimize social and economic losses that are likely to occur. Evaluating the seismic performance of structures is a comprehensive and time-consuming process. However, using well-trained machine learning prediction models instead of traditional structural performance analyses can significantly reduce computation time. This thesis focuses on developing a damage prediction model using classification-based machine learning algorithms, utilizing a two-dimensional reinforced concrete frame system dataset that represents low to mid-rise, non-ductile buildings. The structural features forming the dataset are obtained from a comprehensive literature review on building stock characteristics in the Marmara region. Nonlinear time-history analyses are conducted using actual earthquake records with the OpenSeesPy framework. The maximum inter-story drift ratio is used as an engineering demand parameter to classify the damage state of buildings. Reliable machine learning models are developed with a balanced dataset. Twenty-four models are created using six variant ground motion intensity measures and four classification algorithms: k-Nearest Neighbors, Support Vector Machine, Decision Tree, and Random Forest. The best-performing model is determined by comparing performance metrics and the confusion matrix. In conclusion, the model developed with a dataset incorporating peak ground velocity and utilizing the Random Forest classification algorithm demonstrates the most effective performance with 92% prediction accuracy.
İstatiksel yöntemlerle gerçek zamanlı yapı sağlığı izleme
The detection of structural damage relies on understanding the long-term variation of modal parameters and their relationship to changes in atmospheric conditions. This thesis aims to address this challenge by developing a real-time algorithm for structural health monitoring systems, which are becoming increasingly important. The algorithm uses statistical models developed by analyzing four years of modal frequencies, damping ratios, and mode shapes of Hagia Sophia, a UNESCO World Heritage structure, and their correlation with atmospheric parameters such as temperature, humidity, and wind speed. The algorithm uses four different regression models to predict the modal frequency as a function of the atmospheric conditions and selects the most suitable one.It then compares the predicted and measured frequencies to identify structural anomalies. The algorithm also employs the Modal Assurance Criterion (MAC), Coordinate Modal Assurance Criterion (COMAC), and Enhanced Coordinate Modal Assurance Criterion (ECOMAC) methods to examine the long-term variation of mode shapes. The algorithm is implemented in a user interface software called "AISHM," which displays the modal parameters and the 3-D animation of the structure in real-time. The software also has the capability to track earthquakes and analyze the structural response in real-time. In summary, this thesis presents a comprehensive approach to real-time structural health monitoring using statistical models and advanced analysis techniques, which can have significant implications for maintaining and preserving historical structures.
Yenilikçi teknikler kullanarak sismik güçlendirme tasarımı: Bir okul binası örneği
Seismic retrofitting plays a critical role in ensuring the safety and resilience of structures in earthquake-prone regions. This study investigates the performance of fluid viscous dampers (FVDs) as an alternative retrofitting technique for improving the seismic performance of buildings. The Büyük Halkalı Primary School Building in Istanbul, originally constructed in 1997 and retrofitted twice using conventional methods (in 2006 and 2019), was selected as a case study. The study aims to propose an innovative retrofitting solution that minimizes construction time, operational disruptions, and associated costs while enhancing seismic resilience. A comparative analysis was conducted between the conventional retrofit approach (reinforced concrete shear walls) and the proposed alternative retrofit solution incorporating FVDs. The evaluation considered seismic performance, cost-effectiveness, serviceability, and architectural impact. Nonlinear time-history analyses were performed using TBDY-2018 and ASCE 41-23 standards, with a particular focus on near-fault effects, including forward directivity effects that were not considered in previous retrofits. The results demonstrated that the incorporation of FVDs significantly improved seismic performance by reducing inter-story drift and structural damage. Furthermore, the alternative retrofit method resulted in shorter construction periods and minimized the necessity for building evacuation, ensuring continuous serviceability. The findings highlight that using FVDs in seismic retrofitting can be a viable solution, particularly for structures requiring uninterrupted functionality during construction, such as school buildings.
Gömülü eklemeli boru hatlarının deprem yer hareketi altında davranışının sayısal modellemesi
Earthquakes severely impact infrastructure, disrupting essential services like water pipelines. Understanding and improving the mechanical behavior of pipelines and their joints under permanent ground deformations is crucial to minimize potential damage and ensure the continuity of their service. In this study, three-dimensional numerical models of buried segmented ductile iron pipes were developed to investigate their nonlinear behavior under lateral strike-slip surface faulting. Fault crossing angle, position, and vector were selected as variable parameters, and pipeline performance was evaluated based on different faulting scenarios and two soil models covering a total of 20 cases. The numerical models were validated using experimental and finite element data from the literature. The results indicate that when the fault crossing angle was perpendicular to the pipeline axis, the system was able to accommodate the most amount of fault displacement. Narrower fault crossing angles induced axial separations or compression to the pipeline. Under compression, the pipeline undergoes joint crushing failure by exceeding the material limits, while tensile forces primarily lead to joint pullout. A joint interlocking phenomenon was observed in tension cases when the fault crossed directly through the joint and effectively delayed or prevented failure by uniting adjacent pipe segments. The results also highlighted the sensitivity of pipeline performance to design criteria, where a 2 cm increase in pullout threshold resulted in up to 20 cm of additional fault displacement capacity. Lastly, the study emphasized that while soil models influenced pipeline response under tension, their effect was limited in compression scenarios due to more premature failure.
Istanbul'da bulunan Ayasofya'nın doğrusal olmayan yapısal modellemesi
Hagia Sophia in Istanbul is one of the most iconic architectural and engineering achievements in history. Constructed in the sixth century, the structure has remained standing for over 1500 years, despite being exposed to numerous destructive earthquakes that caused significant damage, including partial collapses. Its location in a high seismic hazard zone makes the evaluation of its structural performance essential. Since the 1990s, studies on Hagia Sophia have mostly relied on linear analyses and idealized geometries, largely neglecting long-term deformations. This thesis focuses on the evaluation of the level and extent of the present-day deformations on the structure; the creation of a finite element model based on the actual geometry rather than the idealized one; the assessment of the contribution of permanent deformations to the static and dynamic structural response; nonlinear static and dynamic modeling to understand the structure's present and future earthquake behavior; and the assessment of potential collapse mechanisms of the structure. The deformed geometry of the building was obtained using three-dimensional laser scanning and converted into a mesh. A model with ideal geometry was first developed in SAP2000 and then updated to reflect the observed deformations. Both deformed and undeformed models were transferred to ANSYS and subjected to static and dynamic analyses. Real earthquake records were used in the linear dynamic analyses. The nonlinear modeling was carried out using calibrated material definitions based on recordings from the Mw 6.1 Silivri earthquake on April 23, 2025. Additional analyses were performed using both real and synthetic ground motion records. The results were evaluated in terms of structural response and collapse mechanisms, with a particular emphasis on the influence of geometric deformation.
Ground motion prediction equations and spatial correlation model for Istanbul - developed by real and simulated ground motions
Bu çalışmada, İstanbul ve yakın bölgesindeki aletsel gözlemlerden (MW 4.0–6.1) ve büyük bir geniş bant benzetimlerinden oluşan veri setlerinden (MW 6.05–7.6) yararlanarak yer hareketi modelleri geliştirilmiştir. İstanbul ve çevresindeki 170'i aşkın istasyondan elde edilen kayıtlar derlenmiş, ve model geliştirmede kullanılmak üzere işlenmiştir. Benzetim oluşturmada kullanılan stokastik benzetim yaklaşımı, zaman ve frekans alanlarında beş küçük-orta büyüklükte Marmara depremine karşı doğrulanmıştır. Doğrulamanın ardından, kırılma modelleri üzerinde beş tarihsel İstanbul senaryosu (1509 MW 7.6; 1766 MW 7.0–7.1; 1894 MW 6.8–6.9) ve buna ek olarak uyarlanmış 13 diğer senaryo (MW 6.05–7.6) için geniş bant yer hareketleri üretilmiştir. Stokastik benzetimler, mevcut 3-B fizik temelli deterministik benzetimlerle birleştirilmiş ve 0.1–20 Hz aralığı kapsaması sağlanmıştır. Üç adet yer hareketi tahmin deklemi (GMPE) oluşturulmuş ve başarımı ölçülmüştür. Bu kapsamda, (i) İstanbul'da kaydedilen Marmara Denizi depremlerine dayanarak oluşturulan ampirik bir GMPE (MW 4.0–6.1); (ii) aynı gözlemsel veri kümesi üzerinde eğitilmiş ve makine öğrenimiyle zenginleştirilmiş bir GMPE; ve (iii) bölgedeki orta-büyük deprem eksikliğini gidermeyi amaçlayan, yalnızca benzetim verisine dayalı bir GMPE (MW 6.05–7.6) geliştirilmiştir. Bu modellerin tahmin başarımı, literatürde yerleşik GMPE'lerle yapılan nicel karşılaştırmalarla değerlendirilmiştir. Mekânsal korelasyon modeli oluşturmak için rezidüel ampirik yarı varyogramları oluşturulmuş ve üstel modellerle karşılaştırılmış; sonuçlar, belirgin bir spektral periyoda bağımlı korelasyon yapısını ortaya koymuştur. Genel olarak, gözlemler ile fiziksel olarak tutarlı geniş bant benzetimlerin bütünleştirilmesi, gerçek verinin sınırlandığı büyüklük–uzaklık aralıklarında tahmin başarımını artırmakta ve İstanbul ve yakın bölgesindeki mühendislik uygulamaları için bölgeye özgü girdiler sağlamaktadır.
Büyük açıklıklı betonarme yapıların deprem performansının zaman tanım alanında doğrusal olmayan yöntemle belirlenmesi ve viskoz sönümleyiciler ile güçlendirilmesi
Özellikle aktif fay kuşağında yer alan mevcut yapı sistemlerinin deprem performanslarının belirlenmesinde, değerlendirme yöntemlerinin seçimi önemli bir unsur olmaktadır. Yapı sistemlerinin deprem etkisi altında dinamik karakterlerine göre seçilecek olan bu değerlendirme yöntemleri, doğrusal ve doğrusal olmayan yöntemler olarak iki gruba ayrılmaktadır. Bu yöntemler, elastik ve elastoplastik yapısal malzeme davranışlarını esas almaktadır. Malzemenin doğrusal yani elastik olduğu kabulü ile seçilen hesap yöntemleri, belirli bir tasarım depremi etkisi altında taşıyıcı sistem elemanlarının taşıma kapasitelerinin belirlenmesine yönelik yürütülen çalışmalardır. Diğer taraftan malzemenin doğrusal olmadığı yani elastoplastik malzeme davranışlarını esas alan hesap yöntemleri, belirli bir tasarım depremi etkisi altında yapısal malzemelerde oluşacak olan uzama/kısalma taleplerinin belirlenmesine yönelik yürütülen çalışmaları kapsamaktadır. Deprem bölgelerinde yer alan mevcut yapı sistemleri ile ilgili ikinci bir konu, performans değerlendirmeleri sonucunda tespit edilen yapısal yetersizliklerin giderilmesi yani dayanım yetersizliği tespit edilen mevcut yapı sistemleri için uygun güçlendirme yöntemlerinin belirlenmesidir. Son yirmi yıldır yapısal teknoloji uygulamalarının gelişmesiyle birlikte, hem yapı sistemlerinin tasarımında hem de mevcut yapıların sismik güçlendirilmelerine yönelik çalışmalarda, pasif kontrol sistemlerinin kullanımı yaygınlaşmaya başlamıştır. Bu pasif kontrol sistemlerinden viskoz sönümleyiciler, paslanmaz çelikten imal edilen silindirik boru ve bu borunun başlıklarında bulunan paslanmaz çelik pistonlardan oluşmaktadır. Yapı sistemlerinin deprem etkisi altında maruz kaldığı hız istemleri, viskoz sönümleyicilerin her iki ucunda bulunan pistonlarda farklı iki basınç oluşturmaktadır. Sönümleyicilerin her iki ucunda oluşan bu basınç farkı, silikon esaslı yağ sayesinde oluşmakta ve bu fark ısı enerjisine dönüştürülmektedir. Böylece sistemin maruz kaldığı deprem enerjisinin bir kısmı sönümlenebilmektedir. Bu çalışma kapsamında, taşıyıcı sistemi genel olarak perde sistemlerle teşkil edilmiş, birbirlerinden dilatasyon hatlarıyla ayrılmış mevcut betonarme yapı bloklarının ve bu blokların bir bütün olarak uzantısı olan yaklaşık 60 m uzunluğundaki betonarme kabuk sistemin deprem performansı belirlenmiştir. Yapı sisteminin deprem performansının belirlenmesinde, sistemin dinamik özellikleri de göz önüne alınarak, zaman tanım alanında doğrusal olmayan hesap yöntemi kullanılmıştır. Yapı sisteminin sismik performans değerlendirmesinde, ilk olarak taşıyıcı sistem elemanların kesit özelliklerine göre ve yapısal malzemelerin elastoplastik davranış gösterdiği yani malzemelerin doğrusal olmadığı yöntem kullanılarak, taşıyıcı elemanlar için yönetmelikçe öngörülen kesit hasar sınırlarına dayanarak, plastik mafsal tanımları belirlenmiş ve bu mafsallar analiz modellerinde tanımlanmıştır. İkinci aşamada ise, yapı sisteminin dinamik karakterine, bölgenin sismolojik ve geoteknik özelliklerine uygun olarak seçilmiş yer hareketi kayıtları tespit edilmiştir. Seçilen yer hareketi kayıtlarının %5 sönüm oranlı ivme spektrumları çıkarılmış ve bu spektrum eğrileri, yapı sistemi hâkim periyoduna göre belirlenen eşleştirme aralığında, bölgenin depremselliği de göz önüne alınarak yönetmelikçe belirlenen %5 elastik tasarım ivme spektrumuna göre ölçeklendirilmiştir. Seçilen yer hareketi kayıtlarının tasarım ivme spektrumuna göre ölçeklendirilmesi, yönetmelikçe belirtilen şartlar doğrultusunda yapılmıştır. Yapı sistemi üzerinde yürütülen sismik performans değerlendirmesi sonuçları iki ana alt başlıkta özetlenmiştir. • Yapı blokları taşıyıcı sistemleri genel olarak yeterli yanal dayanıma sahip değildir. Blokların perde sistemler ile teşkil edilmesi nedeniyle, özellikle planda kısa doğrultuda teşkil edilen perde sistemler, bu deprem doğrultusunda oluşacak olan taban kesme kuvvetinin %95'ine maruz kalmaktadır. Bu denli yüksek oran, bu perde sistemleri başlıklarında kapasitelerinin üzerinde aşırı çekme-basınç talepleri oluşturmaktadır. Bu istemler, söz konusu perde başlıklarında "GB" performans seviyesinde plastik mafsalların oluşmasına neden olmaktadır. Sonuç olarak özellikle Blok 4 ve Blok 5 yapı sistemlerinde meydana gelen plastik mafsallar, sistemin performans seviyesini "GB" bölgesine düşürmektedir. • Yaklaşık 60 m uzunluğundaki betonarme kabuk sistemin yapı bloklarına bağlantısının mafsallı olması nedeniyle, bu sistemin herhangi bir yatay rijitliği bulunmamaktadır. Bu durum, göz önüne alınan deprem etkileri altında kabuk uç yerdeğiştirmelerinin yüksek mertebelerde seyretmesine neden olmaktadır. Ayrıca kabuk elemanların birbirleri ile bağlantılarının olmaması nedeniyle, bu elemanlar birbirlerinden bağımsız ve yüksek periyotlu salınımlar yapmaktadır. Çalışmanın son bölümünde ise, betonarme kabuk sistemin incelenen deprem etkileri altında yerdeğiştirme istemlerinin azaltılması adına güçlendirme yöntemi üzerinde durulmuştur. Bu yöntemde, kabuk elemanlarının her iki uç noktalarına konsol bir sistem olarak çalışan perde sistemler yerleştirilmiştir. Yerleştirilen konsol perde sistemleri üzerine gelecek olan hız istemlerinin azaltılması adına, bu perde sistemleri ile kenar kabuk elemanların bağlantısı dört adet viskoz sönümleyiciler ile yapılmıştır. Viskoz sönümleyicilerin yerleştirilmesindeki esas amaç, göz önüne alınan deprem etkileri altında kabuk uç sistemi hız istemlerinin azaltılmasıdır. Böylece konsol perde sistemler daha az yanal kuvvete maruz kalacak ve bu elemanlar daha ekonomik boyutlarda tasarlanacaktır. Kullanılan dört adet viskoz sönümleyicilerin dinamik karakterlerini ifade eden matematiksel değişkenler, kabuk sisteminin yanal doğrultudaki hâkim periyodu göz önüne alınarak ve uç sistemde yaklaşık %50 oranında bir sönümün öngörülmesiyle, deneme yanılma yöntemi ile tespit edilmiştir. Kabuk sistemin viskoz sönümleyiciler ile güçlendirilmesi kapsamında son bölümde ise, sistemin göz önüne alınan deprem hareketleri altında enerji talepleri ve kapasiteleri belirlenmiştir. Bu enerji değerlendirmeleri sonuçlarına göre tüm yer hareketi kayıtlarında kabuk sistemin enerji kapasitesi, deprem hareketi enerji taleplerinin üzerinde kalmaktadır.
Riskli yapıların tespit edilmesine ilişkin esaslar ve Türk Deprem Yönetmeliğinin karşılaştırılması
Bu çalışmada Riskli Yapıların Tespit Edilmesine İlişkin Esaslar ile Türk Deprem Yönetmeliği arasındaki uyumu test etmek amacıyla yapı özellikleri ve kat adetleri birbirinden farklılık gösteren 8 adet betonarme çerçeve ve 1 adet betonarme yapı incelenmiştir. Mevcut yapı elemanlarının gerekli hesaplarında TS500 esas alınmıştır. Yapıları aynı şatlar altında incelemek amacıyla tüm yapılar birinci derece deprem bölgesinde ve Z3 türü zemin özelliklerinde analiz edilmiştir. Tüm yapılar için bina önem katsayısı 1.0 alınmıştır. Yapıların beklenen deprem performansları- i) Riskli Yapıların Tespit Edilmesine İlişkin Esaslar kullanılarak, ii) Deprem Yönetmeliği Bölüm 7'de belirtilen doğrusal elastik değerlendirme yöntemi kullanılarak ve iii) Doğrusal elastik olmayan değerlendirme yöntemi kapsamında statik itme analizi yöntemi kullanılarak belirlenmiştir.
Boş ve içi dolu çelik yastıkların çevrimsel davranışı
Cladding panels that are assumed as non-structural parts of pre-cast structures contribute to increase the lateral stiffness of the structure during an earthquake.Testing new practical energy dissipative devices called steel cushions is a part of a research project named SAFECLADDING, that has been initiated with the collaboration of European Union universities such as Politecnico di Milano, University of Ljubljana, National Technical University of Athens and Istanbul Technical University.These steel cushions are being used in different locations of cladding panels such as panel to foundation, panel to panel, panel to frame connections.One of the most important advantages of these steel cushions is that they could stand the damage of earthquake and could be replaced easily without any damage to the main parts of the system such as panels and the frame after every imposed earthquake.These specimens have different kinds such as Empty types with the thicknesses of 3, 5 and 8 mm and Infilled types with different filled resistance materials.The infilled specimens have better energy dissipation capacity than empty ones and because of using resistance material inside the specimen they could better carry the weight of the cladding panels and then it is more practical to use them at panel to foundation connections.In order to check the performance of these Infilled specimens four different filled resistance materials are being used inside these specimens with the names of Cord, FRP, Neoprene and Steel layered.Many uni-axial and multi-axial tests been carried out at the Istanbul Technical University laboratory to obtain the performance of these steel specimens and finally the below results obtained:The amount of degradation in stiffness decreases by using infilled material inside the specimen but the amounts of energy dissipation capacity and also the maximum amount of shear force increases by using infilled material inside the specimen.Furthermore among the infilled specimens the amount of maximum force increases by increasing the amount of compression axial load.
Mevcut betonarme bir binanın deprem yönetmeliği çerçevesinde doğrusal olmayan dinamik analizle performansının belirlenmesi
Türkiye, coğrafi konumu itibariyle deprem kuşağında olan bir ülkedir. Depremler, büyük yıkımlara ve can kayıplarına sebep olmaktadır. Bundan dolayı yapılar, depremin etkin karakteristik özellikleri göz önüne alınarak değerlendirilmelidir. Mevcut binaların deprem etkisindeki performansının belirlenmesi, var olan yapı stoğunun, deprem olduğu zaman nasıl davranacağını bilinmesi açısından çok önemlidir. Performansa dayalı değerlendirme, 2007 yılında yürürlüğe giren Deprem Bölgelerinde Yapılacak Binalar Hakkında Yönetmelik'in (DBYBHY) 7. Bölümünde yer verilmiştir. Bu çalışmada, 1975 tarihli Afet Bölgelerinde Yapılacak Yapılar Hakkında Yönetmelik'e (ABYYHY) göre tasarlanmış beş katlı bir betonarme binanın doğrusal elastik olmayan zaman tanım analizi yöntemi kullanılarak performans durumu değerlendirilmiştir. Ayrıca, yapının göreli kat ötelemesi sınır değerleri ASCE 41- 06'dan alınmıştır. Birinci bölümde, çalışmanın amacı ve kapsamı hakkında bilgi verilmiştir.Konu ile ilgili çalışmalara yer verilmiştir. İkinci bölümde, yapı sistemlerinin doğrusal olmayan davranışı hakkında bilgi verilmiştir. Doğrusal olmayan yapıların hesap yöntemlerine değinilmiştir. Malzeme bakımından doğrusal olmayan betonarme sistemler ile ilgili bilgi verilmiştir. Plastik Mafsal hipotezi ve bu hipotezi esas alan hesap yöntemi açıklanmıştır. Üçüncü bölümde, DBYBHY 7. Bölümde tanımlanan performansa dayalı değerlendirme yöntemi hakkında bilgi verilmiştir. DBYHY'de tanımlanan kesit hasar düzeyleri, performans seviyeleri ve çoklu performans hedefleri özetlenmiştir. Ek olarak, doğrusal elastik olmayan analiz yöntemlerinden olan ve bu çalışmada kullanılan zaman tanım alanında analiz yöntemi açıklanmıştır. Dördüncü bölümde, ABYYHY'ye göre tasarlanmış mevcut bir binanın DBYBHY'de yer alan zaman tanım alanında analiz yöntemiyle çözülmüştür ve bu yapının performansı belirlenmiştir.Son bölümde, sayısal sonuçlar değerlendirilip karışılaştırılmıştır.
Betonarme yüksek bir binanın tasarımı ve çelik bağ kirişlerin yapının sismik performansı üzerindeki etkisi
İstanbul gibi tarih boyunca şiddetli depremlerin yaşandığı kozmopolit bir şehirde yüksek binalara olan rağbet özellikle son yıllarda büyük ölçüde artmıştır. Ülkemizde 2008 yılında İstanbul ilinde yapılacak yüksek binaların depreme dayanıklı olarak tasarlanabilmesi için İstanbul Yüksek Binalar Deprem Yönetmeliği yayımlanmıştır. Sunulan bu tez çalışmasında İstanbul'da yapılması planlanan 45 katlı betonarme yüksek bir binanın tasarımı halen taslak halinde olan İstanbul Yüksek Binalar Deprem Yönetmeliği esas alınarak yapılmıştır. İhtiyaç duyulan noktalarda belirtilerek yabancı kaynaklara da başvurulmuştur. Aynı zamanda binadaki betonarme bağ kiriş elemanları, çelik bağ kiriş elemanlar ile değiştirilerek zaman tanım alanında doğrusal elastik olmayan analiz, PERFORM-3D programı kullanılarak tekrarlanmış ve her iki doğrusal olmayan analiz sonuçları ile binanın sismik performansı değerlendirilmiştir.
Earthquake information system: A crowdsourcing mobile application to inform and gather data
It has been observed that large earthquakes, which have taken place in Turkey and around the world during the last 10 years, could cause great social and economic losses in centers that are densely populated. It is crucial that regions, which had been affected by the earthquake, should be identified fast and in the correct way in order that search, and rescue activities could be carried out effectively. Evaluation of place and level of damage promptly following a destructive earthquake through the data received from emergency intervention systems could facilitate the earthquake emergency response process. In this respect, numerous institutes around the world have introduced on-line earthquake intensity surveys in order to establish internet based macro-seismic maps and hence to determine the regions that are affected by the earthquake the most. The purpose of the surveys is to establish earthquake intensity map immediately after the earthquake by collecting macro-seismic intensity data from the people who feel the earthquake. This project aims to collect this information from the individuals, spread around Turkey, using a mobile application which works both ways: One part of the application gives information about the recent earthquakes, seismicity history of the current location of the user, individual's distance to epicenter etc. The other part of the application lets the user to provide KOERI how he/she felt the earthquake by answering some multiple-choice questions. While answering these questions, the application also records the geographic location of the user. This information is then stored in the central database and can be used for further analysis of the impact of the earthquake and for fine-tuning the instrumental intensity maps.
Development of peak ground acceleration (PGA) based pre-code reinforced concrete frame building fragilities for istanbul
An important portion of pre-code building stock in Istanbul runs significant earthquake risk. Given a building class, the uncontrolled construction of pre-code buildings in the past leads to a considerable model variability and complicates the prediction of losses for future earthquakes in Istanbul. However, the social and economic loss estimations are necessary for Istanbul to have planned actions to improve the earthquake resilience in the city. At this point, fragility curves; which represent the exceedance probability of a particular damage state are one of the most important components of resilience-based building inventory studies for large building stocks at large metropolitan areas. This study aims to provide fragility curves for pre-code reinforced concrete frame residential buildings in Istanbul. For this purpose, 800 mid-rise frame buildings located in the Zeytinburnu district in Istanbul are compiled and 16 representative building models are developed to account for the model variability of the same building class. The examined buildings do not comply with the code requirements of any period after 1975 and they can be considered as low code. The fragilities are based on Peak Ground Acceleration because such practical ground-motion intensity measures are being popularly used in the loss assessment of large building stocks. Nonlinear building responses are derived from three-dimensional nonlinear response history analysis that are carried out by using OpenSees Software (Open System for Earthquake Simulation). Incremental Dynamic Analysis is performed to determine the statistical distribution of the response parameters. A set of real ground motions, which are consistent with the disaggregation results of a probabilistic seismic hazard assessment for Istanbul are considered in the development of fragilities for each building model. Therefore, the variability in building models of the same building class as well as the record-to-record variabilities are considered in the developed fragilities. The fragility model is a backbone cure with upper and lower bounds covering the model and ground-motion variabilities for mid-rise low-code reinforced concrete frame buildings in the investigated building stock.
A comparison and evaluation of different soil-structure-interaction approaches for bridges
During the last fifty years, bridge construction has increased extensively throughout the world, including on areas with bad soil conditions, to meet the transportation needs of expanding urban areas. Although Soil-Structure-Interaction (SSI) procedures for performance-based design of buildings have been introduced in design guidelines, seismic provisions are not clearly stated for bridges. There are two main approaches to include SSI in performance-based design of the bridges; direct method and substructure method. In the direct method, bridge and soil systems are analyzed as a single system under seismic shaking, defined at bedrock. As an alternative, the substructure method is introduced to solve the system as substructures in two stages, called kinematic interaction and inertial interaction. The nonlinear response of piled foundation systems of bridges are subjected to kinematic interaction; whereas, the nonlinear response of superstructure is subjected to inertial interaction. In this study, first, he linear design of two different bridges are introduced by considering their geometry and the number of spans. Bridge-I has three spans with uneven pier heights, and Bridge-II has four spans with identical piers and the geometry. Both bridges are designed based on a response spectrum created according to site response analysis and used in the performance-based design of the bridges. 19 different records are selected and scaled according to the criteria given in AASHTO LRFD Bridge Design Specifications Article 4.7.4.3.4 (AASHTO, 2012) Seismic Design Guidelines. Seismic records are categorized with respect to soil parameters, chosen for both strength-based and performance-based design of bridges. Secondly, using the direct method, the Nonlinear Time History (NTH) analyses are performed for both bridges to investigate the behavior of structural elements. The nonlinear responses of the bridges are re-calculated by using the substructure method, including the kinematic and inertial interactions. Responses of the structural elements are combined according to commonly-used combination rules. Finally, results of these methods are compared with each other, as well as the linear response of the structures, to underline how the behavior of the structures vary according to different analysis methods.
Development of fragility functions for code conforming low-rise reinforced concrete buildings
In this study, fragility functions are developed and compared for low-rise (2 and 3-story), reinforced concrete (RC), moment-resisting frame (MRF) buildings, which are designed per the Turkish Seismic Codes (TSC) released in 1998 and 2018, at eight different locations in Istanbul, Turkey. In the preliminary design of each building, the minimum conditions defined in the corresponding seismic code are followed. Moreover, the capacity design principles are taken into consideration as defined in the seismic codes. To increase the representativeness of the dimensions (i.e., footprint, structural member dimensions, story height) of the buildings, the past studies about the characteristics of the low-rise buildings in Turkey, and the structural drawings belonging to the existing buildings designed per the corresponding seismic codes are examined and used. Considering eight different locations, two different story numbers, and two seismic codes, a total of 32 buildings are designed and analyzed. The nonlinear analyses of the buildings are conducted by using the OpenSees Software (Open System for Earthquake Engineering Simulation Pacific Engineering Research (PEER) Center Version 3.0.3). The structural elements (beams and columns) are modeled with frame elements. The distributed plasticity (fiber) is considered for the columns whereas lumped plasticity (plastic hinge) is considered for beams. To generate the fragility functions for the buildings, multiple stripe analysis (MSA) together with the maximum likelihood estimation (MLE) method is utilized. Spectral displacement (Sd) and spectral acceleration (Sa) are selected as the intensity measure (IM) parameters whereas the maximum inter-story drift ratio (MIDR) and top displacement (Dtop) are used as engineering demand parameters (EDP). The fragility functions are developed for four damage states which are slight damage, moderate damage, extensive damage, and complete damage. While deciding the limit values of the EDPs for each damage state, we perform pushover analysis to decide the limit values of top displacements from the idealized pushover curves. With regards to the limit values of MIDR, they are taken from Hazus MR4 Technical Manuel, which is defined for low-rise, high-code MRF structures. For MSA, eleven intensity measure levels (stripes) are defined, and for each stripe, 22 pairs of ground motion records are selected and used. To select the ground motion records for each stripe, a code-based target response spectrum is developed for each IM level. By making use of the developed response spectra for each IM, 22 pairs of ground motion records are selected from PEER Ground Motion Database for each IM level (stripe). The fragility functions based on the different types of IMs (Sa and Sd) and the different types of EDPs (MIDR and Dtop) are developed and compared for the 2 and 3-story low-rise RC buildings designed per TSC1998 and TSC2018.
İstanbul'da yer alan ve yönetmeliklere uymayan orta katlı betonarme çerçeve binaların maksimum yer hızına bağlı kırılganlıkları
16 building models representing a building stock in the Zeytinburnu District in İstanbul that includes approximately 800 mid-rise reinforced concrete (RC) frame buildings are used to develop PGV based fragility models that could partially represent the no-code building vulnerability in Turkey. The 3-D analytical models of the subject frames are modeled with distributed plasticity using the Open System for Earthquake Engineering Simulation (OpenSees) software. The damage states of the fragilities are determined by use of the performance limits of structural members from 2018 version of the Turkish Building Earthquake Code and 2005 version of the Eurocode 8. Peak ground velocity (PGV) is preferred as seismic intensity measure since it has a better correlation with deformation demands. 25 real ground motion pairs are selected using disaggregation results of three different PGV hazard curves determined from three ground motion predictive models that are used in the development of the most recent national seismic hazard maps. Response statistics are kept through incremental dynamic analysis (IDA) to develop fragilities for each model. The fragilities computed from above comprehensive nonlinear response history analyses advocate that consideration of variabilities in (a) structural models, (b) ground motion records and (c) limit states makes a huge impact in the exceedance probabilities of damage states. Therefore, a backbone fragility model, which covers the above uncertainties by up and down scaling of a central model is a must in proper loss assessment of building stocks.
Comparative evaluation of codes and regulations in turkey for earthquake performance assessment of existing buildings
New Turkish Building Seismic Code published in 2018 has been officially in force since January 1, 2019. The new code introduces significant changes not only in the countrywide seismic hazard maps but also in structural modeling and analysis issues for the design of new buildings as well as in the definition of performance objectives and assessment methodologies for existing buildings. In this study, a comparative earthquake performance assessment of a reinforced concrete building in Istanbul is presented. The building, which was constructed in 2006, has four stories rising above a basement floor. The lateral load-carrying system consists of moment-resisting frames with two shear walls around the staircase. Although it is assumed that the building was designed according to the provisions of the Turkish Building Seismic Code-1998, it was identified as a risky building last year based on the simplified guidelines by the Ministry of Environment and Urbanization (Riskli Yapıların Tespit Edilmesine İlişkin Esaslar-2013). Earthquake performance of the study building is evaluated for the requirements of the new Turkish Building Seismic Code (2018) and of its previous version (2007) as well. For this purpose, a three-dimensional finite element model of the building is elaborated on the basis of the blueprints. Geometrical and material characteristics are further verified by the reports on in situ measurements and field tests. Linear and nonlinear static and dynamic analyses procedures are implemented, and a detailed assessment of the building against the performance criteria by each code is performed. Additionally, the building is assessed on the basis of the updated guidelines by the Ministry of Environment and Urbanization (Riskli Yapıların Tespit Edilmesine İlişkin Esaslar-2019). Outcomes of the earthquake performance assessments are presented comparatively, and the differences/changes among the codes and guidelines are highlighted.
Response analysis and damage mitigation of buried continuous pipes subjected to faulting actions
Buried continuous steel pipelines are critical lifelines failure of which under fault rupture incidents may lead to significant and deteriorating environmental and socio-economic outcomes. Proper understanding and estimation of the mechanical behavior of buried steel pipes under such geohazards and investigation of means of mitigating these deleterious effects is of paramount importance. This thesis aimed at developing rigorous and simplified numerical models of the problem to realistically simulate the behavior of buried continuous pipes under strike-slip fault rupture-induced permeant ground deformations. The response of buried pipe cases under the fault load was investigated with respect to the variation of fault crossing angle (β) and pipe wall thickness (t). The second phase of this dissertation involved the investigation of the effect of four mitigation techniques to protect the buried pipe against fault rupture-induced damages. Lastly, a case study involving the evaluation of the effect of using CFRP wraps on the response of Thames Water Pipe which suffered great damage during the devastating 1999 Izmit is presented. The outcomes of this thesis indicate that the performance of the pipeline is sensitive to the variation of fault crossing angle and pipe wall thickness, increasing both parameters lead to overall improved pipe performance. Results indicate that all mitigation approaches offer certain degrees of improvement, where most effective mitigation approach is the wrapping of the pipeline surface with CFRP wraps while the use of controlled-low strength material was the least effective approach. Comparison of simplified and rigorous numerical models revealed that a good agreement exist between the approaches. Lastly, evaluation of the response of Thames Water Pipe protected using CFRP indicates that despite the considerable reduction in stresses and strains complete avoidance of failure for this particular case does not seem to be attainable.
Effects of site improvement technique on seismic performance of geotechnical structures
Earth-retaining structures are widely used in the man-made environment and compose the significant constituents of infrastructural systems worldwide. Besides, they have been constructed broadly in seismically active regions. Earthquakes can cause a lot of damage to geotechnical structures. The prevention of failures in these structures is an important issue. Cost-effective remedies can be applied to retaining structures in order to prevent them from failing under seismic loading. The use of lightweight materials behind the wall as a cushion layer is one of the methods to improve the seismic performance of the retaining system. The objective of this thesis is to investigate the effects of cushion type on the seismic performance of retaining walls by performing shake table tests. The experiments were carried out with a 1/25 scaled retaining wall model with or without a cushion layer. In the experimental study, the cushions were considered as EPS geofoam and a mixture of tire crumb and sand. Additionally, various parameters, such as cushion thicknesses, EPS geofoam densities, mixture ratios of sand-tire crumb mixture, and input characteristics, are also evaluated. The results were examined by comparing the cases having a cushion layer with the case without a cushion layer depending on mentioned parameters. The evaluation of the results indicates that the seismic performance of the retaining wall is very sensitive to cushion type. It is observed that the EPS cushions are more effective than the sand-tire crumb mixtures to improve the seismic performance of the wall. Additionally, the use of cushion layer with higher thickness can be an effective solution to improve the seismic performance of the retaining wall, prevent the future failure of the retaining structure, and mitigate earthquake hazards.
Consideration of structural ageing in the development of analytical fragility functions
This study investigates the ageing effects led by the corrosion of structural materials on the fragility functions analytically derived for reinforced concrete moment-resisting frame type buildings which is the predominant typology in Türkiye. First, in situ and laboratory material testing results for 175 reinforced concrete buildings located in Istanbul, constructed between 1962 and 2004 with different heights and plan features are examined in order to better understand the level of corrosion and its spread in structural members. The level of corrosion and different ways it occurs is then implemented in structural analyses by altering the mechanical properties and constitutive models of materials with the data obtained from the experimental and numerical results in the literature. For this purpose, three-dimensional finite element models for low- and mid-rise buildings designed in accordance with the provisions of the 1975, 1997 and 2018 Turkish earthquake codes are elaborated. The responses of pristine and aged buildings are studied through nonlinear dynamic analyses under strong ground motion acceleration recordings selected and scaled to represent the level of seismic hazard in Istanbul. Multiple-stripe analysis and maximum likelihood method are implemented for the derivation of fragility functions. The results show that the behavior of structures aged by the effects of corrosion is a significant reduction in structural capacity and thus yields higher damage probability estimates by the derived fragility curves.
24 Ocak 2020 Elazığ-Sivrice depremi stokastik simülasyonu
This thesis focuses on the application of stochastic ground motion simulation methodology to the 24 January 2020 Mw 6.8 Elazığ-Sivrice earthquake, which occurred on the Pütürge segment of the East Anatolian Fault in Turkey. In this context, the dynamic corner frequency-based stochastic finite fault method was used to simulate the ground motion fields generated by the 24 January 2020 Elazığ-Sivrice earthquake earthquake. Input parameters for the simulations are derived from regional sources and seismic parameters to ensure the reliable production of synthetic ground motions. The model parameters are evaluated by comparing the real records of the Elazığ-Sivrice earthquake with synthetic records and preferred models are selected accordingly. Moreover, the synthetic records have been compared with regionally suitable ground motion models (GMMs). The stochastic ground motion simulation methodology is used together with the extended fault model, evaluating both random and earthquake specific slip distribution options. Alternative models or values are considered for the stress drop, geometric spreading, Q and duration models as well as for site amplification. A combination of models that yield the lowest error terms both in frequency and time domain parameters is proposed as the preferred model for this study. As a result of this study, it is seen that the simulations of the Elazığ-Sivrice (Mw 6.8) event give reasonable results for frequency ranges higher than 1 Hz and the determined parameters can be further developed and used as input to other studies evaluating seismic hazards in related regions.
Development of empirical fragility functions after the 2020 earthquakes in and around Türkiye
In 2020, two major earthquakes occurred that caused life losses and severe damages to the built environment in Türkiye: On January 24 an earthquake of moment magnitude 6.8 in the East Anatolian Fault Zone nearby Elazığ (Sivrice) province and, an earthquake of moment magnitude 6.6 on the North Samos Fault in the Aegean Sea offshore Izmir (Seferihisar) province on October 30. Immediately following these devastating ground shakings, the Turkish Ministry of Environment, Urbanization and Climate Change conducted large-scale and detailed post-earthquake damage surveys in both regions. The observational damage data collected by the technical staff of the Ministry consisted of 92,800 structures in Elazığ and 213,776 structures in Izmir. This thesis aims to construct comprehensive empirical fragility functions from these two damage datasets by employing statistical methods. In order to examine the uncertainties, fragility curves are produced using different ground motion models and local soil information from different sources, and to consider these effects a ground motion model using a logic tree approach is proposed. Fragility curves for reinforced concrete moment-resisting frame type structures and unreinforced masonry structures, which are the predominant typologies in Türkiye, are proposed with their confidence intervals. Comparisons with the fragility functions for similar structures available in the literature are provided.
Epistemic uncertainties in probabilistic earthquake hazard models and their effects on the results: The case of Marmara Region
Throughout the history and also in the not too distant past, Marmara region has been a center that hosted several of the most destructive earthquakes around the World. Considering the density of population and building stock and the concentration of economic activities, the performance of comprehensive earthquake hazard assessment studies is one of the essential steps towards the mitigation of the seismic risk in the Marmara region. The seismicity and the earthquake characteristics of this region have been studied extensively in the last decades, and various hazard maps have been created. In the light of the increasing amount and quality of data and new studies on seismotectonic and the developments in the earthquake hazard calculation methods, the need for a regular updating of the earthquake hazard estimates for regions with high seismic activity arises. Therefore, new earthquake hazard maps for specific regions or regions covering many countries are being generated continually. In today's practice, the use of the probabilistic earthquake hazard assessment method has become a common implementation in the preparation of earthquake hazard maps. However, as opposed to site-specific assessments, large scale regional studies usually investigate the effects of epistemic uncertainties only in a limited way, and in most cases, only the mean hazard outputs are reported. Nonetheless, analysis of epistemic uncertainties in the hazard assessment and reporting of the uncertainty ranges associated with the ground motion estimations can provide valuable insights towards a better understanding of the seismic hazard and consequently of the seismic risk. Starting from this point of view, developing an earthquake hazard assessment model specific to the Marmara region, dealing specifically with the uncertainties associated with the modelling approaches, is quite meaningful when the earthquake history of the region is also considered. In this thesis, in order to examine the effects of uncertainties on probabilistic earthquake hazard analysis results specific to the Marmara region, the Turkish Seismic Hazard Map developed within the scope of the "Update of seismic hazard maps of Turkey (UDAP-Ç-13-06)" project was evaluated. Alternative models were included in the earthquake hazard calculations by obtaining uncertainties related to the data and modelling parameters and combining them in a logic tree structure. Accordingly, hazard maps are obtained for PGA and 5 % damped Spectral Accelerations at T = 0.2 s and 1.0 s for 475 and 2475 years return periods, and uncertainty ranges for the computed ground motion parameters are presented. The sensitivity of the results to the uncertainties associated with different modelling parameters is investigated. The results indicate that, even for the Marmara region, which is one of the best-studied regions in terms of seismic activity and geological structure, the seismic hazard models can be associated with large uncertainties.
Improvement of seismic behaviour of retaining walls by usingcushions
Damages and collapses of retaining walls that occur after earthquakes cause loss of life and property and huge economic losses. The use of lightweight material as a cushion behind the retaining wall is one of the improvement methods. The main aim of this thesis is to evaluate the effectiveness and efficiency of a new proposed cushion layer as EPS beads and sand mixture (EPSB) for retaining structures. This cushion material placed behind the retaining wall was used for the first time in the literature. The effects of the mixture ratio and thickness of the EPSB cushion layer under different input motions were investigated. The other cushion layers as EPS geofoam and tire waste and sand mixture (TW) were also used. The performances of three cushion materials were compared with each other under the same input motions. In the experiments, a 1/15 scaled retaining wall model was designed to investigate the effectiveness of the cushion materials on the seismic performance of the retaining wall. Firstly, the experiments for the retaining wall model without cushion material were carried out on the shake table in the laminar box. In the second part, three different types of cushion materials were placed behind the retaining wall by changing thickness, density, and mixture ratios. EPS geofoam was found to provide the highest improvement performance compared to the TW and the EPSB cushions. Evaluation of the test results showed that the cushion type is significantly effective in improving the retaining wall model. Additionally, changes in thickness, density/mixing ratio, and input motions affect the results.
A study on fling steps in the turkish strong ground motion dataset
In this study, the existing methodologies on fling step calculation from strong ground motions have been investigated and improvements on the most recent data processing scheme eBASCO (Schiappapietra et al., 2021) have been proposed. Capability of the proposed scheme is verified through comparison of permanent displacements that obtained on the processed records and those derived from the co-located GPS data both from Türkiye and worldwide earthquakes. For the first time, Türkiye permanent displacement inventory is created through processing both horizontal and vertical components of the Turkish strong motion dataset. For this purpose, 288 recordings (Rjb ≤ 50 km) of 20 shallow crustal earthquakes (Mw ≥ 6) occurred between 1983-2023 are utilized. In addition, 36 recordings of the 2023 Kahramanmaraş (Mw 7.7) earthquake are also processed and included in this thesis. Performance of evaluation of two global prediction models for fling amplitudes (Kamai et al. (2014) and Burks and Baker (2016)) are performed using Turkish permanent displacement inventory. Then, fling step prediction model of Burks and Baker (2016) is adjusted and the Türkiye-adjusted equation has been further compared with the recordings of the 6 February 2023 Kahramanmaraş (Mw 7.7) earthquake. Lastly, the permanent displacements in vertical components from Turkish strong motion database and NESS 2.0 database are inspected. Performance of the Kamai et al. (2014) prediction equation for this component is evaluated through residual analyses. In addition, based on the empirical dataset, a new predictive model for this component is proposed. This study will contribute to both seismic design of new structures and more accurate evaluation of existing structures in the vicinity of faults. The presented inventory will greatly help to identify the fling- containing ground motion records to be used in the seismic design of the structures through selecting and scaling procedures. Furthermore, the presented fling inventory will augment to fling values of normal and strike-slip earthquakes in the worldwide fling database by 22% and 33%, respectively.
Mitigation of earthquake hazards of medium-rise buildings by using different soil improvement methods
Earthquakes can be hazardous to occupants and their assets, especially in some regions such as Turkey, Japan, Chile, and the United States of America etc. Nowadays, some regulations were published to mitigate the hazards occurring in buildings during earthquakes. Besides, the hazards can be mitigated by making use of different soil improvement methods such as Geotechnical Seismic Isolation (GSI) Systems which earthquake loads transferred from ground to structure are decreased using geotechnical materials. Gravel and Gravel-Rubber Mixtures (GRM) can be alternative materials for the GSI system because they provide more bearing capacity, less earthquake-induced settlements and high permeability. The aim of this thesis is to evaluate the effectiveness of the proposed Gravel and Gravel Rubber Mixtures (GRM) materials on the seismic performance of low-to medium-rise buildings by means of 1/10 scaled 3 and 5-story building models by shaking table tests. The shaking table experiments were conducted by considering different rubber content, thickness of GSI and the number of stories under various seismic motions. Within the scope of this thesis, all improved cases were compared with unimproved cases. This study showed that surrounding building foundations with Gravel or Gravel Mixtures plays a key and favorable role in the mitigation of earthquake hazards by dissipating earthquake energy inside the soil.
Effectiveness of foundation reinforcement on seismic performance of retaining walls
Soil reinforcement is a widely studied improvement method to improve the strength and stiffness of the soil. The primary goals of soil reinforcement are to increase the bearing capacity and decrease the settlement of the soil along with improving the strength of the soil. Geosynthetic soil reinforcement is founded on the idea of taking advantage of the characteristics of geosynthetic materials like the tensile strength of geosynthetic materials, the pressure distribution potential of geosynthetic materials, and the interlocking mechanism between soil and geosynthetic materials. Many studies in the literature focus on using geosynthetic materials in slopes, embankments, or soil foundations below footings. However, there is not any study focusing on the use of geosynthetic reinforcement under retaining walls. This study aims to investigate the effectiveness of geogrid-reinforcement on the seismic performance of the retaining walls under different earthquake motions by shaking table tests. The effects of the length of reinforcement (L) and the number of reinforcement layers (N) on the seismic performance of the retaining walls constructed on geogrid reinforced sand under the different earthquake motions were investigated.
Eskişehir havzasında yer hareketinin nümerik modellenmesi
Eskişehir basin is located at the boundary of central and western Anatolia tectonic regions. Between two active faults it extends in EW direction with two open ends. So far deep velocity structure of the basin has not been well constrained however, average shear wave velocity for the top 30 m and sedimentary thickness estimations are available at various locations of the basin (e.g., Tün et al. (2016); Yamanaka et al. (2018); Özel et al. (2022). Number of strong motion recordings is rather limited due low seismicity of the region. The largest magnitude event that has ever been recorded within 150 km is the 2011 Simav Earthquake (Mw 5.9). Eskişehir city, with a population close to a million people, has been expanding towards to this sedimentary basin. Long period ground motion is the concern of large scale structures that will be built at this region. Here we first present observed features of strong ground motions of this event recorded in the Eskişehir basin. Firstly, we observed that ground motion from the 19.05.2020 Mw 5.9 earthquake is governed by Rayleigh waves at periods longer than 0.5 s. Retrograde motion is visible almost at all basin-recordings. Among recorded waveforms, PGA and PGV of a basin-edge station (#2610 AFAD station) are formed by Rayleigh waves at periods 1 s. The longest significant duration of recordings is as high as 53 sec. Recorded spectral acceleration for 5% damping at spectral periods longer than 1 s is much higher than the one predicted by region specific ground motion prediction models. In the second phase, we showed formation of an experimental basin geometry utilizing linear interpolation of predominant frequencies at 95 measurement points. Dimensions of the model are 43 km \ 27 km \ 15 km. Basin layer continues across the entire model in EW direction, but bordered by northern and southern hills to mimic the geographical environment. Maximum depth is about 600 m. In the last phase we investigated the 3D wave propagation of small magnitude events, 17.01.2015 Mw 4.3 and 18.09.2015 Mw 3.7, occurred at northwestern part of the region and center of the basin, and compared with observed recordings for a possible validation of the velocity model. The computer code utilized in simulation relies on a finite difference modelling using staggered grids with nonuniform spacing. Ground motion simulation of the Mw 4.3 event reveals that the current velocity model overestimates the velocities in the eastern part of the basin in the NS direction, where E-W direction synthetics are generally smaller than the observed ones. On the other hand, synthetic velocities agree with observed ones at basin-center stations in the west. These findings suggest that more careful definitions of basin boundaries are necessary for the future models. Comparison of 1D and 3D simulation results also suggest that a 3D velocity model may produce longer and -more realistic- duration ground motions. The final step is to perform a blind simulation for the 20 February 1956 Mw 6.5 earthquake. The source was modeled by considering the ambiguities in the source parameters. The previous research was compiled to deal with unknown information about the mechanism and location of this event for consensus. We have compared the simulation outcomes with GMPEs models. The numerical simulation results yielded higher outcomes than estimated spectral ordinates by GMMs.
Earthquake early warning applications using downhole arrays in Istanbul
The Kocaeli (Mw 7.5) and Düzce (Mw 7.2) earthquakes that occurred in 1999 revealed the fact that the earthquakes in Marmara Region should be considered especially in terms of the damage that may result in Istanbul. An Emergency Response and Early Warning System was established to reduce possible losses after a damaging earthquake in Istanbul and to produce Rapid Loss Maps to assist rescue teams with emergency response. The main element of the Earthquake Early Warning is the rapid and reliable estimation of the magnitude of the earthquake. In order to calculate the magnitude of the earthquake, it is necessary to determine whether the earthquake fracture will continue or not. This is generally understood from the characteristics of the initial movement (P waves). For this purpose, the characteristics of P waves have been determined by using the τc - Pd method and the waveforms of earthquakes recorded by the vertical component acceleration sensors located on the bottom of the wells and on the surface. Most of the downhole array data is from ATK station. The surface records used are from the early warning stations operated by KOERI and the strong motion network operated by AFAD. As a result, two models have been developed to predict the magnitude of an impending large earthquake and the peak ground velocity (PGV) amplitudes associated with it. A verification process of the models has been applied to predict the moment magnitude of September 26, 2019 Mw=5.7 offshore Silivri earthquake. The models developed from the ATK downhole array predicted the size of the earthquake as Mw=5.8 within 7 seconds of the origin time which in turn yield about 15 seconds early warning time for most of the Istanbul Metropolitan area. The models developed using waveforms recorded at surface have predicted the size of the earthquake as Mw=6.1 which is comparable to the Mw=6.0 prediction of Wu and Kanamori (2005) model. The size and amplitude of the prediction models obtained in this study have been considerably improved compared to the models published a decade ago.
Experimental study on effects of geogrid reinforced zone on seismic performance of low-to-medium rise buildings
This study aims to investigate the effectiveness and reliability of geogrids as a soil reinforcing system. In order to prevent or minimize the earthquake impact on structures, this study focuses on reducing the effect of earthquake loads by creating the geogrid reinforced zones. This system is composed of various layers of geogrid configurations to be able to create a reinforced geogrid foundation under the structure. To present reliable results through observing the soil-structure interaction and structural behaviour and digital comparisons via data outputs; an experimental setup was established. With this purpose in mind, the seismic behavior of the two 1:10 scaled structure models without and with the different geogrid reinforcement configurations under different earthquake conditions were studied. A series of shaking table tests were performed to evaluate the seismic response of the building models depending on the selected performance criteria. The effects of geogrid reinforced zone which is dependent on the number of geogrid layers on the seismic behaviour of the low-rise and medium rise buildings were discussed with comparing test results of the unreinforced and reinforced cases. Comparison results of the tests revealed that the inclusion of the geogrid reinforcement to the sand can reduce earthquake impacts by decreasing the transmitted seismic energy from soil to structure via the interlocking mechanism between geogrid layers and soil. Significant improvements in reducing forces of strong ground motions are able to make geogrid reinforced soil systems an option to improve seismic performance of the structures.
A parametric study for the characterization of site amplification
In earthquake engineering, the approximation of site amplification by using practical ways has been an important issue. Various site parameters were proposed and applied in the engineering practice. Among these, time averaged shear wave velocity for the top 30 m, Vs30, and fundamental frequency, f0, have been used widely. In this study, we investigated the reliability of Vs30 parameter, and the performance of alternative time averaged shear wave velocities (e.g., Vs40, Vs50, etc.) and shear wave travel times (Ttz) at various depths for the estimation of site amplification. For the same bedrock depth, we considered 17 shear wave velocity profiles, changing from convex (i.e., the velocities changing faster near the surface and slower near the bedrock) to concave (i.e., the velocities changing slower near the surface and faster near the bedrock). We divided the soil media, first into layers with equal thickness, and then into layers with equal wave travel times. For each layering type and soil profile, we calculated the site amplification factors and fundamental frequencies, and studied their correlations with time averaged shear wave velocities (Vsz) and wave travel times (Ttz) for different depths, z. We have also investigated the correlation of site amplification factors, surface PGAs (Peak Ground Accelerations), and fundamental soil frequencies (f0) for each case. We have identified the optimal averaging depths for the averaged shear wave velocity and the wave travel time to characterize site amplification. The study showed that there is a sharp change in the correlations when switching from convex to concave profiles. By gradually increasing the bedrock acceleration levels, we have also studied the nonlinear soil response and its correlations with linear soil response. We presented guidelines to estimate nonlinear soil amplification factors and fundamental frequency from the linear ones. Considering that the linear fundamental frequency and amplification can easily be calculated from field tests (e.g., ambient noise measurements for f0 detection), these guidelines provide a useful tool to estimate nonlinear ones.
An evaluation of the behaviour of rc bridge piers under vertical and horizontal components of earthquake ground motion
Reinforced concrete (RC) bridges with single piers have been used extensively in Turkish highways. During the past earthquakes in Japan, USA and New Zealand extensive damages occurred in the single piers indicates the inadequacy of seismic design. In the design of the concrete bridge piers, generally horizontal earthquake forces are taken into consideration. An additional P-∆ effect occurs when the horizontal earthquake effect and the vertical earthquake effect act together on the bridge piers with a large beam cantilever width. The effect of additional P-∆ effect under the effect of vertical earthquake may increase the bending moment and shear forces values in the columns and the piers supporting the bridge may experience damage. Another circumstance encountered in large-scale projects is the use of filler material as a dump / storage area under bridge piers. This causes a certain part of the bridge pier heights to remain under the soil filling material and shortens the free pier height. For a single column pier of a conventional bridge maximum moment and shear values occur at the bottom of the column under seismic forces. This region where the maximum stress occurs is designed to be the plastic hinge region of the column. Maximum shear and longitudinal reinforcement used in the plastic hinge region to provide the conditions is stated in the regulations. When the part of the column is buried under the soil, maximum moment and shear force values of the bridge columns may not occur at the bottom of the column but at the upper end of the buried height. Therefore, the critical section of the column will be above the bottom of the column which was not considered in the seismic design. The amount of longitudinal and shear reinforcement may also be inadequate than the required reinforcement to resist the seismic forces which may cause the flexural and shear failure. In this study, a single 30 m-tall RC pier of a conventional bridge is examined under horizontal and vertical components of three separate earthquake records for three different deck to pier flexural stiffness ratios. Conventional bridges are constructed with movement joints and connections. The pier has a monolithic 15m-wide cap beam. The height of the cap beam is increased to provide different flexural stiffness ratios between column and cap beam. As the flexural stiffness of the cap beam is increased, the change in the column shear force and moment due to additional P-Δ effect of vertical component of earthquake is investigated. As a result, only the horizontal impact of the earthquake and the effect of both horizontal and vertical earthquakes are compared for the column forces. Secondly, the single pier of the conventional bridge with the same geometric properties is investigated for the cases that it is buried under 5 m, 10 m and 15 m of earth fill. The horizontal components of the same earthquake records are used in the analysis. Force-deformation relation of the soil is represented by non-linear p-y springs for the buried cases.
İstanbul Sapphire binasının dinamik davranış özelliklerinin deprem ve rüzgar verileri ile belirlenmesi
The number of tall buildings has been increasing all around the world due to the current population growth and limited space in city centers. After major earthquakes, countries located in earthquake-prone areas face catastrophic conditions. In addition to building damages, deaths, and injuries, financial losses due to business interruption are also an important part of overall earthquake losses. Therefore, buildings home to organizations such as financial institutions, health care facilities, governmental buildings need to remain functional following an earthquake to constrain financial losses and secure public services. The condition of structures can be estimated by evaluating the change in the in-situ dynamic characteristics of the structures in real time day by day. In this study, the dynamic parameters of the Sapphire Building during strong wind and earthquake records are estimated in the time and frequency domain. Earthquake and wind events were selected from catalogs derived from Bogazici University Kandilli Observatory and Earthquake Research Institute Regional Earthquake-Tsunami Monitoring Center and Bogazici University Kandilli Observatory and Earthquake Research Institute Meteorology Laboratory. In time domain analyses, correlations between peak accelerations, velocities, displacements; and magnitude and distance are estimated. The effects of faraway earthquakes on displacement time histories and damping are also investigated. Average drift ratios, computed from both wind and earthquake records, are compared with the limitations provided in the codes. In the frequency domain, natural frequencies, damping, and mode shapes are identified by means of spectral analysis for wind and earthquake data. The result of wind and earthquake events on the Sapphire building are compared.
Estimation of member forces in Fatih Sultan Mehmet (FSM) Suspension Bridge from ambient vibration records
Suspension bridges are critical lifeline structures in transportation systems. Most suspension bridges, built in recent years, have monitoring systems to identify and track any changes in their dynamic characteristics. Such systems are useful for reducing the cost of maintenance during the life of the bridge, as well as assessing the structural safety for any extreme loading condition, such as those induced by large earthquakes and strong winds. The standard approach for analyzing data from the monitoring systems in suspension bridges has been modal analysis, where the dynamic response is approximated as the sum of modal responses, each defined by its modal frequency, damping ratio and the mode shape, which are identified from vibration records. Theoretically, modal analysis is appropriate for linear structures with mass and/or stiffness proportional viscous damping. Modal analysis is not appropriate for suspension bridges for several reasons. The dynamic behavior of a typical suspension bridge is not linear. Their size and flexibility make them geometrically nonlinear. In addition, their mass is not constant. They have time-varying mass due to moving traffic loads, which can be a significant portion of total mass in modern suspension bridges with lightweight steel decks. Also, all vibration records from suspension bridges show that damping identified, does not satisfy the requirements of classical modal damping (i.e., mass and/or stiffness proportional), and it is not a viscous type. Therefore, alternative methods for the analysis of vibration data from suspension bridges are needed. This study presents an alternative method for system identification of suspension bridges from their vibration records. Instead of identifying the modal properties of the bridge, the method aims to identify the forces in the principal bridge elements (i.e., main suspension, back-stay and hanger cables and towers). Based on some simplifying assumptions, this study first develops the equations that relate the element forces to the fundamental frequency of that element. The fundamental frequencies of the elements are identified from the ambient vibration records taken on the element. Using the equations developed, the forces in each element are calculated, and crosscheck to confirm that they satisfy the boundary conditions at element junctions. The methodology is tested by using the vibration records from one of the suspension bridges in Istanbul. Currently, Istanbul has three suspension bridges over the Bosphorus, and all installed with real-time monitoring systems. These bridges connect Asian and European parts of Istanbul, and are the critical lifelines for the city. The bridge used for the test is the second Bosphorus Bridge, known as the Fatih Sultan Mehmet (FSM) Bridge, which is between the first and the third suspension bridges on the Bosphorus with a daily traffic load of approximately 200,000 vehicles. The bridge is being monitored with a real-time Structural Health Monitoring (SHM) system composed of 44 channels of acceleration sensors. The forces in the members of the bridge are calculated by the methodology presented in this study. The results are compared to those from previous investigations (e.g., field tests, analytical models and design calculations), and are found to be consistent. The study shows that the fundamental frequencies of members identified from ambient vibration records provide a simple means to estimate the forces in the elements of suspension bridges.