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Yapı hasarlarının zemin oturması ile ilişkisi ve risk analizi

The relationship of structural damages with ground settlement and risk analysis

  1. Tez No: 960834
  2. Yazar: EKİN EVRİM LAÇİN AKŞİT
  3. Danışmanlar: PROF. DR. KADİR GÜLER
  4. Tez Türü: Doktora
  5. Konular: İnşaat Mühendisliği, Civil Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 2025
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Lisansüstü Eğitim Enstitüsü
  11. Ana Bilim Dalı: İnşaat Mühendisliği Ana Bilim Dalı
  12. Bilim Dalı: Yapı Mühendisliği Bilim Dalı
  13. Sayfa Sayısı: 135

Özet

Kent içi ulaşım projelerinde, özellikle metro ve tünel inşaatları gibi yeraltı kazıları ile doğrudan etkileşime giren binaların, sadece deprem koşulları değil, aynı zamanda deprem dışı yükleme ve etkiler altındaki davranışlarının detaylı bir şekilde belirlenmesi, bina güvenliği ve yapısal bütünlüğün sağlanması açısından giderek daha kritik bir önem kazanmaktadır. Bu çalışmada, Türkiye'de İstanbul ili sınırları içerisinde yer alan metro tünel güzergahları boyunca bulunan binaların düşey yerdeğiştirme etkilerine karşı hasar görebilirliği, kırılganlık eğrileri aracılığı ile değerlendirilmiştir. Literatürde önerilen mevcut bir yöntem easa alınarak bir okul binası üzerinde detaylı analiz gerçekleştirilmiş ve bu bina için üç boyutlu (3B) bir model oluşturulmuştur. Geliştirilen bu model doğrultusunda, düşey yükler altında doğrusal olmayan artımsal çökme analizine uygun modelleme prensipleri sunulmuştur. Ancak ön proje aşamasında güzergah etki alanı içerisinde bulunan tüm binalar için detaylı 3B analizlerin yapılması, zaman ve iş gücü açısından sürdürülebilir değildir. Bu nedenle, daha geniş bir bina stoğunun değerlendirilmesine olanak tanıyacak şekilde, düşey yerdeğiştirme etkileri altında davranış sergileyen yapı tipleri için kırılganlık eğrilerine dayalı pratik bir analiz yöntemi önerilmiştir. Bu kapsamda, metro tünelleri üzerindeki mevcut bina stoğu incelenmiş; yapıların malzeme özellikleri, kesit geometrileri ve taşıyıcı eleman boyutları gibi parametreler yapılan saha araştırmaları doğrultusunda tanımlanmıştır. Çalışmada, tünel derinlikleri 10m, 15m, 20m ve 30m olan güzergahlarda, açıklık sayısı 1 ila 5 ve kat adedi 1 ila 7 arasında değişen 35 farklı bina tipi için toplamda 70000'in üzerinde doğrusal olmayan artımsal çökme analizi gerçekleştirilmiştir. Hasar değerlendirmeleri için, tünel çapı, tünel derinliği, hacim kaybı ve zemin özelliklerini temsil eden K çukur parametresi dikkate alınarak oluşturulan düşey yerdeğiştirme eğrileri (Gauss eğrileri) kullanılmıştır. Bu eğriler, 11 farklı hacim kaybı değeri için elde edilmiş; K parametresi 0.5 olarak kabul edilmiştir. Her bir bina tipi, bu yerdeğiştirme eğrisi üzerinde 6 farklı konumda analiz edilmiştir. Analiz çıktıları ile yapılacak olan hasar değerlendirmesi için Park ve diğ. (1984) tarafından sunulan hasar indeksi parametresi kullanılarak limit hasar indeksi değerleri elde edilmiştir. Bu limit değerler, Sınırlı Hasar, Kontrollü Hasar ve Göçmenin Önlenmesi durumu için verilmiştir. Analiz sonuçları ve bu limit değerler dikkate alınarak sistem istatistiksel olarak değerlendirilmiş ve bina tiplerine göre kırılganlık eğrileri elde edilmiştir. Bu çalışmada, metro tünel kazılarından kaynaklanan düşey yerdeğiştirme etkileri altındaki binaların hasar görebilirliğini tahmin etmeye yönelik kapsamlı ve uygulanabilir bir yöntem sunulmuştur. Bu çerçevede, tez kapsamında artımsal çökme analizi kullanılarak elde edilen ve sunulan kırılganlık eğrileri kullanılarak tünel güzergahlarındaki bina stoklarının hızlı değerlendirilmesinin mümkün olabileceği belirtilebilir. Geliştirilen kırılganlık eğrileri sayesinde, binalar için hızlı ve pratik değerlendirme yapılarak tünel inşaatı öncesinde zemin veya bina güçlendirme kararları alınabilir, tünel inşaatı sırasında ise riskli yapıların izlenmesi sağlanarak kent içi altyapı projelerinde güvenlik düzeyi arttırılabilir.

Özet (Çeviri)

Engineering structures interact closely with the ground on which they are founded. When the existing conditions of the soil change, the behavior of both the ground and the structure is inevitably affected; therefore, in the design of all engineering structures, the foundation must work in harmony with the ground, fulfilling design criteria from both geotechnical and structural perspectives. Ground settlement refers to the downward movement of the ground surface due to either natural processes or external influences. Settlement occurring as a result of soil compaction and consolidation under applied loads can cause architectural and structural damage to surface structures, potentially rendering them non-functional. Ground settlements may arise from both natural and anthropogenic causes. Natural settlements occur when rock formations dissolve upon contact with groundwater, causing the ground to shift into the resulting cavities. Artificial causes of settlement include excessive extraction of groundwater, construction of structural elements on soils with differing properties, overloading or asymmetric loading of the soil, excavation for retaining systems, movement or collapse of classical retaining structures such as retaining walls, and subsurface excavations such as tunnelling. Among the artificial causes of settlement, underground excavations such as tunnel constructions are primary examples. Tunnels are built by excavating underground and supporting the resulting voids. Their purpose is to provide safe, economical, and time-efficient transportation of people or goods. Road and metro tunnels are commonly used for transportation in urban areas. One of the significant challenges faced by metropolitan areas is traffic congestion. In response to this issue, the construction of metro tunnels has significantly increased. Given the critical role that metro systems play in urban development, the number of metro projects has been steadily rising, leading to a growing frequency of tunnel excavations within densely populated cities. Consequently, the interaction between these tunnels and the surrounding ground has become a subject of considerable importance. Monitoring tunnel excavations both during and after the construction phase enables the estimation of ground settlements and potential structural damage. Through such evaluations, it is possible to mitigate the risks of structural failures and prevent potential casualties. Conducting thorough assessments prior to the initiation of tunnelling activities allows for the identification of vulnerable zones and facilitates the implementation of protective measures, thereby minimizing the extent and impact of possible damage. The primary objective of this study is to develop fragility curves that can be utilized for the rapid assessment, during the early stages of a project, of the probability of damage to buildings located within the influence zone of ground settlements induced by tunnel excavations. The methodology employed for the generation of fragility curves involves several key steps: identification of structural element dimensions and material properties; derivation of the ground settlement profile geometry based on parametric approaches available in the literature; determination of the building's position relative to the settlement trough; selection of an appropriate structural analysis method; and statistical evaluation of the resulting structural response data. In practice, detailed numerical analyses can be conducted using complex computational models to predict potential structural damage in certain critical buildings located along the alignment of a metro tunnel. However, such comprehensive analyses are generally not feasible for evaluating all structures along the tunnel route during the preliminary design stage. In this study, fragility curves were developed by considering vertical ground displacements and planar frames with varying numbers of stories and spans. These curves aim to enable rapid damage assessments of buildings situated along proposed metro tunnel alignments prior to excavation. By identifying structures that exceed predefined damage probability thresholds, more detailed evaluations and, where necessary, mitigation strategies can be focused on a subset of vulnerable buildings. To achieve this, settlement behavior and ground deformation profiles were first established using parametric approaches available in the literature. Vertical displacements corresponding to the buildings' positions along the settlement trough were then applied to structural models using different methods. To represent the behavior of reinforced concrete buildings subjected to differential settlement, incremental settlement analyses were conducted on frame systems, and the resulting structural responses were used to construct damage probability curves. The focus of this thesis is the assessment of vertical displacements affecting existing buildings. Initially, the displacement profile induced on the ground surface by tunnel excavation is investigated. During tunnel excavation, a cavity forms within the soil, prompting the soil to seek equilibrium relative to this void. Consequently, deformations occur at the tunnel depth, commonly described as volumetric loss within the soil mass. This volumetric loss leads to surface settlements, which a semi-empirical Gaussian distribution can characterize. The S-curve equation proposed by Mair et al. (1993) is employed to model this Gaussian profile. The resulting displacement curve attains its maximum at the tunnel axis and exhibits symmetry about this axis. Firstly, to demonstrate that creating a three-dimensional numerical analysis model for all buildings along the tunnel alignment is neither practical nor feasible, an approach method from the literature was applied to an existing structure to illustrate the damage assessment process of buildings under vertical displacement effects. This evaluation method, proposed by Mair et al. (1996), consists of a three-stage assessment procedure. The method was implemented on an existing school building located along the tunnel route. In the first stage, the existing ground conditions were modelled using the PLAXIS 2D software, and the influence of the building stiffness on the settlement curve was neglected. This analysis is referred to as the“greenfield”analysis. As a result of this analysis, the vertical displacement profile induced by tunnel excavation (Gaussian curve) was obtained. Considering the location of the school building on this curve, the maximum displacement value in the building exceeded the 10 mm threshold specified in the approach method, prompting progression to the second stage. In the second stage, it was assumed that the building conformed to the“greenfield”settlement curve. The maximum tensile deformation induced by the settlement and heave zones beneath the building footprint was calculated and compared with the specified limits. Since this limit was also exceeded, the analysis proceeded to the third stage— the detailed assessment. During the detailed assessment, a finite element model of the building was developed using field observations and existing data. SAP2000v23 software was employed to construct a three-dimensional numerical model. Given the risk posed to the school building at the onset of tunnel excavation, monitoring instruments were installed on the structure to measure displacements caused by excavation. Using the vertical displacement data obtained from these instruments, a nonlinear incremental settlement analysis was performed in the vertical direction on the school building. This study examined a damage assessment method from the literature and established principles for nonlinear incremental settlement analysis. The compatibility of the structural model results for the existing school building with field observations validated the appropriateness and reliability of the proposed incremental settlement model and technique. Finally, the analysis outcomes were evaluated according to relevant regulations, and the damage assessment of the building was conducted. The definition of vulnerability refers to the probability of a structure sustaining damage under specific effects. Within the scope of this study, the data defined as specific effects can be considered the ground deformations occurring along the tunnel alignment. Fragility curves are the most commonly used method in vulnerability assessments. In metro tunnel excavations, creating numerical models for all buildings within the tunnel excavation influence zone during the damage assessment phase is not a practical approach. Therefore, it is believed that fragility curves developed for buildings subjected to vertical displacement effects can provide a practical solution for damage assessment in the preliminary design phase. This study aims to develop fragility curves for vertical displacement effects caused by metro tunnel excavations, similar to those established for lateral loads during seismic events. The process of deriving fragility curves consists of five fundamental stages: selection of the building type, determination of the damage input parameter, definition of damage parameters, selection of the analysis method, and statistical evaluation of the results. The development of fragility curves for buildings subjected to vertical displacement effects has been conducted following these five key steps. Firstly, the building type to be studied was determined. For this purpose, the existing building stock along metro tunnel alignments in a specific region of Istanbul was examined. Based on this building inventory, building types to be used in the analyses were identified. To represent reinforced concrete frame systems, numerical analyses were performed on planar frame structures with the number of stories ranging from 1 to 7 and the number of spans between 1 and 5. Secondly, the input parameter for damage—the vertical displacement effect—was modeled using a Gaussian curve. Certain assumptions were made regarding soil type (K), tunnel depth (z₀), tunnel diameter (D), and volume loss (VL) to derive this curve. In the third stage, building damage parameters were defined considering the damage index approach proposed by Park et al. (1984). The fourth stage involved applying incremental settlement analysis using nonlinear material models, based on the vertical displacement values corresponding to the building's position on the Gaussian curve. The incremental settlement analysis was developed in accordance with the principles of the pushover analysis method. The introduction of this incremental settlement analysis method constitutes a novel numerical analysis approach contributed by this study to the literature. Finally, following these four stages, a statistical evaluation was conducted using the obtained analysis outputs, leading to the derivation of the fragility curves. In this study, a total of over 70,000 nonlinear incremental settlement analyses were conducted for 35 different building types, varying between 1 and 5 spans and 1 to 7 stories, along tunnel alignments with depths of 10 m, 15 m, 20 m, and 30 m. For damage assessments, vertical displacement profiles (Gaussian curves) were utilized, which were developed by considering tunnel diameter, tunnel depth, volume loss, and the soil parameter K representing soil characteristics. These curves were generated for 11 different volume loss values, with the K parameter assumed as 0.5. Each building type was analyzed at six distinct positions along the displacement curve. For the damage evaluation based on analysis outputs, limit damage index values were derived using the damage index parameter proposed by Park et al. (1984). These limit values correspond to states of Limited Damage, Controlled Damage, and Collapse Prevention. Taking into account the analysis results and these threshold values, a statistical assessment of the system was performed, and fragility curves were developed for each building type. This study presents a comprehensive and practical methodology for predicting the vulnerability of buildings subjected to vertical displacement effects caused by metro tunnel excavations. Within this framework, it can be stated that the rapid assessment of building stocks along tunnel alignments is achievable by utilizing the fragility curves developed and presented in this thesis, which are obtained through incremental settlement analysis. Thanks to the developed fragility curves, swift and practical evaluations of buildings can be performed, enabling informed decisions regarding soil or structural reinforcement prior to tunnel construction. Moreover, during tunnel excavation, monitoring of at-risk structures can be facilitated, thereby enhancing safety levels in urban infrastructure projects.

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