100 metre açıklıklı çelik kafes demiryolu köprüsündeki eleman kayıplarının kırılganlık eğrileri üzerindeki etkisi
Effect on fragility curves of lose steel member of a 100-m steel truss railway bridge
Yazar: FATİH YILMAZ
Danışman: DOÇ. DR. KADİR ÖZAKGÜL
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Yapı Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2017
Konu: İnşaat Mühendisliği = Civil Engineering

Özet:
Demiryolu köprüleri yapılmış yapılar arasında önemli bir yeri olduğundan dolayı deprem sırasında köprüde meydana gelebilecek hasarın ve oluşabilecek riskin tahmin edilmesinin gerekliliğini son zamanlarda gün yüzüne çıkmıştır çünkü Türkiye'deki demiryolu ulaşımı tek bir hatta sahip olduğu için oluşabilecek eleman kayıpları ve büyük hasarlar demiryolu ulaşımın aksamasına neden olabilmektedir. 
Büyük zarar ve kayıplara neden olmuş depremler sonucunda elde edilen kırılganlık eğrileri kullanılarak yapılardaki hasar durumları deprem olmadan önce tahmin edilmeye çalışılmıştır. Kırılganlık eğrisi son zamanlarda depremlerden dolayı oluşabilecek hasarları tahmin etmede önemli bir yer tutmaktadır. Köprünün lokasyonuna göre sismik performansına bağlı olarak yapılan analiz sonucunda köprünün zarar görebilirliği ve hasar görülebilirlik eğrileri ile daha kolay ve kesin bir sonuç tahmin edilebilmektedir. Bu eğriler oluşabilecek deprem şiddet seviyesinde köprünün hasar seviyesine ulaşma, ya da hasar seviyesini aşma olasılığını verir. 
Bu tez çalışmasında 1900 yılında Türkiye'de yapılmış 100 m açıklıklı çelik köprünün zarar görebilirliğinin belirlenmesinde kullanılacak kırılgan eğrileri analitik yöntemle elde edilmiştir. Köprünün kapsamlı üç boyutlu modeli bilgisayar programına oluşturulmuş ve performans analizleri yapılmıştır. Öncelikle saha da yapılan testler ve test sonuçlarına yer verilmiştir. Saha çalışmasında köprünün ivmesi ölçülerek bilgisayar da yapılan model ile frekansları karşılaştırılmıştır. Çünkü köprü 1900 yılında inşa edildiği için modelin frekansı ile yapının freansı arasında fark olabilmektedir.
Performans analizlerinde daha kesin bir sonuç elde etmek toplam 21 tane köprünün bulunduğu noktadaki deprem riskine yakın olarak seçilmiştir. Bu analiz sonuçları ile saha çalışması sırasındaki elde edilen veriler daha verimli bir model elde etmek için karşılaştırılmıştır ve değerlendirme yapılmıştır. Daha sonra olması muhtemel yaklaşık şiddetdeki sismik deprem yer hareketleri altında zaman tanım alanında doğrusal olmayan analizler SAP2000 sonlu elemanlar programı kullanılarak yapılmıştır. 
Kırılganlık eğrileri bu analizler sonucunda elde edilen köprünün orta noktasındaki yer değiştirmeler baz alınarak elde edilmiştir. Sonra köprüde oluşabilecek bazı eleman kayıplarından dolayı oluşabilecek hasar durumları kırılganlık eğrileri göz önüne alınarak değerlendirilmiştir. Köprünün bazı eleman parçaları modelden çıkartılarak sismik davranışları belirlenmiş ve bunların da kırılganlık eğrileri oluşturulmuştur. Bu eğriler ise hasar görmeden önce oluşturulmuş kırılganlık eğrileri ile karşılaştırılmıştır. Bu çalışmanın ana amacı; şu an hizmet vermekte olan çelik köprünün mevcut halinin ve eleman kaybı sonraki durumunun, performansa dayalı yaklaşım çerçevesinde elde edilmiş olan hasar olasılıklarının kırılganlık eğrisini elde ederek karşılaştırılması ve değerlendirilmesinin yapılmasıdır. Bu çalışma sonucunda köprüde herhangi bir oluşabilecek deprem düzeyinde hasar oluşma durumunda ne olduğu öngörebilmektedir.

Abstract:
Railway bridges are great symbols of mankind's transportation challenge, have had a significant effect on the transportation network.  Especially, in the 19th and 20th centuries, due to the industrial revolution, people needed a larger transportation network so railways were immediately widened. Therefore, both highway and railway bridges have a vital role in connecting areas.
A significant number of railway bridges in TURKEY which are used today have nearly completed their half of a service life.  They were designed and built nearly a hundred years ago when bridge design codes did not have proper earthquake; therefore, they did not include several structural and conceptual susceptibilities to earthquake damage. In this technological age, using fragility curve are needed by scientists for research of damage analysis.  Moreover, by taking into consideration of accident, increasing vehicle loads, the fragility curve of steel bridge has gained importance as a research topic.  
In recently, devastating earthquakes have effected construction such as railway bridges that are one of the most vulnerable components of the network systems. These devastating seismic events have affected the risk resulting from the failure mode of the bridges. Depending on the seismicity of the local site of bridge, the assessment of the bridges could be done based on the fragility curves. These fragility curves are based on probability functions which give the probability of exceeding a damage level or a bridge attaining for an earthquake of a given intensity level.
Fragility curves show the probability of reaching or exceeding a level of damage for a building and some buildings under a ground motion intensity parameter by means of earthquake intensity-damage relations. Fragility curves are very useful tools which could be utilized for estimating of pre-earthquake planning; retrofit; damage/loss estimation and disaster management plans because the railway is significant network system in Turkey due to has only one-way. The fragility curve depends on the probability of exceeding a predefined structural damage limit in terms of a ground motion intensity parameter for instance; peak ground velocity peak ground acceleration (PGV or PGA), elastic spectral acceleration or displacement (Sa or Sd).
In this dissertation, analytical fragility curves are considered for the railway bridge. This steel truss railway bridge is 100-meter and was built nearly in 1900 by German construction company. The bridge was made experimental study to obtain its period and vibration. Then, the bridge was made model on SAP2000 for making non-linear analysis. The dead load and live load were affected on numerical model. The first three mode shapes and their period were obtained from numerical analysis. The result obtained from numerical test is compared to the result from experimental test of validated numerical model. After the numerical model was validated, non-linear analyse was made for an estimate of the bridge durability. 
Furthermore, the different 21-earthquake data were chosen based to its location. To obtain perfect solution the earthquake data must be chosen carefully so for this reason the data was chosen probability of an earthquake in bridge location. The 21-eatquake data are classified according to three soil classes. The bridge was to be used in the assessment of their seismic performance analysis on SAP2000.  Nonlinear response history analyses are conducted for sample bridge with their detailed analytical models under different earthquake ground motions having varying seismic intensities. 
Fragility curves are obtained from the probability of exceeding each specified damage limit state for each mid-span point displacement because the displacement on steel bridge is more important factor for evaluation. 
The component fragility curves were then developed based on the results of nonlinear response history analyses. The steel bridge could be faced having lost some member due to earthquake. The main aim of this study, different fragility curves were derived representing the loss of members on a steel bridge, were compared. Moreover, fragility curves were developed for triaxle, namely X, Y and Z. Furthermore, suitability of the maximum displacement below which the curved bridges could be analysed as their straight counterparts presented in design codes and guidelines was investigated. 
The main contribution of this study is to develop fragility curves for steel truss highway bridges in Turkey and entire study has been evaluated for the loss of member on steel truss bridge.
In this dissertation, the first section of this study describes the introduction, review of previous studies and aim of the study.
The second section provide comprehensive information about the bridge. The experimental study and numerical study methodologies are explained. Non-linear analysis methods in the framework of the bridge is defined. The numerical and experimental test results are compared. In result of the experimental test, the cross-section capacities of the bridge elements and the limit conditions of materials is safety for using.
The third section is mainly about fragility curves. Fragility curves are a significant method for estimating the overall risk to lose member due to potential earthquakes. The fragility curve provides the probability of exceeding a prescribed level of damage for a different wide range of ground motion intensities. In this chapter, fragility curves are explained and are given an example curve model for the bridge. This model is using on this dissertation. Some terminologies are explained related with fragility curve for example, peak ground acceleration (PGA), peak ground velocity (PGV), elastic spectral acceleration (Sa) and elastic spectral displacement (Sd). 
The fourth section is that the bridge model on SAP2000 is made for doing non-linear analysis and then later the live load and the dead load were defined for doing performance analysis. To obtain the periods of modal of the bridge make non-linear analysis. The 21 earthquakes are chosen based on its location. The time-history analysis made for evaluating the bridge performance.  
In the fifth chapter, the fragility curve is derived for bridge and different nine situations are taken consider for evaluate during to lose steel member. The time-history analysis is made for different nine situations because the displacement at the mid-point of the bridge is used to derive the fragility curves. 
In the sixth chapter, the result and future research is taken consider. The nine different situations are compared.