Çok katlı betonarme bir yapının deprem performansına yapı-kazık-zemin etkileşiminin etkisinin incelenmesi
Investigation of the effect of structure-pile-soil interaction on the earthquake performance of a multi-storey reinforced concrete building
Yazar: ESMA GİRER
Danışman: PROF. DR. YASİN FAHJAN
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Yapı Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2022
Konu: İnşaat Mühendisliği = Civil Engineering

Özet:
Türkiye, aktif fay hatları üzerinde yer aldığından depremselliği yüksek olan bir bölgede bulunmaktadır. Geçmiş depremlerde büyük can ve mal kayıpları ile karşılaşılmıştır. Bu durum sonucunda yapıların deprem etkisi altında göstereceği davranışın doğru bir şekilde tahmin edilmesinin önemi ön plana çıkmıştır. Taban kayasında tanımlanan deprem yer hareketinin yapıya nasıl etki edeceği yapı-zemin etkileşiminin araştırılmasıyla mümkündür. Zemin tabakalarında ilerleyen deprem dalgaları değişime uğrar. Zayıf zeminlerde bu değişimden dolayı deprem etkileri büyümektedir. İzmir depreminde de görüldüğü üzere zemin hâkim periyodu ile yapı periyotlarının uyumlu olduğu bölgelerde zemin büyütmesi daha fazladır. Yumuşak zeminlerde zemin hâkim periyodu ile çok katlı yapıların periyodu çakışmaktadır. Bu bölgelerde bulunan çok katlı yapılar daha yüksek deprem kuvvetlerine maruz kalmış ve hasar görmüştür. Bu nedenle zayıf zeminler üzerine inşa edilecek çok katlı yapılarda yapı-zemin etkileşiminin incelenmesi büyük önem taşımaktadır. Nüfus artışı ve şehir planlama sıkıntısı sebebiyle İzmir'de olduğu gibi çok katlı binalar inşa edilmektedir. Taşıyıcı zemin tabakasının derinlerde bulunması ile derin temellerin kullanımı yaygınlaşmıştır. Japonya'da meydana gelen Hyogo-Ken Nanbu depreminde kazıklı temel sistemine sahip zayıf zemine oturan yüksek binalar depremden etkilenmemişken, yüzeysel temele sahip binalar ağır hasar görmüştür. Benzer örnekler Mexico City depreminde olduğu gibi dünya genelinde meydana gelen depremlerde de mevcuttur. Bu nedenle yapı-kazık-zemin etkileşiminin İzmir'in kıyı şeritleri gibi zemin hâkim periyodu yüksek bölgelerde yapılacak yüksek binalarda incelenmesi büyük önem taşımaktadır. Bu tez kapsamında, yerleşim yerleri nüfus artışı sebebiyle sismik aktivitesi yüksek zayıf zeminler üzerine kurulan İzmir İlinde çok katlı yapıların yapımının yaygınlaşması ile birlikte önemli bir konu haline gelen yapı-kazık-zemin etkileşimi Türkiye Bina Deprem Yönetmeliği (TBDY 2018) kapsamında verilen etkileşim hesapları (Yöntem II ve Yöntem III) göz önüne alınarak incelenmiştir. Her iki yöntem kendi içerisinde direk yöntem ve altsistem yöntemi olmak üzere iki farklı yaklaşımla değerlendirilip, kazık iç kuvvetleri kıyaslanmıştır. İki yöntemde de direkt sistem ve altsistem hesap yaklaşımları kullanılarak yapılan yapı-kazık-zemin etkileşim hesapları sonucu elde edilen kazık iç kuvvetlerinin birbirine oldukça yakın olduğu görülmüştür. Direkt sistem yaklaşımında oluşturulan 3 boyutlu ve 2 boyutlu hesap modellerinde 3 boyutlu hesap modelinin daha elverişsiz sonuçlar verdiği ve 2 boyutlu hesap modelinden elde edilen kazık iç kuvvetlerinin de 3 boyutlu direkt yöntem hesap yaklaşımı ve altsistem yöntemi hesap yaklaşımı ile elde edilen sonuçlara oldukça yakın olduğu, aynı zamanda kazık tasarımı hakkında öndeğerlendirme açısından fikir verebileceği gözlenmiştir.

Abstract:
Turkey is located in a region with high seismicity because of it is located on active fault lines. In the past earthquakes, great loss of life and property has been encountered. As a result of this situation, the importance of accurately predicting the behavior of structures under the effect of earthquake has come into prominence. How the earthquake ground motion defined in the bedrock will affect the structure is possible by investigating the soil-structure interaction. Seismic waves traveling through the soil layers changes. Due to this change in weak soils, the effects of earthquakes increase. As seen in the Izmir earthquake, the soil amplification is higher in regions where the soil predominant period and the building vibration periods are compatible. In soft soils, the predominant period of the soil coincides with the period of multi-storey buildings. Multi-storey buildings in these regions were exposed to higher earthquake forces and were damaged. For this reason, it is important to examine the soil-structure interaction in multi-storey buildings to be built on weak soils. Due to population growth and city planning problems, multi-storey buildings are being built as in Izmir. The use of deep foundations has become widespread due to the deep presence of the bearing soil layer. In the Hyogo-Ken Nanbu earthquake that occurred in Japan, high-rise buildings with pile foundation system on weak soil were not affected by the earthquake, while buildings with shallow foundations were severely damaged. Similar examples exist in earthquakes occurring around the world, as in the Mexico City earthquake. For this reason, it is important to examine the structure-pile-soil interaction in high rise buildings to be constructed in areas with high soil predominant periods such as the coastlines of Izmir. The structure-soil interaction can be analyzed by two different methods. One of the proposed methods for investigating the structure-soil interaction is the direct method. In the model created by numerical methods such as finite elements, finite differences or limited elements; superstructure, building foundation, piles and soil environment exist. In the direct analysis method, the nonlinear behavior of the soil environment and the foundation can be taken into account. In this method, the soil environment is cut by the cutting surfaces and transmitting boundaries expressing the infinity of the soil environment are created. With the transmitting boundaries, earthquake waves defined in the bedrock and propagating in the closed environment are prevented from returning to the analysis environment by reflecting from the cut boundaries. Another method used to analyze the structure-soil interaction is the subsystem method. In this method, the soil environment and piles are modeled in one system, while the foundation and superstructure is modeled in a separate system. While modeling the building foundation, the mass of the foundation is not taken into account and transmitting boundaries are defined at the outer boundaries of the soil environment, as in the direct method. In the subsystem method, in the first step, ground motion acting on the system is determined depending on the kinematic interaction. In
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the second stage, the impedance functions of the foundation and soil system are obtained, and in the last stage, the kinematic interaction of the structure is taken into account, and the analysis is made under the effect of ground motion. In this context, it is possible to examine the subsystem method in two stages, namely Kinematic Interaction and Inertial Interaction. Within the scope of this thesis, the structure-pile-soil interaction, which has become an important issue with the spread of construction of multi-storey buildings in Izmir, which was built on weak soils with high seismic activity due to population growth in settlements, interaction calculations (Method-II) given within the scope of Turkish Building Earthquake Code (TBEC-2018) were considered. The effect of the structure-pile-soil interaction on the earthquake performance of multi-storey buildings was investigated by performing a performance-based design with integrated and discrete system solution. According to the results of the analysis, it is aimed that the results obtained by comparing the solution methods in the structure-pile-soil interaction analysis will contribute to the literature. In discrete system calculation approach, the 3D model of the building was used, the structure system and the structure foundation were examined in one model, the structure system and the structure foundation were examined in a separate calculation model. In the calculation model, which includes the foundation and pile system, kinematic interaction analysis was performed without considering the mass of the foundation. Then, the loads transferred to the pile system were obtained by using the displacement records and accelaration spectra obtained from site-responce analysis in the calculation model which the structure system and the building foundation were included. The structure-pile-soil interaction analyzes were completed by effecting the obtained loads on the calculation model including the foundation and pile system. In the integrated system calculation approach, the strucute system, the building foundation and the pile system are modeled in 3D in a single calculation model. Since the solution of the calculation models prepared in this calculation approach takes a long time in today's widely used analysis programs, it is thought that the 2-dimansional model created with a cross-section passed through the system can provide an approximate prediction abaout the pile design. For this purpose, the integrated system calculation approach has been examined through both the 3-dimentional calculation model and the 2-dimentional calculation model, which includes a section taken from the structure. It has been investigated whether a realistic result can be obtained by usign the 2-dimentional calculation model. In both approaches, the response coefficient of the structural system is taken as R=4.8 for the 3-dimensional curtain wall and frame system in the calculation of earthquake forces, while the coefficient of behavior of the structural system for the 2-dimensional frame system is R=8. The above mentioned calculation models were created separately for Method II and Method III, one of the strucutre-pile-soil interaction analysis methods proposed in TBDY 2018 Chapter 16, and the results of kinematic interaction and inertial interaction analysis were compared in both methods. It has been observed that the pile internal forces obtained as a result of the structure-pile-soil interaction calculations using the integrated system and discrete system calculation approaches, which are Method II calculation methods, are quite close to each other. It has been observed that the 3-dimentional calculation model gives more accurate results in the 3-dimentional and 2-dimentional calculation models created in the combined system approach, but the 2-dimetional calculation model can also give an approximate idea in terms of preliminary assesment of the pile internal forces. A simular situation is also present in the calculation methods made with Method III. It has been observed that the pile internal forces obtained as a result of the structure-pile-soil interaction calculations using the integrated system and discrete
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system calculation approaches are quite close to each other. It has been observed that the 3-dimentional calculation model gives more accurate results in the 3-dimentional and 2-dimentional calculation models created in the integraated system spproach, but the 2-dimentional calculation model can also give an approximate idea in terms of preliminary assesment of the pile internal forces. In both methods, it was observed that the effect of the strucutre (inertia effect) was close to each other and the difference was in the kinematic interation. When the results of Method II and Method III and structure-pile-soil interaction analysis were compared, it was observed that the effect of the pavement (inertia effect) was close to each other in both methods and the difference was in the kinematic interaction. The reason for this difference is that in the calculation of the structure-pile-soil interaction with Method III, the envelope of the maximum displacements according to time obtained as a result of the site-specific behavior analysis at the pile nodal points is used, and since the displacements obtained at the joint points are close to each other, internal force does not occur. In the calculation of structure-pile-soil interaction with Method II, since the variation of the displacements obtained at the level of the pile joint points as a result of the site-specific behavior analysis with respect to time is used, the internal forces occur due to the phase difference between the displacements occurring in the line of the pile joint points with respect to time. As a result of the analysis, when the pile evaluation was made Method II, it was seen that the plastic turning capacity remained below the damage limits at the controlled damage and preventaion of collapse performance levels. When pile design was made with Method III, the capacity ratio was found to be %46. In this study, it is aimed to contribute to the literature and applications due to the evaluation of the methods used in the structure-pile-soil interaction calculations that came into with TBDY 2018 and the similarity of the internal forces obtained as a result of the different calculation approaches that can be used for each method.