Zemin-yapı etkileşiminin binalar üzerindeki etkilerinin modellenmesi üzerine bir çalışma
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Date
2019
Authors
Sönmez, Ertan
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Abstract
Zemin-yapı etkileşimi, inşaat mühendisliği uygulamalarındaki çoğu binanın tasarımında genellikle göz önüne alınmaz. Zemin-yapı etkileşiminin bina doğal periyodunun uzamasına sebep olmasından dolayı taban kesme kuvvetinin (ve bina üzerindeki toplam deprem yükünün) azaldığı varsayılarak, çoğu bina yapıları ve zemin koşulları için bu etkileşimin ihmal edilmesi daha güvenli sayılır ve binalar zemine ankastre mesnetlenmiş olarak tasarlanır. Bu varsayım, bazı bina yapıları ve zemin koşulları (ağır yapılar, gökdelenler, ve yumuşak zemin gibi) için geçerli değildir. Bu tezde binalardaki zemin-yapı etkileşimi, genel amaçlı bir yapısal analiz yazılımı (SAP2000) ile hazırlanmış görece basit modeller kullanılarak çalışılmıştır. İki boyutlu (2B) ve üç boyutlu (3B) bina modelleri için simetrik, 6 katlı, 6 açıklıklı moment dayanımlı betonarme bir çerçeve kullanılmıştır. Üç farklı homojen elastik zemin üzerinde üç farklı binanın (farklı dinamik karakteristiklere sahip) sismik tepkileri hesaplanmış ve zemine ankastre modellerin tepkileriyle karşılaştırılmıştır. Zemin-yapı etkileşimi iki farklı yaklaşımla modellenmiştir: (i) zemin empedans fonksiyonlarını temsil eden mesnet yayları kullanarak (altyapı yöntemi) ve (ii) zeminin üst yapı ve temel ile birlikte doğrudan modellenmesi (doğrudan analiz yöntemi) ile. Modellerde tekli temel ve radye temel olmak üzere iki tür temel dikkate alınmıştır. Modellerin sismik tepkileri zemin özelliklerine göre belirlenen ASCE 7-10 ivme spektrumları kullanılarak hesaplanmıştır. Gerçek bir deprem yer ivmesi kaydı (1940 El Centro) kullanılarak zaman tanımlı analizler ile de sınırlı bir çalışma yapılmıştır. 2B ve 3B modellerin analiz sonuçları, zemin-yapı etkileşiminin binanın doğal periyodunu uzatma etkisini net bir şekilde göstermiştir. Bu çalışmada, uygulamada yaygın olarak kullanılan zemin empedans fonksiyonlarına dayalı, zeminin mesnet yayları ile temsil edildiği modellerde (yay modelleri) binanın doğal periyodunu uzatma etkisinin doğrudan analiz modellerine göre daha az olduğu gözlemlenmiştir. Benzer şekilde, taban kesme kuvveti, kat yer değiştirmesi, kat ötelemesi ve temel oturması sonuçları incelendiğinde, doğrudan analiz modellerinde zemin-yapı etkileşiminin, yay modellerine göre daha yüksek hesaplandığı görülmüştür.
Soil-structure interaction is usually not considered in the design of most buildings in civil engineering practice. Based on the assumption that these effects reduce the base shear (and the overall earthquake load) for most building structures and soil conditions due to period lengthening, omission of soil-structure effects is in general considered to be conservative and the buildings are designed as fixed base structures. This assumption does not hold for certain building structures and soil conditions (e.g., massive structures, tall buildings, and structures on soft soil). In this thesis, soil-structure interaction effects in buildings are studied using relatively simple models prepared by a general-purpose structural analysis software (SAP2000). A symmetrical, 6-story, 6-bay reinforced concrete moment resisting frame is considered for both two-dimensional (2D) and three-dimensional (3D) building models. Seismic responses of three different building structures (with varying dynamic characteristics) on three different homogeneous, elastic soil mediums are computed and compared with the responses of the corresponding fixed base models. Soil-structure interaction effects are modeled by two approaches: (i) using soil springs representing the soil impedance functions (substructure method), and (ii) modeling the soil medium directly along with the structure and the foundation (direct analysis method). Two types of foundation are considered in the models: footing foundation (i.e., isolated footings) and raft foundation. ASCE 7-10 acceleration response spectra are determined based on the soil properties and used to examine the seismic response of the models considered. A limited study is also performed by time-history analyses using an actual earthquake ground acceleration record (1940 El Centro). Analyses of 2D and 3D models showed the well-known period lengthening effect of soil-structure interaction clearly. The results of this study indicate that spring models based on soil impedance functions that are widely used in practice lead to a lesser period lengthening effect compared to direct models. Similarly, by examining the base shear, story displacement, story drift, and foundation settlement results, it is observed that the soil-structure interaction effects were more significant in the direct models compared to the spring models.
Soil-structure interaction is usually not considered in the design of most buildings in civil engineering practice. Based on the assumption that these effects reduce the base shear (and the overall earthquake load) for most building structures and soil conditions due to period lengthening, omission of soil-structure effects is in general considered to be conservative and the buildings are designed as fixed base structures. This assumption does not hold for certain building structures and soil conditions (e.g., massive structures, tall buildings, and structures on soft soil). In this thesis, soil-structure interaction effects in buildings are studied using relatively simple models prepared by a general-purpose structural analysis software (SAP2000). A symmetrical, 6-story, 6-bay reinforced concrete moment resisting frame is considered for both two-dimensional (2D) and three-dimensional (3D) building models. Seismic responses of three different building structures (with varying dynamic characteristics) on three different homogeneous, elastic soil mediums are computed and compared with the responses of the corresponding fixed base models. Soil-structure interaction effects are modeled by two approaches: (i) using soil springs representing the soil impedance functions (substructure method), and (ii) modeling the soil medium directly along with the structure and the foundation (direct analysis method). Two types of foundation are considered in the models: footing foundation (i.e., isolated footings) and raft foundation. ASCE 7-10 acceleration response spectra are determined based on the soil properties and used to examine the seismic response of the models considered. A limited study is also performed by time-history analyses using an actual earthquake ground acceleration record (1940 El Centro). Analyses of 2D and 3D models showed the well-known period lengthening effect of soil-structure interaction clearly. The results of this study indicate that spring models based on soil impedance functions that are widely used in practice lead to a lesser period lengthening effect compared to direct models. Similarly, by examining the base shear, story displacement, story drift, and foundation settlement results, it is observed that the soil-structure interaction effects were more significant in the direct models compared to the spring models.
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İnşaat Mühendisliği, Civil Engineering
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