Akademik Veri Yönetim Sistemi
Tezin Türü: Yüksek Lisans
Tezin Yürütüldüğü Kurum: Yıldız Teknik Üniversitesi, Fen Bilimleri Enstitüsü, Türkiye
Tezin Onay Tarihi: 2019
Tezin Dili: İngilizce
Öğrenci: KADİR EKŞİ
Danışman: Fatih Alemdar
Özet:
According to the traditional approach, structures are designed to mainly resist vertical loads. This approach may lead to poor conditioning along horizontal ground movements occurred during an earthquake. Although there are significant improvements in Earthquake Engineering to design the structures with a certain level of earthquake performance, base isolation is used mainly at strategically important structures to reduce the eartquake-induced damage. The modern concept of base isolation works by decoupling the upper-structure from sub-structure. The aim is to reduce the transmission of the earthquake loads to the upper-structure by taking advantage of the horizontal flexibility of the berings.
Elastomeric bearings are one of the most commonly used seismic isolation systems in the market. These bearings are generally consist of vulcanized rubber blocks bonded to steel plates. Rubber blocks provide the flexibility, while the steel plates provide axial rigidity. Although the steel plates have nearly no effect to lateral behavior, they are essential to provide the sufficient axial stiffness in order to transmit vertical loads to foundation properly.
Elastomeric bearings make the horizontal movements under continuous compression loads. This situation is the starting point of the thesis. In this study, behaviors of elastomeric bearing samples with a 100 mm x 100 mm plan dimensions cut from a full-size bearing were examined under different conditions. As a start, compression stiffness and shear modulus of the bearings were determined by using the methods close to ones clarified in AASHTO M251-06 Specification. Later, the change at lateral behavior was observed during repetitive dynamic lateral movement under 3, 4.5 and 6 MPa compression load levels and the results were compared. It was observed that the lateral stiffness decreases as the compression load increases.
After the experimental studies were executed, the finite element model of a bearing sample was prepared by using 5-Parameter Mooney-Rivlin Hyperelastic Material Model. Since some essential test data for simulating the behavior of the rubber material accurately are missed, stress-strain graphs of another rubber material which were found in software documentation were modified with shear data obtained from the experimental studies. Analyses were executed by using the material constants obtained from the modified graphs. Although being lack of some test data for rubber material, accurate results were found -especially for lateral behavior- on certain strain levels.