PREDICTION MODEL FOR BASE SHEAR INCREASE DUE TO VERTICAL GROUND MOTION IN FRICTION PENDULUM ISOLATED STRUCTURES

Öz

Seismic isolation is one of the most effective seismic hazard mitigation techniques, which has been implemented in many structures. Friction pendulum isolators are one of the most popular isolation devices to achieve energy dissipation and shear resistance that depends on the effective radius and instantaneous vertical force on them. So, the horizontal response of this type of isolators is coupled with the axial load on them, which could change due to vertical acceleration during ground shaking. Thus, it makes consideration of the vertical excitation in the design and analysis phase inevitable, especially for structures in those regions where vertical ground accelerations are more pronounced. In this study a model for the prediction of increase in base shear due to vertical motion for friction pendulum isolated structures is proposed. A simple single friction pendulum isolator system is utilized with the assumption of rigid superstructure on top and subjected to a hundred earthquake ground motions with different characteristics. A multi-layer perceptron model with three layers is utilized, and a simple computer program, which is open-source, is prepared to construct probability curves. With the help of the program, within the range of the considered structural parameters in the study, probability curves related to increase in base shear, maximum isolator displacement and residual isolator displacement can be constructed, and designers can have a rough estimation on modification of these parameters due to vertical ground motion.

Anahtar Kelimeler

• Seismic isolation
• Friction pendulum system
• Vertical Ground Motion
• Base Shear Increase

Düşey yer hareketinden dolayı sürtünmeli sarkaç sistemleri ile izole edilmiş yapılarda taban kesme kuvveti artışı tahmin modeli

Öz

Birçok yapıya uygulanan sismik izolasyon, sismik tehlikenin azaltılması için en etkin yollardan biridir. Sürtünmeli sarkaç izolatörleri de enerji sönümü ve etkili yarı çapa ve üzerindeki anlık yüke bağlı olarak kayma direnci oluşturan en popüler sismik izolatörlerdendir. Bu yüzden, bu tür izolatörlerin yatay tepkisi üzerinde bulunan eksenel yüke bağlıdır ve bu yük de düşey yer ivmesine göre sarsıntı boyunca değişebilir. Böylece düşey yer sarsıntısının etkili olduğu bölgelerde bu doğrultudaki ivmeyi tasarım ve analiz aşamasında göz önünde bulundurmayı kaçınılmaz kılar. Bu nedenle, bu çalışmada taban kesme kuvvetinde düşey hareketten dolayı meydana gelen artımın tahmini için bir yöntem sunulmaktadır. Rijit yapı kabulüne dayalı basit bir model oluşturulmuş ve farklı karakterlere sahip yüz deprem hareketine maruz bırakılmıştır. Çok katmanlı algılayıcı modeli kullanılmış ve kırılganlık eğrilerinin oluşturulması için açık kaynak kodlu basit bir bilgisayar programı hazırlanmıştır. Program yardımıyla çalışmada verilen yapısal parametrelerin aralığında taban kesme kuvvetinde, maksimum ve kalıcı izolatör deplasmanında düşey yer ivmesinden dolayı meydana gelecek artışa dair olasılık eğrileri elde edilebilir ve tasarımcılar düşey yer ivmesinden dolayı bu parametrelerde yapılacak olan modifikasyonlar için yaklaşık bir tahmin yapabilir.

Anahtar Kelimeler

• Sismik izolasyon
• Sürtünmeli Sarkaç Sistemi
• Düşey Yer Hareketi
• Taban kesme kuvveti artışı

Kaynakça

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