Investigation of the Effects of Superstructure Damping Ratio on Buildings with Lead Rubber Bearings under Earthquake Effect

Year 2022, Volume: 25 Issue: 2, 655 - 665, 01.06.2022

Zafer Kanbir , Cenk Alhan , Gökhan Özdemir

https://doi.org/10.2339/politeknik.803212

Cited By: 2

Abstract

Lead rubber bearings (LRBs) are among the most commonly used seismic isolation bearing types due to their high energy dissipation capacity. However, the experimental studies reveal that the temperature rise occurring under cyclic loads in the lead core, causes a deterioration in the characteristic strength by decreasing the yield strength of the lead, and it is important to consider this effect. In seismically isolated buildings, in addition to the isolation system, the superstructure also has a degree of energy dissipation capacity thanks to its inherent damping. It is seen that different damping ratios are used in the designs of such structures and research studies dealing with these structures. In this study, the change in the temperature-dependent behavior of seismically isolated buildings is investigated in cases where (i) superstructure damping is taken as 5% similar to fixed base reinforced concrete buildings, (ii) superstructure damping is taken as a smaller value such as 2%, and (iii) superstructure damping is completely neglected. A seismically isolated reinforced concrete building is modeled in the OpenSees program, considering the effect of the lead core heating on the characteristic strength and responses such as floor accelerations, temperature increase in the lead core, bearing shear forces and displacements obtained from nonlinear time history analyses are investigated. The results obtained showed that especially the floor accelerations can vary significantly and the floor accelerations obtained with different superstructure damping ratios can be in different limit ranges.

Keywords

lead rubber bearings, lead core heating, seismic base isolation, superstructure damping

Üstyapı Sönüm Oranının Deprem Etkisindeki Kurşun Çekirdekli Elastomer Yalıtım Birimli Binalardaki Etkilerinin Araştırılması

Abstract

Kurşun çekirdekli elastomer (KÇE) yalıtım birimleri yüksek enerji sönümleme kapasiteleri nedeniyle en çok kullanılan sismik yalıtım birimleri arasında yer almaktadır. Bununla birlikte, yapılan deneysel çalışmalar; kurşun çekirdekte tersinir yükler altında meydana gelen sıcaklık artışının, kurşunun akma dayanımını düşürerek karakteristik dayanımda azalmaya yol açtığını ve bu etkiyi dikkate almanın önemli olduğunu ortaya koymaktadır. Sismik yalıtımlı binalarda yalıtım sisteminin yanı sıra, üstyapı da kendi iç sönümü sayesinde bir dereceye kadar enerji sönümleme özelliğine sahiptir. Ancak, bu yapıların tasarımlarında ve bu tür yapıları ele alan araştırma çalışmalarında üstyapı için farklı sönüm oranlarının kullanıldığı görülmektedir. Bu çalışmada, üstyapı sönümünün, (i) taban ankastre betonarme binalara benzer şekilde % 5 alınması, (ii) % 2 gibi daha küçük bir değer alınması ya da (iii) tamamen ihmal edilmesi durumunda sismik yalıtımlı binaların kurşun çekirdek ısınmasına bağlı davranışlarının değişimi incelenmiştir. Sismik yalıtımlı betonarme bir bina, OpenSees programında, kurşun çekirdek ısınmasının dayanım üzerindeki etkisi göz önünde bulundurularak modellenmiş ve zaman tanım alanında yapılan doğrusal olmayan analizlerden elde edilen kat ivmeleri, kurşun çekirdekteki sıcaklık artışı, yalıtım birimi kesme kuvvetleri ve deplasmanları gibi tepkiler incelenmiştir. Sonuçlar, özellikle kat ivmelerinin önemli ölçüde değişebildiğini ve farklı üstyapı sönüm oranlarıyla elde edilen kat ivmelerinin farklı sınır aralıklarında olabileceğini ortaya koymuştur.

Keywords

kurşun çekirdekli elastomer yalıtım birimleri, kurşun çekirdek ısınması, sismik taban yalıtımı, üst yapı sönümü

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