The Effects of Steel Core Imperfection, Gap Size and Friction Coefficient on the Behavior of All-Steel Buckling Restrained Braces

Abstract

Buckling restrained braces (BRBs) which are generally composed of a steel core and a encasing(buckling restrainers) are utilized to resist lateral forces in high seismic regions since BRBs exhibit high energy dissipation capacity, ductility and stiffness. The steel core carries both compressive and tensile forces. During the compression, the core starts buckling and the encasing tries to prevent this buckling. However, due to the unbonding layer/gap between the encasing and steel core, the steel core eventually buckles and contacts with the encasing. Buckling phenomenon is also associated with the initial imperfection and gap size. In this study, the effects of the initial imperfectionof steel core, gap size (1-5 mm)and friction coefficient (0.01-0.5)between the encasing and steel core on the behavior of BRBs are investigated. Pursuant to this goal, numerical analyses using a finite element tool ABAQUS were conducted. A total of 19 numerical models were developed and monotonically loaded. Initial imperfection was implemented to the models using buckling mode shapes.The results revealed that increasing gap size leads to a reduction in load-carrying capacity. It is recommended to keep gap sizes between 1 and 2 mm. On the other hand, initial imperfection does not significantly affect load-carrying capacity and global behavior. However, it was also observed that the fluctuations in load increase as the amplitude of the mode shape and gap size increase. Moreover, the friction coefficient should be kept between 0.01 and 0.05; otherwise, undesired behaviors can be observed.

Keywords

• Buckling restrained braces
• ABAQUS
• Buckling
• Imperfection
• Gap
• Friction coefficient
• Steel core.

Çelik Çekirdek Kusurunun, Boşluk Boyutunun ve Sürtünme Katsayısının Tamamı Çelik Burkulması Önlenmiş Çaprazların Davranışına Etkileri

Abstract

Burkulması önlenmiş çaprazlar (BÖÇ'ler), genellikle bir çelik çekirdekten ve bir burkulmayı önleyen ortamdan oluşan, yüksek enerji sönümleme kapasiteleri, süneklik ve rijitlik sergiledikleri için, yüksek sismik bölgelerde yanal kuvvetlere direnmek için kullanılır. Çelik çekirdek hem basınç hem de çekme kuvvetlerini taşır. Basınç sırasında çekirdek burkulmaya başlar ve burkulmayı önleyen ortam bu burkulmayı önlemeye çalışır. Bununla birlikte, enkesit ve çelik çekirdek arasındaki boşluk nedeniyle, çelik çekirdek sonunda burkulur. Burkulma fenomeni ayrıca başlangıç kusuru ve sürtünmesiz yüzey/boşluk boyutu ile de ilişkilidir. Bu çalışmada, çelik çekirdeğin başlangıç kusurunun, boşluk boyutunun (1-5 mm) ve sürtünme katsayısının (0.01-0.5) BÖÇ'lerin davranışı üzerindeki etkileri araştırılmıştır. Bu amaç doğrultusunda sonlu elemanlar aracı ABAQUS kullanılarak numerik analizler yapılmıştır. Toplam 19 sayısal model geliştirilmiştir ve tekdüze yüklenmiştir. İlk kusur, burkulma mod şekilleri kullanılarak modellere uygulandı. Sonuçlar, boşluk boyutu artıkça yük taşıma kapasitesinde azalmaya sebep olduğunu ortaya koymuştur. Boşluk boyutunun 1 ile 2 mm arasında tutulması önerilmiştir. Diğer bir yandan, ilk kusurun yük taşıma kapasitesini ve genel davranışı etkilememiştir. Ancak mod şeklinin ölçeği ve boşluk boyutu arttıkça yükteki dalgalanmaların da arttığı görülmüştür. Ayrıca, sürtünme kaysayısı 0.01 ile 0.05 arasında tutulmalıdır yoksa istenmeyen davranışlar gözlemlenebilir.

Keywords

• Burkulması önlenmiş çaprazlar
• ABAQUS
• Burkulma
• Kusur
• Boşluk
• Sürtünme katsayısı
• Çelik çekirdek.

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