Zayıflatılmış Uç Kesitleri Karbon Lifli Polimer Elemanlarla Güçlendirilmiş Çelik Tüp Çaprazların Histeretik Davranışı

Çelik tüp çaprazların deprem etkilerine karşı karbon lifli polimer (CFRP) elemanlarla güçlendirilmesi deneysel olarak incelenmiştir. Zayıflatılmış uç kesitten olası kopmanın geciktirilmesi için bu bölgelerin CFRP elemanlarla (plaka ve kumaş) güçlendirilmesi önerilmiştir. Zayıflatılmış kesitte güçlendirmenin etkinliğini incelemek için üç adet kompakt kesitli, gerçeğe yakın ölçekli numune AISC yönetmeliklerine uygun olarak tasarlanmış ve kopmaya ulaşıncaya kadar yön değiştiren tekrarlı yükler altında denenmişlerdir. Referans numuneyle karşılaştırıldıklarında, beklendiği üzere, güçlendirilmiş numunelerin daha dolu histeretik eğrilere sahip olduğu görülmüştür. Zayıflatılmış uç bölgenin yan yüzlerine önce CFRP plaka sonrasında da kumaş ile sarılmasıyla numunenin kümülatif enerji tüketiminde artış ve kopma ömründe uzama görülmüştür. Güçlendirme, kopma anında en çok %82.5 oranında daha fazla enerjinin tüketilmesine katkıda bulunmuş, kopma ömürlerinde ise en çok %59 oranında artış görülmüştür. Süneklikteki artışa karşın son çevrimlerde kopma başlangıcı nedeniyle dayanım ve rijitlikte önemli denilebilecek azalmalar elde edilmiştir. Çapraz rijitliklerindeki değişim en fazla %10 civarında olduğundan önerilen yöntem çaprazlı çelik sistemlerin deprem etkilerine karşı güçlendirme uygulamaları için uygundur. FEMA 356’ya göre tanımlanan eksenel plastik mafsallı çaprazlara yapılan itme (pushover) analizi sonucunda FEMA’nın basınç bölgesinde gerçek davranışı yansıtmadığı, çekme bölgesinde ise uyumlu sonuçlar elde edildiği görülmüştür.

Anahtar Kelimeler:

Çelik tüp çaprazlar, İnelastik burkulma, Kopma ömrü, CFRP, Zayıflatılmış kesit, Güçlendirme

Hysteretic Behavior of Tubular Steel Braces Having Carbon Fiber Reinforced Polymer Reinforcement Around End Net Sections

This study presents an experimental investigation into the seismic retrofit of tubular steel braces using carbon fiber reinforced polymer (CFRP) members. CFRP retrofitting of net sections for compact tubes are proposed for delaying potential local net section failure. A total of almost full-scale three (TB-1, TB-2, and TB-3) compact steel tubular specimens were designed per AISC specifications, constructed, and cyclically tested to fracture. Retrofitted braces, when compared to the reference specimen, developed fuller hysteretic curves. Increase in cumulative hysteretic energy dissipation and the elongation in fracture life in the specimen retrofitted with CFRP plates and CFRP sheet wraps at net sections are observed during testing. This resulted in a maximum of 82.5% more dissipated energy for compact tube specimens. Also, this retrofit provided a longer experimental fracture life (maximum 59% more). Due to fracture initiation during the last cycles, significant reductions in strength and stiffness have been obtained. No significant change (maximum 10%) in the brace stiffness was observed, which could be desirable in seismic retrofit applications. Pushover analysis per FEMA 356 for the bare specimen shows that FEMA does not represent actual brace behavior in the compression side although pushover and experimental results are in good agreement in the tension side.

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