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

Abstract

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.

Keywords

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

Öz

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

Kaynakça

1. Celik OC, Berman JW, Bruneau M. "Cyclic Testing of Braces Laterally Restrained by Steel Studs". Journal of Structural Engineering, 131(7), 1114-1124, 2005.
2. Celik OC, Berman JW, Bruneau M. “Cyclic Testing of Braces Laterally Restrained by Steel Studs to Enhance Performance during Earthquakes”. Multidisciplinary Center for Earthquake Engineering Research, State University of New York, Buffalo, New York, USA, Technical Report, MCEER-04-0003, 2004.
3. Tremblay R. "Inelastic Seismic Response of Steel Bracing Members". Journal of Constructional Steel Research, 58(5-8), 665-701, 2002.
4. Han S, Kim WT, Foutch DA. "Seismic Behavior of HSS Bracing Members according to Width-Thickness Ratio under Symmetric Cyclic Loading". Journal of Structural Engineering, 133(2), 264-273, 2007.
5. Sabelli R, Roeder CW, Hajjar JF. “Seismic Design of Steel Special Concentrically Braced Frame Systems”. NEHRP, Gaithersburg, USA, Seismic Design Technical Brief ,8, 2013.
6. Haydaroglu C, Turker A, Taskin K, Celik OC. "Improving Hysteretic Behavior of Tubular Steel Braces Using Advanced Composites". 6th International Conference on Thin Walled Structures - Recent Research Advances and Trends, Timisoara, Romania, 5-7 September 2011.
7. Haydaroglu C, Turker A, Taskin K, Celik OC. "Cyclic Testing of Tubular Steel Braces with CFRP Reinforced Net Sections". 4th International Conference on Steel & Composite Structures, Sydney, Australia, 21-23 July, 2010.
8. Applied Technology Council. “Guidelines for Cyclic Seismic Testing of Components of Steel Structures”. Applied Technology Council, California, USA, ATC-24, 1992.

9. American Institute of Steel Construction. “Specification for Structural Steel Buildings”. American Institute of Steel Construction, Chicago, IL, USA, ANSI/AISC 360-05, 2005.
10. American Institute of Steel Construction. “Seismic Provisions for Structural Steel Buildings”. American Institute of Steel Construction, Chicago, IL, USA, ANSI/AISC 341-05, 2005.
11. Zhao XL, Bai Y, Al-Mahaidi R, Rizkalla S. "Effect of Dynamic Loading and Environmental Conditions on the Bond between CFRP and Steel: State-of-the-Art Review". Journal of Composites for Construction, 18(3), A4013005.1-A4013005.11, 2014.
12. Teng JG, Yu T, Fernando D. "Strengthening of Steel Structures with Fiber-Reinforced Polymer Composites". Journal of Constructional Steel Research, 78, 131-143, 2012.
13. El-Tawil S, Ekiz E, Goel S, Chao S. "Retraining Local and Global Buckling Behavior of Steel Plastic Hinges Using CFRP". Journal of Constructional Steel Research, 67(3), 261-269, 2011.
14. Harries KA, Peck AJ, Abraham EJ. "Enhancing Stability of Structural Steel Sections Using FRP". Thin-Walled Structures, 47(10), 1092-1101, 2009.
15. Shaat A, Fam AZ. "Slender Steel Columns Strengthening Using High-Modulus CFRP Plates for Buckling Controls". Journal of Composites for Construction, 13(1), 2-12, 2009.
16. Bambach MR, Elchalakani M. "Plastic Mechanism Analysis of Steel SHS Strengthened with CFRP under Large Axial Deformation". Thin-Walled Structures, 45(2), 159-170, 2007.
17. Shaat A, Fam AZ. "Axial Loading Test on Short and Long Hollow Structural Steel Columns Retrofitted Using Carbon Fibre Reinforced Polymers". Canadian Journal of Civil Engineering, 33(4), 458-470, 2006.
18. Teng JG, Hu YM. "Behaviour of FRP-Jacketed Circular Steel Tubes and Cylindrical Shells under Axial Compression". Construction and Building Materials, 21(4), 827-838, 2007.
19. Türk Standartları Enstitüsü. “Kaynak Sarf MalzemeleriAlaşımsız ve İnce Taneli Çeliklerin Koruyucu Gaz Metal Ark Kaynağı İçin Tel Elektrotlar ve Yığılmış KaynaklarSınıflandırma”. Türk Standartları Enstitüsü, Ankara, Türkiye, TS 5618 EN 440, 2002.
20. American Society for Testing and Materials. “Standard Test Methods and Definitions for Mechanical Testing of Steel Products”. American Society for Testing and Materials, Pennsylvania, USA, ASTM A370-08a, 2008.
21. Computers and Structures Inc. SAP2000, Structural Analysis and Design Software. Berkeley, California, USA, 2000.
22. Federal Emergency Management Agency. “Prestandard and Commentary for the Seismic Rehabilitation of Buildings”, Federal Emergency Management Agency, Washington, USA, FEMA-356, 2000.
23. BASF YKS. “Lifli Polimer (FRP) Güçlendirme Sistemleri”. İstanbul, Türkiye, 2008. [24] Sundarraja MC, Sriram P, Prabhu GG. "Strengthening of Hollow Square Sections under Compression Using FRP Composites". Advances in Materials Science and Engineering, (2014), 1-19, 2014.
24. Lee S, Goel SC. “Seismic Behavior of Hollow and ConcreteFilled Square Tubular Bracing Members”. Department of Civil Engineering, University of Michigan, Ann Arbor, Michigan, USA, Report No. UMEE 87-11, 1987.
25. Lee K, Bruneau M. “Review of Energy Dissipation of Compression Members in Concentrically Braced Frames”. Multidisciplinary Center for Earthquake Engineering Research, State University of New York, Buffalo, New York, USA, Technical Report MCEER-02-0005, 2002.