Efficient Use of Carbon Fiber Reinforced Polymer for Reinforced Concrete Beams in Three-Point Bending

Abstract

Externally bonded fiber reinforced polymer (FRP) sheets are highly popular for reinforced concrete (RC) beams to improve their flexural performance. This paper presents the results of three-point bending tests on seven RC beams externally reinforced with carbon fiber reinforced polymers (CFRP) sheets. Two concrete mixes with different compressive strength values are prepared for the production of experimental beams (150x250x1500 mm). First four beams have been casted with concrete having mean compressive strengths of 25.7 MPa and the other three beams are made of concrete having a very low compressive strength of 6.8 MPa which fall within the expected range for RC buildings constructed before 1990s in Turkey. Three different strengthening schemes are used by bonding of FRP sheets 1) only to bottom surface of the beam; 2) to bottom surface and lateral side’s surfaces of 50 mm height including the tensile reinforcement and the concrete cover; and 3) in U-wrapping. Failure mechanisms and flexural behavior of the strengthened beams are evaluated on the basis of the effectiveness of different wrapping schemes. The results are compared with the recommendations of international code ACI 440.2R-08. The validity of perfect bond assumption of FRP-concrete interface and the tensile strain limits for FRP sheets are also examined.

Keywords

• fiber reinforced polymer,strengthening schemes,reinforced concrete beams,three-point bending,debonding failure

Üç Noktalı Eğilme Altındaki Betonarme Kirişlerde Karbon Lifli Polimerin Etkin ve Ekonomik Kullanımı

Abstract

Lifli polimer kumaşlar betonarme kirişlerin eğilme performanslarını iyileştirmek için oldukça yaygın olarak kullanılmaktadır. Bu çalışma, karbon lifli polimer ile dıştan sargılanmış 7 adet betonarme kiriş üzerinde yapılan üç noktalı eğilme deneyi sonuçlarını içermektedir. 150x250x1500 mm boyutlarındaki deneysel kirişlerin üretilmesi için farklı basınç dayanımı değerine sahip iki adet beton karışımı hazırlanmıştır. İlk gruptaki 4 adet kiriş, ortalama basınç day animi değeri 25,7 MPa olan beton karışımı ile hazırlanırken, diğer gruptaki 3 adet kiriş ise, ülkemizde 1990lı yıllardan önce yapılan betonarme binalarda görülmesi beklenen düşük basınç dayanımını yansıtması amacıyla 6,8 MPa değerindeki beton karışımı ile hazırlanmıştır. Betonarme kirişlerin lifli polimer kumaşlar ile güçlendirilmesinde 3 farklı yöntem kullanılmıştır: 1) Yalnızca kirişin alt yüzeyi; 2) Kirişin alt yüzeyi ile birlikte pas payını ve çekme donatılarını içine alan 50 mm yüksekliğinde yan yüzeyleri; ve 3) U şeklinde sargılama. Deneyler sonucunda güçlendirilmiş kirişlerin göçme mekanizmaları ve eğilme davranışları, farklı güçlendirme yöntemlerinin etkileri göz önüne alınarak değerlendirilmiştir. Sonuçlar ACI 440.2R-08 Amerikan Beton Enstitüsünün Lifli Polimer Sistemleri ile Güçlendirme yönetmeliğindeki öneriler ile karşılaştırılmıştır. Lifli polimer malzeme ile beton arasındaki aderansın kusursuz olduğu varsayımının geçerliliği ile lifli polimer kumaşların çekme birim şekil değiştirme sınırları da bu çalışmada incelenmiştir.

Keywords

• lifli polimer,güçlendirme yöntemleri,betonarme kirişler,üç noktalı eğilme,sıyrılma

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