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

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.