Effect of Long Carbon Fibers on Deflection of One-way Members

This paper describes laboratory tests on simply supported one-way members containing steel reinforcing bars and long (75mm) coated carbon fibers. Carbon fiber yarn is coated to provide 75mm long stiff fiber tape that readily disperses in the concrete matrix. The tests were conducted to compare response to immediate and sustained loads, of members containing carbon fibers, with the response of companion beams without fibers. The specimens are 3.66 m long supported on an 3.35 m span, 300 mm wide, and 125 mm deep with two #3 bars at an effective depth of 100 mm. Two specimens containing 1.5% long carbon fiber by volume were loaded with concentrated loads at mid-span to simulate live load. Applied load and mid-span deflections were recorded. The applied loads were then removed and the beams were monitored for approximately one year to determine deflection response under sustained dead load. Immediate and time dependent responses of the fiber reinforced beams are compared with response of the companion beams containing regular reinforcing bars only. The tests clearly demonstrate the enhanced stiffness provided by carbon fiber under immediate and sustained loads.