Compressive stress-strain behavior of normal and high-strength carbon-fiber concrete reinforced with steel spirals

Carbon-fiber reinforced concrete (CFRC) was combined with traditional trans verse steel reinforcement in the form of steel spirals in an attempt to inc rease the energy absorption and strength of the concrete under both monoton ic and cyclic loading. The stress-strain relationship of concrete in compre ssion in both unconfined and confined states was examined. The descending b ranch of the stress-strain curve was recorded to investigate the ductility of normal and high-strength fiber reinforced concrete confined with steel s pirals. The experimental program consisted of testing 100 x 200-mm concrete cylinde rs under compression at two different strength levels: normal (48 MPa) and high strength (75 MPa), reinforced with different percentages V-f (1.5, 2, and 3 percent) and lengths L-f (7.5, 20, and 30 mm) of high-strength carbon fibers with an equivalent diameter 0.78 mm. These were then repeated with the addition of spiral reinforcement, phi(s)= 5 mm diameter, with different pitches s (25 and 50 mm). This study was carried out to evaluate the optimum combination of fibers an d steel spirals to obtain the same level of fracture energy dissipation as that obtained by using only a high-volume percentage of spiral steel, which is generally used in real structures.