Bond stress-slip behaviour of steel reinforcing bar embedded in hybrid fiber-reinforced concrete

Experimental study was carried out to evaluate the application of metallic fibers to confine the concrete in column-beam joint. Pullout tests on cubic specimens of size 200 x 200 x 200 mm with deformed steel bar embedded for a fixed length of 5 times the diameter of tested deformed bar were performed under monotonic applied displacement at the tip of the bar (displacement controlled tests). The key variable of the experimental study was the different confining conditions; by ordinary reinforcing steel bars, and by metallic fibers. To confine the concrete by the fibers, two different types of metallic fibers were used; amorphous metallic fibers and carbon steel hooked-end fibers. The fibers were investigated both in mono and hybrid forms. The dosage of fibers in mono fiber-reinforced concrete was kept 40 kg/m(3). In case of hybrid fiber-reinforced concrete, two concrete compositions were investigated: one containing 20 kg/m(3) of each fiber and second containing 40 kg/m(3) of each type of fiber. The pullout tests results revealed that both types of fibers contribute to ameliorate the peak bond stress and also to improve the ascending branch of the bond stress versus slip curve in terms of stiffness. Comparison of the bond stress-slip response of anchored bar in concrete confined by the ordinary reinforcing steel bars and by the metallic fibers demonstrated that the concrete confined by the fibers in hybrid form showed better performance than the concrete confined by the ordinary steel bars in terms of peak bond stress and toughness. Since the hybrid form of investigated metallic fibers realize same effect as that by ordinary steel, the congestion of steel in seismic resistant column-beam joint can be avoided by replacing some percentage of steel ratio to confine the concrete by the metallic fibers.