New Ductile Hybrid FRP Reinforcing Bar for Concrete Structures

Abstract

A new ductile hybrid fiber reinforced polymer (FRP) bar has been developed at Drexel University. This new bar is unique in that it has equivalent bilinear stress-strain characteristics, with a Young's modulus approaching that of steel. It has improved bonding characteristics through the direct introduction of ribs during the in-line braiding and pultrusion process used in its manufacture. When used as reinforcement in new or repaired concrete structures, it attains ductile characteristics similar to those of steel and permits limit states design methodology. The new FRP bar, which fails in a gradual manner, has an equivalent bilinear stress-strain tensile curve with a definite yield, an ultimate strength higher than the yield, and an ultimate failure strain between 2% and 3%. It has the distinct advantage of being noncorrosive, it is light in weight, nonconductive, and nonmagnetic, and has high strength. It can be tailored to strength levels that are compatible to current grades of steel reinforcing bars or prestressing tendons. This paper briefly describes the method of designing and manufacturing the new FRP bars. It compares the predicted and experimental stress-strain characteristics of the new bars manufactured using a prototype braiding/pultrusion process, and compares the behavior of these new bars to steel reinforcement in flexure. It examines the implications of the bilinear stress-strain relationship of the reinforcement on the load-deflection and moment-curvature behavior of flexural members. Finally, it describes the ductile behavior of beams reinforced with the new FRP and with steel bars.