Achieving High Strength, Ductility, and Durability in Flexural Members Reinforced.....

Presented by Shih Ho Chao, University of Texas at Arlington Conventional non-prestressing or prestressing steel reinforcement used in reinforced concrete members are susceptible to corrosion especially when subjected to aggressive environments, where deicing salt or seawater induces a corrosive effect. Fiber-reinforced polymer (FRP) offers an attractive replacement for steel reinforcement. Concrete members reinforced with steel rebars are designed to behave in a tension-controlled manner, in which the yielding of steel precedes the crushing of concrete. Yielding of the steel rebars leads to wide cracks and large deformation which gives a warning of pending failure of structural members. On the other hand, FRP bars do not exhibit any ductility. Due to the lower axial stiffness of FRP bars, a concrete member reinforced with FRP bars has a much lower flexural stiffness due to greater crack widths along the member. The deeper cracks and large crack widths also reduce the depth of the compression zone. Thus, the contribution of the aggregate interlock and reduced compression zone to resisting shear is reduced significantly. Rupture of FRP bars prior to crushing of concrete is less desirable as the failure of members is abrupt and disastrous. Consequently, ACI Committee 440 suggests that concrete members reinforced with FRP bars be designed to fail by crushing of concrete prior to rupture of FRP bars (i.e., a compression-controlled design approach). Neither of the two designs offer an equivalent ductile behavior compared to members reinforced with steel rebars. In this regard, use of ultra-high-performance fiber-reinforced concrete (UHP-FRC) reinforced with FRP rebars offers a new solution, which gives flexural members both the required high strength/ductility and corrosion-resistant characteristics. UHP-FRC is an advanced cementitious material with improved mechanical properties and durability.