Concrete columns and beams reinforced with FRP bars and grids under monotonic and reversed cyclic loading

Abstract

The use of fiber reinforced polymer (FRP) reinforcement is currently being explored by the construction industry as a new and innovative material. A significant force behind this consideration is the superior performance of FRP material in corrosive environments. FRP possesses high strength-to-weight ratio, favorable fatigue strength, and low relaxation characteristics when compared with steel reinforcement, offering economically and structurally sound alternative for most applications. The majority of current FRP applications have been in the area of rehabilitation and strengthening of existing structures, although some attempts have been made for application to new construction. The research program consisted of four phases; (i) columns under eccentric monotonic loading; (ii) reinforced cylinders under concentric compression; (iii) columns under constant axial compression and lateral load reversals, and (iv) cantilever beams subjected lateral monotonic or cyclic loading. The results of tests conducted at the Structures Laboratory of the University of Ottawa indicate that CFRP reinforcement can be used effectively in new concrete members. CFRP reinforced columns subjected to eccentric loading were able to develop their expected moment capacities as governed by the crushing of concrete. All columns under cyclic loading sustained a lateral drift level exceeding 2% and 2.5% limits specified for earthquake resistant columns in the National Building Code of Canada (1995, 2005). Failure in these columns was initiated by the spalling of concrete cover, followed by the buckling of FRP bars in compression at approximately 0.45% to 0.60% compressive strain, and subsequent crushing of the core concrete. The failure of FRP bars in compression was due to instability. The stability failure of FRP bars in compression was different than that observed in steel reinforcing bars. The hysteretic relationship of flexure dominant FRP reinforced beams indicated stiffness degradation under cyclic loading due to the progressive cracking of concrete and associated softening in the member, developing approximately 3% lateral drift ratio prior to failure. This level of lateral drift may be considered to be sufficient for earthquake resistant construction. All the flexure dominant members developed their flexural capacities computed on the basis of plane-strain analysis. (Abstract shortened by UMI.)