Behavior of concrete beams reinforced with three-dimensional fiber reinforced plastic grids

The purpose of this research was to study an alternative FRP reinforcement method for concrete beams. Three dimensional grids manufactured from pultruded fiber reinforced plastic grating bars were used to reinforce concrete beams as opposed to FRP rebars and custom made stirrups.;The research was divided into several phases. In the first phase, FRP grids made up of off the shelf pultruded grating bars were used to fabricate thirteen full scale concrete beams. The beams were tested under displacement controlled monotonic loading in four point bending. The next phase involved developing a new fiber architecture for the grating bars to improve their mechanical properties in the transverse direction. Several coupon tests were performed in order to determine the mechanical properties of two newly developed grating bars as well as the commercially available grating bar used in the first phase. Afterwards, a second series of full scale beam tests were conducted. The beams tested were reinforced with three dimensional grids made up of three kinds of grating bars. Several grid geometries and shear span to depth ratios were considered. Moreover, six control beams, four of them reinforced with steel rebars and two of them reinforced with FRP rebars were also tested and the test results were compared to that of FRP grid reinforced beams. Finally the experimental findings of the full scale beams tests were evaluated using the equations proposed in the new ACI 440 document, “Guide for the Design and Specification of Concrete Structures Reinforce with FRP Bars.”;The research revealed that three dimensional grids can be used as effectively as FRP rebars to reinforce concrete beams. For shear span to depth ratio, a/d = 3, the beams failed in shear except for one beam that had inclined stirrups. This beam failed in flexure. The failure modes were generally ductile owing to the gradual failure of the reinforcing grid. Different grid failure types were observed due to the different fiber lay-ups examined during the course of the study. Deflections were the controlling design criteria for FRP grid reinforced beams due to the low elastic modulus of the FRP reinforcing bars.