Design of FRP Reinforced Concrete Structures for Seismic Effects

Fiber reinforced polymer (FRP) reinforcement, in the form of longitudinal bars and transverse grids is currently being developed for use in new building and bridge structures. However, FRP reinforcement shows linear stress-strain characteristics up to failure, without any ductility. Experimental research is currently conducted at the Structures Laboratory of the University of Ottawa to investigate the seismic performance of FRP reinforced concrete structural elements. Large scale columns and beams are being tested under simulated seismic loading. The results of selected tests are summarized in this paper, with the assessment of their significance from seismic performance perspective. Specimens representing part of a first storey building column between a footing and the point of inflection; and the portion of a beam between a column and the point of inflection, were tested under lateral deformation reversals. The members were reinforced with carbon FRP bars in the longitudinal direction, and carbon FRP grids in the transverse direction. Both the columns and the beams sustained a minimum of 2% to 3% lateral drift ratios, meeting seismic drift limitations of most building codes. Test results indicate that FRP reinforced concrete elements exhibit reduced stiffness and softened response, when compared with conventional steel reinforced concrete elements, because of the lower elastic modulus of FRP bars. This may suggest reduced spectral values associated with longer vibration periods, as well as increased deformability, resulting in seismic resistant structures for which elastic design approach with sufficient deformability may be appropriate.