Prevention of Brittle Axial Failure of Lightly Reinforced Concrete Walls Retrofitted with FRP Laminate and Anchors

This study investigates a novel retrofitting technique to prevent premature axial failure and collapse of RC walls during earthquakes, attributed to inadequate compressive strain capacity in boundary regions. The technique involves fiber-reinforced polymer (FRP) confinement using laminate and anchors. To assess its effectiveness, four full-scale RC walls retrofitted with FRP and two reference walls were tested under consistent axial loads and reversed cyclic lateral loads. The experiment examined various variables, including axial load ratio, anchor spacing, anchor cross-sectional area, confinement type, number of confinement units, and confinement zone depth. The findings revealed that FRP confinement significantly enhanced the strain capacity of concrete in the boundary regions, preventing axial failure and instead causing failure controlled by reinforcing bar fracture, resulting in up to a 100% increase in wall drift capacity. Although FRP confinement had little effect on the equivalent viscous damping ratio, it substantially extended energy dissipation by improving the drift capacity. The study suggests that in design processes, FRP confinement should maintain the stress–strain condition of the boundary regions at a prepeak condition until reinforcing bar fracture occurs, to avoid axial failure.