Effect of Out-of-Plane Bending on Steel-Reinforced Masonry Wallettes Strengthened with Fiber-Reinforced Polymer

A significant portion of today’s masonry building stock consists of steel-reinforced concrete masonry unit (CMU) walls, including residential construction in coastal areas subject to extreme hydrometeorological events, as well as earth-retaining walls, resulting in out-of-plane bending. The addition of vertical internal steel reinforcement increases the bending capacity and ductility of CMU walls. However, current design guides for strengthening of masonry walls focus mainly on unreinforced masonry. This paper presents the results of steel-reinforced CMU wallettes strengthened with externally bonded (EB) fiber-reinforced polymer (FRP) systems under out-of-plane bending. Nine steel-reinforced wallettes were constructed using lightweight two-cell CMUs and tested in three-point out-of-plane bending under monotonic loading. One of which served as an unstrengthened control, while the other eight were strengthened on one face with wet lay-up carbon or glass EB-FRP systems. Two failure modes were observed: FRP debonding and FRP rupture. The experimental results show that the flexural load-carrying capacity and postcracking stiffness of all the strengthened wallettes were increased, and the increment is related to the FRP reinforcement ratio. In addition, this paper compares the experimentally measured maximum FRP strain with predictions from existing models. The research provides evidence that the current American Concrete Institute design guide for FRP-strengthened unreinforced CMU walls provides a conservative prediction using the debonding strain limit for the out-of-plane bending capacity generated by layered-sectional analysis of FRP-strengthened steel-reinforced CMU wallettes.