The geometrically nonlinear effects in the out-of-plane flexural response of
unreinforced masonry walls strengthened with externally bonded composite materials
are analytically investigated. The investigation aims to explore the stabilizing or
destabilizing influence of the arching action formed under realistic supporting
conditions (restricted longitudinal deformations) of the wall, and to quantify the
contribution of the strengthening system to improving the stability characteristics of
the wall. The localized buckling effects associated with the development of
compressive stresses in the FRP strip are also examined. Variational principles, large
displacements kinematics, compatibility conditions between the structural
components (masonry units, mortar joints, FRP strips, and adhesive layers), and
the assumption of one-way flexural action are used for the formulation of
the nonlinear analytical model. The cracking of the mortar joints, which is
essential to the development of the arching action, and the formation of
debonded zones are also considered. A numerical example that highlights the
geometrically nonlinear effects in the response of the strengthened wall and examines
the influence of the slenderness ratio is presented. The results quantify the
potential increase of the limit point load and deflection due to the externally
bonded composite system. They also quantitatively reveal the wrinkling
phenomenon of the compressed FRP strip and the shear and peeling stress
concentrations that develop in the vicinity of the cracked mortar joints, the
debonded regions, and the wrinkled FRP layer. The paper closes with concluding
remarks.
