Out-of-plane behavior of unreinforced masonry walls strengthened with FRP strips

Geometrically nonlinear effects in the flexural response of masonry walls strengthened with composite materials

“…However, once the joint is cracked, it is assumed that the crack opening, the extensive longitudinal strains in the FRP strip bridging over the crack, and the inability of the cracked faces to transfer shear stresses trigger the formation of a debonded region along the cracked joint. Studies on externally strengthened concrete beams [Rabinovitch and Frostig 2000;Rabinovitch and Frostig 2001;Teng et al 2002] and preceding studies on the geometrically linear response of strengthened masonry walls [Hamed and Rabinovitch 2005] revealed that the characteristic length scale of the peeling stress concentrations near the edge of the FRP strip, near cracks, or near the mortar joint is about the thickness of the adhesive layer. (The peeling stress concentration decays within a distance of about 2 to 3 times the thickness of the adhesive layer).…”

“…Hence, the analysis must account for this type of physical nonlinear constitutive behavior. Based on the experimental observations of [Velazquez-Dimas et al 2000] and [Hamilton and Dolan 2001], it is assumed that cracking is limited to the mortar joints. Hence, the constitutive relations for the masonry units assume linear elastic behavior, whereas the constitutive model for the mortar assumes a linear elastic behavior in compression and a brittle cracking behavior in tension.…”

“…Although in some cases two-way out-of-plane flexural action is possible, in most practical cases, the boundary conditions of the existing wall (which usually consist of only two opposite supported edges) and the use of strengthening system with one-way FRP strips (which is generally easier to install) yield an overall one-way action of the strengthened wall [Davidson et al 2005]. It is also assumed that the stress and deformation fields are uniform through the width of the FRP strips and the adhesive layers, as well as through the active width of the masonry strip, as seen in Figure 1a,b [Davidson et al 2005;Hamilton and Dolan 2001].…”

“…Perfect bonding and the ability to transfer shear and normal stresses are assumed at the interfaces between the various components. Yet, the formation of debonded regions, in which the adhesive-mortar interface cannot transfer shear stresses, is considered in case the mortar joint is cracked, or in case the masonry-mortar interface is partially detached [Hamilton and Dolan 2001;Albert et al 2001]. Finally, it is assumed that the debonded regions do not grow under loading.…”

“…Recently, the use of externally bonded composite materials in the form of fiber reinforced polymer (FRP) laminates and fabrics has gained widespread acceptance. The behavior of URM walls strengthened with composite materials and subjected to out-ofplane loading was examined in many experimental studies [Gilstrap and Dolan 1998;Velazquez-Dimas et al 2000;Albert et al 2001;Hamilton and Dolan 2001;Hamoush et al 2002;Kiss et al 2002;Kuzik et al 2003;Ghobarah and El Mandooh Galal 2004;Tan and Patoary 2004]. These studies reveal that the use of the externally bonded FRP system leads to an increase of 10-50 times the strength of the masonry Keywords: arching, buckling, composite materials, cracking, debonding, masonry, nonlinear analysis, strengthening, wrinkling.…”