Active Confinement of Masonry Walls with Stainless Steel Straps: The Effect of Strap Arrangement on the in-Plane Behavior of Strength, Poisson’s Ratio, and Pseudo-Ductility

Abstract

Among all the active confinement techniques, the use of pre-tensioned stainless steel straps has recently gained much attention. The flexibility of the stainless steel straps allows us to bend and pass them through the thickness of the masonry, thus creating a three-dimensional strengthening system between the two opposite facings. The use of the same perforation for the passage of several straps closed in a loop generates a continuous strengthening system that prevents parts of the structure from falling and injuring the occupants during seismic events. However, the perforations can nullify the in-plane strengthening, as they act as cylindrical hinges and make the reinforcement system labile for certain strap arrangements. Diagonal compression tests on square masonry panels performed in the present study show that the straps improve neither strength nor ductility when running along the mortar head and bed joints, arranged in square meshes. Conversely, they improve both strength and ductility when the straps make angles of ±45° with the mortar joints. Furthermore, the experimental results show that the straps exert an anisotropic effect that decreases the apparent in-plane Poisson ratio. They also provide new insights into the diagonal compression test and allow formulating a new proposal for the pseudo-ductility factor.

A new Proposal for the Interpretation of the Diagonal Compression Test on Masonry Wallettes: the Identification of Young’s Modulus, Poisson’s Ratio, and Modulus of Rigidity

“…Figure 9 shows the comparison between the Mohr circles of the ASTM, RILEM, and new interpretations of the diagonal compression test. As predicted in Reference [10], the center of the new Mohr circle is further from the origin of the axes, B (Figure 9), than is the center of the RILEM circle. This means that the actual hydrostatic stress state at point A is greater than that hypothesized in the RILEM guidelines.…”

“…To tell the truth, τ0 has a weak variation for k > 1 (Figure 10), especially for values of k greater than those assumed in the RILEM guidelines (k = 3.24). As predicted in Reference [10], the center of the new Mohr circle is further from the origin of the axes, 𝐵 (Figure 9), than is the center of the RILEM circle. This means that the actual hydrostatic stress state at point 𝐴 is greater than that hypothesized in the RILEM guidelines.…”

“…As shown in Figure 11b, the 𝜈 𝑅𝐼𝐸𝐿𝑀 value for the URM specimen of Reference [10] does not comply with the limiting values for the Poisson ratio:…”

“…By the statement of Theorem 2 (for further details see Reference [10]), a pure shear stress, ±τ 0 , acts on the planes in the neighborhood of point A whose traces form angles of amplitude β ≶ 0 with the horizontal direction in the x/y plane (Figure 4):…”

A New Proposal for the Interpretation of the Diagonal Compression Test on Masonry Wallettes: The Identification of Young’s Modulus, Poisson’s Ratio, and Modulus of Rigidity

“…In the Mohr plane, the assumption σ x = σ y = 0 results in a Mohr circle centered at the origin [10].…”