PSI - Issue 44

Ingrid Boem et al. / Procedia Structural Integrity 44 (2023) 2238–2245 I. Boem, B. Patzák, A. Kohoutková / Structural Integrity Procedia 00 (2022) 000–000

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t (1) The numerical and experimental results are reported in Fig. 4a, Fig. 5a and Fig. 6a in terms of applied horizontal load varying the horizontal displacement of the control point; in Fig. 4b, Fig. 5b and Fig. 6b the trends of the principal tensile strains at collapse are reported, in comparison with the experimental crack pattern. It generally emerged a good accordance of the numerical capacity curves with the envelope of the cyclic experimental ones in terms of initial stiffness, peak load and resistance decrease; also the damage patterns resulted in agreement. The capacity curve of the unstrengthened sample (Fig. 4a) began to lose stiffness at about 90 kN, when the principal tensile stresses in the center of the panel approached the masonry tensile strength; then, progressively involved a wider area along the diagonal. Once attained the sample peak resistance (114 kN, at a displacement of 5.2 mm), the tensile strength at the center of the panel was exceeded and tensions drop rapidly down. A displacement of 9.6 mm (drift 0.49%) corresponded to a resistance decrease of 20%. The higher principal tensile strains values clearly followed a corner-to-corner inclined trend, indicating that the diagonal cracking failure mode activated (Fig. 4b), coherently with the experimental crack pattern. t t f b l t V 0 1  

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Fig. 4. Capacity curves and principal tensile strain at ultimate displacement for the unstrengthened sample.

In the sample strengthened at both sides (Fig. 5a), the former stiffness reduction in the capacity curve, at about 140 kN, was due to the cracking at two opposite corners (right-top and left-down), for the bending action. Suddenly, at about 190 kN, also diagonal cracking emerged from the center of the panel (left-top to right-down direction). As the loading prosecuted, both diagonal and corners damaging increased. The peak load (213 kN, corresponding to an increase of 87% in respect to the unstrengthened sample) was reached at about 17 mm; then the load gradually drop down, with the higher tensile strains localized at the corners (Fig. 5b). Thus, a mixed damaging occurred, with activation of both the diagonal cracking and the in-plane bending failure mechanism, in agreement with the experimental evidences; but, at the end, the bending failure prevailed. It was necessary to reach a displacement of 37.3 mm (drift 1.9%) to get a resistance decrease of 20%.

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Fig. 5. Capacity curves and principal tensile strain at ultimate displacement for the sample strengthened with CRM at both sides.