PSI - Issue 44

Sara S. Lucchini et al. / Procedia Structural Integrity 44 (2023) 2286–2293 Lucchini et al. / Structural Integrity Procedia 00 (2022) 000–000

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Table 3. Experimental building: axial load and resistance of retrofitted piers in positive loading direction. Direction +X Pier 1 Pier 2 Pier 3 Pier 4 Pier 5 Pier 6 Axial load N t [kN] 45.75 48.65 33.38 47.52 50.42 33.38 Axial load N b [kN] 55.43 58.10 40.35 56.31 58.98 40.35 V R,t [kN] 120.98 120.90 101.25 121.13 121.20 101.25 V R,s [kN] 61.51 142.91 75.30 61.88 60.16 75.30 V R,flex [kN] 71.01 141.81 66.52 71.47 80.74 66.52 V R [kN] 61.51 120.90 66.52 61.88 60.16 66.52 Predicted failure mode S D F S S F

The failure mechanisms predicted by the analytical model were quite consistent with the experimental ones. As reported in Table 3, pier 2 exhibited a diagonal shear failure, piers 3 and 6 were governed by flexure and piers 1, 4 and 5 by sliding shear. The experimental crack pattern shown in Fig. 1b-c pointed out that piers 3 and 6 exhibited diagonal shear cracks in addition to flexural ones. Retrofitted building – negative loading direction (-X) The same approach was applied in the negative loading direction to identify the effective height H eff of each pier, based on the critical sections depicted in Fig. 2b. In this loading direction the axial load increase was applied on piers 3 and 6, to consider the uplift of North façade after the application of the horizontal load. The sum of the resistances of the six piers in the negative loading direction provided an underestimation of the global resistance of 18%, i.e., 479.0 kN versus 584.6 kN. Regarding the failure modes, as reported in Table 4, piers 2 and 5 exhibited a diagonal shear failure, piers 1 and 4 were governed by flexure and piers 3 and 6 by sliding shear. The analytical mechanisms are quite consistent with the experimental ones, shown in Fig. 1b-c, except for pier 5 that did not exhibit a diagonal shear failure. Furthermore, at the end of the test, piers 1 and 4 exhibited diagonal shear cracks in addition to flexural ones.

Table 4. Experimental building: axial load and resistance of retrofitted piers in negative loading direction. Direction -X Pier 1 Pier 2 Pier 3 Pier 4 Pier 5 Pier 6 Axial load N t [kN] 33.38 48.65 45.75 35.14 50.42 45.75 Axial load N b [kN] 40.35 58.10 55.43 41.23 58.98 55.43 V R,t [kN] 101.25 120.90 120.98 118.37 121.11 120.98 V R,s [kN] 75.30 142.91 61.51 55.61 143.54 61.51 V R,flex [kN] 66.52 141.81 71.01 47.44 142.81 71.01 V R [kN] 66.52 120.90 61.51 47.44 121.11 61.51 Predicted failure mode F D S F D S

3.2. In-plane capacity of a real two-story residential building The analytical model was also applied to a real two-story residential building made of 330 mm thick concrete hollow units, which was constructed in the 1960’s. The structure has plan dimensions of 11.4 × 10.0 m 2 (see Fig. 3a), a total height of about 8.2 m, one-way concrete slabs forming the two floors and a pitched roof. The building was retrofitted by the application of a 20 mm thick SFRM coating not connected to the building foundation by rebars. The analytical prediction of the global seismic resistance of the building, before and after retrofitting, was compared with that obtained by means of non-linear static analyses carried out with the FE program Midas FEA in previous research, described in Facconi et al. (2021). The comparison focuses only on the +X loading direction. The main mechanical properties of masonry and SFRM coating, used both in numerical and analytical models, are listed in Table 5.