PSI - Issue 44

Sara S. Lucchini et al. / Procedia Structural Integrity 44 (2023) 2206–2213 Lucchini et al. / Structural Integrity Procedia 00 (2022) 000–000

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1.3. Results of the out-of-plane tests Cyclic test

The present section reports the results of the quasi-static reverse cyclic test described in the previous section. The hysteretic load-midspan displacement (i.e., net displacement=HC3-0.5·(HC5+HC1)) response and the corresponding envelope are shown in Fig. 2a. a b c 100

+76.4kN ; +3.0mm

80

Hysteretic response

60

Envelope

40

+18.0kN ; +6.0mm

20

0

-20

Lateral Load [kN]

-40

-53.4kN ; -13.5mm

-60

-68.0kN ; -6.0mm

-80

-100

-16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12

Midspan displacement [mm]

Fig. 2. Cyclic test: (a) load vs. midspan deflection response; (b) outer and (c) inner view of the specimen at the end of the test.

The response of the specimen was essentially linear in both loading directions up to a load of about 53 kN and - 44 kN. With increasing lateral deflections, a progressive reduction of stiffness was observed as the first horizontal cracks occurred on the URM side of the wall. In more detail, a crack appeared at mid-height during negative loading at a deflection of about -0.8 mm; on the contrary, while loading in the positive direction, the first crack appeared at a deflection of +1.4 mm along the first mortar joint located under the RC chord. After first cracking the lateral resistance continued to increase as new cracks appeared in the masonry units forming the upper portion of the wall. The attainment of the maximum load (+76.4 kN; +3 mm) in the positive direction was followed by a steep decrease of the lateral capacity probably caused by cracks developed within masonry located above the upper loading point. Except for a pre-existing horizontal crack detected close to the upper loading beam, no new cracks grew on the SFRM layer while the wall was displaced in the positive direction. As observed in the positive loading direction, the wall presented a gradual loss of bending stiffness after cracking in the negative direction. Again, damages were possibly spread within masonry located above and below the top and the bottom loading beam, respectively. By increasing the negative deflection, the capacity increased up to a maximum value of about -68 kN. At that point, the severe damages involving the upper portion of the wall led to the formation of a new horizontal crack on the SFRM coating located right above the existing one (see Fig. 2b). Further deflections higher than -6 mm caused a reduction of the flexural stiffness as well as of the lateral resistance of the wall. The maximum negative displacement (i.e., -13.5 mm) attained at the end of the test was 2.25 times higher than the displacement at peak (i.e. -6 mm). The maximum displacement in the positive loading direction was +6 mm and the corresponding ultimate load (i.e., 18 kN) was about 25% of the peak load. Failure occurred because of the severe damages involving the uncoated side of the wall (Fig. 2c). Despite the geometrical asymmetry of the wall due to single-sided retrofitting, the response of the specimen was approximately symmetric in terms of maximum resistance. This fact is well highlighted by the envelope curve of Fig. 2a, which presents similar pre-peak branches in both loading directions. On the other hand, the displacement capacities observed in the two directions were considerably different. The higher ductility detected in the negative direction can be explained considering the tensile contribution to flexural resistance provided by both the SFRM coating and the reinforcing bars