PSI - Issue 44

7

Francesca Ferretti et al. / Procedia Structural Integrity 44 (2023) 2254–2261 Ferretti et al./ Structural Integrity Procedia 00 (2022) 000–000

2260

CD_URM CD_2

CD_4

CD_URM CD_2

CD_4

300

300

250

250

200

200

150

150

100

100 P (kN)

P (kN)

50

50

0

0

-14

-12

-10

-8

-6

-4

-2

0

0

2

4

6

8

10

12

14

δ v (mm)

δ H (mm)

(a) (b) Fig. 6. Comparison of the results for panels strengthened with FRCM: (a) load vs mean vertical displacement diagram; (b) load vs mean horizontal displacement diagram

CD_URM CD_3

CD_URM CD_3

300

300

250

250

200

200

150

150

100

100 P (kN)

P (kN)

50

50

0

0

-14

-12

-10

-8

-6

-4

-2

0

0

2

4

6

8

10

12

14

δ v (mm)

δ H (mm)

(a) (b) Fig. 7. Comparison of the results for panel strengthened with CRM: (a) load vs mean vertical displacement diagram; (b) load vs mean horizontal displacement diagram The results of the tests, in terms of peak load, strength increment, shear stiffness and pseudo-ductility are reported in Table 4. The pseudo-ductility µ, assuming a simplified elastic perfectly plastic behavior, was determined as the ratio between the ultimate shear strain γ u , taken in correspondence with a 20% drop in the load bearing capacity after the peak, and the shear strain γ y , identified along the initial linearized branch in correspondence with a load value equal to 0.8 P u (Ferretti & Mazzotti, 2021).

Table 4. Comparison between the efficiency of different strengthening systems

Average strength Increment

τ El (MPa)

P max (kN)

G (MPa)

f t (MPa)

Specimen

μ

P max /P max (CD_URM)

CD_URM

168.8 232.1 202.3 259.2

-

0.55 0.72 0.66 0.84

2659 2579 2215 2413

0.26 0.34 0.31 0.40

3.6 5.1

CD_2 CD_3 CD_4

+37.50% +19.88% +53.61%

15.0 13.9

For all the samples, the first peak load (i.e., maximum load) corresponded to the appearance of the first macroscopic cracks. The average percentage strength increments are calculated as the ratio between the maximum load P max of the strengthened panels and the maximum load of the unreinforced sample (Table 4). CD_2, CD_3 and CD_4 samples showed a considerable increase in strength, highlighting the critical significance of all the adopted strengthening techniques in improving the shear strength of masonry panels, provided their good redistribution capacity. In detail, CD_4 showed the highest strength increment (around 54%), highlighting the efficiency and importance of symmetrical strengthening layout. It was evident ( Table 4) that the presence of the strengthening