PSI - Issue 44

Laura Giovanna Guidi et al. / Procedia Structural Integrity 44 (2023) 1284–1291 Laura Giovanna Guidi et al. / Structural Integrity Procedia 00 (2022) 000–000

1288

5

4. Stability of elastomeric bearings valued through experimental data Previous theoretic evaluations and the recommendations from current building codes are compared with the results from an experimental campaign on full-scale high damping rubber bearings, partially described by authors (De Luca et al., 2022). To evaluate stability issues for rubber devices, results from static shear tests at large deformations are compared. In this way, theoretical evaluations on instability phenomena have been matched with the effective instability occurrence for devices recoded during tests. 4.1. Specimen and experimental procedure The experimental campaign referred to full-scale high damping rubber bearings, HDRB. These bearings are made of “soft” natural rubber, having G= 0.4MPa (at γ =100%) and an equivalent damping factor ξ = 10÷15. Three different diameters (500 mm, 600 mm, 700 mm) are involved. Table 1 summarizes the main features of tested bearings, also including the value of critical load in absence of lateral deformation, V crit,0 , and the corresponding vertical stress, σ crit,0 . The experimental campaign has ben performed at SisLaB Laboratory (Laboratorio Prove Materiali e Strutture) of the Università degli Studi della Basilicata - Scuola di Ingegneria. The test machine for rubber devices consists of a MTS system, a 1800 l/min hydraulic pump and a dynamic actuator (Model 244.51S), bounded to RC reactor and to a steel structure, where devices are installed to be tested. The apparatus guarantees to test full-scale devices, with a maximum plan dimension of 800mm, and allows a final horizontal displacement of ± 500 mm.

Table 1. Specimen Characteristics Main features

SI-S-500-176

SI-S-600-217

SI-S-700-207

Diameter [mm]

ɸ [mm] t i [mm] t e [mm]

500 5,50 176

600 7,00 217

700 9,00 207

Single rubber layer thickness

Total rubber thickness Number of rubber layer

n r S 1 S 2

32

31

23

Primary Shape Factor ( ɸ /4ti) Secondary Shape Factor ( ɸ /te)

22,72 2,84 5579 28,4

21,42 2,76 7371 26,1

19,44

3,38

V crit,0 σ crit,0

Critical load in absence of horizontal deformations [kN] Critical vertical stress in absence of horizontal deformations [MPa]

11132

28,9

Table 2. Main aspects of the experimental campaign SI-S-500-176

SI-S-600-217

SI-S-700-207

No.

Type

σ v [MPa]

γ max [%]

d H / ɸ

σ v [MPa]

γ max [%]

d H / ɸ

σ v [MPa]

γ max [%]

d H / ɸ

1 2

SC SC CS SS SS SS SS SS SS SS SS

6 5 6

- -

- -

6 5 6

- -

- -

6 5 6

- -

- -

3 -6-16

150% 206% 206% 175% 200% 220% 250% 280% 430%

53% 73% 73% 62% 70% 78% 88% 99%

150% 206% 206% 175% 200% 220% 250%

54% 74% 74% 63% 72% 80%

150% 206% 206% 175% 200% 220% 250% 250% 326%

44% 49% 49% 53% 59% 64% 71% 72% 96%

4 5

8.5

8.5

8.5

2

2

2

7-8-9

6-10-14 6-10-14 6-10-14 6-10-14

6-10-14 6-10-14 6-10-14 6-10-14

6-10-14 6-10-14 6-10-14 6-10-14

10-11-12 13-14-15 17-18-19

- - -

20 21

0.6 2,8

- -

- -

20 20

>100%

The whole experimental program includes of 58 test and comprises: SC, static compression tests at σ v = 5-6MPa; CS, cyclic shear at γ max = 150% and σ v = 6MPa; SS, static shear monotonic tests, assuming σ v variable from 6MPa to 20MPa, with γ max from 175% to 250%, as synthetized in Table 2. For the scope of this paper, results from static shear tests have been considered. These data have been elaborated to evaluate the conditions that lead devices to buckle.