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

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simplified formulation, also the corresponding horizontal displacement can be estimated. Finally, the maximum shear strain can be obtained. Table 4. Codes requirements for the design of devices ɸ [mm] σ v [MPa] V crit /V V [k N ] V crit [k N ] Ar [cm 2 ] Ar/A d H [mm] d H / ɸ γ max [%] 500 6 2 1178 2356 830 42% 289 0,58 164% 600 6 2 1696 3393 1304 46% 323 0,54 184% 700 6 2 2309 4618 1597 42% 409 0,58 233% 500 10 2 1963 3927 1383 70% 148 0,30 84% 600 10 2 2827 5655 2174 77% 139 0,23 79% 700 10 2 3848 7697 2662 69% 216 0,31 123% 500 14 2 2749 5498 1936 99% 7 0,01 4% 600 14 2 3958 7917 3043 > 100% - - - 700 14 2 5388 10776 3727 97% 22 0,03 13% Assuming the limit V crit /V =2, only in the case of σ v= 6MPa the horizontal displacement can exceed 50% of device diameter, valuing a maximum shear strain of 233% for the squattest devices (HDRB700, having S 2 > 3 At σ v= 10MPa, the maximum allowable displacement cannot be greater than 30% of device diameters, with a γ max varying in the range 79-123%. Finally, at σ v= 14MPa, to guarantee a safety factor of 2, no horizontal displacement should occur. Comparing experimental evidences with analytical evaluations, the theoretical approach appears more precautionary. Conclusion and contributions The analytical formulations proposed by the authors to evaluate instability phenomenon for rubber devices point out the main involved parameters: G related to material, A r , function of the horizontal displacement, σ v , the applied vertical stress, the product of shape factors, S 1 associated to local geometry and S 2 related to bearing global squatness. In terms of dimensionless factors, the ratio γ /S 2 , equal to the dimensionless horizontal displacement d H / ɸ , appears an effective design parameter to synthetize the global behaviour of elastomeric device. Data from experimental shear tests on full-scale HDRBs show that device responses to the applied vertical plus seismic loads are strictly related to the value of S 2 , having evaluated a more stable behaviour for the bearing having S 2 >3. A comparison between results from different specimen often shows a theoretical instability occurrence (V crit