PSI - Issue 44

Fabio Mazza et al. / Procedia Structural Integrity 44 (2023) 1172–1179 F. Mazza / Structural Integrity Procedia 00 (2022) 000–000

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Table 2. Design properties of a HDRL for the BI.HV system (units in kN, m and s). Nominal Upper bound Lower bound

Mixed

D

t

T 1V

D

t

T 1V

D

t

T 1V

D

t

T 1V

a Ke

50 0.463 0.074 0.378 0.515 0.074 0.320 0.536 0.099 0.421 0.556 0.086 0.333 100 0.463 0.056 0.272 0.515 0.057 0.230 0.536 0.074 0.302 0.556 0.065 0.242 200 0.463 0.043 0.200 0.515 0.043 0.172 0.536 0.056 0.220 0.556 0.050 0.179 400 0.463 0.032 0.150 0.515 0.033 0.131 0.536 0.042 0.164 0.556 0.038 0.135 800 0.463 0.023 0.115 0.515 0.024 0.103 0.536 0.031 0.125 0.556 0.027 0.106 1200 0.463 0.018 0.101 0.515 0.019 0.091 0.536 0.024 0.108 0.556 0.022 0.093 1600 0.463 0.014 0.093 0.515 0.015 0.085 0.536 0.019 0.099 0.556 0.017 0.087 2000 0.463 0.010 0.087 0.515 0.011 0.081 0.536 0.014 0.093 0.556 0.013 0.082

3. Horizontal and vertical near-fault earthquakes In order to assess the effectiveness of the combination of horizontal and vertical base-isolation systems of the original (fixed-base) test structure against seismic effects induced by the vertical component of near-fault earthquakes, ten records from those recommended by FEMA P695 (FEMA (2009)) are extracted from the PEER database (PEER (2014)) for medium subsoil (i.e. class C, corresponding to moderately soft-site, in accordance with the NTC18 classification). Only records whose acceleration response spectrum matches the NTC18 target design spectrum at the life safety (LS) limit state, to a certain value of the root mean square difference between a real and a target spectrum, are scaled by using the In-Spector software (Acunzo et al. (2014)). The main data of these earthquakes are reported in Table 3: i.e. year and recording station; moment magnitude (M w ); epicentral distance ( D ); peak ground horizontal accelerations (PGA H,1 and PGA H,2 ); peak ground vertical acceleration (PGA V ); shear wave velocity of the upper 30 m (V s,30 ); scale factor (SF) of each pair of horizontal components. It should be noted that the SF value in the vertical direction is assumed equal to the horizontal one.

Table 3. Main data of the selected near-fault earthquakes (FEMA (2009); PEER (2014)). Earthquake Year Station M w D (km) PGA H1 (g)

PGA H2 (g)

PGA V (g)

V s,30 (m/s)

SF 1.4 1.8 1.0 1.5 1.1 1.0 0.5 1.3 1.0 1.2

Imperial Valley-06 Imperial Valley-06 Imperial Valley-06

1979 Bonds Corner 1979 Chihuahua

6.5 6.19 6.5 18.88 6.5 27.64 6.9 27.23 6.7 8.97 6.7 8.48 6.7 10.91 7.5 19.3 7.6 26.67 7.1 1.61

0.599 0.270 0.341 0.514 0.389 0.753 0.874 0.227 0.790 0.404

0.777 0.254 0.469 0.326 0.496 0.932 0.472 0.322 0.575 0.515

0.532 0.216 0.578 0.396 0.235 0.318 0.958 0.242 0.263 0.346

316 242 192 289 350 353 354 356 306 282

1979 El Centro Array #7 1989 Saratoga - Aloha Ave

Loma Prieta

Erzincan

1992 Erzincan

Northridge-01 Northridge-01

1994 LA - Sepulveda VA 1994 Rinaldi Receiving Sta

Kocaeli Chi-Chi

1999 Yarimca 1999 TCU065 1999 Duzce

Duzce

4. Numerical results Nonlinear dynamic analyses of the test structures subjected to the horizontal and vertical components of ten near fault earthquakes are carried out, assuming the horizontal base-isolation acting alone (i.e. BI.H structures) or in combination with the vertical one (i.e. BI.HV structures). Specifically, four design approaches of the isolation system (i.e. nominal, upper, lower and mixed) are considered, with reference to eight values of the stiffness ratio α Ke (=K e,Vtot /K e,H1 ) for the BI.HV structures (i.e. 50, 100, 200, 400, 800, 1200, 1600 and 2000). A homemade computer code, proposed in a previous work (Mazza (2021)), is updated to introduce an advanced model of the base-isolation