PSI - Issue 78

Fabio Mazza et al. / Procedia Structural Integrity 78 (2026) 33–40

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3. Seismic input Nonlinear seismic analysis of the test structures is performed accounting for a set of fifteen near-fault ground motions selected from the PEER database (PEER (2004)), whose horizontal components are rotated in the direction of the strongest pulse according to Shahi and Baker (2014). The average spectral compatibility is obtained applying a scale factor (SF) to both horizontal components of each earthquake, matching the 5% damped elastic design response spectrum of acceleration for the horizontal component provided by the Italian seismic code (NTC18 (2018)) at the life-safety (LS) limit state, for a subsoil class C (i.e. PGA H =0.405g and S H =1.095). Specifically, the resulting mean acceleration spectrum, obtained averaging the above-defined spectra, is characterized by values ranging within the 90% (lower limit) and the 130% (upper limit) of the 5% damped elastic design response spectrum in the interval of vibration periods from T min =0.2T BI,1H to T max =1.2T BI,1H (Eurocode 8 (2005)). It is noteworthy mentioning that the same scale factor (SF) is also applied to the vertical component of each record. Table 3 summarizes the main data of the selected ground motions, reporting information about: year, recording station, moment magnitude (M w ), closest distance (Δ), peak ground accelerations along the horizontal (PGA H1 and PGA H2 ) and vertical (PGA V ) directions, scale factor (SF), pulse period (T P ) and strongest pulse orientation (Φ P ) with respect to east and counter-clockwise. Φ P Imperial Valley 1979 El Centro Array #4 6.5 7.0 0.484 0.370 0.292 2.00 4.79 -89.38 Imperial Valley 1979 El Centro Array #5 6.5 0.6 0.340 0.469 0.578 1.60 4.37 84.22 Imperial Valley 1979 Holtville Post Office 6.5 7.0 0.258 0.221 0.257 2.00 4.82 -38.39 Loma Prieta 1989 Gilroy Array #3 7.3 23.6 0.559 0.368 0.342 1.60 2.64 82.51 Landers 1992 Yermo Fire Station 6.5 5.1 0.244 0.152 0.136 2.50 7.50 31.51 Northridge-01 1994 J. F. P. Generator 6.7 5.4 0.571 0.995 0.764 1.00 3.54 -12.03 Northridge-01 1994 Newhall - Fire Sta 6.7 5.9 0.583 0.590 0.548 1.40 1.37 68.75 Northridge-01 1994 Rinaldi Receiving Sta 6.7 6.5 0.874 0.472 0.958 0.50 1.25 19.48 Bam, Iran 2003 Bam 6.6 1.7 0.808 0.629 0.969 0.70 2.02 1.15 Niigata, Japan 2004 NIGH11 6.6 8.9 0.599 0.464 0.320 1.50 1.80 46.98 El Mayor-Cucapah 2010 TAMAULIPAS 7.2 26.6 0.207 0.226 0.212 1.80 8.43 75.63 Darfield 2010 DSLC 7.0 8.5 0.257 0.237 0.317 2.00 7.83 -71.05 Darfield 2010 GDLC 7.0 1.2 0.765 0.708 1.250 0.70 6.23 9.85 Darfield 2010 ROLC 7.0 1.5 0.390 0.325 0.710 1.40 7.14 -0.36 El Mayor-Cucapah 2010 W. Elementary School 7.2 11.4 0.281 0.256 0.241 2.00 7.08 -40.68 4. Numerical results Nonlinear seismic analyses of the base-isolated (BI) test structures described in Section 2, with (BIHV , α Ke =200) and without (BIH , α Ke =2400) vertical base-isolation, are carried out in their bare (BF, MIs only as weight) and infilled (IF, MIs modelled as in Mazza (2021)) framed configurations. Impact of the vertical component of near-fault ground motions on the nonlinear dynamic response of such structures is investigated. A purpose-built C++ code is developed for the nonlinear seismic analysis of the RC test structures, including a lumped plasticity model of RC frame members, assuming a two halves sub-element discretisation with uniformly distributed mass for beams, and adopting a three spring-three-dashpot model for predicting the horizontal and vertical nonlinear response of HDRBs, with and without HDRLs (Mazza and Labernarda (2021)). Fundamental vibration periods along the horizontal and vertical directions are considered to build the Rayleigh damping matrices of BIHV and BIH test structures, assuming different viscous damping ratios for BF (i.e. ξ H,BIH.BF =2%, ξ V,BIH.BF =5%, ξ H,BIHV.BF =2% and ξ V,BIHV.BF =2%) and IF (i.e. ξ H,BIH.IF =1%, ξ V,BIH.IF =2%, ξ H,BIHV.IF =1%and ξ V,BIHV.IF =1%) configurations. Table 3: Main data of the selected near-fault records (units in km, g, s and °). Earthquake Year Station M w Δ PGA H1 PGA H2 PGA V SF T P