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Report - PEER - University of California, Berkeley

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oscillator didn’t respond in-elastically; instead it remained linear in most <strong>of</strong> the casesor did not go far into the inelastic range in other cases.0.501.50Spectral Displacement (m)0.400.300.200.104.0% 8.0%14.0% 18.0%27.0% 32.0%0.000.0 1.0 2.0 3.0 4.0 5.0Period (sec)(a) Displacement response spectrum1.501.25D TH / D DESIGN1.251.000.750.504.0% 6.0%0.258.0% 10.0%12.0% 14.0%0.000.0 1.0 2.0 3.0 4.0 5.0Effective Period (sec)1.501.25(b) Ring-Spring modelD TH / D DESIGN1.000.750.500.250.004.0% 6.0%8.0% 10.0%12.0% 14.0%16.0% 18.0%0.0 1.0 2.0 3.0 4.0 5.0Effective Period (sec)(c) Takeda small loop modelD TH / D DESIGN1.000.750.500.250.004.0%8.0%6.0%10.0%12.0% 14.0%16.0%22.0%18.0%27.0%32.0%0.0 1.0 2.0 3.0 4.0 5.0Effective Period (sec)(d) Takeda large loop modelFigure 5. Time-history to design displacement ratio for sinusoidal earthquake(ω =10 Hz).In the case where the ratio is nearly one, there was good agreement between thenonlinear and linear oscillator displacement time histories, the loops were developedgradually with sufficient amount <strong>of</strong> ductility into the system as shown in figure 6b.After investigating some <strong>of</strong> the cases where the displacements wereunderestimated (i.e., ratio greater than one), the hysteretic loops show a shift in thevibrating position <strong>of</strong> the nonlinear oscillator; this behavior is shown in figure 6c. Thisbehavior is attributed to a large pulse that pushes the structure into the inelastic rangeand as a result, when it starts to unload, it vibrates around a new position whichcauses the shift in the loops as shown.4.2 Typical Real Earthquake ResultsSince real earthquake records are unlikely to have a specific frequency, but rather arange <strong>of</strong> frequencies, the sudden change in the results seen in figures 5 will be lessapparent. Due to an expected increase in the scatter and to show a sample <strong>of</strong> realearthquakes results, two typical real earthquake records with different characteristicswere selected: (1) Northridge 1994, and (2) Kobe 1995.500

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