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Report - PEER - University of California, Berkeley

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ecords, Jacbson’s approach is not only sensitive to the earthquake characteristics butalso to the oscillator fundamental period and level <strong>of</strong> ductility. Clearly the best way toquantify the scatter, in order to introduce any modification, will be through obtaininga large number <strong>of</strong> such results and utilizing a simple statistical analysis.D TH / DDESIGND TH / D DESIGN0.60.50.40.30.20.10.04.0% 8.0%14.0% 18.0%27.0% 32.0%0.0 1.0 2.0 3.0 4.0 5.0Effective Period (sec)(a) Displacement response spectra2.01.81.61.41.21.00.80.60.40.20.04.0% 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 DesignD TH / DDESIGN2.001.751.501.251.000.750.500.250.002.01.81.61.41.21.00.80.60.40.20.04.0% 6.0%8.0% 10.0%12.0% 14.0%0.0 1.0 2.0 3.0 4.0 5.0Effective Period (sec)(b) Ring-Spring model4.0% 6.0%8.0% 10.0%12.0% 14.0%16.0% 18.0%22.0% 27.0%32.0%0.0 1.0 2.0 3.0 4.0 5.0Effective Period (sec)(d) Takeda large loop modelFigure 7. Time history to design displacement ratio for the Northridgeearthquake, 1994.4.3 Comprehensive Evaluation <strong>of</strong> the Equivalent Damping ApproachGiven the variation <strong>of</strong> the results for real earthquakes and due to the significance <strong>of</strong>Jacobsen’s approach in the direct displacement-based design, it was decided toevaluate the equivalent viscous damping approach for a large number <strong>of</strong> realearthquake records. In this study 100 earthquake records were selected, in order toevaluate the accuracy <strong>of</strong> the approach and to obtain more reliable and simplestatistical data. The 100 records were collected and categorized based on the soil type,namely: B, C, D, E and NF by Miranda [9]. The previously discussed assessmentalgorithm was carried out for each one <strong>of</strong> the records, assuming the Takeda small andlarge loop models in addition to Ring-Spring hysteretic model. 50 oscillators wereused with fundamental periods range from 0.1 to 5.0 seconds, for various levels <strong>of</strong>equivalent viscous damping. Each oscillator was assumed to be designed according tothe DDBD approach, the nonlinear oscillator was identified and inelastic time-historyanalysis was carried out to determine its actual maximum displacement. The totalnumber <strong>of</strong> inelastic time-history analysis conducted in this part <strong>of</strong> the study is125,000.502

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