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Report - PEER - University of California, Berkeley

Report - PEER - University of California, Berkeley

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4.1.3 Soil-Foundation-Structure Interaction (SFSI) EffectsThe flexibility <strong>of</strong> the soil-foundation system was found to play a significant role in theresponse <strong>of</strong> the viaduct. Neglecting SFSI effects can result in a vastly differentassessment <strong>of</strong> the bridge performance. As shown in Figure 9 the closure probabilityvaries significantly depending on whether SFSI effects were incorporated or ignored.The likelihood <strong>of</strong> bridge closure in a 50-year period decreases by a factor <strong>of</strong> 5 (from0.95% to 0.19%) if soil-foundation flexibility is disregarded.EDP, Drift (%)4321with SFSIwithout SFSIP(Closure|IM)0.40.30.20.1with SFSIwithout SFSI00 1 2 3 4IM, S a (T), g00 1 2 3 4IM, S a (T), gFigure 9. Effect <strong>of</strong> SFSI on EDP-IM relationship and P(DV).4.2 Issues Related to Scaling and Transforming Ground MotionsSince the hazard curve is a function <strong>of</strong> the uniform hazard spectra, the process <strong>of</strong>scaling and transforming records can have a significant impact on the evaluation.Figure 9 shows the spectra <strong>of</strong> the original records, and the spectra after scaling andafter transforming the fault normal records to the transverse direction <strong>of</strong> the bent.Since the transformation process alters the spectra and the magnitude at thecharacteristic period, the resulting peak responses exhibit larger dispersions.Spectral Acceleration (g)5432100 1 2 3 4Period, T (sec)5(a) 4(b) 4(c)32100 1 2 3 4Period, T (sec)Figure 10. Effect <strong>of</strong> record transformation on spectral demand: (a) originalrecords; (b) scaled to characteristic period; (c) transformed records.532100 1 2 3 4Period, T (sec)74

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