Report - PEER - University of California, Berkeley

The increased dispersion leads to higher closure probabilities. The effects oftransforming ground motions and the effects of increased dispersion are confirmed inFigures 11–12. In Figure 12, the influence of scaling ground motions to a differentcharacteristic period is demonstrated. Scaling the records at T=0.6s results inincreased demands and dispersion leading to higher closure probabilities. Forexample, the probability of closure in 50 years based on the evaluation using recordsscaled at T=1.2 seconds was previously reported to be 0.46% for the single bentmodel. When the records are scaled at T = 0.6 seconds instead, the probabilityincreases to 1.69%. Additionally, if the dispersion in the latter case is assumed toincrease from 0.614 to 0.75, the probability of closure becomes 2.95%.EDP, Drift (%)54321Scaled, Transformed RecordsScaled, Non-transformedP(Closure|IM)0.50.40.30.20.1Scaled, Transformed RecordsScaled, Non-transformed00 1 2 3 4IM, S a (T), g00 1 2 3 4IM, S a (T), gFigure 11. Effect of scaling and transformation on EDP-IM and P(DV).EDP, Drift (%)54321Scaled at T=1.2 (original)Scaled at T=0.6P(Closure|IM)0.50.40.30.20.1Scaled at T=1.2s (original)Scaled at T=0.6s00 1 2 3 4IM, S a (T), g00 1 2 3 4IM, S a (T), gFigure 12. Effect of hazard curve and response dispersion on EDP-IMrelationship and P(DV|IM).The choice of the characteristic period at which the ground motion scaling is carriedout presents certain challenges. For example, the initial period of the fixed-basemodel of the viaduct is in fact 0.6 seconds. The initial period of the model with soilfoundationsprings increases to about 0.8 seconds for the single bent model. Thevalue of T = 1.2 seconds corresponds to the system with effective stiffness properties.75