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Report - PEER - University of California, Berkeley

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<strong>of</strong> Figure 7a will be used. It is assumed that the relativity <strong>of</strong> this pair <strong>of</strong> fragilitycurves for a given structure remains the same, and that seismic retr<strong>of</strong>it prior to anearthquake is equivalent to sliding <strong>of</strong> the fragility curves along the horizontal axissuch that a greater earthquake is required after retr<strong>of</strong>it to produce the same probableloss <strong>of</strong> the structural investment. Failing the availability <strong>of</strong> a theory to quantitativelysubstantiate this assumption <strong>of</strong> constant relationship between pairs <strong>of</strong> fragility curvesfor a given structural condition, this will be referred here as the “Reinhorn-BruneauSliding Pair <strong>of</strong> Fragility Curves” assumption. As shown in Figure 8, once thestructure has been retr<strong>of</strong>itted, the investment in the structural system has beenincreased, which translates into the elevated resilience curve <strong>of</strong> Figure 8b.Furthermore, should the same expected earthquake occurs (with a return periodcorresponding to 10% change <strong>of</strong> exceedence in 50 years for the example in Figure8a), the probable loss in structural investment due to damage is also reduced, asshown by the corresponding drop between time t 0 - and t 0 + in Figure 8b.P LSP LSN INVP SL-1Retr<strong>of</strong>it Prior toEarthquakeStructuralInvestm entRetr<strong>of</strong>itP SL-2P SL-1 < P SL-250% in50 Years10% in50 Years2% in50 YearsHazardTimeFigure 8. Non-linear structural seismic response: (a) Bruneau/Reinhornassumption <strong>of</strong> sliding proportional fragility curve sets; (b) Enhancement <strong>of</strong>resilience curve to reduced probability <strong>of</strong> losses due to seismic retr<strong>of</strong>it prior toearthquake.The corresponding impact <strong>of</strong> either structural damage or seismic retr<strong>of</strong>it on thefragility and resilience curves <strong>of</strong> non-structural component for the case <strong>of</strong> non-linearstructural seismic response and non-retr<strong>of</strong>itted non-structural components issomewhat unknown. For example, structural damage could result in a more flexiblestructure, which would have greater displacements but smaller floor accelerationsupon a recurrence <strong>of</strong> the same earthquake at time t 0 + . The total probability <strong>of</strong> lossesin non-structural component would depend on the response distribution (the Demand)and the limit space (the Capacity).t 0t 1169

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