Report - PEER - University of California, Berkeley

Peak Interstory Drfit Ratio0.120.10.080.060.040.0200 0.25 0.5 0.75 1 1.25 1.5First Mode Spectra ResponseAcceleration, Sa (g)Median90% chance ofexceedance10% chance ofexceedanceFigure 3. Representative structural response function.In developing the structural response function illustrated in figure 3, the stiffness,mass, damping and hysteretic parameters for the structure were held invariant, as ifthe true value of these parameters was precisely known. While most likely values forthese parameters can be estimated, in fact, the true values are seldom, if ever known,and there is some uncertainty as to their precise values. To the extent the values formodeling parameters used in the analyses are inaccurate, the resulting structuralresponse function for the building may either over- or under- predict response at agiven ground motion intensity. While it is essentially impossible to predict the exactvalue of any of these parameters, it is possible to estimate most likely values for each,as well as measures of the potential variation. If a series of analyses are performed,varying these parameters consistent with the expected distributions, it is possible topredict the additional variation in response resulting from these uncertainties. Theeffect of these additional uncertainties is to broaden the scatter associated with theresponse function. This is illustrated in Figure 4.Peak Interstory Drfit Ratio0.120.10.080.060.040.0200 0.25 0.5 0.75 1 1.25 1.5First Mode Spectra ResponseAcceleration, Sa (g)Median90% chance ofexceedance10% chance ofexceedance10% conf. 90%chance of exc.90% conf. 10%chance of exc.Figure 4. Structural response with aleatory and epistemic uncertainty.95