Report - PEER - University of California, Berkeley

are predicted from structural analysis for given values of IMs (and representativeground motions); local collapse fragility curves (e.g., for floor slabs that may dropbecause of shear failure at column-to-slab connection) and global collapse fragilitycurves of the type shown in Figure 6 are used to predict local and global collapseprobabilities; and as a last (and not yet fully resolved) step, predictions are made ofthe number of lives lost and the number of injuries. Similarly, for performanceassociated with losses and downtime, the process of determining DVs is illustrated inthe right half of Figure 1, again with the information flowing from right to left.Life safety / collapse$ losses / downtimeDV2Numberof liveslostNumberof injuriesDV1Globalor localcollapseDM(Fragility)Cladding,ShearfailureEDPDrift,StrengthdemandDeterioratingSystemsIMDV$ Losses,DowntimeRepaircost,Loss offunctionDMComponentFragilityStructuralNonstruct.ContentEDPDrift,Rotation,FlooraccelerationIMGlobalInstabilityEngineering DesignParameters forLimit State 1StrengthStiffnessDuctilityDesign for multipleperformanceobjectivesEngineering DesignParameters forLimit State 2StrengthStiffnessDuctilityFigure 1. Design for multiple performance objectives (Krawinkler 2004).The mathematical formulation for evaluating decision variables and providingdecision support to the owner/user, considering uncertainties inherent in all parts ofthe process, is provided by the PEER framework equation expressed as follows:( DV ) ∫∫∫λ = G DV DM dG DM EDP dG EDP IM dλ(IM ) (1)Design is different from performance assessment, simply by virtue of the fact thatthe building and its structural components and system first have to be created. Onecan view design as an iterative assessment process that starts with a judgmentalconceptual design for which performance assessment is carried out, and the design isimproved (tuned) in successive iterations until the performance targets are met. Thisdesign process is an option, but not a very attractive one. A poor initial conceptualdesign may be tuned to an extent that it fulfills the performance targets, but it likelywill not become a good design. Good designs are based on concepts that incorporateperformance targets up front in the conceptual design process, so that subsequentperformance assessment becomes more of a verification process of an efficient designrather than a design improvement process that may require radical changes.506