Report - PEER - University of California, Berkeley

more general, as a tolerable mean annual frequency of collapse. Both options arepursued in Section 3.2.3. DECISION SUPPORT IN CONCEPTUAL DESIGNIn the up-front conceptual design process, decisions have to be made on the type ofstructural system and its global strength, stiffness, and ductility properties. In thefollowing discussion general comments are made on design decisions based on theperformance targets summarized in the previous section, with implementationsillustrated for moment resisting frames, simply because many “design decision aids”have been developed for such frames. The development of similar design decisionaids for wall structures is in progress.3.1 Design Decisions Derived from Loss-Based Performance TargetsThe conceptual process of making design decisions based on acceptable dollar losses,is illustrated in Figure 2. The lower portion illustrates the expected loss-EDPrelationship for the dominant subsystem (e.g., NSDSS). The left upper portion showsthe mean S a hazard curve for the specific site, for the estimated first mode period ofthe structure. The right upper portion shows mean S a -EDP relationships for severaldesign alternatives. The process is to enter the lower graph with a value of acceptableloss and obtain the associated EDP, and to enter the left upper portion with the hazardlevel at which the loss is acceptable and obtain the associated S a . The intersection ofthe S a value and the EDP value in the design alternatives graph can be viewed as a“design target”. All system solutions that intersect the S a line to the left of the designpoint are “feasible” solutions, i.e., the associated expected losses are smaller than thetarget acceptable loss. The “best” solution will depend on many considerations, someof them being discussed in the example given in Section 3.1.1.Mean HazardCurveSa/gMean IM-EDP relations forvarious design alternativesDesignTargetPointH(Sa/g )EDPExpected subsystem lossEDPFigure 2. Designing for acceptable monetary loss (or for targeted EDP).510