Report - PEER - University of California, Berkeley

2.1 Performance ObjectivesAn important goal of the ATC-58 project is to utilize performance objectives that arequantifiable and predictable, as well as meaningful and useful for the decision makerswho must select or approve the objectives used as a basis for design. Decisionmakers are a disparate group that includes building developers, facility managers, riskmanagers, lenders, insurers, public agencies, regulators and individual members of thepublic. Each of these decision makers view seismic performance from a differentperspective and select desired performance using different decision making processes.Regardless of the specific process used, selection of appropriate performance willinvolve development of an understanding of the risk associated with a given choiceand the resources that must be invested to reduce this risk beyond certain thresholds.To facilitate this process, in the ATC-58 project performance objectives are expressedas the risk of incurring three specific kinds of earthquake induced loss. These includedirect financial losses (dollars) associated with the cost of repairing or replacingdamaged facilities, earthquake-induced life losses (deaths and serious injuries) andlost use of facilities (downtime) while they are being repaired, replaced or otherwiserestored to service.Different decision makers characterize these risks and determine acceptablelevels of risk in different ways. Therefore the next-generation guidelines permitalternative methods of stating performance objectives including: expected losses,given the occurrence of a specific earthquake scenario, annualized losses, or theexpected loss over a given period of years, each expressed together with a level ofconfidence associated with the estimate. Examples include Probable MaximumLosses (estimates of the 90% confidence level loss given a specific event), averageannual loss (the mean loss per year averaged over many years) or the 500-year loss(that loss which has a 10% chance of being exceed in 50 years). Many other similarmeans of expression will be accommodated.2.2 Perform Preliminary DesignThe preliminary design for a building includes definition of all features that aresignificant to its probable future seismic performance. This includes the building’ssite characteristics, its basic configuration, materials of construction and structuralsystems, foundation type, stiffness and strength, and to the extent that responsemodification technologies such as seismic isolation or energy dissipation systems areincorporated in the design, the characteristics of these systems. Review of lossesexperienced by buildings in past earthquakes clearly indicates that except in thosebuildings where gross structural failure or collapse occurred, most economic andoccupancy losses were the result of damage to nonstructural components and systems.Therefore, the preliminary design must also include consideration of the types ofnonstructural components and systems that are to be installed in the building and theway in which they will be installed.92