Report - PEER - University of California, Berkeley

economic losses resulting from the last major events in the U.S. and Japan can beconsidered as the motivation for PBEE, which is deemed to provide an appropriateplatform to achieve safer and more economic constructions.The conceptual frameworks proposed in the USA for PBEE (Krawinkler, 1999),such as Vision 2000, can be considered as a step forward on a more rational seismicdesign and assessment/redesign of engineered facilities. In fact, explicit considerationof multi-level performance objectives together with specific seismic intensities leadsto a more controllable/predictable seismic performance. This represents a significantimprovement relatively to the single-level explicit approach of current design codesbecause it requires explicit consideration and check of key performance objectivesand it conveys it clearly to the designer that a structure is likely to be subjected todifferent seismic intensities during its life, including severe ones with low probabilityof occurrence.However, this multi-performance approach still embeds a prescriptive concept, inthe sense that the association of a series of performance objectives with specific inputlevels does not leave space to differentiated choices and might not satisfy therequirements and expectations of different stakeholders (the general public, owners,lenders, insurers, businesses and government). It is believed that decisions regardingacceptable earthquake risk should be left to the stakeholders and thescientific/technical communities should focus on the issues related to calculation ofthese risks and associated costs.It is however advocated that a risk-based approach should be followed forseismic design. It should include prescriptive performance objectives related to safetyas well as to other relevant macroeconomic minimum requirements (stakeholders:state and authorities) and leave the economic aspects on the other stakeholders, whoare deemed to focus on the mitigation of the adverse economic consequences(Hadjian 2002). This mixed approach (minimum requirement performance –optimum-risk based) imposes minimum safety levels as well as minimum socialadverse consequences and brings seismic design to a new level, where safety, designoptimization (allowed trade-off between different performance levels) and innovationcan coexist.3. PERFORMANCE AND EXPECTED LOSSES FOR STRUCTURES DESIGNEDACCORDING TO CURRENT DESIGN CODES — ILLUSTRATIVE EXAMPLEReliability analysis and risk assessment of structures can be carried out followingwell-established methodologies. Difficulties may be encountered in system reliabilityapproaches, for which correlation between different failure mechanisms exists as wellas in the quantification of demand and capacity variabilities and loss (cost) functions.An application of reliability and risk assessment tools and methodologies to structuresdesigned according to the Eurocodes was made by (Pinto, 1998). A case studied inthis work is herein revisited to underline a few important aspects relevant to riskassessment and also to the definition of appropriate earthquake testing protocols.283