Report - PEER - University of California, Berkeley

to be sent soon to the 28 members of the European Committee for Standardisation(CEN) for voting. Concepts and approaches for Performance-based seismic design,assessment and retrofitting have deeply penetrated these three standards. So, they willsoon find their way into everyday engineering practice, as within 2007 the about 60Eurocode Parts will be put in parallel use with existing national codes and by year2010 they will be the exclusive structural design standards in Europe.Although the philosophy is the same as in the US, several aspects of theperformance-based approach in Eurocode 8 have developed independently and bear astrong European flavor. Due to the importance of these recent developments forEurope, Parts 1 and 3 of Eurocode 8 have a central place in the paper. The emphasisis on concrete buildings, where the author’s expertise and technical contribution lie.In Europe Performance Levels are associated to, or identified with, Limit States.The Limit State concept appeared in Europe in the ’60s, to define states of unfitnessof the structure for its intended purpose (CEB 1970). They are termed Ultimate LimitStates if they concern the safety of people or structures, or Serviceability Limit Statesif they concern the normal function and use of the structure, the comfort of occupants,or damage to property (mainly to non-structural elements and finishes). According tothe Eurocode on the basis of structural design (CEN 2002) the Limit States approachis the backbone of structural design for any type of loads, including seismic.The CEB Model Code for seismic design of concrete structures (CEB, 1985)introduced two Limit States: (a) Structural Safety (no-collapse) and (b) Serviceability.Design for both was for a single hazard level of unspecified mean return period. TheEuropean Prestandard (ENV) for the seismic design of new buildings (CEN 1994)differs from the 1985 CEB seismic Model Code in that its scope covers practically allmaterials and types of structures, and in the requirement to check two Limit States atdistinct Hazard Levels: (a) the Ultimate Limit State against Life-threatening Collapseand (b) the Serviceability Limit State against damage and loss of use. For ordinarystructures the first Limit State is associated with the 475-year (10%/50yr) earthquakeand checked by as in the 1985 CEB seismic Model Code, except the interstory driftlimitations. The second Limit State is checked only in buildings, where interstorydrifts under 40% to 50% of the 475-year earthquake are limited to values that dependon the brittleness of non-structural partitions. As in the CEB seismic Model Code,alternative levels of ductility for concrete buildings — termed “Ductility Classes” —are three. The performance-based requirements of the 1994 ENV (CEN 1994) wereretained and expanded in the 2004 EN (CEN 2004a), described in the sequel.The European Prestandard (ENV) for repair and seismic strengthening of existingbuildings (CEN 1996) does not present any conceptual advances over its 1994counterpart for new buildings. Except that the interstory drift limits for theServiceability earthquake are not checked, the evaluation criteria for the existingbuilding are limited to full conformity with the requirements of one of the three“Ductility Classes” of the ENV for new buildings (CEN 1994), under a seismic actionreduced due to the shorter remaining lifetime of the building. Retrofitting is also tofull conformity with the rules of the ENV for new buildings.2