ADVANCES IN PERFORMANCE-BASED EARTHQUAKE ENGINEERING

Historically, introduction and enforcement of structural design codes and standards has been the responsibility of competent Authorities, with public safety as their overriding consideration. So, traditional seismic design codes or standards, espe¬cially for buildings, aim at protecting human life by preventing local or global ollapse under a specific earthquake level with low probability of exceedance. However, in the 1960s the international earthquake engineering community was already aware of the importance of property loss and other economic consequences caused by more frequent seismic events. Recognizing that it is not feasible to avoid any damage under strong earthquakes, the Structural Engineers Association of California (SEAOC) adopted in its 1968 recommendations the following require¬ments for seismic design:“Structures should, in general, be able to: - Resist a minor level of earthquake ground motion without damage. Resist a moderate level of earthquake ground motion without structural damage, but possibly experience some nonstructural damage. - Resist a major level of earthquake ground motion having an intensity equal to the strongest either experienced or forecast for the building site, without collapse, but possibly with some structural as well as nonstructural damage. ” Major earthquakes that hit developed countries in the second half of the 1980s and the first half of the 1990s caused relatively few casualties but very large dam¬age to property and other economic losses. In response to this, “Performance based earthquake engineering” emerged in the SEAOC Vision 2000 document and devel¬oped into the single most important idea of recent years for seismic design or retrofitting of buildings. “Performance-based engineering” focuses on the ends, notably on the ability of the engineered facility to fulfil its intended purpose, taking into account the conse¬quences of its failure to meet it. Conventional structural design codes, by contrast, are process-oriented, emphasizing the means, i.e., the prescriptive, easy to apply, but often opaque rules (hat disguise thepursuit of satisfactory performance. These rules have been developed over time as a convenient means to provide safe-sided, yet economical solutions for common combinations of structural layout, dimensions