Performance-Based Design Procedures: Neither Validated Nor Invalidated

Abstract eng:
Performance-based design (PBD) is a term used to describe techniques that have been promoted as rational improvements -- relative to prescriptive codified procedures --- for evaluating and upgrading existing buildings, and for designing new buildings, to resist earthquake-induced ground motion. Recent examples of such procedures are included in ASCE/SEI 4113 and the PEER Guidelines for Performance Based Seismic Design of Tall Buildings. No buildings designed by such procedures are known to have been field-verified by design-level earthquake shaking; thus, verification that PBD delivers reliable performance is limited to analysis procedures and laboratory testing. PBD remains, therefore, a hypothesis supported by engineering theory but not by empirics. Development of an empirical basis for PBD, even if indirect, is therefore essential before the built environment becomes chock-a-block with PBD structures, especially those with critical function and high occupancies. Example of indirect empirics include verification that PBD methods can retroactively predict damage to non-PBD structures during prior earthquakes or, yet more indirectly, success in blindly predicting damage to laboratory-shaken specimens. Buildings that have been damaged by earthquake ground motion have been studied by many professionals including the authors, and by many professional groups in recent decades, primarily using methods whose specifics pre-date the publication of the most recent PBE procedures, but whose underlying concepts and analysis techniques remain in common use. These earlier studies demonstrate, however, that post-earthquake predictive studies regularly failed to match the observed damage, casting doubt on the use of these methods if reliability is the raison d'être for employing PBD methods. Logical questions we all should be asking ourselves are, “what justification exists for using PBD to design and assess other than its theoretical bases, and how sound are those bases?” The scope of this paper is to explore this subject from various perspectives with the goal of illuminating if PBD analysis procedures, as currently articulated in published standards and guidelines, are likely to meet with better success in predicting damage that will occur from strong ground motion than was possible earlier. Attention will be given to differences between various analysis/design procedures and tools; the influence of variations in ground motion, from recorded to design to actual ground motion at the building site, and to differences between as-built, as-analyzed and as-designed conditions.

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