Report - PEER - University of California, Berkeley

Vulnerability of buildings to losses related to nonstructural performance is highlydependent on the occupancy of the building. Laboratories and manufacturingfacilities with clean room environments, for example, have systems with differentvulnerabilities, and are more likely to experience occupancy interruption as a failureof these systems, than do office and residential occupancies. Thus, the preliminarydesign for a building must consider not only the typical building systems, such aselectric power supply and distribution, heating ventilating and air conditioningsystems, and fire protection but also critical tenant-installed systems and equipment.Current performance-based design procedures provide little guidance todesigners on how to select or proportion the structural and nonstructural systems intheir buildings to achieve desired performance. Designers engaged in performancebaseddesign must rely heavily on their personal intuition and judgment to developdesigns they believe will be capable of the desired performance, and which they canthen evaluate for performance acceptability. Although generally, increased structuralstiffness, strength and energy dissipation capacity improve performance of structuralsystems, it is not clear that they have the same effect on the performance ofnonstructural systems. Stronger and stiffer structures, though more resistant tostructural damage then weaker, more flexible structures, transmit greater shaking tothe nonstructural components and systems mounted in the building and may actuallycause greater damage of these systems. Therefore, arriving at preliminary designs tosatisfy a given set of performance objectives is not a trivial task. Later phases of theATC-58 project will focus on developing tools to assist the designer to efficientlyprepare preliminary designs that are suitable to buildings of different configurations,occupancies and performance objectives.2.3 Performance Capability AssessmentFigure 2 illustrates the performance assessment process. It initiates with acharacterization of the site hazard, that is, the probability that the building willexperience various levels of ground shaking, characterized by an intensity measure(IM), such as peak ground acceleration, spectral response acceleration at thefundamental mode of the structure, inelastic spectral displacement at the fundamentalmode of the structure, or other similar measure. It is possible that hazard functionsfor several different intensity measures will be required to assess the performance of agiven building. As an example, spectral response acceleration or displacement at thefundamental mode of the structure may be the best IM to predict structural damage,while the damage experienced by nonstructural components and systems, particularlythose mounted at grade, may be better predicted by peak ground acceleration.Structural analysis is used for two basic purposes: prediction of structuralresponse quantities (engineering demand parameters or EDPs) that can be used aspredictors of the damage sustained by the structure, and, prediction of the intensity ofdemands placed on nonstructural elements and systems supported by the structure, atdifferent intensities of ground motion.93