Demand and capacity factor design (DCFD) is a probability-based load and resistance factor (LRFD)-like format used for performance-based seismic design and assessment of structures. The DCFD format is based on a technical framework that provides a closed-form analytical expression for the mean annual frequency of exceeding (or not exceeding) a structural performance level, which is usually defined as specified structural parameters (e.g., ductility, strength, maximum drift ratio) reaching a structural limit state (e.g., onset of yield, collapse).
This report, which is presented in two parts, provides a step-by-step and detailed description of the development of the technical framework underlying the DCFD format, accompanied by helpful illustrations and numerical examples. In the first part, a closed-form analytic expression for the mean annual frequency of exceeding a structural limit state is derived based on certain simplifying assumptions. The expression for mean annual frequency of exceedance is derived by taking into account the aleatory uncertainty (due to inherent randomness) and the epistemic uncertainty (due to limited knowledge) in three main elements, seismic hazard, structural response (as a function of ground motion intensity) and capacity.
In the second part of this report, the closed-form expression for the mean annual frequency of exceeding a limit state is re-arranged into alternative formats, suitable for implementation in seismic design and assessment guidelines. These formats can be used to ensure that the structural seismic design can be expected to satisfy specified probabilistic performance objectives, and perhap s (more novel) that it does so with a desired, guaranteed degree of confidence. The degree of confidence in meeting the specified performance objectives may be quantified through the upper confidence bound on the (uncertain) probability. These proposed formats are based on alternative conv entional design methods such as LRFD design and fragility-hazard design. Versions of the new developments reported here are already in place in recently completed seismic guidelines such as the FEMA 350-352 documents and the ISO seismic design guidelines for offshore platforms. Numerical applications of the DCFD format and its underlying framework can be found in pa pers by the authors a nd other researchers, instances of which are outlined in this report.
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