Site-specific load models and hazards for probability-based design

Structural design codes have evolved continuously since modern codes were established. The allowable stress design format has been widely used since the late 19th century. During the past two decades, probability-based limit states design concepts have evolved and are increasingly being used for various material and structural types. Limit state design, such as LRFD in the U.S., has requirements to ensure that structures perform satisfactorily under various loads and load combinations and that properly designed structures have reliable and consistent safety levels. Performance-based design concepts recently have gained interest among designers and researchers as an alternative to traditional (strength) design procedures. Performance-based engineering procedures require reliable predictions of structural response in order to quantify and limit damage to acceptable levels during the service-life of the structure. The objective of this study is to develop new contributions in performance-based design of engineered woodframe structures. Specially, fragility curves are developed for structures subjected to various natural hazards (and combinations of hazards) and new site-specific snow load models and hazard models are developed for use in probabilistic design. To accomplish these objectives, fragility curves are developed for assessing probabilistic response of engineered woodframe structures under wind, snow and earthquake hazards. The fragility curves developed herein can be used to develop performance-based design guidelines for woodframe structures built in high hazard regions as well as to provide information on which to base structural safety or expected structural (and economic loss) assessments. Probabilistic snow load models and snow hazard curves also are developed in this study. Updated snow load models can be used in code calibration studies and in the development of next-generation partial safety factors. The snow hazard curves can be used in a number of reliability-based design and performance-based design applications including assessment of partial safety factors for limit states design, evaluation of load combinations (coincidence) factors considering multiple hazards, evaluation of failure probabilities (by convolving with fragility curves for different performance levels, and development of risk-based assessment procedures for structures (and inventories of structures) under extreme snow loading.