There are about 80 million single-family dwellings (SFDs) in the United States, predominantly of wood-frame construction. Of these, 68% are owner-occupied. A home is typically the largest single investment of a family, and is often not covered by earthquake insurance, even where it is available. Of all the houses in America, 50% were built before 1974, and 76% built before 1990. Most wood-frame SFDs (WFSFDs) were built to prescriptive code provisions before seismic requirements were introduced. After the introduction of seismic design requirements, the importance of examining structures as an assembly of connected elements became more common. Much of the seismic design information on SFD construction is based on educated opinion or limited research. This review examines research that can be applied to WFSFD seismic analysis and the design and retrofit of existing WFSFDs. The review is intended to cover most readily available papers published in major U.S. journals and at major conferences in the area of seismic modeling, testing and evaluation. The state of the art is reviewed of seismic experimentation and seismic evaluation, and observations and recommendations are provided for future research.
Ten full size (3.7 x 4.9 m) plywood roof diaphragms were constructed using metal plate connected (MPC) common and hip wood trusses or joists, typical of single-family dwelling (SFD) construction. The specimens included three gable roof slopes of 33, 67 and 100%, a hip roof of 33% slope, and a flat roof, with a horizontal bottom chord. These roofs were constructed and tested in duplicate to make the total of ten roofs. Gable and hip roofs were tested with plywood sheathing applied to the eaves, with plywood sheathing removed from the eaves, and with a gypsum ceiling attached to the bottom chord of the trusses. Roofs were tested following the ASTM E455 standard procedures and analysis. Results showed eave plywood had negligible effect on diaphragm apparent stiffness; pitch affected gable roof apparent stiffness significantly but did not affect gable roof strength; hip roofs had almost the same apparent stiffness as flat roofs, and had the same strength as flat roofs; gable roofs had apparent stiffnesses which were about 50% that of the flat roofs; and gypsum provided more than 1/3 of the total roof apparent stiffness at slopes of less than 33%. There was no effect of pitch on roof strength in any configuration; all roofs exhibited approximately the same shear strength. Failure modes of roofs included nail withdrawal, nail tear-through, metal plate tear-out on trusses and chord tensile failure.
A four story, 22,200 m 2 (239,000 ft 2 ) wood light-framed assisted-living residential structure was examined for the causes of multiple alleged construction and design defects. The structure was framed using certain "advanced framing" techniques. Observed defects included uneven floors, window and door operation problems, misaligned I-joists and detailing problems with the building envelope. Alleged design defects related to structural engineering included wood shrinkage, uneven and excessive settlement and inadequate design documents. We discuss our approach and methods towards the investigation, including steps taken to ensure fairness in our examination. We present the possible defects in design and construction that we discovered which were easily preventable. We will present recommendations for practicing design professionals and code officials including: • Reasonable tolerances for light framed wood construction,• Additional details or specifications to clarify design intent,
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