Effects of Roof Pitch and Gypsum Ceilings on the Behavior of Wood Roof Diaphragms

摘要

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 10 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 standard procedures and analysis. Results showed eave plywood had a 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 that were about 50% that of the flat roofs; and gypsum provided more than one-third 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. (C) 2014 American Society of Civil Engineers.