Design Methodology of Diaphragm

Six diaphragms were tested using cyclic displacements to determine the effect various construction details have on stiffness. Three diaphragm aspect ratios were investigated, 16 x 20 ft (4:5), 20 x 16 ft (5:4), and 10 x 40 ft (1:4). Two loading cases were investigated, Case 1 with the load oriented parallel to the joists and perpendicular to the continuous joint in the sheathing, and Case 2, with the load oriented perpendicular to the joists and parallel to the continuous joints in the sheathing. Construction details investigated include blocking, adhesives, presence of designated chord members, openings (center and corner), and walls on top of the diaphragm.

Results show that blocking is the most effective method of stiffening the diaphragm and adhesives augment their effect. There is significant ability to resist loads through bending action, but the presence of designated chord members significantly increases the bending stiffness. The effect of openings on shear stiffness is proportional to the size of the opening, but not necessarily linearly proportional to the size of the opening. Finally, the effect of walls on top of the diaphragm on the bending stiffness of the diaphragm is significant if they are attached well.