An experimental investigation was conducted to study the stiffness of wood diaphragms. Currently there is no method to calculate wood diaphragm stiffness that can reliably account for all of the various framing configurations. Diaphragm stiffness is important in the design of wood framed structures to calculate the predicted deflection and thereby determine if a diaphragm may be classified as rigid or flexible. This classification controls the method by which load is transferred from the diaphragm to the supporting structure below.

Multiple nondestructive experimental tests were performed on six full-scale wood diaphragms of varying sizes, aspect ratios, and load-orientations. Each test of each specimen involved a different combination of construction parameters. The construction parameters investigated were blocking, foam adhesive, presence of designated chord members, corner and center sheathing openings, and presence of walls on top of the diaphragm.

The experimental results are analyzed and compared in terms of equivalent viscous damping, global stiffness, shear stiffness, and flexural stiffness in order to evaluate the characteristics of each construction parameter and combinations thereof. Recommendations are presented at the end of this study as to the next steps toward development of an empirical method for calculating wood diaphragm stiffness.