Diaphragm Behavior


Diaphragms comprise the horizontal elements in the lateral force resisting system (LFRS) for many structures. In particular, floor systems and roof/ceiling systems are designed to function as horizontal diaphragms in typical wood structures. Diaphragms transfer the resultant forces from applied lateral loads into the shear walls (or other vertical elements) that support the diaphragm. In plan view for a typical wood structure, a floor or roof diaphragm is essentially a deep, thin beam supported by shear walls at each edge of the diaphragm. The basic form of resistance provided by a diaphragm is that of a shear element. When designing wood diaphragms, the following items should be considered:

1. Sheathing grade and thickness
2. Diaphragm nailing
3. Intermediate blocking between framing members
4. Boundary elements and chord design
5. Diaphragm dimension ratios
6. Deflection

Before beginning a discussion on the design of diaphragms, let us first look at the load path for lateral forces in a simple low-rise wood-frame building.

Load Path Demo

Allowable Shear Table - Wood Diaphragms

Diaphragm Loads

Diaphragm Construction

Support for development of the Diaphragms Tutorial was provided by CUREE, PEER, and WSU.

The Diaphragms Tutorial was designed and created by the following Research Assistants and Faculty at Washington State University: Mike Dodson, Cameron Knudson, Aaron Henson, Dave Pollock (Professor), Michael Symans (Professor), and Ken Fridley (Professor).