When analyzing a diaphragm, is there an easy way to see how the forces are being transferred into and out of the diaphragm?
One method of analyzing diaphragms, particularly with offsets and openings, is called the Visual Shear Transfer Method. This method is based on assigning 1 foot by 1 foot pieces of sheathing referred to as “sheathing element symbols” onto the diaphragm plan. The directions of the shears applied at each edge of the sheathing elements indicate whether the shears are positive or negative. The shears that are transferred into the diaphragm boundary members are equal in magnitude to the shear acting on the edges of the sheathing elements, but act in the opposite direction.
The lateral load path is visually identified by the direction of the shears that are transferred into the boundary elements, which helps determine if the diaphragm strut and collector forces are in tension or compression. This method is an easy and systematic way to determine the diaphragm forces without punching numbers into a calculator.
In this video clip from the January 2015 SE University session, Load Transfer Through Diaphragms, Terry Malone, PE, SE, from WoodWorks works through an example on how to apply the Visual Shear Transfer Method to a typical diaphragm analysis for a horizontally offset diaphragm.