Problem 8.4

 

Given

4x8, 5-ply plywood panel

spans roof joists, 16 in. OC

 

Strong direction means the 8-ft dimension runs perpendicular to the joists.  (see textbook figure 8.6, page 8.9)

The plies that would support a sheathing load are the face and back, because the wood grain in these plies runs parallel to the tensile and compressive bending stresses that the panel would experience.  The center ply would be at the neutral axis and therefore have little or no bending stress.  The grain in the crossband plies would run perpendicular to the bending stresses and therefore not be able to support as much load.