Influence of Insulation on the Behavior of Steel-Clad Wood Frame Diaphragms

Twenty-five steel-clad wood frame diaphragms were built and loaded to failure to determine the influence of insulation on diaphragm strength and stiffness. Varying thicknesses of foam board insulation and 50.8 mm (2 in.) fiberglass batts were placed between the steel sheeting and the wood frames. Both strength and stiffness significantly decreased when foam board insulation was introduced into the diaphragms. At a given load level, shear deflection was found to be linearly related to the compressed thickness of the insulation. The addition of insulation was also found to influence the mode of failure of the diaphragms as well as the amount of permanent deflection measured after load removal.