Thermal Degradation of Lateral Yield Strength of Nailed Wood Connections

This study investigated the effect of exposure to elevated temperature on the yield strength of single-shear nail connections when subjected to lateral loading. Solid sawn lumber and laminated veneer lumber were used as framing members and two different thicknesses of both oriented strand board and plywood were used as the sheathing members. The connection geometries evaluated were typical of those encountered in lateral force resisting systems such as shear walls or roof diaphragms. The connection geometries were (1) edge connection—nail positioned 19 mm from the panel edge, loaded parallel to the grain of the main member, and (2) plate connection—nail positioned 19 mm from the panel end, loaded perpendicular to grain of the main member. Data collected from monotonic tests on 480 nail connections, after exposure to elevated temperatures, were analyzed for yield strength. In addition, 210 dowel bearing strengths were evaluated for the same treatments. The results indicated that exposure to elevated temperature caused significant degradation in lateral yield strength after exposure. The highest degradation occurred when exposed to 200°C for 2 h. For example, for plywood (11.2 mm) and solid lumber connections, the decrease in yield strength after exposure to 200°C for 2 h was 26% for edge connections and 56% for plate connections. The results further indicated that, given thermal degradation of the dowel bearing capacity of a material, the existing yield models stipulated in National Design Specifications (NDS) can predict yield load values for nailed connections for a given sheathing and framing member combination under those thermal degradation conditions. Additionally, the yield models predicted a predominant yield mode (${\mathrm{III}}_s$), consisting of a single plastic hinge being formed just beneath the surface of the thicker member. These predictions were consistent with observed yield modes.