Determination of Screw and Nail Withdrawal Strengths in Parallel and Perpendicular to Grain of some Hardwoods of Iran

In this study، screw and nail withdrawal strengths parallel and perpendicular longitudinal to grain of some hardwoods; oak (Quercus castaneifolia)، hornbeam (Carpinus betulus)، beech (Fagus orientalis)، Sycamore (Platanus oriantalis) and poplar (Populus deltoids) were investigated. The tests were conducted following ASTM D 1761 with specimen dimension of 15×5×5 (T×R×L). Three kinds of screws namely sheet metal screw، wood screw and coarse drywall screw with diameter of 4 and 5 mm were used. Three different nails with nominal diameter of 2. 5، 3. 25 and 3. 75 mm were also used. The highest screw withdrawal strengths parallel and perpendicular to grain were related to hornbeam، beech، oak، Sycamore and poplar respectively. Furthermore، the highest nail withdrawal strengths parallel and perpendicular to grain were related to hornbeam، oak، beech، Sycamore and poplar respectively for nails with 3. 75 mm diameter. Higher density and shear strength of hornbeam compared to the other species accounts for its high screw and nail withdrawal strengths parallel and perpendicular to grain.