Impact of Thermal Modification of Spruce Wood on Screw Direct Withdrawal Load Resistance

Miroslav Gašparík, Štefan Barcík, Vlastimil Borůvka, Tomáš Holeček


This paper reports on the dependence of screw direct withdrawal load resistance on thermal modification of spruce wood. Screw direct withdrawal load resistance was measured in native and thermally modified spruce wood. The thermal modification was performed at three different temperatures: 140, 180, and 220 °C. Tests were carried out using two types of screws in three anatomical directions. The effect of the thermal modification was unambiguous: the screw direct withdrawal load resistance decreased with increasing modification temperatures. The largest decline 44.2% was found in the axial direction and at a temperature of 200 °C, while the lowest decrease 4.1% was found in radial direction and at temperature 140 °C for conventional screws without pre-drilling. The highest values were identified in the radial direction, and the lowest in the axial direction. While conventional screws without pre-drilled holes may be regarded as the most suitable, the self-drilling screws achieved the lowest values.


Screw; Direct withdrawal load resistance; Spruce wood; Thermal modification; Temperature; Anatomical direction

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