The Effect of Heat Treatment on the Withdrawal Capacity of Screws in Spruce Wood

Mirko Kariz, Manja Kitek Kuzman, Milan Sernek


The withdrawal capacity of screws in heat-treated spruce wood (Picea abies Karst.) was measured in the radial and tangential directions. Wood was heat-treated at temperatures of 150, 170, 190, 210, and 230 °C. Screw withdrawal capacity decreased as the degree of thermal modification was increased. Also, image analysis was used to measure the size of the deformed wood area around the screw, which increased with higher thermal modification temperatures. This leads to the practical recommendation that connections in heat-treated wood should be constructed with screws with larger diameters and deeper penetration. Moreover, larger spacing between screws is needed to ensure sufficient withdrawal capacity compared to non-treated wood.


Deformed area; Heat-treated spruce; Image analysis; Screw withdrawal capacity

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