Five structural self-tapping screws with a diameter of 6~12 mm and a length of 200~302 mm
were used to investigate the withdrawal resistance performance in wood species of Japanese cedar,
Douglas fir, southern pine, and Kapur. Based on results of the penetration-through tests, the withdrawal
unit force of a structural self-tapping screw for Kapur was 65.3% higher than that of Japanese
cedar. Douglas fir and southern pine showed similar withdrawal resistance values and were
49.6% higher than that of Japanese cedar. The average withdrawal unit force obtained using 10-
and 12-mm structural self-tapping screws was 50.0 and 33.3% higher than that using 6- and 8-mm
self-tapping screws, respectively. Based on the test results of the screw length fully embedded in
wood, the withdrawal capacity of a single structural self-tapping screw in Kapur was 28.8% higher
than that in Japanese cedar. The results obtained from both Douglas fir and southern pine were
close to that of Japanese cedar. The withdrawal capacities of single12- and 10-mm structural selftapping
screws were 2.42-and 2-times, respectively, that of 6-mm screws. The withdrawal capacity
of single 8-mm structural self-tapping screws with a wood-drilling tip was 32.1% higher than
that of screws with a metal-drilling tip. The withdrawal resistance performance of the structural
self-tapping screws in wood was mainly influenced by the wood density, screw diameter, effective
screw length, And type of screw tip.