The Effect of Thread Geometry on Screw Withdrawal Strength

Doug Gaunt, New Zealand Forest Research Institute, Rotorua, New Zealand

Ultimate withdrawal values for a steel 16mm diameter screw type fixing into dry end grain radiata pine, ranging between 50 and 60 kNs were achieved for the embedment depth of 150mm. The thread profiles used have the thread pitch, thread projection and root depth as variables.

No significant difference in withdrawal capacity was found for the five new thread profiles. All the new thread profiles were however 25% stronger the original 1996 profile.

Due to the inconclusive nature of the results it has not been able to develop relationships between thread profile, timber properties and withdrawal.

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