Withdrawal capacity and stiffness of re-inserted selftapping screw´s

The stiffness and withdrawal capacity of screws are one of the most critical aspects of screws joints to function correctly. These joints are essential for achieving stability and durability in wooden structures. Their capacity, reliability and simplicity are contributing factors to why they are one of the most widely used methods for joining wooden elements today. Withdrawal capacity is determined by how much tensil stress the material is capable of before collapse. Stiffness is defined by the joint’s ability to maintain its shape and structure under load. In this study, both stiffness and withdrawal capacity were tested through three different test series. Each test series is comprised of 20 tests. The first test series was tested by screwing in the screw and testing the withdrawal capacity. The second series was drilled in and drilled out, then back into the same hole and subsequently tested for withdrawal capacity. The third series, like the second series, had the screw drilled in and screwed out, then screwed into a nearby hole to test the withdrawal capacity. A practical experiment was conducted to investigate the differences in withdrawal capacity of axially loaded screws in glued laminated timber (glulam) based on the screws’ condition. The tests were performed on homogeneous glulam (GL30h). The screws were drilled in and embedded 115 mm. The results of the investigation indicated that there was no significant difference in withdrawal capacity between the first two series, while the third test serie was 19,8% weaker. The difference in stiffness between the different test series was small. Even though there was a difference, the difference was not tested to see if it had a statical significance of the outcome of the results.