Performance of self-tapping screw connections under moisture content change

Self-tapping screws are widely used in timber connections due to their ease of installation and reliable mechanical performance. However, moisture variations during construction can significantly affect the performance of these connections. Changes in moisture content in steel-to-wood connections may induce additional stress on self-tapping screws, potentially compromising structural integrity. This study investigates the short-term performance of self-tapping screw in steel-to-glulam connections, focusing on the effects of installation torque and moisture-induced dimensional changes in glulam. Experiments were conducted to quantify the axial load generated by torque and to assess the additional load induced by wood swelling due to moisture content increase. During wood shrinkage in drying condition, however, a reduction in axial load was observed, and no screw failure occurred in any test scenarios. Additionally, a finite element model was developed to simulate the connection response to moisture content change. The simulation successfully captured the development of stress in the screws caused by torque and moisture content increase. The results indicate that the combination of torque and swelling can increase axial stresses up to 60% of the ultimate tensile capacity of the screw.