Experimental investigation of the shear characteristics of steel-to-timber composite joints with inclined self-tapping screws

摘要

In an H-steel-to-timber composite beam, a joint connected by self-tapping screws perpendicular to the steel flange may have problems such as inconvenient construction and a limitation of the embedded depth of the screws due to the thickness of the timber panel. This study proposes a steel-to-timber composite (STC) joint with inclined screws. Push-out tests with double shear planes are carried out for 10 groups of specimens, in which each group includes 3 identical specimens, and the load-slip behaviour and failure modes are analysed. Test results demonstrate that longer self-tapping screws can be used in the STC joint with inclined screws to increase the embedded depth in the timber to obtain a higher shear capacity and that this does cause a drop in shear stiffness. For joints with inclined screws, the use of tapper washers is proposed. The test results show that the shear stiffness of a joint with inclined screws is significantly improved through the use of tapper washers and is approximately the same as that of a joint connected by screws perpendicular to the flange, but the shear capacity is not similarly affected. By analysing the causes of shear failure and comparing subsequent test results, it is found that the screws with a sufficiently long smooth shank should be selected to be used in a joint with inclined screws. Thus, the transition from the smooth shank to the threaded shank is away from the steel-to-timber shear plane, and shear failure can be prevented to obtain good ductility. Furthermore, compared to the joint with a single row of screws, the joint with multiple rows of screws has a similar stiffness, but the shear capacity is reduced by 10.5%. Finally, the calculation method proposed by Eurocode 5 can accurately and safely estimate the shear capacity of the steel-to-glulam screwed joints tested in this paper and accurately predicts the failure modes.