Transmission of perpendicular to grain forces using self-tapping screws

The results presented in this paper show that self-tapping screws applied from opposite member edgesand featuring an overlap in the area of half themember depth are an efficient means to transmitconcentrated perpendicular to grain forces throughtimber members. The tested configurations exhibitload-carrying capacities and stiffness which are at leastdoubled compared to the unreinforced case. To enablegood performance of such details, it is recommendedto adhere to the following specifications, see also Fig.13:•••••••The contact areas should be arranged axiallysymmetric on opposite sides of the member;The screws should be arranged symmetrically to thecontact area;The overlap length should be at least ℓlap = 10·d.Larger overlap lengths do not result in higher load-carrying capacities;The distance between the screw tips and theopposite contact area should be at least ℓtc = 15·d.Smaller distances ℓtc result in lower load-carryingcapacities;It is recommended to apply minimum spacing in thearea of overlapping screws;An alternating arrangement of the STS (alternativearrangement in Figs. 9 and 13) with an even numberof STS applied from both member sides, leads tothe highest improvement in load-carrying capacityand stiffness.A variation of screw diameter only showed marginalinfluence on the described relationships. However,in view of missing experimental data for large