Abstract
Screwed-in threaded rods with wood screw threads feature high axial capacity and stiffness and can be used as fasteners in highly resistant and stiff timber connections. The purpose of the present paper is to review the existing literature and design rules in the present version of Eurocode 5 (EN 1995-1-1) and European Technical Assessments, to identify gaps of knowledge and to provide some proposals for the strength and stiffness of threaded rods. A collection of experimental results is used to derive simple expressions for the withdrawal capacity and stiffness. Finally, theoretical expressions for the stiffness and the capacity of laterally-loaded threaded rods are provided.
Highlights
Screwed-in threaded rods feature high axial capacity and stiffness and they may be a promising alternative to dowel-type fasteners or axially-loaded glued-in rods for highly resistant and stiff connections in timber structures
Some expressions which provide the withdrawal stiffness of self-tapping screws can be found in their ETAs, but they cannot be extrapolated for threaded rods [33]
The collection consists of 221 test results in total, arranged in 31 sets according to the varied parameters: the diameter, the angle to grain and the penetration length
Summary
Screwed-in threaded rods (i.e. rods with wood screw threads and greater diameters than self-tapping screws) feature high axial capacity and stiffness and they may be a promising alternative to dowel-type fasteners or axially-loaded glued-in rods for highly resistant and stiff connections in timber structures. To the knowledge of the authors, no ETA provides rules for the block shear capacity of threaded rods. EN 1995-1-1 [31] does not provide rules for the withdrawal stiffness of screws and threaded rods. Some expressions which provide the withdrawal stiffness of self-tapping screws can be found in their ETAs, but they cannot be extrapolated for threaded rods [33]. The existing literature and the design rules given by EN 1995-1-1 [31] and some ETAs for screws and threaded rods are reviewed. The scope of this paper is limited to threaded rods embedded in softwood unidirectional timber elements (e.g. solid timber or glued-laminated timber) and only short-term loading is considered. Glued-in rods are outside the scope of this paper and the reader is referred to relevant publications, e.g. [34,35]
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