by Alexander C. Schreyer
This is a research report for a study that investigated various kinds of dowel-type wood fasteners and their structural behavior under monotonic and cyclic loads. Bolts, dowels and SFS self-drilling fasteners were investigated and compared.
Abstract: The objective of this study was to investigate the monotonic and cyclic behaviour of different kinds of slender dowel-type fasteners. To accomplish this, four types of fasteners were tested in a series of 73 monotonic and cyclic tests. All tests used either one or two slotted-in steel plates in PARALLAM®, a Parallel Strand Lumber (PSL) product. The fastener types were a) plain shank steel dowel of 6.35 mm diameter (SH), b) plain shank steel dowel of 6.35 mm diameter with threads on both ends to allow for nuts and washers to be attached (SHT), and c) two types of a new commercially available self-drilling dowel of 7 and 5 mm diameter which feature a threaded end on one side and a cutting bit on the other (SFS WS-T7 and -T5).
In addition to the test regimen, the monotonic and cyclic behaviour of the fasteners was modeled using a finite element program based on the theory of an elasto-plastic beam on a nonlinear foundation. The existing program was extended to include fastener head behaviour, hole tolerances and fastener material fatigue.
Testing results illustrated a direct influence of the head type on the monotonic as well as cyclic load-deformation behaviour of the tested fasteners. Strength and stiffness increases were observed with increasing head resistance. In the cyclic tests, it was found that this head restraint was influenced by permanent elongation of the fasteners. In addition, cyclic test results were influenced by slack in the connection due to oversized holes as well as fastener material fatigue.
The analytical model yielded good representations of the monotonic as well as the cyclic load-displacement behaviour of the tested fasteners. Inclusion of hole tolerances, fastener fatigue and fastener head behaviour was found to be essential to correctly approximate real fastener behaviour.
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