Rods glued in engineered hardwood products part I: Experimental results under quasi-static loading

Glued-in Rods (GiR) represent an adhesively bonded structural connection widely used in timber engineering. Up to now, common practice largely focused on softwood. Most structural adhesives have been, accordingly, specifically formulated to perform on softwood, in particular spruce. The increased use of hardwood, and corresponding engineered wood products (EWP), calls for deeper insights regarding GiR for the connection thereof. This paper, the first of a two part series, presents an overview over extensive research carried with 9 adhesives,3 EWP, and 4 types of rods. Investigations started at component level, by fully characterising all adhesives, EWP, and rods. They were then extended to characterise the behaviour of interfaces, providing by this a methodology for selecting adhesives. Investigations at full scale followed, involving 5 different adhesives, 3 EWP, and 4 rod types. A total of 180 individual samples were tested. The results allowed to draw conclusions about the relationship between performance of GiR connections, and mechanical properties of their components. This relationship, however, has been found to be relatively weak. The companion paper will present a design methodology based on the material properties determined herein, and explain the ambiguous relationship between performance of the GiR and the mechanical properties of the adhesive, wood, and rods.