Experimental investigation of the axial strength of glued-in rods in cross laminated timber

Abstract

This paper presents results from an experimental assessment of glued-in rods in cross laminated timber (CLT). For the purposes of the study more than 60 pull-pull tests were performed, where the specimens varied in terms of bonded-in length (from 80 to 400 mm), rod diameter (16-24 mm) and rod-to-grain angle (parallel and perpendicular). Several different failure modes that are not common for other applications of glued-in rods (e.g., a failure between CLT layers) were obtained for the analysed CLT specimens. It was found that these failure mechanisms can substantially influence the obtained ultimate tension loads. At the end, the experimental results were compared with empirical and semi-empirical equations for estimating the pull-out strength of glued-in rods in structural timber and glulam. The comparison showed that most of the existing equations overestimate the ultimate tension loads for specimens with the rod parallel to the grain and underestimate the ultimate tension load for specimens with the rod perpendicular to the grain. The results vary because the possible CLT failure modes were not included in previous studies. Further studies are proposed to improve the equations for glued-in rods in CLT. Keywords Glued-in rods Á Cross laminated timber (CLT) Á Pull-pull experiment Á Glued-in length Á Rodto-grain angle Á Failure mechanisms in CLT The original version of this article was revised due to a retrospective Open Access order.

Enhancement of strength of adhesive bond between wood and metal using atmospheric plasma treatment

“…Still, the compatibility of these materials with adhesives used must be sufficient. The surface roughness, joints geometry and glue line thickness are important parameters that greatly affect the mechanical performance of the joint (Azinović et al 2018;Budhe et al 2015;Chans et al 2013;Peng and Zhang 2018). The selection of an appropriate surface modification to increase the effectiveness of a joint depends on the material to be bonded and the bonding asset (Da Ponte et al 2015;Williams et al 2014).…”

Performance of glued-in-rod connections in cross-laminated timber

“…Because timber is generally strongest in the longitudinal axis, one would assume GiR joints positioned parallel to this axis would have higher strength. While one study [69] affirmed this, several others [16,42,61] suggested that the specimens with GiR positioned perpendicular to the longitudinal axis exhibited higher pull-out strength.…”

“…While in practice a single GiR connection is seldom used, previous research mostly focused on single rod configurations to isolate the effects of these parameters on the joint performance. In examining these parameters, previous studies focused on solid structural timber [11,12], Glue-laminated Timber (Glulam) [13,14], Laminated Veneer Lumber (LVL) [15], and more recently CLT [16,17].…”

“…Only a few studies are available on the performance of GiR connections in CLT. Azinovic et al [16,17] reported on different failure modes such as the edge lamination tear out, complete tear out of CLT layer, failure along non-glued timber edges and failure of timber next to adhesive, all of which deviate from the regular failure modes seen in other wood products and recommended further studies. Research gaps exist regarding the performance of single and multiple rods GiR in CLT such as the impact of rod edge spacing, shifting of anchorage length to inner members, load-to-grain angle and spacing between multiple rods.…”

“…Although many studies e.g. [13,16,43,57] have shown that the GiR strength increase with the anchorage length, some studies have reported that this increase is not linear due to stress concentrations [43,58,59]. Gehri [45] suggested moving the anchorage zone of steel rod away from the surface of timber into the inner part by leaving a gap at the face of the drilled hole where no adhesive is applied along the anchorage length, thus preventing the mechanical interlock around this zone, see The rod diameter (d) is one of the most commonly investigated GiR parameters.…”