Experimental assessment of the pull-out strength of single rods bonded in glulam parallel to the grain

Abstract

The use of glued-in rods is a very efficient technique for connecting timber elements either in restoration or in the construction of new structures. It has been used for about 30 years in several countries all over the world. However, despite multiple research efforts, there is still a lack of consensus on a standard method to design such connections and to compute their carrying capacity. If a company wishes to include this system in its design possibilities, it has to validate it by testing. This paper reports on the results of a test program aiming at situating the glued-in rod connecting technique of the Belgian glulam company Lamcol with the main existing design methods. A total of 60 specimens of glued-in rod joints were tested in pull-pull configuration. The varying parameters were the anchoring length and the rod diameter. The rods were threaded steel bars. They were bonded into glulam Norway spruce lamellas parallel to the grain by means of an epoxy-type adhesive injection. The preparation of the specimens was kept very simple, as close as possible to the actual production technique of the company. The main difference with previously reported test results comes from the failure modes. Failure occurred mainly by splitting of the wood element along the anchorage although the standard recommendations for the distance between the rods and the edges of the specimens were respected. Two strength models are derived empirically from the analysis of the test results which are also compared with predictions from computation methods proposed in the literature.