The impact of defects on the capacity of timber joints with glued-in steel rods

Timber joints with glued-in rods are an increasingly used technical solution for numerous structural applications, and show the potential of adhesively bonded connections involving timber and other materials [1]. These joints partially still face scepticism with regard to manufacturing defects that may impact the structural performance of the bonded joint. A major concern is the possible lack of adhesion resulting from inadequate preparation of the joint on site. Previous studies on the effect of bonding defects on the capacity of bonded joints [2] pointed out a nuanced relationship between defects and joint capacity that depends on the brittleness or ductility of the adhesive. This paper presents experimental evidence followed by numerical investigations to shed light on the relationship between defects and capacity of glued timber joints. For this purpose, timber joints with glued-in steel rods were manufactured with different types of defects likely to be encountered during their manufacturing on-site: i) rods placed at an angle to the drill hole instead of being in the joint axis, and ii) rod placed at the edge of the drill hole instead of fully centred. The effect of these defects on joint capacity was investigated with three different adhesives in combination with three different rod anchorage lengths: firstly, on the stresses caused by uniaxial tension loading using numerical modelling, secondly on the joint capacities using experiments. The experimental investigating of the influence of manufacturing defects on the capacity of timber joints with glued-in steel rods, completed by numerical calculations, demonstrated that joints with sufficient rod anchorage (herein 10 times the rod diameter) do not exhibit a statistically significant loss of capacity, if compared to defect free joints