Pull-out strength of axially loaded steel rods bonded in glulam perpendicular to the grain

A total of 86 pull-out strength tests on glued-in steel rods with metric threads M12, M16 and M20 are reported in this paper. The rods were bonded in glulam made of Norway spruce lamellas perpendicular to the grain by means of an epoxy-type adhesive using the GSA®-system. The slenderness ratios of the rods λ calculated from the anchoring lengths ℓ with respect to the diameter of the drill hole d h (λ=ℓ/d h) varied between 7.5 and 12.5. Registered failure loads were considerably higher than design values derived from different existing approaches. The pull-out strength was found to be almost directly proportional to the surface area of the bond line. Based on this an approach to estimate the pull-out strength is suggested. Dependence between pull-out strength and anchoring length ℓ as well as slenderness ratio λ exists, whereas such dependence for the diameter of the rod was not found. The pull-out strength is influenced by the wood density. Compared to rods bonded in parallel to the grain, pull-out strength of rods with same diameter and anchoring length set perpendicular to the grain are 20-50% highe