Steel-to-Timber Joints with Very High Strength Steel Dowels Using Spruce, Beech and Azobé

Present-day very high strength steel (vhss) grades show high plastic deformation capacity whilst reaching tension strengths of up to 1400 MPa. These properties open new application fields in timber engineering. Replacing mild steel dowels in timber joints with vhss dowels should lead to higher load carrying capacities or to leaner joints (thinner dowels and smaller cross sections) without losing the desired joint failure mode with one or two plastic hinges per shear plane. Extensive test series on double-shear timber joints with slotted-in steel plates have been carried out using 12 mm and 24 mm dowels. The chosen timber species were spruce, beech and azobé. One, three and five dowels in a row were tested and the used dowel steel grades were high strength steel (hss) with a mean tension strength of 590 MPa and vhss with a mean tension strength of 1390 MPa. The test outcomes have shown that joints with vhss dowels reach a higher load carrying capacity than the same joints using hss dowels, but are still able to develop plastic hinges. No correlation between density, load carrying capacity and stiffness within one wood species could be found. The effective number of fasteners showed a trend to be lower for the joints with vhss dowels and at the same time, is dependent on the used wood species as generally, ductile species such as beech show large deformations and subsequently high load carrying capacities if one dowel is used.