Load-bearing behaviour of partially threaded screws in hardwood

ABSTRACT

Partially threaded screws are essential fasteners in timber structures, and their use in combination with hardwoods is promising in order to obtain high-performance connections. Depending on the used wood species, the load-displacement behaviour and failure mechanisms of connections change, and, in particular for high-density species, brittle failures may occur more frequently with rather low ductility of the connection. Consequently, a good understanding of the mechanical behaviour of connections at different displacement levels helps to assess where previous rules reach their limits for hardwoods. The determination of all input parameters serves as a basis for a subsequent test programme on single-shear timber-to-timber connections using beech laminated veneer lumber, birch, spruce glulam and predrilled and non-predrilled partially threaded screws. Tests on connections with one screw and groups of screws are conducted, stopped at predefined displacement stages of 5, 10 and 25 mm, and opened. A comparison of the screw deformation at the different displacement stages reveals that non-linear connection behaviour is quite different in softwood and hardwood. Essential aspects of the analysis are particularities of the load-displacement behaviour, fastener spacing, ductility of connections and the progressive plasticising of the fasteners.

KEYWORDS:

• Screws
• connections
• timber
• hardwood
• beech LVL
• birch

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work has been carried out within the project hardwood_joint that is supported under the umbrella of ERA-NET Cofund ForestValue by BMLFUW (AT), ADEME (FR), FNR (DE) and Vinnova, Swedish Energy Agency and Formas (SE). ForestValue has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement N° 773324.