Withdrawal capacity
Withdrawal capacity is a fastener's rated axial pull-out resistance in timber. AS 1720.1 sets it by joint group, diameter, and penetration depth.
Ask Chalkline about this →Withdrawal capacity is the rated load a fastener resists along its own axis before pulling out of the timber. It is distinct from lateral (shear) capacity: the two are separate design checks, and a fastener can have adequate shear capacity but inadequate withdrawal capacity for the same connection.
Under AS 1720.1-2010 (Amdt 3:2015), the characteristic withdrawal capacity for screws is expressed as a force per millimetre of thread penetration into the receiving member (Table 4.13). Three factors set the value:
- Joint group: denser species (JD1/JD2 hardwood) grip fasteners better than low-density softwood (JD5/JD6). The same screw in blackbutt develops significantly higher capacity than in MGP10 pine.
- Fastener diameter: larger diameter means more thread-to-fibre contact per millimetre, so capacity scales with diameter.
- Penetration depth: only the threaded length in the main member (not the outer member) counts. The standard sets minimum penetration by joint group.
Smooth nails have poor withdrawal capacity. A smooth shank resists pull-out by friction only. Threaded fasteners (screws, ring-shank nails) interlock mechanically with wood fibres and can be three or more times stronger in withdrawal for the same diameter (verified 2026-06-11, calcs.com AS 1720.1 guide).
Where withdrawal governs: roof batten fixing under wind uplift, rafter-to-top-plate tie-downs, and deck ledger uplift. In cyclonic regions, fastener type, count, and penetration depth all require engineering.
Also known as: axial pull-out capacity, pull-out capacity.
Category: Design / structural / connections.
Related
See also
Last updated: 2026-06-11. Verified: 2026-06-11. Quarterly review for AS 1720.1 currency.