Nailplates / Shearplates
Nailplates have long been used in bearer pallet repair in North America, for top-frames and export packing but were rarely used in Europe in the timber packaging industry until the potato storage box industry discovered that they were an ideal way to eliminate diagonal timber bracing in bulk storage boxes for high stacking. Placed on sides and ends they do this by locking together several sawn timber boards which then exhibit high panel-shear strength in a similar manner to a thick plywood box side. They are now widely used in that industry (see 31c & 31f below)
Nailplate (top), shearplates (center),
with a coach-bolt and washer needed
when using the shearplates
Nail plates are an authorised alternative to damaged bearer replacement in EN ISO 18613: 2003: Pallets for materials handling - repair of flat wooden pallets, they do this in an effective way but are still little used in commercial European pallet repair where bearer pallets are not common.
Box designs in nailed sawn and planed wood strengthened by appropriately positioned length and width nailplates when tested for compliance with BS 7611 - Potato Boxes, just meet the tough lateral load test requirements that ensure normal storage loads of up to 8 tons will be safe. PalletLink has carried out some tests on potato storage box designs using nailplates for some manufacturers and results are available from them. However, although nailplates are more efficient, less troublesome alternatives to timber bracing, they do require special proof testing and machinery to apply them to sawn wood in the form of a wide platten hydraulic press with several tons capacity. They cannot be used merely with plate makers steel strength certificates, designs need testing to BS 7611.
Shear plates are widely used in timber house building, but not often in the timber packaging industry. They are circular, with a diameter of 40 or 50mm, tightly sandwiched between two timber boards or battens and when drawn together with a coachbolt and nut the joint exhibits high shear strength. One shearplate at a joint is equal to several large diameter ring nails, but unlike nails they can be tightened as wood shrinks during drying over the early life of a structure. Their use in the timber packaging industry is restricted to special constructions such as export cases, skids and packing cases and crates. We are able to supply members with working loads for shearplates for various end uses. Their use in highly stressed A-frames for glass sheet carriage is not covered by BS or European (CEN) standards but given development of an EN or BS could be worthwhile.
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31c Proposed revision to BS 7611. (PDF 66kb)35f Punched steel nailplates in 1000kg potato boxes. (PDF 84kb)54b Coach screws in wood packaging. (PDF 35kb)54c Double sided toothed shearplates in wood packaging. (PDF 79kb)