Fully threaded timber structural screws are the primary mechanical fixing method used for walls, posts and beams. The length, width and thread of the screw, along with the fixing centres determined by the thickness of the timber components being fixed and the stresses being imposed by the structure.
Beam, column and mass slab elements generally require off-set screw patterns which alternate by 300mm on the opposite or underneath side. Additional screws can be installed to ensure adjoining elements are flush, to minimise cupping and to achieve diagram action where required.
Fixing a floor section to a beam will generally require fixings at 100mm centres to achieve diaphragm action and up to 400mm centres where this is not required.
NOTE: Screw specification and fixing centres must be determined by a suitably qualified and experienced engineer.
Both Isocyanate and cold set Resorcinol glues can be used to chemically laminate e-beam and e-slab elements.
Isocyanate based adhesive glues combine with the mechanical fixings to provide a strong and durable bonding of the components within an assembly. A range of benefits associated with Isocyanate based adhesives have been identified by Forest Wood Products Australia1, such as:
- Clear glue lines
- Lower resin usage
- 100% solids and hence no water to be removed from the glue line, opening up the possibility of gluing at higher wood moisture contents
- Shorter cure times and hence potential increases in processing efficiencies
- No mixing of glue batches, minimising waste and reducing handling costs
- The possibility of gluing timbers that have been traditionally difficult to glue with PRF resins.
1FWPA, The durability of isocyanate based adhesives under service in Australian conditions. The results from a 3-year exposure study and accelerated testing regime, Project Number: PNB034-0506 April 2010.
Cold set Resorcinol glues set with a brown appearance. Resorcinol glues require a hardener and can be used for interior or exterior applications where a durable, strong, waterproof wood to wood bond is required.