Not all timber connectors are equal
There is much more to timber connectors than just bending bits of steel and punching holes in them.
Every State or Territory in Australia has building regulations that call up the Building Code of Australia (BCA). The BCA is volumes 1 and 2 of the National Construction Code (NCC) and the NCC provides minimum standards to meet performance requirements of buildings. The NCC includes relevant health, amenity, sustainability objectives as well as safety requirements. Meeting the performance requirements can be achieved through Deemed-to-Satisfy (DTS) solutions or Performance Solutions. For Timber Structures the NCC calls up Australian Standards AS1684 Residential Timber-Framed Construction and AS1720 Timber Structures. AS1684 provides DTS solutions for residential structures however it is important to realise that AS1684 has limitations and assumptions that may not be applicable to all structures. When these limitations are exceeded an engineered solution is required. Simpson Strong-Tie has been manufacturing high quality timber connectors for over 60 years and provide solutions that help people build safer, stronger houses. Simpson invest heavily in research and development and all of their structural connectors are extensively tested to meet or exceed the minimum requirements. The testing of connectors has highlighted that there is much more to timber connectors than just bending bits of steel and punching holes in them. The entire connection of timber, connectors and fastener (nails or screws) need to work together to ensure a sound connection. Simpson also go beyond the minimum and do not just test for the strength of the connection but they also look at the deflection of the overall mechanism to ensure that the end result will be structurally sound and perform as intended. Simpson Strong-Tie, like most other connector manufacturers, provides load data for the connections and the lowest result of all 3 criteria is what is used in all published data. Many connector companies will use Nail withdrawal as the only factor to derive load data from, and while this is 1 of the 3 methods, it is not always the most conservative. Nail withdrawal is a calculation which is allowed within the Australian Standard, and assists in getting the load that a connector should hold, based on the number of nails that are installed, providing the nail withdrawing is the failure mode of the connection. If the failure mode is the timber failing or some other element, then nail calculation may be irrelevant. This is the beauty of multiple tests to create a failure. These tests take time and cost money, and is the reason that many connector companies do not do them. At Simpson, this is the only way to do them. Strength is not the only consideration. Simpson are always looking at innovative ways to improve the products and reduce the “Installed Cost” such as including speed prongs to make installation easier and quicker. The addition of double shear nailing in our LUS Joist hanger will reduce the number of nails required and therefore increasing productivity on site while still exceeding the capacity of the connector. The Double Shear feature on the LUS connector forces the installer to skew nail 2 of the 64mm nails which gives the performance of 8 nails in typical length and configuration. These benefits can only be seen by testing the connector. The correct installation of timber connectors is vital to the performance of the connection and the structure. As such Simpson has introduced a nailing tool that locates the specified connector nails into the required holes and the multi-blow action quickly hammers the nail home without risk of over driving or damaging the connector. For many years in Australia, builders have been allowed to install timber connectors incorrectly by firing pneumatic nails through the connector randomly. Simpson Strong- Tie does not support or condone this practice and has introduced the solution with the connector Nailer. Now the nail can be placed into the hole, where it was designed to go and not affect the integrity of the connector. This is all done with the speed of a pneumatic Nailgun as opposed to hand nailing. Durability of the connector should also be considered. AS1684 mentions that all metal used shall be provided with appropriate corrosion protection. Most timber connectors are manufactured from a Z275 galvanised steel (275g/ m2 zinc coating) which is suitable for internal applications in non-corrosive environments. For external applications in a beach side environment it is recommended to use stainless steel connectors, however Simpson also has a range of ZMax® which has 550g/m2 zinc coating for extra protection in less corrosive environments or for use with treated timbers. A large number of the Simpson Strong-Tie connectors are already available in the ZMax® coating and the ability to use these connectors externally makes them so much more versatile. For greater corrosion performance, 316 stainless steel should be used with stainless steel nails. The use of structural screws as a replacement for some of the connectors has also been a benefit in reducing the installed cost by saving labour. The introduction of a Stud screw or the SDWS structural screw as a replacement for the strap used to fix the stud to top and bottom plate reduces time and prevents issues when fixing plasterboard. Another fastener—the SDWC for Truss fixing—means that one screw replaces many nails that are typically just fired through the connector when fixing the Truss to top plate.