This unit covers connections for trusses, platform frames, panel systems, and curved and double-curved lattices. There are no clear-cut rules for which connection type is used where – as long as the correct design principles are followed, timber gives the designer freedom to choose from an infinite range of shape and form.
The main criteria designers should take into account when selecting and detailing connections for a particular application are: load transfer (stiffness, ductility, robustness and differential movement), appearance, fire resistance and durability.
In relation to load transfer, connections mainly have to resist gravitational loads, such as structure self-weight, imposed floor loads and snow. As timber is a lightweight material, structures made from timber are also vulnerable to wind or earthquake – instantaneous loads which may be larger than the normal gravitational loads. The net effect may cause load reversal. It is important therefore that wind and uplift effects are taken into account within the design process.
Roof trusses can be made with purlins and rafters, using solid timber for small spans and glulam or other engineered wood product members for roofs that are much beyond a domestic scale.
Traditional trusses are in-plane trusses made almost entirely of timber.
Lapped trusses made up of timbers in more than one plane use connectors such as bolts or dowels.
For in-line trusses with gusset connections, typically plywood gussets are used, fixed with nails or screws.