Civil Engineering Reference
In-Depth Information
to approved manufacturers, many of whom are also timber merchants. The timber used is
both graded for strength and machined on all surfaces to give accuracy to the finished
product. Trussed rafters can also be assembled using plywood gussets, the plywood being
either nailed to a defined pattern or nailed and glued to the truss members to form the
joint. Ply gusseted trusses are not as popular as metal plated trusses, but do offer a method
of manufacture not requiring specialist equipment. Similarly the galvanised steel plates
punched with a pattern of holes to receive nails can also be used to form truss joints and
these too can be fabricated on site.
The punched metal nail plates used in factory trussed rafter production are mechanically
pressed into the timbers on both sides of each joint to form a trussed rafter. This trussed
rafter is then placed on the roof at approximately 600 mm centres taking the place of the
common rafter. Hence its term 'trussed rafter', as distinct from the TRADA type principal
truss, although it will be seen later in Chapter 5 that trussed rafters themselves can be used
to form principal or girder trusses. A typical 'fink' trussed rafter is illustrated in Fig. 1.12.
