Connections
Connections greatly influence appearance, economy and ease of construction. A key issue is the number of members intersecting at a connection (i.e. truss nodes). For instance, there are various configurations that can broadly be grouped into: single web and single chord connections; double web and single chord connections; single web and double chord connections; and more complex connections. A number of these options are shown in Figure 8.
 

Figure 9: Interleaved plate connection

Steel Plates used with Nails or Screws
Truss members are commonly joined with metal plates that incorporate nails or screws. Nails are the most economical option, and are commonly used in mass production situations. Here, ‘nail plates’ are pressed into place, and the many small nails serve to distribute the load over a broad area. As a result, there is better transfer of stresses, reduced impact from imperfections such as knots, and less concern about using low strength timbers. In contrast, bolts concentrate the load, and are therefore structurally less efficient.

In some cases where aesthetics dictate, greater effort may be made to conceal the plate connectors. Here, the plates may be cut into insertion slots in the webs and chords - as shown in Figure 9. This also provides an efficient structural design. During fabrication, it is also useful to take advantage of machine driven nails which can penetrate steel plates up to 2mm in thickness . For thicker plates, screws may be necessary, and can be efficiently applied using self-drilling screws. Screws are typically Type 17 wood screws – often termed ‘batten screws’ – and come in a number of head types to facilitate driving. The ability to drive these screws is somewhat dependent on the depth and density of the substrate timber. For instance, there are limitations with the use of self-drilling screws in hardwood, and in such instances, pre-drilling is required.

Bolts with Steel Side Plates
Under this scenario, thick steel side plates or gussets are used in conjunction with bolts to transfer the load. Here, gussets may become long and obtrusive due to the need to space bolts far enough apart to spread the load. Plates can also be expensive to fabricate as the plate must mimic the complex shapes of the member intersections. If appropriate, a way around this issue is to use hidden plates – as discussed previously.

Bolts and Timber Connections
In traditional trusses, connections are often made using bolts which hold multiple chord and web components together like a pin joint (Refer to Figure 8). Though common in older structures, these types of connections have difficulty in developing sufficient rigidity, and also cause eccentric loading. It is hard to prevent this, but the usual method of managing the problem is to make a more compact joint by using a large number of small diameter bolts. As a result, this method tends to be more expensive than the steel plate options discussed previously.
 

Timber to timber connections

Timber to Timber Connections
A wide range of options prevail for multiple member timber trusses. Timber to timber is very efficient and economically fabricated on-site using screw fixings. The following photos reflect some examples of this form of construction.
 

Spliced Members
On some occasions, splices are necessary in long chord members. In such instances, splice locations should be chosen to coincide with areas of low loading. Such positions are best determined by a structural engineer, but as a guide, if the chord is in compression the splice should be at the node where lateral restraint can be provided. An economical method of splicing tension members is to use Type 17 screws in conjunction with a metal plate – as shown in Figure 10. Note the use of a staggered screw pattern to reduce the chance of splitting.

Figure 10: Staggered screw pattern in connector plate