Wood Structural Systems


Truss



Wood can be used in many popular structural forms from the light duty repetitive small structures to the larger and heavier framing systems used in commercial projects such as arenas or storage facilities. Because wood has a high strength to weight ratio, dead load is a smaller component of the total load factor than for heavier materials. Usually the lightest or least involved construction type appropriate for a given span that is capable of carrying the design load is the most preferable. A table of typical spans is presented below to aid the designer in selecting an appropriate structural system.

Figure 4.3 Estimated span capabilities of wood members (for illustration purpuses only)
Decking, joists and beams Typical spans,
m
Approximate
span
to depth ratio
(l/d)
Wood decking 1 to 2.5 25 to 35
Panels 0.3 to 0.6 20 to 40
Dimension Lumber 3 to 7 15 to 25
Wood I-joists 6 to 10 20 to 25
Stressed-skin panels 3 to 7 24 to 30
Plywood box beams 4 to 9 18 to 20
Parallel strand lumber 4 to 18 18 to 20
Laminated veneer lumber 4 to 18 18 to 20
Glulam 4 to 25 18 to 20


Trusses and Arches Typical spans,
m
Approximate
span
to depth ratio
(l/d)
Pitched trusses 6 to 30 2 to 5
Parallel chord trusses 6 to 30 10 to 15
Bowstring trusses 20 to 50 5 to 10