What is a Truss?
- In Architecture and Structural Engineering, a truss is a structure comprising one or more triangular units constructed with straight slender members whose ends are connected at joints referred to as nodes.
- External forces and reactions to those forces are considered to act only at the nodes and result in forces in the members which are either tensile or compressive forces.
- Moments (torsional forces) are explicitly excluded because, and only because, all the joints in a truss are treated as revolutes.
In this article, we are going to discuss the various types of roof trusses in wood and steel and their uses in various kinds of construction.
Different types of Wooden and Steel Roof Trusses:
- King Post Truss
- Queen Post Truss
- Howe Truss
- Pratt Truss
- Fan Truss
- North Light Roof Truss
- Quadrangular Roof Truss
Trusses for large span constructions
King Post Truss
- King Post Truss is a wooden truss.
- It can also be built of combination of wood and steel.
- It can be used for spans upto 8m.
Queen Post Truss
- Queen Post Truss is also a wooden truss.
- It can be used for spans upto 10m.
- It is made of combination of wood and steel.
- The vertical members or tension members are made of steel.
- It can be used for spans from 6-30m.
- Pratt Truss is made of steel.
- These are less economical than the Fink Trusses.
- Vertical members are tension and diagonal members are compression.
- Fink Trusses are very economical form of roof trusses.
- It can be used for spans from 6-10m.
- It is made of steel.
- Fan trusses are form of Fink roof truss.
- In Fan Trusses, top chords are divided into small lengths in order to provide supports for purlins which would not come at joints in Fink trusses.
- It can be used for spans from 10-15m.
North Light Roof Truss
- When the floor span exceeds 15m, it is generally more economical to change from a simple truss arrangement to one employing wide span lattice girders which support trusses at right angles.
- In order to light up the space satisfactorily, roof lighting has to replace or supplement, side lighting provision must also be made for ventilation form the roof.
- One of the oldest and economical methods of covering large areas is the North Light and Lattice girder.
- This roof consists of a series of trusses fixed to girders. The short vertical side of the truss is glazed so that when the roof is used in the Northern Hemisphere, the glazed portion faces North for the best light.
- It can be used for spans from 20-30m.
- Used for industrial buildings, drawing rooms etc.
Quadrangular roof Trusses
- These trusses are used for large spans such as railway sheds and Auditoriums.
Large Span Trusses