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 roof truss (spans upto8M)
- 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 (spans upto 10M)
- Queen Post Truss is also a wooden truss.
- It can be used for spans upto 10m.
Howe Truss
Howe Truss (spans upto 6M to 30M)
- 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
Pratt truss (spans upto 6M to 10M)
- 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.
Fan Truss
Fan Truss (spans upto 10M to 15M)
- 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
North light roof truss (spans upto 20M to 30M)
- 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
Quadrangular Roof Truss (for large spans)
- These trusses are used for large spans such as railway sheds and Auditoriums.
Large Span Trusses
Large span trusses
#1 by Jolas Famularcano on July 28, 2010 - 3:49 am
does anyone knows the figure of combined howe and pratt truss? A roof truss..
#2 by BenzuJK on July 28, 2010 - 6:36 am
Warren Truss is similar to the combination of Howe and Pratt Truss. Maybe that is what you are looking for.
#3 by Muhasin on March 13, 2011 - 1:10 am
Hai Benzu, Gud day
Could u help me 4 my project? i need to design a roof truss for a span of 25m*13m, plz lemme knw which type f truss is 2 b used and design considerations if any
Thank you
#4 by nawin kumar on April 23, 2011 - 11:12 am
the queen truss shown above are not according to the concept used in books but seems like scissors truss,why?……if it’s right, please rectify it.
#5 by BenzuJK on April 24, 2011 - 4:32 am
Hello Nawin,
This is a typical queen’s truss. This is not a scissor’s truss and does not resemble a scissor’s truss in anyway. Scissor’s truss resembles an inverted V-shaped arch.