1. Truss Roof By
PATEL POOJA D

2. TRUSSED ROOFS
When the span of the roof exceeds 4.8 m and where there are no inside
walls to support the purlins, framed structures known as trusses are
provided at suitable interval along the length of the room.
The trusses carry the ridge piece and purlins on which the common rafters
Rest.
Spacing of trusses depends upon the load on the roof, position of cross
walls, span and material of the truss.
The spacing is generally 3m for wooden trusses
The roof consists of 3 major elements:
Rafters: to support the roofing material
Purlins: to provide intermediate support to the rafters
Trusses: to provide support to the ends of the purlins

3. TYPES OF TRUSSES The various types of trusses are as follows:
King-post truss
Queen-post truss
Combination of king-post and queen-post truss
Mansard truss
Truncated truss
Bel-fast truss or Bow- string truss
Steel truss
Composite truss

4. KING-POST TRUSS
A king-post truss consists of the following components:
Lower tie beam
Two inclined principal rafters - supports the purlins
Two struts - supports the principal rafters
A king-post - prevents sagging of tie-beam at the centre
Two purlins - placed at right angles to the principle rafters and supports the common rafters
Common Rafters - supports the roof covering
Cleats - prevent the purlins from sliding (tilting)
The spacing of king-post truss is limited to 3 m centre to centre and it is suitable for spans varying from 5 to 8 meter.

6. QUEEN POST ROOF TRUSS
A queen-post truss has two vertical posts known as Queen-posts unlike king-post where there is only one.
A queen post roof truss has the following components:
Straining Beam - horizontal beam that connects the top of the queen posts
Two struts - join the feet of the queen post to the principle rafter
Straining sill - to counteract the thrust from the struts which are in compression
Purlins with cleats
Principle rafters and common rafters
Tie beams
Queen post roof truss are suitable for spans between 8-12 m.

8. COMBINATION OF KING POST AND QUEEN POST TRUSSES
Queen post trusses are suitable for spans up to 12 metres. For greater spans, the queen-post truss can be strengthened by one more upright member, called princess-post to each side. A combination of the king-post and queen-post is suitable up to 18 m span.

9. MANSARD ROOF TRUSS
This truss is named after a French architect, Francois Mansard ( ), who designed this truss to satisfy the requirements of municipal laws. designer and is a combination of king-post and queen-post truss.
It is a 2- storey truss, with the upper portion consisting of king-post truss and lower portion of queen-post truss.
Mansard truss has two pitches. The upper pitch varies from 30⁰-40⁰ while that of lower pitch varies from 60⁰ - 70⁰.
The use of this truss results in economy in space and a room may be provided in the roof between two queen-posts.
However it has now become obsolete because of it odd shape.

10. TRUNCATED TRUSS
It is similar to Mansard truss, except that its top is formed flat, with a gentle slope to one side.
Generally used when it is required to provide a room in the roof, between the two queen posts of the truss.

11. BEL-FAST ROOF TRUSS
It is also called Bow-string roof truss since it is in the form of a bow, with its top chord being curved.
This can be used up to a span of 30 m if the roof covering is light.
This is also sometimes known as the latticed roof truss or low string truss.

12. COMPOSITE ROOF TRUSS
Roof made of two materials, such as timber and steel, are known as composite roof truss. Normally the tension members are made of steel and the compression members of timber.

13. STEEL ROOF TRUSSES
When the span exceeds 12m, timber trusses become heavy and uneconomical.
Steel trusses are used economically over larger spans.
The mild steel is easily available in rolled sections of standard shapes and sizes.

14. ADVANTAGES OF STEEL TRUSSES
Section comprising of steel trusses are readily available in required dimensions resulting in minimum wastage of material.
They are light in weight, easy to construct and can be fabricated in any shape depending upon structural and architectural requirements.
Steel trusses are stronger and more durable (rigid) in comparison to timber trusses.
They can be used for any span.
Steel trusses are fire-proof & termite proof.
They are more resistant to other environmental agencies and have longer life.
They are economical.

15. TYPES OF STEEL TRUSSES Open trusses North light trusses
Bow string trusses
Arched rib trusses and solid arched ribs

16. THANK YOU