1. ROOFS

2. C. TRIPLE / TRUSSED/ FRAMED ROOF
When span exceed 5m, where there is no inside walls to support purlin, framed structures known as trusses provide along length of room.
Consist of 3 elements: rafter to support roofing material, purlin for intermediate support to rafter and trusses to provide support to ends of purlins.
Types of triple roof:
KING POST ROOF TRUSS (5-9m)
QUEEN POST ROOF TRUSS (9-14m)
COMBINATION OF KING AND QUEEN POST TRUSS
MANSARD TRUSS (2 slopes on same sides )
TRUNCATED TRUSS (flat at top)
BEL-FAST TRUSS (bow string – curve on top, upto 30m span)
STEEL TRUSS
COMPOSITE TRUSS (combination of steel and timber)

3. KING POST ROOF TRUSS

4. KING POST ROOF TRUSS

5. C. TRIPLE / TRUSSED/ FRAMED ROOF
i KING POST ROOF TRUSS (5-9m)
Consists of lower tie beam, 2 inclined principle rafters, 2 struts and king post.
Principle rafter support purlins.
Purlin support common rafter.
Common rafter support roofing material as usual.
Trusses spaced not more than 3m c/c.
Lower, horizontal tie beam receive end of principle rafter, and prevent wall from spreading out due to thrust.

6. C. TRIPLE / TRUSSED/ FRAMED ROOF
KING POST ROOF TRUSS (5-9m)
King post prevent tie-beam from sagging at its centre of span.
Struts connected to tie beam and principle rafter in inclined direction, prevent sagging of principal rafter.
Tie Beam rests on stone pad embedded on either sides of wall so that load is distributed to a greater area.
King post rests on tie-beam which is attached with ridge and connected with rafters with help of struts.
Lower face of tie beam provides space for ceiling joists which are designed for the provision of false ceiling.

7. C. TRIPLE / TRUSSED/ FRAMED ROOF
KING POST ROOF TRUSS (5-9m)
JOINT BETWEEN PRINCIPLE RAFTER AND TIE – BEAM
At feet principle rafter is joined to tie beam by “Single abutment(Lie adjacent to another or share a boundary) end tenon (A projection at the end of a piece of wood that is shaped to fit into a mortise (A square hole made to receive a tenon and so to form a joint)and form a mortise joint) joint” or “ bridle joint”.
Joint may be further strengthened by a wrought iron heel strap, wound round joint.

8. C. TRIPLE / TRUSSED/ FRAMED ROOF
KING POST ROOF TRUSS (5-9m)

9. C. TRIPLE / TRUSSED/ FRAMED ROOF
QUEEN POST ROOF TRUSS (9-14m)
Differs from king post by having 2 vertical posts, rather than one.
Vertical posts known as queen post, whose tops are connected by a horizontal piece know as straining beam.
2 struts are provided to principle rafter.
Straining sill provided in tie beam to counteract thrust from inclined struts.
Queen posts are tension members.

10. C. TRIPLE / TRUSSED/ FRAMED ROOF
QUEEN POST ROOF TRUSS (9-14m)
Joint at head of queen post is formed due to junction of 2 compression members ( principle rafter and straining beam) and tension member (queen post)

11. C. TRIPLE / TRUSSED/ FRAMED ROOF
QUEEN POST ROOF TRUSS

12. C. TRIPLE / TRUSSED/ FRAMED ROOF
QUEEN POST ROOF TRUSS

13. C. TRIPLE / TRUSSED/ FRAMED ROOF
iii. COMBINATION OF KING AND QUEEN TRUSSES
For greater spans, queen-post truss can be strengthened by one more upright member, princess-post to each side.
Span suitable upto 18m.

14. C. TRIPLE / TRUSSED/ FRAMED ROOF
iii. COMBINATION OF KING AND QUEEN TRUSSES

15. TYPICAL ROOF TRUSS

16. C. TRIPLE / TRUSSED/ FRAMED ROOF
vii. STEEL TRUSSES
When span exceeds 10m, timber truss become heavy and uneconomical.
Truss are more economical for larger spans.
More economical, easy to construct, fire proof, rigid and permanent.
Trusses fabricated (constructed) from steel structural members such as channels, angle,T-sections and plates.
Most roof truss are from angle- sections as they can resist both tension and compression.

17. C. TRIPLE / TRUSSED/ FRAMED ROOF
vii. STEEL TRUSSES
May be grouped in following categories:
Open trusses
North light trusses
Bow string trusses
Arched rib trusses and solid arched ribs

18. C. TRIPLE / TRUSSED/ FRAMED ROOF
vii. STEEL TRUSSES
ADVANTAGES OF STEEL TRUSSES
Stronger than timber truss
Light in weight and can be fabricated in any desired pattern to suit architectural pattern
Free from attack of white ants, termites, insects
More fire resisting capacity than timber truss
Do not have restriction of the span >> used for any required large spans
Easy in transportation
Process of roofing is fast

19. C. TRIPLE / TRUSSED/ FRAMED ROOF
vii. STEEL TRUSSES

20. C. TRIPLE / TRUSSED/ FRAMED ROOF
vii. STEEL TRUSSES

21. C. TRIPLE / TRUSSED/ FRAMED ROOF
vii. STEEL TRUSSES

22. C. TRIPLE / TRUSSED/ FRAMED ROOF
vii. STEEL TRUSSES
DETAILS
Commonly fabricated from angle sections and plates, though channel sections and T- sections can also be used.
Roof truss is so designed that the members carry only direct stress (compression or tension), no bending stress is induced.
Principle rafter and main tie made of two angle sections placed side be side, while struts and ties generally made of single angle sections.
Members joined together using a gusset plate, either through rivets or by welding.
When rivets used, minimum pitch should not be less than three times the rivet diameter, while maximum pitch is limited to 15cm for compression member and 20cm for tension members.
Generally 15mm dia. rivets is used for small spans and 20mm dia. is used for large spans.
At least 2 rivets should be used at each span.
Gusset plate should not be less than 6mm thick.
At foot of truss, short angles are fitted on both sides of gusset plate, which are connected to bearing plate.
Bearing plate is joined to concrete bed through rag bolts.
At apex, suitable ridge section is fitted.

23. C. TRIPLE / TRUSSED/ FRAMED ROOF
vii. STEEL TRUSSES

24. C. TRIPLE / TRUSSED/ FRAMED ROOF
vii. STEEL TRUSSES

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