ROOFS 1 C TRIPLE TRUSSED FRAMED ROOF When

ROOFS 1

C. TRIPLE / TRUSSED/ FRAMED ROOF § When span exceed 5 m, 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: i. KING POST ROOF TRUSS (5 -9 m) ii. QUEEN POST ROOF TRUSS (9 -14 m) iii. COMBINATION OF KING AND QUEEN POST TRUSS iv. MANSARD TRUSS (2 slopes on same sides ) v. TRUNCATED TRUSS (flat at top) vi. BEL-FAST TRUSS (bow string – curve on top, upto 30 m span) vii. STEEL TRUSS viii. COMPOSITE TRUSS (combination of steel and timber) 2

KING POST ROOF TRUSS 3

KING POST ROOF TRUSS 4

C. TRIPLE / TRUSSED/ FRAMED ROOF i. KING POST ROOF TRUSS (5 -9 m) § 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 3 m c/c. § Lower, horizontal tie beam receive end of principle rafter, and prevent wall from spreading out due to thrust. 5

C. TRIPLE / TRUSSED/ FRAMED ROOF i. KING POST ROOF TRUSS (5 -9 m) § 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. 6

C. TRIPLE / TRUSSED/ FRAMED ROOF i. KING POST ROOF TRUSS (5 -9 m) a. 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. 7

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

C. TRIPLE / TRUSSED/ FRAMED ROOF ii. QUEEN POST ROOF TRUSS (9 -14 m) � 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. 9

C. TRIPLE / TRUSSED/ FRAMED ROOF ii. QUEEN POST ROOF TRUSS (9 -14 m) � 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) 10

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

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

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 18 m. 13

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

TYPICAL ROOF TRUSS 15

C. TRIPLE / TRUSSED/ FRAMED ROOF vii. STEEL TRUSSES § § § When span exceeds 10 m, 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. 16

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

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 18 § Process of roofing is fast

C. TRIPLE / TRUSSED/ FRAMED ROOF vii. STEEL TRUSSES 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 DETAILS § Commonly fabricated from angle sections and plates, though channel sections and Tsections 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 15 cm for compression member and 20 cm for tension members. § Generally 15 mm dia. rivets is used for small spans and 20 mm dia. is used for large spans. § At least 2 rivets should be used at each span. § Gusset plate should not be less than 6 mm thick. § At foot of truss, short angles are fitted on both sides of gusset plate, which are connected to bearing plate. 22 § Bearing plate is joined to concrete bed through rag bolts. § At apex, suitable ridge section is fitted.

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

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

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