Types of Various Trusses | Wooden Trusses...? - Ishwaranand

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Types of Various Trusses | Wooden Trusses...?

The various types of trusses in use are

The first 8 types are essentially wooden trusses.

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King-post truss

A king-post truss consists of the following components

  1. lower tie beam,
  2. two inclined principal rafters,
  3. two struts, and
  4. a king post.
  • The principal rafters support the purlins.
  • The purlins support the closely-spaced common rafters which have the same slope as the principal rafters.
  • The common rafters support the roof covering as usual.
  • The spacing of the kingpost truss is limited to 3 m centre to centre.
  • The truss is suitable for spans varying from 5 to 8 metres.
  • The principal rafter is jointed to the tie beam by a single abutment and ‘tenon joint’ or by a ‘bridle joint’.
  • The joint is further strengthened by a wrought iron heel strap, would round the joint.
  • The king-post is provided with splayed shoulders and feet and is tenoned into the upper edge of the tie beam for a sufficient distance.
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Queen-post truss

  • A queen-post truss differs from a king-post truss in having two vertical posts, rather than one.
  • The vertical posts are known as queen-posts, the tops of which are connected by a horizontal piece, known as straining beam.
  •  Two struts are provided to join the feet of each queen-post to the principal rafter, The queen-posts are the tension members.
  • The straining beams receive the thrust from the principal rafters and keep the junction in a stable position.
  •  A straining sill is introduced on the tie beam between the queen-posts to counteract the thrust from inclined struts which are in compression.
  • In absence of the straining sill, the thrust from the strut would tend to force the foot of the queen-post inwards.
  • These trusses are suitable for spans between 8 to 12 metres.
  • The joint at the head of queen-post -is formed due to the junction of two compression members (principal rafter and straining beam) and a tension member(queen-post).
Types Various Trusses, Trusses, Various Trusses, King-post, truss, Queen post truss, Types of Trusses, The first 8 types are essentially wooden trusses, Mansard truss, Truncated truss, Bel-fast truss, Steel truss, Composite trusses,

Combination of king-post and queen post truss

Types Various Trusses, Trusses, Various Trusses, King-post, truss, Queen post truss, Types of Trusses, The first 8 types are essentially wooden trusses, Mansard truss, Truncated truss, Bel-fast truss, Steel truss, Composite trusses,

Mansard roof truss

  • This roof truss named given by its designer Francois Mansard, a French architect.
  • A mansard roof truss is a combination of king-post and queen-post trusses.
  •  It is a two-storey truss, with upper portion consisting of king-post truss and the lower portion of a queen-post truss.
  • The entire truss has two pitches. The upper pitch (king-post truss) varies from 30° to 40° while two lower pitch (queen-truss) varies from 60° to 70°.
  • The use of these truss results in an economy in space.
Types Various Trusses, Trusses, Various Trusses, King-post, truss, Queen post truss, Types of Trusses, The first 8 types are essentially wooden trusses, Mansard truss, Truncated truss, Bel-fast truss, Steel truss, Composite trusses,

Truncated truss

  • A truncated truss is similar to Mansard truss, except that its top is formed flat, with a gentle slope to one side.
  • This type of truss is used when it is required to provide a room in the roof, between the two queen-posts of the truss, as shown in Fig.

Bel-fast roof truss (Bowstring truss)

  • This truss, in the form of a bow, consists of thin sections of timber, with its top chord curved.
  •  If the roof covering is light, this roof truss can be used up to 30 m.
Types Various Trusses, Trusses, Various Trusses, King-post, truss, Queen post truss, Types of Trusses, The first 8 types are essentially wooden trusses, Mansard truss, Truncated truss, Bel-fast truss, Steel truss, Composite trusses,

Composite roof trusses

  • Roof trusses made of two materials, such as timber and steel, are known as composite roof trusses.
  • In a composite truss, the tension members are made of steel, while compression members are made of timber.
  • If tension members are made of timber, their section becomes very heavy because of the reduction of a section at the joints.
  • Special fittings are required at the junction of steel and timber members.

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