Their are various types of trusses are used in the construction of house and building, etc.
Trusses are structures in which members are interconnected so that they form a steady state and they do not allow any rotation of the joints.
There are two fundamental types of trusses i.e. pitched truss or common truss characterized by its triangular shape usually used for roof construction, few trusses are named in accordance with their web configuration.
The cord size and web configuration are determined by span, load, and spacing.
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Different types of trusses:
These king post truss are made of the smooth plane by saw and jack planes, then joined to the tie beam by a bridle joint or tenon joint while desired joints are made for the purpose of connecting components.
These joints are fastened and strengthened by an iron strap, the two struts are fixed to the principal rafter by a slant and tenon joint.
The king post is fixed by the tenon joint in the upper edge of the tenon beam, while heads of the king post are joined by mortise and tenon joints at the ends of the principal rafter.
These joints are fixed more tightly with the help of a three-way mild steel strap on each side and purlins are placed at right angles to the principal rafters connected through cogged joints and cleats.
In these queen-post trusses, there is one vertical post but in the case of the queen-post there are two vertical posts called queen-posts.
A horizontal beam connected at the top of the queen-posts is called a straining beam each queen-post and principal rafter is subsequently joined by two interested members known as struts.
The two struts are subjected to compression are called compression members, while the two queen-posts are subjected to tension are called tension members.
The purpose of providing a straining beam is to keep the junction in a stable condition.
In addition, a tensioning sill is attached to the tie beam between the parts of the queen posts to counter the load coming from the struts , the queen-post truss is more suitable for span ranges from 8 m to 12 m.
These types of trusses are made by the combination of king post and queen post truss for a span up to 18 meters, it is more appropriate for the combination of king-post trusses and queen-post trusses.
Steel trusses are light in weight and can be fabricated into various shapes and sizes as required.
When the span exceeds 10 m, the wooden trusses become heavy and uneven, while the use of mild steel trusses proves to be economical for large spans.
The safe work stress on mild steel is about 20 times that of ordinary structural wood under direct stress consists of thin parts of wood with a curved and light roof material at the top.
This variety may be suitable up to a maximum of 30 meters.
Properties of stell trusses:
- These types of trusses are tire-proof.
- Free from attack by white ants.
- They are stronger than wooden trusses.
4.Mansard Roof Truss:
When steel trusses are launched, the mansard roof truss is a very rare used having two pitches.
One has a king-post truss from 30 ° to 40 ° at the upper-post and the other has a queen-post truss that varies from 60 ° to 70 ° at the bottom.
In these trusses, there is more or less use of the combination of king-post on the upper side and queen-post truss on the lower side hence it is also called two-storey truss.
It provides economy in space and cost since this truss has an odd shape, while uses has become obsolete nowadays.
Trimmed trusses are similar to mansard trusses, but their top is flat with a slight slope to one side, suitable when a roof is required between the posts of two queens.
6.Composite Trusses types:
When roof trusses are made of two materials such as wood and steel, it is called a composite roof truss.
In this truss, the members are subjected to tension and compression, so the tension members are made of steel and the compression members are made of wood.
If the tension members are made of wood, the wood section becomes heavy so it is necessary to make in steel.
At the junction of steel and wood members, special fittings such as C.I. head, C.I. shoe, straps, steel angle, bolt, kingbolt, etc.
Also read: Pitched Roof & GFRG Panels
Uses of various types of trusses:
- Trusses are used in large spans to offer shelter and don’t resist superimposed ground loads apart from mud, rain, and winds.
- It is used to support the roofs of auditoriums, cinema halls, sports activities stadiums, railway stations, airports.
- When the spans exceed a certain limit the stable beams become heavy and uneven, so trusses are used instead of beams.
Also read: Types of Doors, Types of Arches, Types of Windows