What Is Roof Truss?
A roof truss is a simple assembly of members forming a rigid framework of triangular shape.
A truss is generally a triangulated system of straight and diagonal members that are interconnected. The most commonly used truss in buildings.
Any type of roof trusses, the main aim is to support the roofs, loading system, and floors.
The main reason for using trusses are
- Long span
- Light weight
- Controlled deflection
- Controlled thrust action
- To support considerable loads.
Types of Trusses
- King post truss
- Warren truss
- Queen post truss
- Howe truss
- Fink or French truss
- Gambrel truss
- Pratt truss
- Fan truss
- Double fink truss
- Flat truss
- Scissors truss
- North light truss
- Mansard truss
King Post Truss
In king post truss two inclined principal rafter meet at the apex point
Two inclined members provided on both sides of the king post truss is known as strut. This strut prevents the principal rafter from bending at the Centre and the central vertical post member to support the tie beam.
It is used for spans of up to 5m to 8m and it is not suitable for a long span.
Components of King Post Truss
- Central vertical king post
- Two inclined Principal rafter
- Common rafter
- Purlin cleat
- Tie beam
- Wall plate
- Ridge board
- Brick infill
- Two Strut
- Stone template
- Supporting wall
Analysis of Trusses
- Truss members are act as being pinned joints.
- They are joined together so as to transfer only the axial forces and not shears and moments from one member to another members.
- In analysis to assumed the loads are to be acting only at the nodes of the trusses.
- The trusses may be provided over
- a simply supported over the two end supports ,single span simply supported over the two end supports, in which case they are generally statically determinate.
- Such types of trusses can be analyzed by manually
– Method of Joints
– Method of Sections.
- Computer programs are also used for the analysis of trusses.
The economical span of the pitched type roof trusses ranges from 6 m to 12 m. The Mansard trusses can be used in the span of up to 12 m to 30 m.
Manufacturing of Trusses
- The computer design of light frame structure results in the generation of fabrication instruction.
- That indicate the precise cutting pattern wise for each of members and the size, location of plate connectors and type etc. required.
- The layout is made for each configuration to ensure that the trusses are exact in dimension.
- In manufacturing the various member are cut to correct dimension and assembled in the correct position, which is located on a truss, floor, heavy table or jig.
- The following important information are
- location of all supports
- overall truss dimensions
- web and chord sizes and grades
- size of plate, type of plate and location for each joint
- The webs and chord are connected together by the using of truss plates, which transfer the tensile force, compressive force and shear forces.
Once the pressing of the plates has been completed, the truss is checked for size, gaps, dimension and species, plate size, positioning, and embedment and then moved into a storage area.
- In some cases, industry have a quality control program then they are checking quality and production for each truss.
- The completed truss is then wrapped together and placed in the storage station in preparation for shipping the truss.
Connection Used in Kingpost Truss
- Bolted connection
- Rivet connection
- Gusset plate connection
- Welded connection
King Post Truss Construction Details
- The triangular shape of truss provides to greater rigidity.
- In king post truss two inclined principal rafter meet at the apex of the truss.
- The central vertical king post provide support for tie beam.
- In king post truss bottom chord member act as a tie beam.
- This tie beam in king post truss receives the end of principal rafter and prevent wall spreading against thrust action.
- Principal rafter is also providing to support of purlin and purlin support the common rafter of the truss.
- Two inclined members provided on both side of king post truss is known as strut. This strut to prevent the principal rafter from bending at the Centre.
- The main difference in principal rafter and common rafter is, common rafter provides for support the roof covering material.
- Vertical post is used for prevent the sagging of the tie beam at the center part.
- In truss both rafter slopes are same.
- It is used for span up to 5m to 8m.
- It is not suitable for long span.
- The king post truss is used to support the weight of an expensive roof.
- It is also used for short span bridges and simple roofline.
- King post truss does not provide storage space in the frame.
Advantage of King Post Truss
- King post truss is mostly used in construction of aircraft, terminals to support the top cables.
- King post truss is able the maximum load in any direction.
- It is easy to constructed.
- It is used for aesthetic purpose.
- King post truss is easily available in any size and shape.
Disadvantage of King Post Truss
- King post truss is not suitable for long span.
- It is not suitable for big project like shopping complex, business hub and commercial building
Factor Affecting Selection of Roof Truss
- Roof covering material
- Fire protection
- Energy efficiency
- Building codes
What Is a Roof Truss?
A roof truss is a simple assembly of members forming a rigid framework of triangular shape. A truss is generally a triangulated system of straight and diagonal members that are interconnected. The most commonly used truss in buildings. Any type of roof trusses, the main aim is to support the roofs, loading system, and floors.
Component of Roof Truss?
1. Central vertical king post
3. Two inclined Principal rafter
4. Common rafter
5. Purlin cleat
6. Tie beam
8. Ridge board
9. Brick infill
10. Two Strut
11. Stone template
12. Supporting wall
Advantages and Disadvantages of Roof Truss?
Advantage of Roof Truss
1. King post truss is mostly used in the construction of aircraft, terminals
2. To support the top cables.
3. King post truss is able the maximum load in any direction.
4. It is easy to construct.
5. It is used for aesthetic purposes.
6. King post truss is easily available in any size and shape.
The disadvantage of King Post Truss
1. King post truss is not suitable for long spans.
2. It is not suitable for big projects like a shopping complex
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