Truss – King Post, Queen Post, Mansard, Bel-Fast, Steel and Composite
A truss is a structural framework used to support roofs and bridges. It consists of a system of interconnected members arranged in triangular units to distribute loads efficiently. In ITI Draughtsman Civil, understanding different types of trusses is essential for preparing structural drawings and roof designs.
1. Definition of Truss
A truss is a rigid framework composed of straight members connected at joints, designed to carry loads and transfer them to supports. It is commonly used in roof construction to cover large spans without intermediate supports.
2. Components of a Truss
- Top Chord: Upper inclined members supporting the roof.
- Bottom Chord: Horizontal member connecting the ends.
- Web Members: Internal members forming triangular patterns.
- Joints: Points where members are connected.
3. Types of Trusses
(a) King Post Truss
- Simplest type of truss.
- Consists of a central vertical post called king post.
- Suitable for spans up to 8 meters.
- Commonly used in small buildings.
(b) Queen Post Truss
- Has two vertical posts called queen posts.
- Stronger than king post truss.
- Suitable for spans up to 12 meters.
- Provides more open space in the center.
(c) Mansard Truss
- Has two slopes on each side.
- Lower slope is steeper than the upper slope.
- Provides additional usable space under the roof.
- Used in residential buildings.
(d) Bel-Fast (Belfast) Truss
- Also known as bowstring truss.
- Has a curved top chord and straight bottom chord.
- Lightweight and economical.
- Used in factories, sheds, and large-span buildings.
(e) Steel Truss
- Made of steel sections such as angles and channels.
- Strong and suitable for large spans.
- Used in industrial buildings, bridges, and warehouses.
- Requires protection against corrosion.
(f) Composite Truss
- Combination of different materials such as steel and timber or steel and concrete.
- Utilizes advantages of multiple materials.
- Provides strength, durability, and cost efficiency.
4. Advantages of Trusses
- Efficient load distribution.
- Suitable for large spans without intermediate supports.
- Lightweight compared to solid beams.
- Economical use of materials.
5. Applications of Trusses
- Roof structures in buildings.
- Bridges and industrial sheds.
- Railway platforms and auditoriums.
Role of Draughtsman Civil
A Draughtsman Civil prepares detailed drawings of trusses showing member sizes, joints, and connections. Proper understanding of truss types helps in selecting suitable designs for different structures.
Conclusion
Trusses are important structural systems used to support roofs and large spans. Different types such as king post, queen post, mansard, Belfast, steel, and composite trusses are used depending on requirements. Knowledge of trusses is essential for designing safe and economical structures.