Types Of Trusses 196y2s

Introduction : • A framework, typically consisting of rafters, posts, and struts, ing a roof, bridge, or other structure is known as truss. • The main reasons for using trusses are: Long span, Lightweight, Reduced deflection (compared to plain ), Opportunity to considerable loads. • Truss is assembled in such a way that forces are applied only on the ends. • The are connected with a gusset t that is either riveted, bolted or welded in such a

 Component parts of trusses :

Purlin : A horizontal beam along the length of a roof, resting on principal rafter and ing the common rafters or boards. Principal Rafter : one of the upper diagonal of a roof truss ing the purlins and common rafters or those ts to which the roof boarding is secured. Common Rafter : A rafter having no function other than to bear roofing. Ridge Board : The horizontal timber or member at the top of a roof, to which the upper ends of the rafters are fastened. Strut : Provided to resist longitudinal compression.

 Types of Trusses : There are variety of trusses available depending on the requirement including span length and loading condition. Basically two types of trusses exists :a) Bridge Truss b) Roof Truss

a)Bridge Truss : 1. Pratt Truss -

• A Pratt Truss has been used over the past two centuries as an effective truss method. • The vertical are in compression, whilst the diagonal are in tension. • This has a few effects - it reduces the cost of the structure due to more efficient , reduces the self weight and eases the constructability of the structure. • This type of truss is most appropriate for horizontal spans, where the force is predominantly in the vertical direction.

Pratt Truss

Advantages: • Aware of member's behavior - diagonal are in tension, vertical in compression • The above can be used to design a cost effective structure • Simple design • Well accepted and used design

Disadvantages: • Not as advantageous if the load is not vertical

Applications: • Where a cost effective design is required • Where a mix of loads are applied • Where a simple structure is required

2. Warren Truss

• The Warren Truss is another very popular truss structure and is easily identified by its construction from isosceles triangles. • One of the main advantages of a Warren Truss is its ability to spread the load evenly across a number of different ; this is however generally for cases when the structure is undergoing a spanned load (a distributed load) • It's main advantage is also the cause of it's disadvantage the truss structure will undergo concentrated force under a point load. • Under these concentrated load scenarios, the structure is not as good at distributing the load evenly across its . • Therefore the Warren truss type is more advantageous for spanned loads, but not suitable where the load is concentrated at a single point or node.

Advantages: • Spreads load fairly evenly between • Fairly simple design

Disadvantages: • Poorer performance under concentrated loads • Increased constructability due to additional

Applications: • Long span structures • Where an evenly distributed load is to be ed • Where a simple structure is required

3. Howe bridge Truss • It includes vertical and diagonals that slope up towards the center. • Has diagonal that slant away from the middle. • Howe truss were designed a long time ago when bridges needed to fill a specific role, and for the particular resources that people had available.  • The Howe truss design used a lot of wood as opposed to the Pratt which used more iron. • This made the Howe popular earlier on when iron was expensive to produce.

Howe Bridge Truss

 Advantage: • The advantages of truss bridges is that it is economical, light, strong and uses short timbers. • Greater strength with less material. • Easier to repair and maintain.

Disadvantage: • Disadvantage can be wasted material if not designed properly. • Longer build time, more complex construction.

4. Bailey Bridge Truss • It is designed for military use, the prefabricated and standardized truss elements may be easily combined in various configurations to adapt to the needs. • The military utilizes the Bailey design, which is easily disassembled and portable. • Most of the design has vertical attaching to horizontal as well as diagonal braces located between the vertical .

Bailey Truss

Advantages: • A Bailey bridge had the advantages of requiring no special tools or heavy equipment to assemble. • The wood and steel bridge elements were small and light enough to be carried in trucks and lifted into place by hand, without requiring the use of a crane. • The bridges were strong enough to carry tanks. • Bailey bridges continue to be extensively used in civil engineering construction projects and to provide temporary crossings for foot and vehicle traffic

 Roof Truss :

1.King Post Truss :

• If span length is in the range of 5 to 8 meter, then king post trusses are used. • The trusses are spaced not more than 3m c/c. • A vertical post is provided in the center that is called the king post. • A king post extends vertically from a crossbeam to the apex of a triangular truss. • It connects the apex of the truss with its base, holding up the beam (in tension) at the base of the truss.

2. Queen Post Truss

• If the span length is in between 8 to 12 meter then queen post trusses are used. • Two vertical posts are provided in 2 sides at a distance which are termed as queen posts. • Straining beam and straining seal is used to keep the queen posts in exact position. • Queen post is a tension member in a truss that can span longer openings than a king post truss. • A queen-post bridge has two uprights, placed about one-third of the way from each end of the truss.  • The central square between the two verticals was either unbraced on shorter spans, or had diagonal

3. Fink Roof Truss

• They are used for longer spans having high pitch roof, since the web in such truss are subdivided to obtain shorter . • A Fink truss is the most commonly used type of residential construction truss.  • It is composed of several boards or steel bars that connect together to form an intersection at the top angle of the roof.  • These trusses provide for the rafters and give the roof its rigidity. •  A Fink truss is the perfect solution for many architectural designs and allows for several different types of rooflines, while providing the

4. Howe Roof Truss

• It is a roof truss with vertical web to take tension forces and with angled braces to take compression. • The converse of the Pratt truss is the Howe truss. • The Howe truss can be advantageous for very lightly loaded roofs in which reversal of load due to wind will occur. • In addition the tension chord is more heavily loaded than the compression chord at mid-span under normal vertical loading. • The Howe truss offers greater economy in of steel weight for long-span high-pitched roofs as the are subdivided into shorter

5. Warren Roof Truss

• Warren truss is a kind of design that is used in different types of construction for ing a load. • In warren roof truss diagonal  are alternatively in tension and compression are used in a building ranging from 20-100 m in length. • The unique design of a Warren truss structure ensures that no strut, beam or tie bends or withstands torsional straining forces but is only subject to tension or compression. • The use of the Warren truss design is common

 Advantages -

• There is less material required for the construction of a Warren truss bridge. • There is less blockage of view. • The constituents of a Warren truss bridge can be assembled piece wise.

Disadvantages – • The maintenance of the ts and fittings of a Warren truss bridge could be expensive

• The calculations to determine the load-bearing capacity of a Warren truss bridge can be hassling.

• There could be too much deflection for long spans