Truss Definition, Design & Types of Truss

Trusses are the most important engineering feature in the emerging civil engineering competition, there are different Types of Truss. Indeed, the increase in demand for trusses in the construction industry is primarily due to long-span structures with lightweight.

Trusses have played an important role in civil structures alongside the advancement of the steel industry since the use of steel as a construction material, owing to its higher strength with lower mass.

These trusses have been made with timber planks for many years, and they continue to be made with these planks for aesthetic reasons. These trusses are used as integral structural forms in roof trusses, bridges, electricity and telecom towers, and even structural frames.

What is a truss?

A truss is a type of load-bearing (in most of the cases) structure whose components resist tension and compression loads. There are various types of structures in Civil Engineering, and a truss is one of them. You may have seen trusses as railway bridges or as the support structure for long-span structures such as airport terminals, aircraft hangers, sports stadiums, and auditoriums.

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The ability of trusses to carry heavy loads despite their lightweight is the main reason for their popularity and demand in engineering. Trusses are well-known for their ability to build strong, long-lasting structures with minimal deflection. The majority of such trusses are made of steel because it is lighter in weight and has a higher strength than other building materials such as wood.

Truss Components

Upper chord, bottom chord, diagonal member, and vertical member are the basic components of a typical truss. These elements are combined to form a single panel. The total span of the truss is divided into panels of uniform or variable length.

Although the members can be arranged to form any shape or configuration, trusses are typically made up of triangular units that are straight members connected at the end joints known as “nodes.”

Forces and reactions are only considered at the nodes in a typical truss, and they are either compressive or tensile forces. Bending moments are excluded in order to meet the requirement of two-force members.

Types of Truss

Truss designs are typically classified as open or closed. A closed truss is one that has a tie beam or where the roof framing is not visible, such as a king post or a queen post truss. An open truss, on the other hand, has an interrupted tie beam that allows for a vaulted ceiling or exposed roof framing. Open trusses include scissor trusses, arch trusses, types of steel roof truss and hammer trusses. The ten different types of truss structures are as follows:

Types of Truss
Types of Truss

What are common trusses?

1. KING POST Truss

A king post truss, also known as a turkey track truss, is made up of two main rafters, a tie beam, a central vertical post, and two struts. The triangle shape of the king post truss is provided by the central vertical post. On each side, one strut is placed at a 45° angle for added support. The king truss is one of the most basic and low-cost truss designs.

2. QUEEN POST Truss

The queen post truss differs slightly from the king post truss in design and has some additional capabilities. The main distinction between king post truss and queen post truss designs is that a queen truss has two central supporting posts instead of one. Queen post trusses can span wider openings than king post trusses, making them ideal for larger residential projects.

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In comparison to a king post, a queen post has a slightly larger span of about 10 metres. The queen post is a tension member composed of two vertical posts connected by a beam in compression at the centre node.

3. SCISSORS Truss

A scissor truss, also known as a vaulted ceiling truss, is a popular type of wood truss. It’s formed when two bottom truss beams cross and connect to the angled top beams. The crossing trusses form an inverted V-shape (similar to a pair of scissors) and allow for the design of a sloped interior ceiling.

4. Warren Truss

In a typical warren truss, diagonal members are alternately arranged to form a “W.” There are equilateral triangles in such a truss, with each diagonal member alternating between tension and compression. This type of truss requires fewer members than a Pratt truss and can be used for buildings with spans ranging from 20 to 100 metres.

5. MULTIPLE KING POST

A multiple king post truss is a type of longitudinal truss that is similar to a king post truss and a queen post truss. Installing this type of truss is a simple way to increase a truss’s span capability.

A multiple king post truss has diagonal beams, also known as gunstock verticals, for support between each panel. These trusses can be constructed with an odd number of panels, so that all diagonals are in tension and compression. Diagonals are opposing for multiple king post trusses with an odd number of panels (or crossing).

6. Planar Truss

A planar truss, as the name implies, is made up of elements that only have one plan. These trusses are typically used as structural members for a building’s roof or a bridge deck. One of the most significant advantages of using such a truss is that it is significantly lighter and stronger than a solid beam or girder. Such a truss would be more cost effective.

The depth or height of the truss is determined by the length of the given span, but the design is again adjusted to optimise the material in the truss chords.

7. TRUSS: HAMMER BEAM

The hammer beam truss is inspired by old-style cathedrals. Rather than using a single log to span the entire length of a room, it employs short beams, known as hammer beams, that protrude from the wall. Additional hammer posts are built on top to support the rafters, giving the structure a decorative appearance.

8. Truss: space frame

Consider an electrical power transmission tower to better understand this truss classification. As a result, a space truss is a three-dimensional framework of members hinged at the nodes. In the preceding example, a tetrahedron-shaped space truss with 6 individual members and 2 members in common with adjacent trusses is used.

9. TRUSS ARCH BOTTOM

Consider an arch bottom truss to be a higher-level version of a king post truss. While the overall truss design concept remains unchanged, the bottom beam is curved, or arched, for a more decorative appearance.

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10. Truss with Bowstrings

Bowstring truss is a type of arch truss that is commonly used in buildings and bridges but is less commonly used in industrial buildings. In a larger space, bowstring truss can be used to create a column-free space.

Truss design

Assumptions:

  • All of the members are straight and have a uniform cross-section along their length.
  • The members’ weight is regarded as insignificant.
  • Members’ nodes or joints are regarded as pin connections, which are also frictionless.
  • Only at the nodes or joints are external forces or stresses applied.
  • As a result, the members only have axial forces, which are either compression or tension.
  • Couple or bending moments must not act on truss members.
  • The centroid of the members must be aligned with the centroid of the joints.

Truss design Steps

Step 1: Create a three-dimensional model of the walls, roofs, ceilings, flooring, and major beams.

Trusses rely on other pieces in the structure model and, therefore, must be integrated with the environment. Some components are not functioning as bearing components. Walls, beams, roofs, ceilings, and floors may all function as bearing components to a certain extent.

Step 2: Create trusses and truss areas

The truss volume is limited by objects, thus the truss areas are produced.

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Step 3: Create truss members

User-provided rules generate truss members.

Step 4: Examine the connections between the members

Connections must be established between truss members. Connections are being added to the frame of truss members by the user, but manually inserted ones should be verified.

Step 5: Examine the supports

There must be bodily contact or a relationship between the supported and supporting objects. User needs to connect trusses that are supported by another truss.

Step 6: Create truss labels and drawings

Truss Design automatically assigns the truss and truss member labels, which are based on a sketch. Before Truss Design may be used, the truss drawing must first be created and updated. Labels are utilized to identify engineering findings.

Step 7: Generate internal pressure area

The outside pressure area is the interior space limited by the exterior walls and internal ceiling or roof. If the ceiling is porous, then the roof restricts the internal pressure area.

Step 8: Calculate wind loads for the ceiling and roofs

According to the selected building code, wind loads are produced.

Step 9: Add other line, point, and area loads.

Point, line, or area loads can all be modeled manually. The bearing object should be used in each drawing-model pair that includes a load. To apply a point or line load to the bottom chord, first apply the weight to the ceiling and then transfer it to come into touch with the bottom chord.

Step 10: Run Analysis

Trusses, which are pieces of wood or metal that span between two supports and support a ceiling, can be engineered in one of three ways. The engineering label is placed near the end of the truss label. Engineering may be performed on either one or many trusses or rafters. A passed truss after engineering is indicated by a green coloration label.

Step 11: Examine the engineering results

The engineer’s report is typically just a summary of the findings and conclusions drawn during the investigation. 3D models or 2D drawings can be used to open the results. The stress index for each member is shown in drawing. If the stress index for a specific member is greater than 1, it indicates that its capacity has been exceeded.

Conclusion

The use of trusses in modern construction has led to the development of lightweight, long-span structures that are becoming increasingly popular. With their ability to span large distances while being light in weight, trusses have become an important part of the civil engineering competition. We also discussed 4 types of truss bridges along with the design of trusses.

As technology continues to progress and new materials are developed, it is likely that the use of trusses in construction will only continue to grow. What do you think? Are there other applications for trusses in civil engineering that we haven’t considered? Let us know in the comments below!

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