What is Truss? Applications, Advantages and Limitation
Trusses are an essential structural element used in construction and engineering to support roofs, bridges, towers, and other structures. They consist of interconnected triangles that distribute weight throughout the structure. Trusses are designed to provide stability, strength, and durability to a building or structure, allowing it to withstand the forces of nature and load. This article will explore what trusses are, how they work, their application, advantages and limitation.
What is a Truss?
A truss is a stable structure made of interconnected straight members arranged into triangles, creating a rigid framework. A truss structure is composed of members such as beams connected by pin joints known as nodes. The members are arranged and connected in a manner such that all the forces and reactions act solely at the nodes. These members are considered two-force members as the forces are only applied at the ends of the member. As a result, the truss members are only subjected to axial loads (compression or tension force) and not moments.
A planar truss is a two-dimensional structure in which all members and nodes are confined to a single plane. In contrast, a space truss has members and nodes that extend into three dimensions. The top beams of a truss, also known as top chords, are usually subjected to compression. In contrast, the bottom beams, known as bottom chords, are subjected to tension. Top and bottom chords are connected by diagonal members called web members, and the areas inside the webs are called panels.
There are many different types of trusses available, each with its unique characteristics, advantages and disadvantages. Common types of trusses include Pratt trusses, Warren trusses, Howe trusses, K trusses, and Fink trusses.
How Do Trusses Work?
Trusses work by transferring weight from the point of application to the supports. The connections between truss members are typically pinned, ensuring that no shear or moment forces are transferred from one member to another. The weight of the structure is distributed across the truss, which means that each member of the truss is under a smaller load than it would be if it were the sole support. Pin joints in truss structures are theoretically intended to provide no resistance to rotation and function like hinges. However, this may not be the case in practice.
A truss structure is considered statically determinate when all member forces can be determined using equilibrium equations; otherwise, it is considered statically indeterminate.
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How Trusses Differed From Frame Structures
Truss and frame structures are not the same, yet they are often misunderstood. Trusses are constructed of rod members arranged in triangular configurations with pinned joints. In contrast, frames are structures made of arbitrarily oriented beam members connected rigidly or by pins at joints. Truss members transmit only axial forces and do not experience bending moments, while frame members typically experience a combination of shear, axial, and bending forces.
Applications of Truss
In today's civil engineering context, trusses have become a crucial engineering feature, particularly due to their ability to support long-span structures with lightweight. The rise of steel as a construction material due to its high strength and low mass has also contributed significantly to the growth of truss usage in civil structures.
The use of timber planks to create trusses has gained popularity in recent years, mainly due to their aesthetic appeal. As a result, these trusses have become an integral part of the structural design of roof trusses, bridges, electricity and telecom towers, and even structural frames.
Advantages of Truss
Strong load-bearing capacity: One of the main benefits of trusses is their strong load-bearing capacity, which is due to the fact that their members are predominantly subjected to axial loads. As a result, these members are either in compression force, tension, or have no force at all, also known as zero-force members. This makes trusses an extremely efficient structural form.
Versatile and adaptable design: The design of trusses is highly versatile and adaptable, making them well-suited for a wide range of applications. Although commonly used for shorter bridges, trusses can also span longer distances and handle heavy loads.
Effective use of materials: When appropriately designed, trusses are a highly efficient solution for spanning long distances while minimizing material usage. This is because the truss members are subjected to axial loads through compression or tension. This makes the system more efficient and requires less material as the force is distributed among the number of members. Additionally, using less material makes construction easier and more cost-effective.
One of the most significant advantages of truss structures is their quick installation as they are pre-fabricated in the factory and then assembled on-site. Another advantage of truss structures is their ability to span long distances due to the force distribution in its member, which minimizes force concentration. Additionally, the triangular spaces created between truss members provide easy access for the installation of electrical and mechanical systems.
Affordable to construct: Truss bridges are often a perfect choice for accelerated bridge construction techniques due to their simplicity.
Disadvantages of Truss Structure
The major drawback of truss structures is that they occupy a large amount of space. The large interconnected triangular components are necessary to support and distribute heavy loads. This means that existing structures may need to be modified to make space for truss bridges in certain locations.
Another drawback of truss bridges is their expensive maintenance. Because of the multitude of materials and components, keeping up with the maintenance of truss bridges can be challenging. Identifying and pinpointing the exact problem when it has an issue is also challenging.
