Difference Between Beam and Girder (with Table)

Each and every structural material has to undergo the standard acceptance tests for structural materials which are prescribed by the ACI (American Concrete Institute) Code, a leading authority for inspection, project management, and consulting for individuals and organizations involved in construction and concrete design. The ACI revises its specifications regularly after a particular span of time to facilitate improvements in production methods, materials, and testing.

Both of these are subjected to flexural loads and also act as a primary part of the structural framing system. Both beam and girder are horizontal members and falls among the most commonly designed elements of the structure. Both the terms are often used in place of one another but there are certain factors that distinguish one from the other. Understanding the difference between these two is extremely crucial to the construction scene.

The difference between a beam and a girder is that a beam is used to support distributed loads whereas a girder is used to support concentrated loads.

Comparison Table between Beam and Girder

Parameter of ComparisonBeamGirder
DefinitionHorizontal members and one of the most commonly designed elements of structureThese are smaller beams and acts as the main horizontal support of a structure
FunctionIntended to carry distributed loadsDesigned to support major concentrated loads
UsesUsed for residential projectsUsed for commercial structures
ClassificationAn be classified as simply supported, fixed, and cantilever beamOnly one particular type of beam namely the I-beam is used mostly
RequirementsDo not require  considering additional requirements while fabricatingRequires essential factors like erection, stability, plate sizing, etc. while fabricating.

What is Beam?

The primary part of a structural framing system which is specially designed to carry distributed loads such as parallel walls or roof systems is called a beam. These are one of the most commonly used elements of structure in engineering which is intended to resist loads and its primary mode of deflection is bending. Beams are mainly used to resist bending moments, shear forces, and vertical loads.

Thus, beams can be defined with the help of their bending moments which are calculated for the primary requirements for building a structure. In other words, any horizontal structural member which can undergo lateral load and is highly capable of withstanding load can be called a beam.

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What is Girder?

Girders are basically beams that can support other smaller beams and also can act as the main horizontal support of a structure. Girders were designed to support major concentrated loads like columns or beam reactions and their load-bearing capacity is much greater than beams.

Girders can be made from a wide variety of construction materials such as stainless steel, concrete, or also by the combination of both. Girders can support vertical loads and may even consist of a single piece or more than one piece bound together.

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Main Differences Between Beam and Girder

  1. Beams are always horizontal structures and one of the most commonly designed elements of structure mostly intended to carry distributed loads such as parallel walls or tributary areas of the floor and roof systems. It is a structural element that is capable of withstanding heavy loads primarily by bending which are used for support in residential construction projects. A beam that can support other beams is usually called a girder; however, it is also a beam. Girders can support smaller beams and also act as the main horizontal support of a commercial structure, usually designed to support major concentrated loads such as columns or beam reactions.
  2. The main difference between a beam and a girder is mainly the size of the component. Beams are usually referred to as girders in the construction sites and girders are the main horizontal support structure for smaller beams. So, it can be said that all Girders are beams, but all beams are not necessarily girders. Both can be classified as bending members that are distinguished primarily by the manner in which they are loaded. If it is the main structural support which consists of smaller beams, it can be called a girder.
  3. In civil engineering, beams can be classified into several types based on many factors. Based on the type of support, beams are mainly classified into the following types: Simply supported, Fixed, and Continuous Cantilever. Beams can also be classified based on its geometry as a straight beam, curved beam, or tapered beam. Based on the cross-sectional shape, beams can be divided into I-beam, T-beam, and C-beam. A Girder is specifically used to refer to a steel beam. I-beam Girders are the most common type of Girders and are mainly used in bridge construction. Box Girders are mainly used in the construction of elevated bridges and roadway flyovers.
  4. Beams are usually the choice of a structural member because they possess incredible load-bearing capacity against all conditions. Girders are used to mainly support smaller beams and are specifically used to construct bridges and flyovers because they are highly capable of carrying extremely heavy loads.
  5. While fabricating a beam it does not require any additional requirements, whereas, on the other hand, while fabricating a girder it does require additional requirements like erection, stability, plate sizing, etc.
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Conclusion

Beams are always the horizontal members which are considered among the most commonly designed elements of the structure whereas girders are also horizontal members that can support smaller beams but act as the main support of a structure with dynamic load-bearing capacity.

However, beams can be known by alternative names based on their location in a system and the material used to fabricate it. For example, a basic floor joint is a beam that is lightly loaded but a roof joint that commonly goes by the name “rafter”, is also a beam.

A beam that provides support to other smaller beams is commonly called a girder, though it is still a beam, the load-bearing capacity it possesses is much greater than a beam and it is also designed to support major portions of a structure.

Thus, we can say that girders are mainly used for building bridges and flyovers, whereas beams are ideal for residential structures. In other words, all girders are beams, but all beams are not necessarily girders.

Reference

  1. https://ascelibrary.org/doi/abs/10.1061/(ASCE)EM.1943-7889.0000156
  2. https://www.sciencedirect.com/science/article/abs/pii/S0263823108002322