How is a Girder Different From a Beam?

Girder and beam are both important load-bearing elements in building structures, but they are not exactly the same. While the two terms are frequently used as synonyms, there exist distinct differences in their design and utilization. 

We will take a deep look at the differences between girder and beam to help you better understand their respective roles and when to choose one over the other. Making the right choice can guarantee the stability and safety of the structure throughout the design and construction phases.

What is the relationship between girder and beam?

Girder and beam are two important elements in building structures. Their relationship can be understood through the following points:

Functional relationship:

• Girder is usually the primary load-bearing structure, responsible for supporting and distributing weight to other structures. It is usually used to support multiple beams, so the girder carries a larger load than the beam.

• Beams are secondary load-bearing members, usually used to support floors, roofs or other small-scale structures. They transfer the load to the girder, which in turn transfers the load to the column or foundation.

Position relationship:

• In many building structures, the girder is located in the primary support position, usually in the core or outside of the building, and is responsible for supporting and transferring most of the load.
• Beams are usually placed on girders as a supporting element that carries a secondary structure.

Working order:

• In building design, the girder is usually designed and built before the beam. The design of the beam needs to take into account the load-bearing capacity of the girder and ensure that the load can be effectively transferred to the girder.

In general, girders and beams complement each other. Girder is responsible for carrying larger loads and providing support for beam, while beam transfers load to girder, jointly ensuring the stability and safety of building structure.

What is a Girder? 

A girder is a large, primary structural element used to support the weight of beams and other structures, distributing loads across a wide area. It is typically the main horizontal support in larger buildings or bridges. Girders bear the brunt of the load from the floors or roof, transferring this weight to vertical supports such as columns or walls. They are crucial in maintaining the stability and strength of the entire structure.

Common materials used for girders

Common materials for girders include:

• Steel: Because of its strength, durability, and capacity to span extensive distances, steel is frequently utilized for girders in large-scale buildings and bridges.
• Concrete: Reinforced concrete is another popular material for girders, especially in bridge construction or in buildings where large spans are required.
• Wood: In smaller structures or residential buildings, wooden girders may be used, although they are less common for large or heavy loads.

Typical applications of girders in construction

Girders are commonly used in:

• Bridges: Girders made of steel or concrete are employed to support the weight of vehicles and infrastructure.
• Large commercial buildings: Girders help support floors and roofs in skyscrapers and large office buildings.
• Industrial buildings: Girders are used to support heavy machinery or large, open spaces where no other supports are feasible.
• Railroad tracks: Large steel girders are used to support railroads, providing a sturdy foundation for the trains.

What is a Beam?

A beam is a horizontal structural component that is specifically designed to support loads applied perpendicular to its axis. It has a vital function in transmitting loads from the floor, roof, or other structural components to vertical supports such as columns or walls. While girders are typically the primary supports in a structure, beams often serve as secondary supports, carrying loads over shorter spans. Beams are crucial in preventing bending and deflection under weight.

Common materials used for beams

Beams can be constructed from a range of materials, including:

• Wood: Wood is commonly used for beams in residential homes and smaller structures.
• Steel: Steel beams are widely used in both residential and commercial construction for their strength and ability to handle heavy loads.
• Concrete: Reinforced concrete beams are typical in larger construction projects, providing the necessary strength for multi-story buildings and bridges.
• Composite materials: Some modern beams are made from a combination of materials, such as steel and concrete, to increase their strength and durability.

Typical applications of beams in construction

• Residential buildings: Wooden beams are often used in homes to support roofs or floors.
• Commercial buildings: In larger buildings, steel or concrete beams are utilized to provide structural support for floors and ceilings.
• Bridges: Beams are a crucial part of the structural framework, supporting the weight of the roadway and the vehicles traveling on it.
• Warehouses and factories: In industrial settings, beams support large roof systems and heavy machinery.

Key Differences Between Girders and Beams 

Size and load-bearing capacity

Girders are generally much larger and more robust than beams. Their primary purpose is to support significant loads over long spans, which is why they are designed with higher load-bearing capacities. 

Beams, on the other hand, are typically smaller and support less weight, acting as secondary support structures. While beams can be made from materials like wood or steel, girder materials need to be much stronger (like steel or reinforced concrete) to withstand the heavier loads they carry.

Placement and structural role

Girders typically serve as the main horizontal supports in a structure and are placed at the primary level of support. They usually sit on top of columns or large vertical supports and distribute the weight of the entire structure. 

Beams, however, are placed on top of girders or columns and are used to support smaller sections, such as floors or roof structures. Beams act as secondary load carriers, transferring the load to the girders, which then distribute the load further to the foundation or other supporting structures.

Support and span differences

Girders are designed to handle large spans and heavy loads, often found in large buildings, bridges, or industrial settings. They can support more significant distances between supports due to their strength and design. 

Beams typically cover shorter spans and are used in less demanding applications. For example, beams in residential buildings may only span a few meters, while girders in bridges or high-rise buildings can span much greater distances, providing primary structural support over the entire area.

Material and design differences

Girders are often made from heavy-duty materials like steel or reinforced concrete because they need to withstand substantial loads and span long distances. Their design is often more complex to account for their role as the main support structure. 

Due to their relatively lower structural demands, beams can be crafted from a diverse array of materials, including wood, steel, and reinforced concrete. Depending on the specific application and load requirements, beams can be designed in various shapes, such as I-beams, H-beams, and box beams.

Application differences

Girders are employed in more critical structural applications, encompassing bridges, high-rise buildings, industrial structures, and large-scale infrastructure projects. They form the foundation of the structure and support major loads. 

Beams are more commonly used in residential buildings, commercial properties, and smaller structures, where they support floors, roofs, and ceilings. Beams also play a role in lighter-duty applications such as small bridges, warehouses, and some factory buildings.

When to Use a Girder vs. a Beam

When deciding whether to use a girder or a beam, it largely depends on the structural requirements, the load to be supported, and the span length.

Use a Girder when

• Large spans and heavy loads are involved. Girders are designed to support substantial weight over longer distances, making them ideal for large buildings, bridges, and industrial structures.
• Primary support is needed. Girders often serve as the main horizontal support structure that carries the load of beams or other structural elements.
• The structure requires multiple smaller beams or load distribution. Girders are capable of supporting the weight of numerous beams, transferring their loads to vertical supports like columns or walls.

Use a Beam when

• The load requirements are moderate and the spans are shorter. Beams are generally used in residential buildings, commercial spaces, or smaller bridges where they provide support over shorter distances.
• Secondary support is needed. Beams typically work with girders to carry load, supporting floors, ceilings, or roofs in smaller structures.
• The construction project doesn’t require the strength of a girder but still needs support for specific sections of the structure, like in floor systems or roof structures.

FAQs

Can you build without girders and beams?

In some small buildings or low-load structures, it may be possible to do without girders and beams, but this is usually rare. Many buildings require these structures to support weight and ensure stability. In some specific cases, other forms of support such as arches or columns may be used instead, but for most common building projects, using girders and beams is essential.

What is the difference between a box girder and an I-beam?

Box girder: A box girder has a hollow rectangular or square cross-section and is usually used when high strength and lightness are required. Due to its design, a box girder is able to carry large loads and provide support over longer spans. It is commonly found in bridges, viaducts, and large buildings.

I-beam: An I-beam boasts a cross-sectional shape resembling the letter “I,” consisting mainly of a vertical web and two horizontal flanges. I-beams have good bending resistance and are widely used in building frames and structures, especially for supporting smaller spans and loads.

How is a girder different from a secondary beam?

Girder: A primary beam is the core structure that carries the primary loads and is usually larger in span and has a higher load-bearing capacity, supporting other secondary beams or structural elements. They are usually placed in the most important support positions.

Secondary beam: Secondary beams are usually located above the primary beams and are responsible for supporting lighter loads such as floors, roofs or walls. They transfer the load to the primary beams and are usually shorter in span and have a lower load-bearing capacity.

What is the difference between girders and beams and joists?

Girder: A beam is the primary load-bearing structure that supports other secondary structural elements (such as beams or joists). They are usually longer in span and have a higher load-bearing capacity, and are the main supporting element of the building.

Beam: A beam is a structure that carries secondary loads and is usually used to support smaller parts such as floors or roofs. Their load is usually transferred through the primary beams.

Joist: A joist is a generally smaller, lighter lateral support element, usually used to support a floor or roof, with the load being transferred through beams or girders. They are generally used for smaller spans and lighter loads, and are found in greater numbers and are widely distributed.