Understanding Steel Beams in Construction Drawings


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updated 28/08/2023

Steel is one of the best materials for providing strength and structural soundness, which is essential for construction. It’s possible to create structural pieces with steel that are durable and flexible. These are only a few reasons steel is often chosen for construction projects. 

Engineers have used steel beams to create mountainous skyscrapers, bridges, and much more. 

It can be challenging to understand steel beam references on construction drawings. So, we’ve put together a quick guide to help you understand the acronyms!


1. Open Steel Sections: Common Open Sections

There are three types of open steel section beams: 

  • Universal Beam [UB]: UBs are always taller than they are wide; UBs are often used in construction and civil engineering projects.


  • Universal Column [UC]: UCs are approximately equal in height and width; UCs are the most used sections of structural steel. They’re most often used for columns; however, their small depth makes them a great choice for load-bearing members when height is limited. 


  • Parallel Flanged Channel [PFC]: PFCs are used as columns or support for floor joists and can easily bear weight. PFCs are also used with RSJ steel beams, UCs, and other forms of structural steel. 


The Benefits of UBs


Distribute Weight Evenly

UBs distribute weight evenly and can handle a uniform load across the beam. When there’s weight on the beam, the maximum deflection falls on the center of the beam. This increases tension on the sides of the beam. 


Available in Various Dimensions

UBs also come in a variety of weights, section depths, web thicknesses, flange widths, and other specifications. These beams can be used for a wide range of purposes. 


Bears Higher Loads

UBs are designed in such a way that they are capable of bending under high stress without buckling. 


Nominal Size vs Actual Size of Open Section 

Each nominal serial size has a range of sections that have different thicknesses of flanges and web. This makes it possible for engineers to specify the most efficient beam possible. These variations of the same serial seize are differentiated by their weight per meter. 

The different weight beams have slightly different overall dimensions. The manufacturing rolling process means the internal distance between the top and bottom flange remains constant, so the thicker flanges of the heavier beams result in a slightly taller (and generally wider) section. The web of heavier sections is also thicker. 

When a project has sections of the same serial size but different weights, these small differences need to be considered to ensure consistent levels and fit are achieved. 

PFCs only have 1 weight per serial size, and they match their listed dimensions exactly.


2. Closed Hollow Sections

Common Closed Sections include: 

  • Circular Hollow Section [CHS]: these beams are round tubular steel sections that can be used for a variety of purposes. They are usually available as hot-rolled or cold-formed sections. 
  • Square Hollow Section [SHS]: these beams have a flat surface around the outer rim. The hollow section is often used for joining, welding, and anything that needs little to no edge prep. 
  • Rectangular Hollow Section [RHS]: RHS beams are one of the strongest hollow sections and have the broadest functionality. The beams are often used for joining, welding, and more. 

Like UBs and UCs, hollow sections are available in a range of sizes for each serial size; however, they are distinguished by wall thickness rather than weight. Regardless of wall thickness, the outside dimensions remain the same, so it’s necessary to always match the listed serial size. 

The corner radii of SHS and RHS sections can vary depending on the wall thickness and manufacturing process (hot-formed or cold-formed). Hot-formed sections should be specified for use in structural applications. 


The Benefits of Closed Hollow Beams


High Strength-to-Weight Ratio

CHBs offer high torsional resistance and superior compression performance with significant weight savings. 


Closed Section 

The closed sides resist torsional load, and they can be used in food processing and clean facilities where cleanliness is required. These beams minimise surfaces that would otherwise collect debris and dust.


Aesthetic Appeal

These beams have smooth sides, rounded corners, and closed sections, making them a favorite with architects, especially in structures where the beams are exposed. 



CHBs also have less surface area to prepare than other steel beams, making them a cost-saving choice. 


3. Steel Grade and Hot/Cold Forming

What is Steel Grade? 

Steel grade refers to the strength of the steel. In UK buildings, the grade for structural steel that is used the most is S275 and S355. The higher the grade number, the stronger the steel. For instance, S355 is stronger than S275. 

The different grades of structural steel usually have the same stiffness, so using a higher grade doesn’t reduce deflections. 


Steel Grade Availability

In the UK, until fairly recently, open sections were most commonly grade S275 and closed sections grade S355. Today, open sections are usually manufactured in S355, with S275 availability limited, if at all. S355 is the standard for closed sections; however, S240 is also becoming more available for more demanding applications. 

Steel plate, such as the kind used for fabricating connections, is usually grade S275, but S355 is also easy to find. 


How Do I Know Which Steel Grade Has Been Specified? 

The steel grade for a project is usually shown within the beam references. For instance, you may see this: 203 x 203 x UC S355. Or you may find a “Notes” or “Specifications” section in the engineering drawings. 


What are Hot- and Cold-Formed Sections? 

Closed hollow sections are available in two different manufacturing methods: hot-formed and cold-formed. 

Cold-formed sections are weaker. This is because the cold bending process of converting a flat plate into a hollow section shape puts permanent stresses into the steel. Cold sections also have restrictions associated with welding. 

The hot-forming process relieves the forming stress, leaving a section with more capacity to resist external load. 


How Do I Know if Hot- or Cold-formed Members are Specified? 

Structural drawings need to be checked to see what type of section the engineer has specified. This information is often included in the “Notes” or “Specifications” section. 

Using cold-formed steel in place of hot-formed steel invalidates the design. 

In addition, structural open sections are always hot-formed steel. 


Substituting Steel Grade & Forming Method

Steel beams cannot be substituted with a lower steel grade or a different forming method (cold or hot) without verification from the beam designer. 

Specifically, cold-rolled closed sections are often available in grade S235 at a lower cost than S355; however, substituting results in a structure with grossly reduced capacity. This may invalidate the structural design. S235 is not typically used for structural applications. 


Summing It Up

So, there you have it! We hope this short guide helps you determine the different types of steel beam references in construction drawings and why specific types of steel beams are used in different ways. 

FAQs about Understanding Steel Beams in Construction Drawings

How do I determine the appropriate type of steel beam for my project?

The choice of steel beam type depends on factors such as the span length, load-bearing requirements, and the overall design of the structure. Consulting with a structural engineer can help you make the right decision based on your project’s specific needs.

Can I alter the size of steel beams during construction if needed?

While it’s possible to make adjustments during construction, it’s advisable to finalize the beam sizes during the design phase. Changes made on-site can lead to complications and may require further structural analysis.

Are steel beams the only option for structural support in construction?

No, there are other materials like wood and concrete that can be used for structural support. However, steel beams are preferred for their strength-to-weight ratio, making them highly effective for supporting heavy loads.

How can I ensure that steel beams are placed correctly according to the drawings?

Precise measurements and alignment are key. Working closely with a qualified contractor and referring to the construction drawings regularly can help ensure accurate placement.

Are there any safety considerations specific to steel beams?

Yes, safety is paramount when working with steel beams. Proper installation techniques, securing the beams adequately, and adhering to safety guidelines are essential to prevent accidents during construction.

Can I use reclaimed or salvaged steel beams for my project?

Using reclaimed steel beams is possible, but they must meet structural requirements and pass safety inspections. It’s recommended to consult with an engineer to determine the viability of using reclaimed materials.


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