STEEL BEAM BASICS: USES, TYPES, & READING SIZES EXPLAINED

November 17, 2021 | Categorised in:

steel beam structure

Steel beams can seem simple when you glance at them, but there is a huge mix of types, variations, measurements, and more that are tailored to different applications and purposes. We’ve created guides like this for other product categories as well, such as rebar, piping, angles, plates, and grating. Whether you’re just looking to learn or you’re planning on buying some, we’re here to break it down so you can feel confident talking about and buying the right beams for your needs.

What is a steel beam?

A steel beam is a structural shape that’s widely used across many industries and projects. Their profile is shaped like a capital I (or an H if you turn it on its side). Steel beams are very strong but often also very heavy, which is why they can also be cut in half along their length to create tee beams (in the shape of a capital T).

What are they used for?

At their most basic, steel beams are for supporting heavy loads due to their immense strength. More specifically, they’re often used in construction and civil engineering structures such as supports for bridges or the primary frames of buildings. As we’ll discuss, they have excellent strength and weight-bearing characteristics for things like supporting floors and roofs, which makes them ideal choices for most construction and infrastructure projects.

Parts of a steel beam

While a beam’s strength partially comes from the strength of steel, is also is a result of their shape. A steel beam is made up of two basic parts, both of which can vary in dimensions for different applications.

  • Flanges: When looking at the profile of a steel beam, it looks like an I. The (typically shorter) horizontal pieces on the top and bottom are called the flanges. Their edges can be parallel or tapered depending on the type of beam.
    • Purpose: Flanges act to resist the bending moment or forces experienced by the beam.
  • Web: The web of a beam is the (typically longer) vertical piece that connects the two flanges in the center. The radius of the corner where each flange meets the web can also vary depending on the beam.
    • Purpose: The web resists shear forces that could cause collapses or breaking.

The web and flanges work together to provide great strength for shearing and bending, which is why beams are so common in bridges and building frames. However, a beam’s shape has relatively low resistance to torsional (or twisting) forces.

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Steel beam types

Within the “beam” category, there are a couple of common types (or letters) you’ll likely run across. The most common of these are I, H, and W:

H beams vs. I beams

Relatively similar in height-to-width ratio, I-beams and H-beams are both shaped like their letter designation. The primary differentiator between these two product types is that while H-beam flanges are parallel and flat, I-beam flanges are tapered and get thinner further from the web.

W beams vs. I beams

Now when we compare I-beams to another beam variation, W-beams (also known as wide flange beams), we see a more obvious shift simply from the name. As you might have guessed, W-beams have flanges that are wider than your standard I-beam, and this is the main difference between the two. Because of this, W-beams can often hold more weight and resist higher forces than I or H-beams.

How to read steel beam sizes

When reading beam sizes, they often are written like “W 27 x 178#” or “S 24 x 121#”. This might seem confusing if you’ve never tried to purchase or work with steel beams before, but it’s very straightforward once you understand the format.

The letter indicates the general shape or type of beam, in this case, W means it’s a W-(or wide flange) beam whereas S is for an S-(or Standard American) beam. The number that follows the letter is called the section number and is the “height” of the I. The second number is the pounds per lineal foot, or how much each foot of the beam weighs. Sometimes, there will be a third number that represents the length of the beam (in feet).

Using these examples, the wide flange beam is 27 inches tall and weighs 178 pounds per foot of beam. If that beam is 40 feet long, we can multiply the weight per foot by the length to estimate that the total weight would be 7,120 pounds. The S-beam is 24 inches tall and weighs 121 pounds per foot, leading to a 4,840 total weight if the beam is 40 feet long.

While these are the major pieces of information for reading a steel beam size, the flanges and web also have individual dimensions and characteristics that are often displayed in full sizing charts. For more information, visit our I-beam or W-beam pages to view their sizing charts.

Get the right beams for your project today

No matter what type, size, or specification of beams you need, Service Steel can supply it. Now that you understand how to understand beam sizes and what your project needs, call us or request a quote today!