Category Archives: Working Property Owner
Steel I-Beams Explained: How They Support Rigid-Frame Metal Buildings
Search for steel beams, metal beams, or structural steel beams and you will find everything from skyscraper framing to garage lintels. If you are planning a metal building, only one part of that story matters: how the I-beams in your frame carry the building’s weight and loads, and why that lets you have a large, open interior.
Worldwide Steel Buildings manufactures rigid-frame metal building kits built around solid I-beam primary framing. This guide explains what an I-beam is, what it does in a rigid frame, what determines its size, and how it fits with the rest of your kit.
What Is a Steel I-Beam?
A steel I-beam is a structural member shaped like a capital letter I when you look at its end. Two wide horizontal plates, called flanges, are joined by a vertical plate between them, called the web. The shape is efficient for a reason: the flanges sit far from the center of the beam, where they do most of the work resisting bending, while the web keeps the flanges apart and resists shear.
That efficiency is why I-beams carry heavy loads over long distances without needing the bulk of a solid steel bar. You may also hear them called H-beams, wide-flange beams, or girders, depending on their proportions and role.
Steel Beam, Metal Beam, Iron Beam: Are They the Same Thing?
In everyday searches, yes. “Steel beam,” “metal beam,” and “iron beam” are mostly used interchangeably, though structural beams today are made of steel, not iron. In the metal building industry you will also hear “red iron,” which refers to I-beam framing finished with a red oxide primer.
How I-Beams Work in a Rigid-Frame Building
A rigid frame is a series of I-beam frames set at regular intervals down the length of the building. Each frame has two columns on the sidewalls and two rafters rising to the ridge. The key word is rigid: the connections where column meets rafter (the knee) and where the two rafters meet (the ridge) are designed to resist rotation. That lets the frame stand on its own and carry loads without interior posts or diagonal bracing across the open space.
Each part of the frame has a job:
- Columns: carry roof loads down to the foundation and resist the sideways push of wind.
- Rafters: span across the building and carry roof weight, snow, and wind uplift back to the columns.
- Knee and ridge connections: transfer bending forces between members so the frame acts as one rigid unit.
Because the frame carries the structural load, the interior can stay open. That is the design behind clear-span buildings: WWSB rigid-frame buildings can clear span up to 225 feet with no interior columns. For a comparison with an alternative framing method, see our post on open web truss versus rigid frame buildings.
Why the Beams Are Tapered
Look at a rigid frame and you will notice the members are not a uniform depth. They are deeper at the knee, where bending forces are highest, and shallower toward the ridge and the column base, where forces are lower. Fabricating each I-beam with a depth that follows the force it carries puts steel where it is needed and saves it where it is not. Our rigid frame members are laser cut, pre-punched, and sub-arc welded, and we use high-yield-strength material, which lets the web be thinner without giving up strength.
Built-Up vs. Hot-Rolled I-Beams
Hot-rolled I-beams are formed at the mill in standard sizes. Built-up I-beams are fabricated by welding three plates together: two flanges and a web. Because each plate can be cut to the exact size and thickness required, built-up members can be tapered and matched to the engineering for a specific building. This is the approach behind most pre-engineered metal buildings, and it is why your frame is designed for your building rather than picked from a standard catalog size.
What Determines I-Beam Size?
There is no single beam size for a given building width. The engineered size of each column and rafter depends on several inputs:
- Span: the distance the rafters must cross. Longer spans require deeper members.
- Frame spacing: the distance between frames, called the bay spacing. Wider bays put more load on each frame.
- Roof pitch and eave height: both change the geometry and the forces at the knee.
- Snow, wind, and live loads: set by your location and the building code that applies to your site.
- Collateral loads: anything the frame must carry beyond the building itself, such as lighting, HVAC equipment, or a small crane.
Our buildings are designed to the Metal Building Manufacturers Association (MBMA) Metal Building Systems Manual and the building code you specify, and your kit ships with stamped engineered drawings. That is why you give us your location and intended use early: those details drive the frame design.
How I-Beams Connect to the Rest of Your Kit
The I-beam frames are your primary framing. They support the secondary framing: purlins across the roof and girts along the walls, which in turn support your roof and wall panels. Bracing ties the frames together and keeps the building square under wind. Primary frame connections are made with high-strength bolts, and the members arrive pre-punched so the pieces line up on site. See the full list of parts on our steel building components page, or read how it all goes together in our assembly process overview.
What Buildings Are Rigid-Frame I-Beams Best For?
Rigid-frame construction is a strong fit when you need wide, open floor space or a taller building than a basic straight-wall kit allows. Common uses include warehouses and manufacturing space, churches and rec centers, equipment storage, aircraft hangars, mini storage, and agricultural buildings. Rigid-frame buildings can clear span up to 225 feet with no interior columns, and interior columns can be added for overall building widths up to 300 feet.
Browse our commercial and industrial steel buildings to see examples, or compare framing options on our rigid frame steel building page and open web truss page.
Steel I-Beam FAQs
What is the purpose of an I-beam in a metal building?
In a rigid-frame metal building, I-beams form the columns and rafters that carry the roof, snow, and wind loads down to the foundation. Their shape resists bending efficiently, which lets the frame span a wide area without interior support posts.
What is the difference between an I-beam and an H-beam?
Both have flanges joined by a web. An H-beam typically has wider flanges relative to its depth. In practice, the terms are often used loosely, and the engineering for your building decides which proportions are used.
How wide can a rigid-frame building be?
WWSB rigid-frame buildings can clear span up to 225 feet with no interior columns. For wider buildings, interior columns can be added, and overall building widths reach up to 300 feet.
How do I know what size I-beams my building needs?
Beam size comes from engineering your building’s span, bay spacing, height, and the snow and wind loads for your site. We provide stamped engineered drawings with your kit, so you do not need to size the beams yourself.
Is red iron the same as an I-beam?
Red iron is the industry term for I-beam framing finished with a red oxide primer. So a red iron frame is an I-beam frame; the term describes the finish and the framing type together.
Plan Your Rigid-Frame Building
The right frame depends on your span, your loads, and how you plan to use the space. Start by exploring sizes in our 3D Building Designer, then request a quote and our team will walk you through your options. Every kit is backed by our 50-year structural warranty.
Worldwide Steel Buildings sells the building kit. Foundation, erection, and interior finish-out are separate from your kit price.