If you've priced out a steel building, you've probably run into a wall of terms: I-beams, purlins, gusset plates, girts. The drawings show shapes and labels, but they don't usually explain what each part is, what job it does, or how it connects to the rest of the frame. That gap is what makes quotes hard to compare and decisions harder to make.
This guide covers three things: the main types of steel structure components, the function each type performs, and how all of these parts work together as one system. By the end, you should be able to look at a steel building drawing and actually know what you're looking at.
What Are Components of A Steel Building?
Steel structure components are the individual parts that form the frame, envelope, and connections of a steel building. People in the industry also call these steel building components or steel building parts, and the terms mean the same thing. Each part has a type and a function. Some carry weight, some resist wind, and some just keep water out.
These parts fall into four groups: primary framing, secondary framing, the building envelope, and connections. The sections below cover the types within each group, the function each type performs, and how the groups connect to form one working system.
The Four Types of Steel Building Components
When you look at a steel building quote, the line items usually sort into four groups, even if the supplier never labels them that way. One group covers the main frame. One covers the supports that tie that frame together. One covers the panels and insulation that keep weather out. And one covers the bolts, plates, and hardware that hold everything in place.
Here is the short version:
- Primary framing: The main structure. Columns, rafters, and I-beams carry the bulk of the load.
- Secondary framing: Supports that tie the frame together. Purlins, girts, and bracing hold the shape and resist wind.
- Building envelope: The outer covering. Roof panels, wall panels, and insulation keep out weather.
- Connections and fasteners: The hardware. Gusset plates, bolts, and base plates hold every part in place.
Each group depends on the one below it. A strong frame with a weak connection still fails, and a good envelope wrapped around a poor frame won't last either way. Once you can sort a quote into these four groups, the document gets a lot easier to read.
Primary Framing: The Main Load-Bearing Structure
Primary framing is the core structure of the building. It carries the main loads and sends them down to the foundation.
Columns stand upright and carry the weight of the roof and any floors above them. Their spacing sets the open floor space inside the building, so wider column spacing means more open floor area, but it also raises the cost of each beam.
Rafters span across the top of the building and support the roof. They rest on the columns and carry roof loads such as snow, wind, and the weight of the roof panels themselves.
I-beams get their name from their shape, which looks like the letter I when you view it end-on. That shape puts more material at the top and bottom flanges, where bending stress runs highest, and less in the middle web, where the steel isn't doing as much work. The result is a strong beam that uses steel where it actually counts. Most steel buildings use wide-flange beams, a common type of I-beam with wider flanges than older styles.
For buyers, primary framing decisions drive both cost and function at the same time. Larger spans and heavier loads call for bigger beams and columns, so before you sign off on a design, it's worth asking how the column spacing affects your floor plan and any changes you might want down the road.
Secondary Framing: Supporting the Main Frame
Secondary framing fills the gaps between the primary frame and holds the building's shape.
Purlins run across the top of the rafters and support the roof panels. Their spacing sets how much load the roof can carry, including snow and foot traffic during maintenance.
Girts do the same job on the walls, running between columns to hold the wall panels in place.
Bracing keeps the building from swaying or twisting under wind or seismic force. X-bracing uses crossed steel rods or angles between columns, while portal frames rely on rigid beam-to-column joints instead of diagonal bracing, which keeps openings clear for doors and windows.
Secondary framing choices matter more than they seem to at first, especially for future plans. Wall openings, mezzanines, and equipment mounts all depend on where girts and purlins sit, so if you're thinking about expanding later, it's worth raising that with your supplier now rather than after the frame goes up.
Connection Components: Gusset Plates and Fasteners
Connections hold the frame together at each joint, and a frame is only ever as strong as its weakest connection.
Gusset plates are flat steel plates that join two or more structural members at a single point, such as where a beam meets a column or where truss members cross. The plate spreads the load across the joint instead of letting it concentrate at one small spot. Without a proper gusset plate, a joint can crack or fail well before the beams themselves reach their limit.
Connections generally come in two forms. Bolted connections go together in the field, cost less to install, don't need a welder on site, and allow easy inspection later, since loose bolts are visible and easy to fix. Welded connections offer a continuous, rigid joint instead; they often cost more in labor and require a certified welder, but they can carry loads that bolts alone can't handle.
Base plates sit at the bottom of each column and spread its load across a wider area of the foundation, while anchor bolts run through the base plate into the concrete to hold the column in place.
When you review a quote, it helps to check whether the connections are bolted, welded, or some mix of both, since that choice affects your build schedule, your crew requirements, and your maintenance down the line.
Building Envelope Components
The envelope is what most people notice first, and it's also what keeps the inside of the building usable.
Roof and wall panels come in several profiles, such as standing seam and corrugated. Standing seam panels have raised seams that hide the fasteners, which gives a cleaner look and usually a longer service life, while corrugated panels cost less and go up faster, though the fasteners stay visible on the surface.
Steel building insulation keeps heat in during winter and out during summer, and it also plays a role in meeting local building codes, so it's worth checking your insulation plan against code requirements before you finalize a design.
Trim, flashing, and closures seal the gaps where panels meet, at corners, eaves, and door openings. These parts look small on paper but matter a lot in practice: a building with strong framing and poor trim will still leak. Buyers often underestimate this cost, so it's worth asking your supplier for a full trim package price up front instead of a rough estimate.
How These Components Work Together
Every part of a steel building sits somewhere in a load path, the route that carries force from the roof down to the ground.
Here's how it plays out in practice. A snow load lands on the roof panel, which passes that load to the purlins below it. The purlins carry it to the rafters, the rafters send it down through the columns, and the columns pass it to the base plates and, finally, into the foundation.
At each step along the way, a connection transfers the load from one part to the next. That's why gusset plates and bolted or welded joints matter just as much as the beams themselves. A weak link anywhere in that chain puts the whole structure at risk, no matter how well the rest of it is built.
Choosing the Right Components for Your Project
A steel structure building is a complete system, not just a collection of separate parts. Once you understand how these components work together, a quote or design drawing will no longer look like a list of confusing terms.
Before moving forward with a steel building supplier, make sure you review the included components, design approach, and whether the system fits your project needs. A well-designed steel building starts with choosing the right components for the job.
FAQ
What are the main elements of a steel structure?
The main elements of a steel structure include primary framing (columns and beams), secondary framing (purlins and girts), bracing systems, the building envelope (roof and wall panels, insulation), and connections such as bolts and base plates.
What's the difference between an I-beam and other beam shapes?
An I-beam has a cross-section shaped like the letter I, with wide flanges at the top and bottom and a thinner web in the middle. That shape resists bending well and uses less steel than a solid rectangular beam of the same strength would.
Are purlins and girts the same thing?
Not quite. Purlins support the roof, girts support the walls, and while both are secondary framing members that hold panels in place, they sit in different parts of the building.
