If you’re anything like the construction project managers I chat with every week (seriously, I lose count of the times someone dms me panicking about a purlin or girt failing mid-install), you probably don’t spend a lot of time scrolling through spec sheets for these metal bits. But here’s the thing: purlins and girts are the unsung heroes of almost every building—they’re the horizontal metal beams that hold up your roof sheeting, wall panels, even extra stuff like solar panels or HVAC units. And if they don’t hold up? The whole project goes sideways. Purlins & Girts
When I started in this game 12 years ago, I thought durability was just “it doesn’t rust” or “it doesn’t bend.” Boy, was I wrong. Now, as a purlins and girts supplier, I’ve seen firsthand how cutting corners on testing leads to everything from a 10-year-old warehouse’s roof caving in during a snowstorm to a retail building’s wall panels blowing off in a summer thunderstorm. Today, I’m breaking down the actual durability tests we run (and you should ask your supplier about) because, trust me, not all purlins and girts are created equal.
First, let’s get clear on what we’re even testing: purlins are for roofs (running along the slope, holding up the sheeting above), girts are for walls (running horizontally between columns, holding up your exterior wall). Both take constant, repeated stress—wind, snow, rain, temperature shifts, even that random 50-pound AC unit someone decides to bolt on later. So their durability isn’t just about being strong once; it’s about holding up over decades of that constant, tiny wear and tear.
Let’s start with the big one: structural load testing. This is the test that actually puts a purlin or girt through its paces, and it’s non-negotiable. Here’s how it works: we mount a sample (usually 8 to 10 feet long, since that’s a common span) between two supports, then apply controlled, increasing weights to mimic exactly what it’ll face on-site. For purlins, that means roof-specific loads: dead load (the weight of the sheeting, insulation, any snow/sleet/ice in your area), live load (maintenance workers walking on the roof, for example), sometimes even uplift loads (that’s wind trying to yank the roof off). For girts, it’s similar but adjusted for wall loads—wind pressure pushing against the panel, plus any heavy equipment mounted later.
Last year, we had a client who skipped this test on a cheap batch of girts they bought from overseas. The supplier quoted them a “high weight capacity” number that sounded great, but it was a theoretical number, not a tested one. They installed them on a warehouse in a coastal area where winter wind gusts hit 70 mph, and within three years, half the girts bent so bad the wall panels were bulging. We had to come in and replace them, and let’s just say the client ended up paying way more than if they’d gone with tested parts in the first place. The good news? Modern structural load testing is super precise now—we use hydraulic jacks that apply loads incrementally, and we track deflection (how much the beam bends) in real time. The industry standard is that a purlin shouldn’t deflect more than 1/180th of its span under full live load, and girts are similar (usually 1/120th for wall applications, since they’re under different stress). If a sample bends more than that, it’s a no-go for us.
Next up: corrosion resistance testing. This is huge, especially for anyone building in coastal areas, industrial zones (think near a factory that pumps out chemicals), or places with harsh winters where they salt the roads. Rust doesn’t just make your purlins look bad—it weakens the metal over time, turning a 100-pound capacity beam into a 60-pound one before you know it.
We run two main corrosion tests. The first is salt spray testing (aka the neutral salt spray test, or NSS test for short). Here, we spray a fine mist of 5% salt water onto a coated purlin or girt sample 24/7 in a controlled chamber, for 1,000 hours minimum (that’s the equivalent of about 10 years of exposure to coastal salt air, for anyone keeping track). We check the sample every 200 hours for rust, chipping, or peeling coating. If after 1,000 hours, less than 5% of the surface has any rust, it passes—anything more, we reject it. The second test is cyclic corrosion testing, which is more realistic than just salt spray: it alternates between periods of salt spray, drying, and humidity, mimicking real weather changes way better. We use that for projects in super harsh areas, like oil fields or beachfront high-rises. I’ve had clients in Florida specifically ask for parts that pass 1,500 hours of cyclic testing, and that’s non-negotiable for us—we don’t sell anything that flunks that.
Then there’s fatigue testing. This is the test that no one talks about, but it’s probably the most important for long-term durability. Think about it: a purlin doesn’t just hold static weight forever. Every time a wind gust hits, that beam bends a tiny bit, then springs back. Every time snow melts and refreezes, that’s another tiny stress. Over 20, 30, 40 years, those tiny, repeated bends add up—this is metal fatigue, and it can cause a beam to crack or break even if it never went over its maximum load at once.
Fatigue testing works by cycling a load on a sample thousands, sometimes millions of times, to simulate decades of that tiny stress. We use a machine that pulls and pushes the beam up to 2 million times (that’s like, once every 10 minutes for 3 years straight) to mimic the constant, small stress of wind and temperature shifts. We track for cracks or permanent bending after the cycle. Last year, we tested a batch of steel girts that looked great on structural load and corrosion tests, but failed fatigue testing. Turned out their welds were too thin, so after 500,000 cycles, they started cracking at the support points. We rejected the whole batch, and the client went with our tested ones—they’ve had zero issues in their 5-year-old building, which has faced some brutal storms in the Midwest.
Wait, I can’t forget about temperature testing either, especially for places with extreme hot or cold. If you’re building in Arizona, where summer temperatures hit 120°F during the day and drop to 50°F at night, metal expands and contracts a lot. If a purlin or girt’s coating can’t handle that expansion/contraction, it will crack, and then corrosion starts to set in. We run thermal cycling tests: we heat samples up to 150°F, then cool them down to -20°F, over and over, for hundreds of cycles, then check for cracking, peeling, or delamination of the coating. For clients in places like Alaska or the Arizona desert, we up that to 500 cycles, because that’s how many temperature shifts they’ll face in 20 years.
Let me also be real with you: some suppliers cut corners on these tests, and it’s not because they’re trying to scam you (well, sometimes it is, but sometimes they just don’t have the equipment). A lot of cheap purlins and girts only get a visual inspection, maybe a quick load test that doesn’t go to full capacity, and call it a day. That’s why, when I talk to a new client, the first thing I tell them is to ask their supplier: “What durability tests did you run on these parts? Can you share the test reports?” If they can’t, or if the tests only go half as long as the industry standard, keep looking. We have a binder full of test reports for every single batch we ship, and if a client ever wants to see one, we send it over within 10 minutes—no hoops to jump through.
Here’s the thing: as a purlins and girts supplier, our job isn’t just to sell you metal beams. It’s to make sure your building is safe, that you don’t have to deal with costly repairs down the line, and that your investment lasts. I’ve seen too many projects go wrong because someone picked the cheapest parts instead of the tested ones, and it’s not worth it. A few extra dollars for tested purlins and girts will save you tens of thousands (even hundreds of thousands) in repairs and replacements later.
If you’re working on a new build, a renovation, or just replacing some old purlins and girts and want to make sure they’re up to snuff, hit me up. We can walk through what tests are right for your project, share test reports for our current stock, and work with you to get exactly what you need—no fine print, no hidden costs, just straight talk about durability.
Fasteners References:
- American Iron and Steel Institute. (2020). Cold-Formed Steel Design Manual, Section on Purlins and Girts Durability Testing.
- International Code Council. (2021). International Building Code (IBC) Chapter 16: Structural Design Requirements for Metal Components.
- ASTM International. (2018). Standard Test Methods for Salt Spray (Fog) Testing (ASTM B117).
- ASTM International. (2020). Standard Practice for Cyclic Corrosion Testing of Coated Steel Products (ASTM G85).
- American Society of Civil Engineers. (2019). ASCE 7-16: Minimum Design Loads and Associated Criteria for Buildings and Other Structures.
GNEE Steel Structure (Tianjin) Co., Ltd.
As one of the most professional purlins & girts manufacturers and suppliers in China, we have world-leading production equipment and strong manufacturing capabilities. Please rest assured to buy customized purlins & girts at competitive price from our factory. For quotation, contact us now.
Address: No.4-1114, Beichen Building, Beicang Town, Beichen District, Tianjin, China
E-mail: info@gescosteel.com
WebSite: https://www.gneesteelstructure.com/
