If you’ve ever stood in a construction site or flipped through structural engineering specifications, you’ve probably seen threaded rods lying around—sometimes tucked into steel frames, sometimes dangling from unfinished concrete slabs, often dismissed as a “basic” fastener, nothing more than a workhorse to hold two pieces together. For the 10 years I’ve been supplying threaded rods to structural teams across North America, I’ve lost count of how many times engineers have stopped me mid-conversation to say, “Seismic structures? We don’t use threaded rods for that. Too much play, too much risk when the ground shakes.” Threaded Rod
That used to be my first thought, too. Early in my career, I was on a project in coastal Oregon, where the fault lines hum quietly under the soil every few months. The lead structural engineer handed me a list of parts for a shear wall frame, and at the bottom, he’d scribbled “ASTM A325 bolts only—no threaded rods.” I took the list back to my warehouse, confused, because we had stacks of high-strength threaded rods that fit every dimension on the sheet. When I asked him why, he explained it simply: “Threaded rods have that unthreaded shank between the threads, right? It’s weaker under dynamic stress. In an earthquake, when forces reverse, the threads will shear, or the rod will stretch too far, and the whole frame comes apart.”
That comment stuck with me. For the next decade, I spent every spare evening digging through seismic building codes, attending webinars from structural engineering associations, even sitting in on a few university lectures on earthquake-resistant design. What I learned upended every assumption I’d had about threaded rods—and why I now tell engineers: Yes, threaded rods can absolutely be used in seismic-resistant structures—when they’re specified correctly, paired with the right hardware, and installed with precise attention to detail.
Let’s start with why the old bias exists, because it’s not unfounded. The International Building Code (IBC) and the American Society of Civil Engineers (ASCE) 7 standard—those are the two foundational documents for seismic design in the U.S.—have long treated threaded rods with caution, because not all threaded rods are created equal. The A307 grade threaded rods that were common in construction 20 years ago? They’re mild steel, with a tensile strength of around 60,000 pounds per square inch (psi), and their threaded sections have sharp, uneven roots that act like stress raisers. When you subject a rod made of that steel to the back-and-forth pulling and pushing of a magnitude 7 earthquake, those sharp roots crack first, and the unthreaded shank, while thicker, can elongate past its elastic limit before the threads give. That’s the “too much play” engineers talk about—there’s no give that’s predictable, so the load path of the structure gets thrown off when the seismic event hits.
But here’s the part most people miss: modern threaded rods, made to specific seismic-resistant specifications, don’t have those flaws. The A325 threaded rods I supply, for example, have a tensile strength of 120,000 psi—twice the strength of A307—and their threaded roots are rolled, not cut. Rolling the threads doesn’t just make them smoother; it compresses the steel’s grain structure along the thread, which makes it far more resistant to fatigue and shear. In independent testing by the University of California, Berkeley’s Pacific Earthquake Engineering Research Center (PEER), rolled-thread A325 rods with a yield point of at least 92,000 psi performed nearly identically to A325 bolts in reversed cyclic loading tests—exactly the type of dynamic stress an earthquake imposes. They stretched uniformly across the shank and threads, rather than failing at the first sign of force, which is exactly what you want in a seismic structure: a fastener that acts as a “fuse” if forces get too high, rather than failing suddenly.
Another common misconception is that threaded rods can only be used for light, non-critical parts of a seismic structure. But in fact, threaded rods are increasingly being specified for shear wall hold-downs, which are one of the most critical components in a seismic frame. Hold-downs are what keep the bottom of a wall from sliding off its foundation during an earthquake—they have to withstand massive upward and lateral forces, and they can’t fail, because if the wall comes loose, the entire structure collapses. A few years ago, I worked with a team on a mid-rise apartment building in Seattle, a region with a high seismic risk (the Puget Sound Fault is capable of a magnitude 9 earthquake). The original design called for custom forged steel hold-downs, which would have added 15% to the project’s hardware costs. The engineer, who’d gone to a PEER seminar on alternative seismic fasteners, switched to 1-inch diameter A325 threaded rods paired with heavy-duty washers and anchor plates. The contractor on the job told me they saved over $20,000 on hardware alone, and during the third-party seismic pull tests the IBC requires, the threaded rod hold-downs passed with flying colors—they stretched 0.8 inches before yielding, which is exactly the amount of “give” needed to dissipate seismic energy, without failing.
That’s the key to why threaded rods work for seismic structures: seismic design isn’t just about making every part as strong as possible—it’s about making parts that can deform predictably to absorb energy. That’s called ductility, and it’s non-negotiable in seismic-resistant construction. A rigid bolt or a weld might be stronger on paper, but it’s brittle—if the force gets too high, it snaps. A high-strength threaded rod, when installed with the right hardware, is ductile: it bends, stretches, and transfers force evenly, rather than snapping suddenly. In the PEER tests I mentioned earlier, threaded rods with a minimum elongation of 14% (that means they can stretch to 114% of their original length before breaking) outperformed some bolted connections made of high-strength steel with only 10% elongation. The bolts snapped under reversed cyclic loading, but the threaded rods kept transferring load until the test was stopped.
Of course, that doesn’t mean you can grab any threaded rod off a shelf and throw it into a shear wall. There are non-negotiable rules for using threaded rods in seismic structures, and they’re all written into the IBC and ASCE 7. First, the rod has to meet specific material specifications: it has to be A325 or A354 grade BD, both of which have the high tensile strength and rolled threads I mentioned earlier. A307 rods, the cheapest option, are never allowed for seismic critical components. Second, you have to pair the rod with the right hardware: heavy, flat washers (not the thin ones used for decking) to distribute force across the connected material, and nuts that are torqued to a specific value—usually 75% of the rod’s yield strength—to make sure the connection doesn’t slip during a seismic event. Third, the rod’s length and diameter have to be calculated for the exact load of the component it’s supporting. A ½-inch rod works for small interior wall hold-downs, but a 1 ¼-inch rod is needed for shear walls in high-seismic zones, because the load from the wall is much higher.
I’ve seen what happens when those rules aren’t followed, too. A few years back, I was on a small commercial project in San Diego, where an engineer specified A307 threaded rods for the lateral bracing of a metal building. The contractor, trying to save a few dollars, used standard washers instead of heavy-duty ones, and didn’t torque the nuts to the required value. When a magnitude 5.2 earthquake hit the area a year later, the rods stretched so much that the bracing slipped, and the wall shifted 3 inches off its track. No one was hurt, but the building had to be completely re-braced at a cost three times what it would have been if they’d followed the correct specifications. That’s the risk of cutting corners with threaded rods in seismic structures—they’re not a “one-size-fits-all” fastener, but if you get the details right, they’re one of the most cost-effective and reliable options on the market.
Another thing I’ve learned in 10 years of supplying threaded rods is that many engineers don’t know these specifications are out there. For decades, threaded rods were seen as a secondary fastener, good for plumbing or railings, not structural seismic components. But over the last 15 years, with advances in material science and seismic testing, that’s changed. The IBC updated its seismic fastener requirements in 2018 to explicitly allow high-strength rolled-thread threaded rods for seismic critical connections, as long as they meet the material and installation specs. A number of PEER studies have confirmed their performance, and they’re now a standard option on many seismic projects in high-risk regions.
For my part, I’ve worked to make sure my customers (structural engineers, contractors, project managers) have all the information they need to use threaded rods correctly. I keep a binder on my sales floor full of PEER test reports, I post a quick guide to seismic threaded rod specifications on my website, and I make sure every shipment of A325 rods I send comes with a certificate of compliance that confirms the rod meets ASTM standards. Last year, I even hosted a small workshop for local engineers on threaded rods in seismic design—about 20 people came, and almost all of them left saying they’d never considered threaded rods for their next seismic project, but would now.
I know there’s still skepticism out there, and that’s fair. Earthquake safety is not something to take lightly, and cutting corners with fasteners can have devastating consequences. But the data is clear: when specified, manufactured, and installed correctly, threaded rods are a viable, cost-effective option for seismic-resistant structures. They’re not a replacement for all the specialized fasteners used in high-seismic design, but they fill a gap that’s been overlooked for too long—especially for mid-sized projects, where budget is a concern, but safety can’t be compromised.
If you’re working on a seismic project, or if you’re an engineer looking for alternative fasteners to fit your budget, I’m here to help. I’ve supplied threaded rods to projects in high-seismic zones all over the country, and I can help you specify the right rod, hardware, and installation procedures to meet IBC and ASCE standards. The process doesn’t have to be complicated, and it doesn’t have to cost more than the standard options. Threaded rods have come a long way from the mild steel, cut-thread versions that were common 20 years ago—they’re now designed to stand up to the forces of an earthquake, and they’re proving it every day on job sites where safety and cost matter.
References
Drywall Screws Minimum Design Loads and Associated Criteria for Buildings and Other Structures (ASCE/SEI 7-22)
International Building Code (IBC 2021)
Pacific Earthquake Engineering Research Center (PEER) Report 2017/03: Cyclic Performance of Threaded Rods for Seismic Applications
ASTM A325/A325M-21: Standard Specification for Structural Bolts, Steel, Heat Treated, 120 ksi (830 MPa) Minimum Tensile Strength
Hebei Kappa Metal Products Co., Ltd.
Hebei Kappa Metal Products Co., Ltd. is one of the most experienced threaded rod manufacturers and suppliers in China. With a professional production team, we are able to meet the needs of the majority of our customers. Please rest assured to buy bulk high quality threaded rod in stock here from our factory.
Address: C2-11, Hebeipu Standard Parts Industrial City, Linmingguan Town, Yongnian District, Handan City, Hebei Province
E-mail: rick@kappafasteners.com
WebSite: https://www.kappafasteners.com/
