A325 structural bolts provide a strong and reliable connection between steel elements. Specifically designed to withstand significant loads, these high-strength bolts are the workhorse of structural bolting. As the most commonly used structural fasteners, they’re popular in many construction projects, especially involving bridges and highways.
A325 bolts can be made of medium carbon steel (Type 1) or weathering steel (Type 3). Neither type is as strong as A490 bolts, but Type 1 A325 bolts have a big advantage – they can be galvanized. This means it’s relatively quick and easy to coat these heavy hex fasteners for rust protection.
Although A325 bolts are known for their durability and long-term performance, they’re not immune to problems that can jeopardize the structural integrity of a project. To help prevent common reasons for bolting failures, use these best practices.
Follow Proper Installation and Testing Procedures
Installation mistakes are the biggest reason that A325 bolts fail. Incorrect torque or installation techniques can weaken the bolt connection and increase the risk of failure.
Installing a fastener isn’t as straightforward as it may seem. All the necessary steps must be followed every time to confirm a secure connection.
Preinstallation verification testing is required by RCSC/AISC specifications and conducted onsite to make sure bolt assemblies can achieve the minimum bolt tension. It’s meant to uncover issues and ensure safety before installation – which often happens hundreds of feet above the ground.
You can use a Skidmore Wilhelm device, also known as a bolt tension measuring device, to perform this test. It’s a mobile unit meant to be used in the field. To see a test on a 2¾-inch A325 bolt, check out this video.
This testing is the final safeguard before the bolts get installed – think of it like a sound check before a concert, where you’re making sure everything is tuned up and in sync. For more details on testing, refer to the RCSC.
Use the Right Lubrication and Reapply if Needed
Whether uncoated or galvanized, structural bolting components are lubricated for installation purposes. The nut can strip out the A325 bolt without the proper lubrication.
If lack of lubrication is identified as an issue during preinstallation verification tests, you may need to reapply lubricant before installation. On uncoated components, you can reapply an oil-based structural bolt lubricant, like stick wax or liquid wax.
For galvanized assemblies, use a dry, wax-based lubricant -- stick wax is acceptable as well. Apply a small amount of the lubricant to the bearing face of the nut as well as the first few threads of the bolt. Note: The application of additional lubrication to any tension control bolt assembly is strictly prohibited.
A rotational capacity (ROCAP) test provides additional assurance of quality designed for galvanized bolts since they have a thick coating that may impact the compatibility between the threads of the bolt and nut. This is done offsite at a lab testing facility, typically prior to shipment, and goes further than preinstallation verification testing in evaluating the efficacy of lubrication and compatibility of the assembly.
Take Jobsite Storage Seriously
Lot traceability is critical to correctly handling and storing A325 at the jobsite. Improperly stored bolts can develop rust or dirt buildup, especially in the threads. This requires cleaning, relubricating and retesting components before installation, which adds costs and can delay projects.
Never throw a tarp over containers. This will cause condensation to develop and wash water-soluble lubricants away.
While galvanized bolts do usually have a lubricant that isn’t water-soluble, they still need to be stored properly. Some lubricants can degrade or melt if exposed to high temperatures.
Protect Your A325 Bolts
A325 bolts are small but play a big role in holding parts together throughout the structural steel industry. Understanding how these bolts can fail will help you prevent problems by installing them properly, running the right tests, checking the lubrication and following jobsite storage standards.
Looking to use A325 bolts for your next project? Tap into the nation’s largest inventory of structural bolts and fasteners at Birmingham Fastener.
06/9/2021
