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Structural Bolt Stickout: Minimums and Maximums

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Structural bolt stickout is just what it sounds like – it’s the amount of threads protruding beyond the nut after installation. While the RCSC does specify a minimum for bolt stickout, they do not specify a maximum. That being said, there are risks to consider with too much bolt stickout. Here, we’ll go over the requirements, risks, and best practices regarding structural bolt stickout.

Structural Bolt Stickout Minimum

The RCSC requires that the end of the bolt must, at minimum, be flush with the outer face of the nut. The nut may not be hanging off the end of the bolt after tightening is completed. When the outer face of the nut is flush with the end of the bolt, the bolt’s ductility is at its greatest. This is because the maximum amount of threads are exposed, allowing the bolt to stretch as much as possible.

Structural Bolt Stickout Maximum

While the RCSC does not specify a maximum for bolt stickout, there are risks to take into consideration. If the threads extend too far beyond the nut, there is a chance that the nut has reached the thread runout. This could cause quite a few different risks. Depending on your installation method, the following could occur:

  • Calibrated Wrench or Twist-Off Methods: The bolt will not be properly pretensioned, due to the nut ceasing rotation, while the torque remains high. This causes the bolt to remain loose.
  • Turn-of-Nut Method: The required turns cannot be applied.
  • Direct Tension Indicator (DTI) Method: The gap requirements will not be met.

There is also a risk of thread stripping with bolt stickout. During pretensioning, the bolt will stretch, reducing the thread contact between the bolt and the nut.

General Guidelines for Structual Bolt Stickout

Acceptable bolt stickout is established by the bolt and nut combination. Below is a chart that details general guidelines for acceptable bolt stickout. Note that any protrusion beyond these guidelines may still be suitable.

Bolt Size (Inches) Permissable Bolt Stickout/Protrusion
1/2" 6 Threads
5/8" 6 Threads
3/4" 6 Threads
1 1/8" 6 Threads
7/8" 5 Threads
1” 5 Threads
1 1/4" 5 Threads
1 3/8" 5 Threads
1 1/2" 4 Threads
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Structural Bolt Reuse – Can I Reuse a Structural Bolt?

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structural-bolt-reuse

Every now and again, we get questions on structural bolt reuse, and the answer is always the same: maybe. When we talk about reusing a bolt, we’re referring to when a pretensioned bolt is loosened and then re-pretensioned. Here, we’ll discuss whether or not a bolt can be reused according to RCSC standards. Note that this blog is for informational purposes only. You should always defer to the RCSC standards and your engineer.

Previously Pretensioned Structural Bolt Reuse

Sometimes, you may need to remove a pretensioned bolt and then need to reinstall it. Depending on the type of bolt, and the express permission from your engineer, you may be able to reinstall it. RCSC Section 2.3.3 allows uncoated F3125 Grade A325 bolts to be reused with the engineer’s permission. Galvanized bolts and F3125 Grade A490 bolts that have been pretensioned may not be reused at all.

Snugged Bolt Reuse

Snugging a bolt refers to tightening a bolt with a few impacts of an impact wrench or with the full effort of a worker using an ordinary wrench. F3125 Grade A325 bolts that are snugged can usually be reused. Snugged F3125 Grade A490 bolts and galvanized Grade A325 bolts can only be considered for reuse if snugged by hand or very lightly snugged with an impact wrench.

Determining the Possibility of Pretensioned or Snugged Bolt Reuse

So, your bolt meets the above qualification, but can you actually reuse it? Reuse of a structural bolt is permitted only when a bolt has not been stressed past its yield point. A quick way of telling if a F3125 Grade A325 bolt has yielded is to attempt to screw a nut onto the bolt. If the nut does not fasten onto the entirety of the bolt’s threads, the bolt has been stressed beyond its yield point. This is because the bolt has stretched, and the threads are farther apart than they should be. Note that because of overtapping of nut threads for galvanized bolting assemblies, you cannot use this method for galvanized bolts.

Bottom Line

Though there are ways to check whether a bolt can be reused after pretensioning or snugging, Birmingham Fastener strongly recommends discussing bolt reuse with the engineer on your project.

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White Rust Prevention on Structural Bolting Components

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White rust is a common problem in the structural steel industry. It is typically caused by improper jobsite storage and a lack of air circulation. Aside from it harming the physical appearance of the bolt, white rust can break down the layer of protective coating on the bolt.

Many structural bolts are galvanized for their protection and durability. This galvanized coating is made of zinc, which is one of the best ways to prevent corrosion on steel. White rust is made up of zinc hydroxide, which is formed when zinc reacts with water and air. Zinc hydroxide is unstable and consumes the protective zinc coating. This typically happens when fasteners are “nested” together (packed flat one on top of another) and water gets in between the fasteners. It looks like white powder covering the surface of the coating (see image below). Fortunately, there are a few simple ways to prevent white rust from forming on your structural bolting components.

Jobsite Storage

Proper jobsite storage is something we often stress, because it is the number one way to prevent issues with fasteners. There is always a greater chance for white rust formations when fasteners are improperly stored outdoors and exposed to the elements. It’s important to make sure your fasteners are receiving proper care from the moment they enter your jobsite. When the fasteners are delivered, make sure they are stored properly at the time you receive them. For more information on proper jobsite storage, check out our blog post.

Air Circulation

As we mentioned, when fasteners are “nested” together, white rust is more likely to form due to a lack of air flow and moisture getting trapped in between the fasteners. Fasteners are sent in bins that ensure proper air circulation. It’s important to keep the fasteners stored in a way that maintains air flow and allows any moisture to evaporate.

Bottom Line

White rust typically occurs when fasteners are stored improperly and exposed to moisture. Be sure your products are not “nested” and have proper air circulation to prevent white rust from forming. Though there are ways to treat white rust (depending on severity), prevention will save you time, money, and frustration. As always, proper jobsite storage is vital to the protection of your fasteners.
 

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Torque vs. Tension – What’s More Important in Structural Bolting?

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Torque vs. Tension: Why Torque is Not a Reliable Means for Measuring Tension

Often, our customers will ask us to discuss torque values in regards to pretensioning structural bolts. Birmingham Fastener makes it a point to educate our customers on the difference between torque vs. tension and the importance of measuring the tension of structural bolts instead of just relying on torque.

Torque is often associated with installation, tightening, or inspection of structural bolts. Bolts are tightened in order to achieve tension – torque is only a by-product of this relationship to reach proper tension. Torque can vary greatly in this relationship to reach the desired tension, therefore, Birmingham Fastener stresses that you focus on tension first and foremost.

Lubrication, bearing surface condition, thread fit, and the use of a flat washer are some of the variable in the torque-tension relationship. About 60% of the torque required to tighten a bolt is consumed by overcoming the friction between the nut and the flat washer, about 30% overcoming the friction between bolt and nut threads, and 10% to elongate the bolt. According to multiple tests, torque-tension relationships can vary by as much as 40% for structural bolts.

Torque charts are not permitted to be used for installation or inspection. The only accepted method is the use of a Skidmore Wilhelm device (Bolt Tension Measurement Device) to actually measure tension, then proceed to measure the torque required. The charts below are listed for convenience and can be used to estimate the torque ranges for our structural bolts.

Measuring the Torque-Tension Relationship

The following is the basic equation to estimate the torque-tension relationship:

T = K x P x D

Where:

T = torque in foot-pounds
K = coefficient of friction
P = bolt tension in foot-pounds
D = Bolt diameter in inches

An accepted industry value for K is 0.0167. That said, lubrication or a lack of lubrication can cause the K factor to range from 0.01 to 0.025.

The tables below are estimated of the approximate torques for F3125 Grades A325 and A490 structural bolts. Because torque can vary so greatly, these tables are not to be used for installation or inspection purposes.

F3125 Grade A325 Approximate Torques (foot-pounds)

Note: These are estimates only and are not to be used for installation or inspection purposes. Torque can vary greatly depending on several factors listed above. Tension is actually what you are trying to achieve.

Bolt Diameter Required Tension Kips Torque Average
1/2" 12 100
5/8" 19 200
3/4" 28 350
7/8" 39 550
1" 51 850
1-1/8" 56 1050
1-1/4" 71 1500
1-1/2" 103 2600

F3125 Grade A490 Approximate Torques (foot-pounds)

Note: These are estimates only and are not to be used for installation or inspection purposes. Torque can vary greatly depending on several factors listed above. Tension is actually what you are trying to achieve.

Bolt Diameter Required Tension Kips Torque Average
1/2" 15 130
5/8" 24 250
3/4" 35 450
7/8" 49 700
1" 64 1100
1-1/8" 80 1500
1-1/4" 102 2100
1-1/2" 148 3700
bolt tension measuring
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Structural Bolting – How Should I Store Components on the Jobsite?

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Proper jobsite storage and handling of structural bolting components can mean the difference between an organized, timely project and having to buy completely new bolting components – costing your team time and money. At Birmingham Fastener, we take jobsite storage seriously. Here are a few key reasons you want to spend a little extra time properly storing your fasteners.

Lot Traceability of Structural Bolting

Most jobs require lot traceability for fastener storage. Lot traceability entails having production lot numbers on each container of nuts, bolts, and washers. Each type of structural bolting component must be stored separately by lot. This level of organization ensures that the correct fastening components are installed in each portion of the job. It is also required for pre-installation verification testing. Though some jobs do not require lot traceability, we highly recommend it for all jobs, due to the level of organization it provides.

The Elemental Effects on Uncoated Components

Uncoated bolting components have a water-soluble lubricant that aids installation and allows for protection. Containers must be kept closed in order to protect the nuts, bolts, and washers from the elements, including high temperatures, rain, and snow. Too often, our sales team sees improper storage of bolting components on jobsites – typically a tarp covering containers. This is one of the worst things you can do. Throwing a tarp over containers will cause condensation to develop on the components. This causes the water-soluble lubricant to wash away.

Other times, we simply see uncovered containers which, in hot and dry weather, will cause the lubricant to evaporate. If the lubricant evaporates, one should re-lubricate the components (this excludes twist-off TC bolts). Bolts that are improperly stored for too long can develop rust or dirt build-up –particularly in the threads. If this occurs, you must clean, re-lubricate, and retest the components prior to installation. That said, sometimes a bolting component is left in the elements so long that it cannot be fixed. This sort of neglect can cost your company major time and money, therefore, it is best to keep these components stored properly.

A Note on Galvanized Components

While it is true that galvanized structural bolting components typically have a stronger, more durable lubricant that is not water soluble, it is still important that these are stored properly. Some types of lubricants can still degrade or melt when exposed to high temperatures. If this happens, reapply before installation.

Bottom Line

Ultimately, simple steps toward proper jobsite storage of structural bolting can save you countless hours between hunting for the right components, having to clean and/or reapply lubricant, or –worst case scenario – having to purchase entirely new bolts. If you have further questions regarding jobsite storage or any other fastener related queries, our expert sales team is here to help. Contact them today.

Reference: RCSC 2.1 and 2.2

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F3125 Grade A325 and A490 Tensions Control Bolt Dimensions

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Birmingham Fastener carries F3125 A325 and A490 TC Bolts in the following dimensions. If you have any questions, please contact our sales team.

Diameter of Bolt Bearing Surface Diameter Bolt Head Height (max) Bolt Head Height (min) Length of Spline Diameter of Spline Reference
5/8 1.102 .403 .378 .60 .43
3/4 1.338 .483 .455 .65 .53
7/8 1.535 .563 .531 .72 .61
1 1.771 .627 .591 .80 .70
1 1/8 1.991 .718 .658 .90 .80
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