When assembling structural steel connections, achieving the proper bolt tension is critical to the performance, safety, and integrity of the connection. Before bolts can be pretensioned—or when a connection is designed to remain snug-tight—the connected steel plies must first be brought into firm contact.
This is known as the snug-tight condition.
But what does snug-tight actually mean? How is it achieved in the field? And when is additional pretensioning required?
In this guide, we’ll explain the snug-tight condition, when it is used, how to achieve it, and why it is an important part of structural bolting.
Key Takeaways
- Snug-tight is a term used in structural steel for when connected steel plies are brought into firm contact and the bolt cannot be loosened by hand.
- Snug tightening is either the final condition or the starting point for pretensioning. Some connections remain snug-tight, while others require additional tightening to achieve the specified tension.
- All five installation methods, including Turn-of-Nut, calibrated wrench, tension control, DTI, and combined method, begin with a snug-tight connection before pretensioning is performed.
- When tightening a steel connection, snug tightening should progress from the most rigid part of the connection toward the free edges. Multiple passes through the bolt pattern may be necessary.
- There is no specific torque value for achieving snug-tight condition. This is different from the initial tensioning step of the Combined Method, which does use a specified torque.
- Properly achieving snug-tight condition is essential to getting the connection right, whether the bolts remain snug-tight or will be further tightened to achieve minimum tension.
What Is Snug Tight?
The snug-tight condition is achieved when the bolting components are tightened enough to bring the connected steel plies into firm contact and prevent the bolt assembly from loosening by hand.
For connections that require pretensioning, snug-tight is the starting point for the specified installation method. The connected plies must be brought into firm contact before the required pretension can be reliably applied.
According to the American Institute of Steel Construction (AISC) and the Research Council of Structural Connections (RCSC), snug tightening is typically achieved with a few impacts of an impact wrench or the full effort of an ironworker using a spud wrench. Depending on the connection, more than one cycle through the bolt pattern may be necessary to achieve the snug-tight condition.
When Is Snug Tight Used?
Snug tightening is used in two primary situations:
1. Snug-Tightened Joints
Some structural connections are designed to remain in the snug-tight condition. These are commonly bearing-type connections where pretensioning is not required by the design or applicable specifications.
For these connections, snug-tight condition completes the bolt installation.
2. Pretensioned Connections
When a connection requires pretensioning, snug-tight is the first step in the installation process. Once the connection has reached the snug-tight condition, the specified installation method is used to achieve the required tension.
Recognized installation methods are:
- Turn-of-Nut
- Calibrated Wrench
- Tension-Control Bolts
- Direct-Tension Indicators
- Combined Method
Regardless of the method used, the connection must first reach the snug-tight condition before pretensioning.
How Is Snug-Tight Achieved?
Snug tightening begins after the bolts, washers, and nuts have been properly assembled in the connection.
The connection should be tightened systematically, started at the most rigid part of the joint and working toward the free edges. As the plies are drawn together, tightening one bolt can affect the condition of surrounding bolts.
Because of this movement, more than one cycle through the bolt pattern may be required. Cycling through the pattern helps bring the entire connection into the required snug-tight condition and can reduce the potential for rework.
Tools Used for Snug Tightening
Snug tightening can be performed using tools such as:
- Spud wrench: Uses the full effort of an ironworker to bring the connection into firm contact. Typically done on smaller or fewer bolts.
- Impact wrench: A few impacts can be used to achieve the snug-tight condition and efficiently work through a bolt pattern.
- Torque wrench: Set to a predetermined torque to get tight iron condition. Typically done on larger bolts to reduce the physical effort required during installation.
The appropriate tool depends on the connection, project requirements, and the equipment available to the installation crew.
Does Snug Tight Require a Specific Torque?
No. There is no specific torque value required to achieve the snug-tight condition.
This is an important distinction because snug tightening should not be confused with the initial tensioning step used in the Combined Method. With the Combined Method, the initial tensioning step is performed to a specified torque to establish the starting point for the final rotation. That torque value is commonly provided by the bolt supplier.
Snug tightening itself, however, is based on bringing the connected plies into firm contact, not reaching a predetermined torque value.
Snug Tight vs. Pretension
Snug-tight and pretension are not interchangeable terms.
A snug-tightened connection is complete once the connected plies have been brought into firm contact.
A pretensioned connection starts at snug tight and then undergoes an additional tightening procedure to achieve the required bolt tension.
Understanding this distinction is important when determining the appropriate installation method, equipment, and inspection requirements for a structural connection.
Why Proper Snug Tightening Matters
Snug tightening may seem like a simple step, but it establishes the proper starting condition for the connection.
If the plies are not brought into firm contact before pretensioning, the specified installation method may not produce the intended result. Properly cycling through the bolt pattern and achieving a consistent snug-tight condition helps ensure the connection is ready for the next step of installation.
For connections that remain snug-tight, achieving the correct condition is the final step of installation.
For pretensioned connections, it is the foundation for achieving the required pretension.
Whether your connection is designed to remain snug-tight or requires additional pretensioning, understanding the required installation condition is essential to getting the connection right.
Have questions about snug tightening or choosing the right bolting equipment for your project? Contact GWY for assistance or learn more about structural bolting training and how it can help your team install structural connections correctly.
FAQs
What does “snug tight” mean?
It’s the point at which two steel plies are in firm contact with no gaps, typically achieved with the full effort of a worker using a spud wrench or a few impacts from an impact wrench.
Is there a required torque value for snug tightening?
No, there’s no required torque value, though some states have their own regulations for verifying snug tightness.
Can snug tightening be the final step in a connection?
Yes, snug-tight connections are used in non-critical applications since they do not have a pre-load requirement.
Is snug tightening used for wood or residential construction?
No, it applies specifically to large-scale industrial construction involving steel plies, not wood or small-scale residential projects.
How do you check if a bolt is properly snug tight?
By testing whether the plies are in firm contact with no looseness. If there’s any gap, the connection isn’t snug tight.
What happens if a connection isn’t snug tightened before final tensioning?
The connection may not reach the required tension and that bolt installation would not pass inspection.
What tools are used to achieve snug tightness?
A spud wrench, impact wrench, or an electric torque wrench set to a predetermined torque.
