The turn-of-nut connection is a method used to tighten high-strength bolts in steel structures. It involves rotating the nut a specified number of degrees beyond snug tight to achieve the desired bolt preload. This method ensures that the bolts are properly tensioned and provide sufficient clamping force to maintain the integrity of the connection.
Here is a step-by-step procedure for making a turn-of-nut connection:
- Design and Preparation:
- Determine the required bolt preload and load-bearing capacity for the connection based on the structural requirements.
- Select the appropriate high-strength bolts, nuts, washers, and other connection components based on the design specifications, considering factors such as material strength, size, and corrosion resistance.
- Ensure that the surfaces of the steel components to be connected are clean, smooth, and free from any debris, rust, or paint.
- Alignment and Positioning:
- Position the steel components, such as beams, columns, or plates, in their designated locations, ensuring proper alignment and fit.
- Use temporary clamps or tack welds to hold the components in place, preventing movement during the connection process.
- Marking and Drilling:
- Mark the positions for the bolt holes on the steel components, following the specified spacing and pattern.
- Use a drill press or portable drilling machine to drill holes through the marked positions on the components. Ensure that the holes are aligned and perpendicular to the surface.
- Deburring and Cleaning:
- Remove any burrs or sharp edges around the drilled holes using a deburring tool or file.
- Clean the holes and surfaces of the components to remove any debris, oil, or grease that may affect the connection’s integrity.
- Inserting Bolts:
- Insert high-strength bolts through the holes in one of the components.
- Place washers and nuts onto the exposed ends of the bolts.
- Snug Tightening:
- Use a suitable wrench or impact wrench to snugly tighten the nuts until they are in contact with the washer and the joint is fully closed.
- Marking the Starting Point:
- Mark a reference point on the nut and the bolt to indicate the starting position before the final tightening.
- Turn-of-Nut Rotation:
- Determine the specified rotation angle based on the bolt diameter and length. The rotation angle is typically specified as a fraction of a turn or degrees.
- Rotate the nut using a wrench or calibrated turn-of-nut wrench to achieve the specified rotation angle beyond the snug tight position.
- The rotation should be applied gradually and uniformly to all the bolts in the connection.
- Final Inspection:
- Inspect the connection to ensure that the bolts, nuts, and washers are properly seated and tightened.
- Check for any gaps, misalignment, or visible signs of damage or distortion.
- Verify that the connection provides the required bolt preload and can withstand the specified loads.
Example and Application: The turn-of-nut connection method is commonly used in steel structures such as buildings, bridges, and industrial facilities. It provides a reliable and cost-effective means of achieving proper bolt preload and maintaining the integrity of the connection under load.
Applications of turn-of-nut connections include:
- Building construction, where turn-of-nut connections are used to join steel beams, columns, and other structural components.
- Bridge construction, where turn-of-nut connections are employed to connect steel girders, trusses, and other bridge elements.
- Industrial structures, such as power plants, offshore platforms, or manufacturing facilities, where turn-of-nut connections are used for connecting steel components subject to significant loads and dynamic forces.
The turn-of-nut connection method is advantageous as it does not require sophisticated equipment and can be easily implemented on-site. It provides a reliable and standardized approach to achieve the desired bolt preload and ensure the structural integrity of the connection.
