What is bolted High-Strength Friction Grip Joints? Explain in details of bolted High-Strength Friction Grip Joints with step by step procedure and example of application
Bolted high-strength friction grip (HSFG) joints, also known as preloaded bolted joints or tension control (TC) bolted joints, are a type of connection used in steel structures where the bolts are tightened to a specified preload to create friction between the connected members. The joint relies on the friction generated between the mating surfaces to transfer the applied loads. Here is a step-by-step procedure for creating a bolted high-strength friction grip joint:
- Design the Joint: Determine the required number of HSFG bolts, their size, grade, and spacing based on the applied loads, member dimensions, and design requirements. Consider factors such as the friction capacity of the bolts, load transfer capacity of the joint, and required factor of safety.
- Prepare the Members: Ensure that the surfaces of both members to be joined are clean, free from any rust, paint, or debris that may affect the connection’s integrity. If necessary, clean the surfaces using wire brushes or other suitable methods.
- Align the Members: Position the members so that their mating surfaces are in direct contact, ensuring proper alignment. Use temporary clamps or fixtures, if needed, to hold the members in place during the assembly.
- Mark Hole Locations: Use a center punch or other marking tool to mark the hole locations on both members. Ensure the hole spacing is uniform and follows the specified bolt pattern. The hole spacing and size depend on factors such as the bolt diameter, load transfer requirements, and connection strength.
- Drill Holes: Use a drill machine and appropriate drill bits to create holes through both members at the marked locations. The hole diameter should be slightly larger than the bolt diameter to allow for easy insertion and accommodate any potential misalignment.
- Clean the Holes: Remove any debris or burrs from the drilled holes using compressed air or a wire brush. This ensures that the bolts can be inserted smoothly and that the contact surfaces are clean.
- Insert HSFG Bolts: Place the HSFG bolts through the holes, ensuring that they pass through both members. The bolts should be long enough to extend beyond the nuts by an appropriate amount to allow for proper engagement and tightening.
- Install Nuts and Washers: On the opposite side of the joint, place washers over the bolt ends, followed by the nuts. Ensure that the washers are properly sized and positioned to provide sufficient contact with the mating surface.
- Tension the Bolts: Use a calibrated tensioning device specifically designed for HSFG bolts to apply the specified preload to the bolts. This device ensures that the correct tension is achieved and maintained in each bolt.
- Verify and Inspect: After tensioning the bolts, visually inspect the joint to ensure that all bolts are properly tightened and under tension. Check for any signs of gaps, misalignment, or other potential issues. Perform a thorough inspection to verify the integrity and load-carrying capacity of the HSFG joint.
Example of Application: Bolted high-strength friction grip joints find applications in various steel structures, such as bridges, high-rise buildings, and industrial facilities. One common example is in bridge construction, where HSFG joints are used to connect steel girders, trusses, and other structural members.
In a bridge application, HSFG bolts are tightened to achieve the specified preload, creating friction between the connected members. This friction ensures that the load is effectively transferred from one member to another, allowing the bridge structure to withstand the applied forces, including traffic loads, wind loads, and seismic forces.
It is important to note that the above steps provide a general guideline, and the specific procedures may vary depending on the design requirements, bolt specifications, and construction practices. Always refer to the relevant codes, standards, and manufacturer recommendations for the proper