A bolted slip-critical joint is a type of connection used in steel structures where the resistance to slip or movement between the connected members is critical to the joint’s performance. This type of joint ensures that the bolts maintain sufficient preload and prevent slippage under applied loads. Here is a step-by-step procedure for creating a bolted slip-critical joint:
- Design the Joint: Determine the required number of bolts, their size, grade, and spacing based on the applied loads, member dimensions, and design requirements. Consider factors such as the slip resistance 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 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 match the bolt diameter precisely to allow for a snug fit and optimal load transfer.
- Remove Burrs: After drilling the holes, remove any burrs or sharp edges from the holes using a deburring tool or a suitable method. This ensures that the bolts can be inserted smoothly without interference.
- Insert Bolts: Place the 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.
- Add Washers and Nuts: On the opposite side of the joint, place washers over the bolt ends, followed by the nuts. Tighten the nuts by hand until they are snug, but do not apply full torque at this stage.
- Torque the Bolts: Using a torque wrench, tighten the nuts in a specific sequence and to the specified torque values. Follow the recommended tightening procedures and torque values provided by the bolt manufacturer or the applicable design standards.
- Inspect and Verify: After torqueing the bolts, visually inspect the joint to ensure that all bolts are properly tightened. Check for any signs of gaps, misalignment, or other potential issues. Perform a thorough inspection to verify the integrity and slip resistance of the joint.
Example of Application: Bolted slip-critical joints are commonly used in connections between steel beams, trusses, and columns in structures such as industrial buildings, bridges, and high-rise buildings. These connections are crucial where movement or slippage between the connected members must be minimized to ensure the structural integrity and safety of the overall structure.
One example is the connection between the steel columns and beams in a steel frame structure. The bolted slip-critical joints in this application ensure that the beams remain securely connected to the columns and can resist the applied loads without slippage or separation.
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 installation of bolted slip-critical joints in steel structures.
