SLIP-CRITICAL CONNECTION WITH LONG-SLOTTED connection

A slip-critical connection, as defined by the American Institute of Steel Construction (AISC), is a type of bolted connection where slip at the connection is a serviceability concern or could adversely affect the performance of the structure. In these connections, the friction between the connected parts, generated by the clamping force of the high-strength bolts, resists the service loads.

Long slotted holes are used in structural connections where some degree of adjustability is needed during the erection process. The long dimension of these holes is perpendicular to the direction of the load.

In a slip-critical connection with long slotted holes, the bolts are pretensioned so that movement or slip does not occur under service loads. The design of these connections is based on the principle that the friction between the plies (induced by the bolt pretension) is sufficient to resist the applied shear force.

The AISC provides specific provisions for the design of slip-critical connections with long slotted holes. These provisions include:

1. Bolt Pretension: The bolts in a slip-critical connection must be pretensioned to a specified minimum value to generate the necessary clamping force.

2. Slip Resistance: The design slip resistance is determined based on the type of surface (Class A, B, or C), the type of hole (standard, oversized, or slotted), and the condition of the faying surface (clean and free of paint, galvanized, etc.).

3. Bolt Spacing and Edge Distance: The AISC specifies minimum and maximum spacing requirements for bolts and minimum edge distances, particularly for long slotted holes.

4. Combined Shear and Tension: If the connection is subjected to both shear and tension, the interaction of these forces must be considered in the design.

5. Installation: The bolts must be installed using a specified method (turn-of-nut, direct tension indicator, calibrated wrench, or twist-off-type tension control bolt) to ensure the required pretension is achieved.

6. Inspection: Slip-critical connections require verification of the bolt pretension and are subject to more rigorous inspection requirements.

Calculation Reference

Welding

Weld Strength LRFD

AISC