What is a slip-critical connection and why is bolt pretension important?

• A. A slip-critical connection transfers load through friction from pretensioned bolts, not through bearing.
• B. A slip-critical connection transfers load through bearing contact between parts to transfer load.
• C. A slip-critical connection uses welded studs to transmit shear without bolts.
• D. A slip-critical connection relies on dynamic bolts that slip to absorb movement.

Answer: (A)

The key idea is that slip-critical connections transfer load through friction between the mating surfaces, controlled by the pretension in the bolts. Pretensioned bolts clamp the parts together, creating a normal force on the faying surfaces. When a shear load is applied, resistance comes from this frictional force, which is essentially the friction coefficient times the total clamping force. The connection’s capacity thus depends on how much pretension is maintained in the bolts and the surface condition that governs friction. If pretension is lost or insufficient, the surfaces can start to slip, reducing capacity and potentially compromising alignment and strength. This differs from bearing-type connections, where load is carried by bearing contact (through the bolt holes and the bearing surfaces) rather than by friction between the surfaces. Welded studs or other mechanisms described aren’t the typical basis for slip-critical behavior. So the correct understanding is that slip-critical connections rely on friction from pretensioned bolts to transfer shear, not on bearing.