For slip-critical bolt connections, which practice is essential to achieve the intended friction-based load transfer?

• A. Bolt pretensioning to specified level with proper washers and nuts.
• B. Using only bolts without pretensioning.
• C. Not using washers or nuts.
• D. Relying on friction from gravity.

Answer: (C)

Slip-critical connections depend on friction between the clamped surfaces to transfer load, and that friction comes from the clamping force created by tightened bolts. To achieve the required friction, bolts must be pretensioned to a specified level using proper washers and nuts. This pretension creates a consistent clamping force that resists shear and keeps the plates from sliding relative to each other. Washers help distribute the load and prevent embedment or gouging of the surfaces, while the nuts secure the tightening and maintain the pretension.

Without pretensioning, there isn’t enough clamping to develop the needed friction, so the joint can slip under design loads. Not using washers or nuts removes essential components that maintain pretension and load distribution, weakening the connection. Relying on gravity for friction is unreliable and not a controlled method to achieve the required frictional resistance.

So, pretensioning the bolt to the specified level with proper washers and nuts is the essential practice for effective friction-based load transfer in slip-critical connections.