Combinations of Fasteners

The AISC ASD and LRFD Specification for Structural Steel for Buildings distinguish between existing and new framing in setting conditions for use of fasteners in connection design.
In new work, A307 bolts or high-strength bolts in bearing-type connections should not be considered as sharing the load with welds. If welds are used, they should be designed to carry the load in the connection. However, when one leg of a connection angle is connected with one type of fastener and the other leg with a different type, this rule does not apply. The load is transferred across each joint by one type of fastener. Such connections are commonly used, since one type of fastener may be selected for shop work and a different type for field work.
High-strength bolts in slip-critical joints may share the load with welds on the same connection interface if the bolts are fully tightened before the welds are made.
For connections in existing frames, existing rivets and high-strength bolts may be used for carrying stresses from existing dead loads, and welds may be provided for additional dead loads and design live loads. This provision assumes that whatever slip that could occur in the existing joint has already occurred.

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