What is the minimum distance from the edge of a member for a fillet weld?

The minimum distance from the edge of a member for a fillet weld is specified in the AWS D1.1 Structural Welding Code to ensure that the weld is sufficiently away from the edge to provide adequate strength, prevent excessive stress concentration, and allow for proper weld penetration and fusion. A distance of 3/8 inch allows for these considerations, providing a balance between ensuring that the weld is effective and minimizing the risk of issues such as weld cracking or inadequate joint strength.

Choosing a distance that is too small could risk compromising the weld's integrity, while a distance that is too large could add unnecessary weight and cost to the fabrication. Therefore, 3/8 inch is set as the minimum allowable distance to optimize performance and structural reliability.