Minimum edge distance for fillet weld

[structengr90]

We are repairing an existing column by adding a new plate to the flange. The new 3/8" plate will be welded with a 1/4" fillet weld. How much should we reduce the new plate width, to allow enough room to weld the plate to the flange? Is 3/8" (1/4" weld size + 1/8") on each side enough for proper welding? I'm I'm having trouble finding any guidance in AISC, any help you can provide would be great. First time poster, although I have used the forums in the past, but this is my first post. Thanks.

 

[WillisV]

Fig. 8-11 13th ed. manual. 1/2" min shelf dimension rq'd for 1/4" fillet.

 

[DanAshby]

Just wondering what the reason for this minimum shelf recommendation is?

My understanding is that a fillet weld should be kept 1/16" from a plate edge to prevent the edge from being burnt away, as the plate edge serves as a reference point from which a welding inspector can verify the leg lengths of the fillet weld, and therefore confirm the effective throat of the weld is as designed.

I imagine that the minimum shelf given is intended to avoid burning the edge away as above, while also giving some construction tolerance to allow for the misalignment of the two elements being connected. Is this correct?

Thanks!