How to protect yourself from existing dimension problems

[B16A2]

When working in or next to an existing structure, there's always an element of uncertainty when it comes to dimensions. The engineer can show a dimension that is close, but when it comes to something like steel fabrication, an inch off can be a huge deal.

I'm just wondering how others go about providing notes and dimensioning existing structures so that it doesn't come back later and bite you an an error or omission.

My current method is to provide a note saying that all dimensions must be field verified, and then use a +/- indicator on the dimension strings that are especially critical.

 

[Teguci]

In addition to the note, I use details that can be modified in the field. Lot of field welding and cutting. Field bolting is limited to connections I have control over (new to new).

 

[epitome1170]

I would say that your current method is as good as any... at least that is what I do. I say something to the effect that the design was based off the best available information, but all dimensions shall be field verified prior to fabrication and to contact the E.O.R. if an existing condition differs from what is shown.

 

[steellion]

I agree with +/- and Field Verify. I also agree to design with flexibility in mind when possible, knowing that the in-situ dimensions WILL vary from what you have assumed. Field welds and horizontal-slotted connections are useful. Add a couple specific notes to the drawings to make sure your liability is covered:

"Design is based on information drawings by... dated..."
"Contractor shall field verify all existing dimensions."
"Notify structural EOR if existing conditions differ from shown"