Shop drawings from Engineering drawings

[Mixtli]

Hi all,

What are your thoughts on a precasting company utilizing engineering drawings as shop drawings?.
What they do is mark up the stamped drawing with their piece mark, attach a bar list, doing a take off from the stamped drawing, i.e. counting the bars on the stamped drawing (dots) and doing the typical N=(concrete width)/spacing+1.

Thanks


M.

 

[KootK]

I specifically prohibit this practice in my drawing notes as it is always our hope that the supplier will work out the dimensions of things on their own and that will serve as a check on our work. That said, I've yet to actually enforce the provision, push come to shove. They even lift my details off of our PDF's with Bluebeam sometimes.

Fundamentally, I don't see this as much different than when we supply CAD drawings to fabricators. We generally do that too when asked. As long as I've expressed my desire for the supplier to be figuring things out independently of the structural drawings, I feel that I have some degree of liability protection.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[bridgebuster]

It's done all the time in NY on DOT projects. We give contractors our CAD files. As long as they change the border and remove the EOR's seal it's OK.

 

[MotorCity]

Like KootK, we also prohibit this practice and put the note in a big bold box on our drawings. This is done for a number of reasons. First, it is our work and it is copyrighted. Reproducing copyrighted work with out permission is a no-no. Second, you are essentially doing the drafting work for the fabricator. If they were to pay you for doing so, I might consider it. Third, when people have to re-create drawings themselves, they may encounter errors, interferences, etc. that were overlooked on the design drawings. We do enforce this practice by rejecting any submittals where this occurs.

 

[TehMightyEngineer]

If it's a simple structure or something that's highly standardized in our shop then we will often skip the fabrication drawing phase and fabricate directly from the plan drawings (or my engineering sketches if we've engineered it in house).

For pretty much everything else we draw full 3D fabrication drawings. Especially jobs which are complicated, have high tolerance requirements (state jobs), or jobs where we don't trust the engineering drawings/dimensions and want to verify it on our own.

Having worked on both sides I personally don't think it's wrong as long as the rational behind it makes sense. For example, I'd rather see someone cut and paste a detail from the engineers drawings into the fabrication drawings rather than use a small note that says "see detail X on sheet Y of drawing Z" which will likely be missed or (hopefully not) ignored. The guys in the shop will happily refer to a drawing if they have it in the shop; if they have to hunt for it and they don't have much oversight they may just guess.

Again, it has to make sense to do this in my mind. There are many instances where it's in everyone's interest to redraw it as a double check of the numbers. We've often found many errors or unfeasable details that the engineers put into the drawings when we re-drew it in 3D.

One way around this (and this is one reason I have a job at a precast plant) is we see a lot of engineers stating that the contractor/precaster provides the engineering for a precast structure. I would hope that the engineer is reducing their fee for this practice (but probably not) but it does solve this problem and often an engineer more familiar with precast fabrication can detail a more feasible structure that keeps the guys in the shop happy.

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com

 

[Mixtli]

Hey Bridgebuster, so do the shop people count the bars you drafted for their take off? and if not accurate do they blame it on you?
That is what happens most of the times: people in charge of the shop drawing just copy and paste or count the "dots" on the engineering drawing on their take offs, and then, rather than verify the number, they just blame the engineer for not drawing the right number of "dots".

Bridgebuster: do you keep your stamp on the acad drawing? wouldn't it be a bit dangerous? they may not mistakenly remove it and if something goes wrong.... by the time you demonstrate the error you already have a charge upon.

Anyways guys, thanks for your input. if anyone has more to contribute, please feel free.

Cheers

 

[TehMightyEngineer]

Mixtli: Not who you addressed the question to but when I've done similar things I always either took the care to make sure the number of "dots" was correct (or at least met a standard level of care and combined that with the general note that the contractor must verify all dimensions and such before ordering and fabrication) or we would show a single bar with a reference to the number of bars required/their spacing, and the width to distribute them over.

For an autocad drawing we would remove any engineering stamp blocks from the drawing prior to submitting for exactly this reason. Official version would always be the PDF or paper copy.

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com

 

[bridgebuster]

Mixtli -to answer your questions:

We provide bar lists in our drawings as well. If a discrepancy is noted the contractor sends and RFI.

Nobody thinks to remove the seal from the CAD files. Even if we did, somebody can always steal it from the PDF.