Drafting Standards for Concrete Pits 4

[swearingen]

I have a peer that swears that all pits, tanks, clarifiers, etc., have and should be dimensioned fully in every view.

I've always gone by the standard drafting rule of dimensioning something once only to avoid mistakes and aid in checking. For example, for a concrete box pit, you would show the out-to-out dimensions and wall thicknesses in plan, but show only the depth and base thickness in section. Similarly, in steel design, the plan members and plan dimensions are only shown on the plans, the column members and heights are shown on the elevations (but plan dimensions are not repeated).

What say you guys?


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[SwinnyGG]

You're right, he's not. His method leads to mistakes.

The way I usually explain this to people is that for a given feature 'X', I want there to be exactly one controlling drawing whenever possible. If I dimension that feature in other drawings that I intend to control other features but not 'X', it is now not clear to the fabricator/contractor/installer/engineer who has to interpret my drawing set in 10 years which drawing should be used to control what.

The other side effect that if a change is made, I only have to correct 1 sheet instead of 2 or 10 or 100.

 

[dflva]

I will respond with reference to below-grade concrete tanks only. Steel, masonry, timber may have special situations to which my comments don't apply.

I may not say every view must show every dimension, but generally, I agree with your peer.

The minimalist dimensioning practice you refer to as a standard drafting rule hasn't always been so standard. Avoiding dimensions is more a defense mechanism than a drafting rule. As budgets have decreased and finger-pointing has increased, it has come about to aid the design team by preventing conflicting dimensions from showing up in the drawings - understood. And I will admit that when amendments, addendums, etc are issued, fewer sheets need to be re-issued when fewer sheets have a changed dimension - great. However, for the following reasons, I don't let a potential conflict prevent me from showing dimensions:

* We owe the client a set of drawings that can be easily interpreted. The drawings should be useful - they should not be a puzzle to be solved each time they are opened.

* Each time someone looks at an undimensioned view (happens hundreds of times throughout design, redesign, shop drawing production, construction administration) and needs a dimension, they have to find it or worse, derive it --> multiple chances for error. Compute the dimensions in the relative calm of the office, use your cad software to help, and show them. Remember a contractor's error in computing a dimension often becomes the design team's problem as you help bail him out of his predicament. As a team player, you're not likely to be remunerated for your effort.

* Showing dimensions in multiple views helps the reader identify components of the structure among the views; e.g. the interior wall I see in plan is the same wall I see in section. Helps everyone.

* Showing dimensions in multiple views allows for coordination among the disciplines. Helps other design team members, not as familiar with your structural drawings, see at a glance if there may be a size/fit/clearance problem with their equipment, etc.

* Showing dimensions in multiple views aids in quick check of the design. If I see a given span length with given reinforcing steel, I can make a quick judgment regarding the reasonableness of the design. Without the span length, height, or other critical dimension, I can't do spot checks, over-the-shoulder checks. Spot checks, while not a replacement for a formal checking process, have prevented a lot of problems over the years.

* You need the dimensions readily available for easily comparing calculations with drawings during the QC process. A dimension (e.g. wall thickness or span) that is not readily available, may go unchecked, or the component may may go unchecked.

* When your office is QCing the documents, the only way you know if a dimension is missing, is to go on a scouting trip through all the sheets to see if it might be shown somewhere else, or worse, might be derivable from dimensions shown somewhere else. You might as well use this time up front to just show the dimensions.

* Shop drawings are not created from just one view, not just the view on which dimensions are shown. Being able to go view to view without recreating dimensions aids the Contractor's detailer greatly. Don't be a jerk, help the man out.

It's not a drafting sin, nor a bad business decision, to show the same dimension in multiple views. In fact, in the long run, it's a good idea.

 

[robyengIT]

As a field engineer I agree with DFLVA : abundance of dimensions means "no mistakes or at least less mistakes" in the confusion of a starting project with unskilled local people speaking their own language, translated by someone you don't know what and if he understands from You and what and if they understand from his translation.
Abundance does not mean superfluous or unnecessary

 

[swearingen]

I understand my peer's point of view, along with you DFLVA and robyengIT, and I'm not an advocate of strictly following this rule at all costs. I'd like to respond to your points, DFLVA:


* We owe the client a set of drawings that can be easily interpreted. The drawings should be useful - they should not be a puzzle to be solved each time they are opened.

Absolutely. This is where consistency in drawing setup and presentation is important. It must be easy to find the dimensions, and this is where drawing order, plan/section order, and consistency pay off. Single dimensioning should not be a hindrance here.​

* Each time someone looks at an undimensioned view (happens hundreds of times throughout design, redesign, shop drawing production, construction administration) and needs a dimension, they have to find it or worse, derive it --> multiple chances for error. Compute the dimensions in the relative calm of the office, use your cad software to help, and show them. Remember a contractor's error in computing a dimension often becomes the design team's problem as you help bail him out of his predicament. As a team player, you're not likely to be remunerated for your effort.

In my case, there was one plan and three sections on one drawing, with a few sections and details on the subsequent two drawings. You cannot convince me that putting overalls and bar callouts on every depiction is worth the chance of missing one. When it comes to large sets of drawings, when something changes during a project it means you must remember all of the places that dimension shows up and get them updated. The chance for error skyrockets. I'm also not asking him to compute dimensions.​

* Showing dimensions in multiple views helps the reader identify components of the structure among the views; e.g. the interior wall I see in plan is the same wall I see in section. Helps everyone.

Here, I do see some benefit on drawings that are far removed from each other in a set to provide some basic overalls to orient the reader. Column line callouts and simple overall dimensions can be helpful in this case, are relatively easy to stay on top of, and are less likely to change.​

* Showing dimensions in multiple views allows for coordination among the disciplines. Helps other design team members, not as familiar with your structural drawings, see at a glance if there may be a size/fit/clearance problem with their equipment, etc.

I can't excuse my fellow professionals from not being able to read the drawings. All of the companies I have worked for have mechanical, civil, structural, process, electrical, and instrument disciplines reviewing my drawings. When I review theirs, I am expected to understand their standards and conventions. Electrical drawings and P&IDs look nothing like structural drawings, yet I am expected to be able to follow them.​

* Showing dimensions in multiple views aids in quick check of the design. If I see a given span length with given reinforcing steel, I can make a quick judgment regarding the reasonableness of the design. Without the span length, height, or other critical dimension, I can't do spot checks, over-the-shoulder checks. Spot checks, while not a replacement for a formal checking process, have prevented a lot of problems over the years.

You are correct, however this is what a formal checking process is for. The formal checker will quickly be familiar with the dimensions he/she is working with. Hampering an over-the-shoulder check is worth the risks inherent in over-dimensioning.​

* You need the dimensions readily available for easily comparing calculations with drawings during the QC process. A dimension (e.g. wall thickness or span) that is not readily available, may go unchecked, or the component may may go unchecked.

Again, this should be no problem for a formal checker. If he can't find a dimension in a well organized set of drawings, then either the dimension is not there, or you need a new checker.​

* When your office is QCing the documents, the only way you know if a dimension is missing, is to go on a scouting trip through all the sheets to see if it might be shown somewhere else, or worse, might be derivable from dimensions shown somewhere else. You might as well use this time up front to just show the dimensions.

I'm not a big fan of heavily derived dimenions and will over-dimension at times to prevent this. However, a clearly presented system means that the dimension will be easy to find, even though it's only shown once.​

* Shop drawings are not created from just one view, not just the view on which dimensions are shown. Being able to go view to view without recreating dimensions aids the Contractor's detailer greatly. Don't be a jerk, help the man out.

I'll help him out to a point, as stated in the 3rd bullet, above. As I said before, this should not be a problem with an organized, consistent set of drawings.​

It's not a drafting sin, nor a bad business decision, to show the same dimension in multiple views.

Agreed, on occasion.​

In fact, in the long run, it's a good idea.

Other than the rare exceptions noted, I completely disagree. ​

The motto here should be "fit for purpose." It should be no more or no less than what is required to get the point across. Drawings are strictly a communication tool and a concise, well organized set beats a bloated, over-dimensioned set every day.



-5^2 = -25 ;-)

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[SwinnyGG]

"a concise, well organized set beats a bloated, over-dimensioned set every day"

Well said.

 

[Leftwow]

I have been taught that contractor looks at the plan and says "how do we building this?" then, "ok, that's how to do that let's build it". I have had multiple engineers saying it can decrease mistakes when issuing a package by detailing less and I agree with them basically because they have the information on there to build it and that's it.

 

[FoxSE14]

Showing too much can be a very, very bad thing. Especially when your colleague has quadruple-dimensioned a foundation elevation that is critical to a last-minute client design change....so, I get your sentiments dflva, especially on spot-checking, but in my experience has proven to be a poor business decision to over-dimension. It only takes one instance of a colleague's over-dimensioning (and causing the firm to buy our client a new $40k foundation), to get everyone off of the "dimension everything" bus and onto the "NEVER showing any dimensions twice" bus. Funny how threatened bonuses and job security do that to a group.

The benefits have been: things are much easier, more efficient, clearer, sets are more concise, and less error-prone when we avoid over-dimensioning. Yes, there's a bit more page-flipping, but if the drawings are assembled correctly, there should not be a question/overlap, and there should be a single point to go to for every dimension/elevation. If the set is poorly detailed, however, that is a different story (i.e.: common sense inclusion of gridlines, property lines, notes such as "see plan" coordinating to a 'real' plan dimension, etc. are critical to help this idea).

 

[FoxSE14]

Question: has anyone had input from their insurance carriers on this topic?

 

[MacGruber22]

Though I agree that duplicate dimensions can take away from clarity and can be risky, I am not sold on implementing the rigid "no repeat" rule for structural documents. Besides, there are ways to have your cake and eat it too if the management of your drafting standards is good. In AutoCAD you can use custom fields that are linked to the "original" dimension string. I do this with section numbers, etc. to mitigate the chances that I miss coordinating changes in my cad files. Using view ports efficiently can also achieve repetition without increasing risk for error.

"It is imperative Cunth doesn't get his hands on those codes."

 

[swearingen]

As I stated before, there are times when it makes sense to have a dimension in more than one place, but it is certainly the exception. CAD has helped to narrow the chasm between the two schools of thought because of the tools you mentioned, but I'm still firmly in the single-dimension camp.


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