Dimensions on structural drawings... 7

[cva1993r]

Hello all,

My question pertains to structrural engineers refusing to show dimensions such as gridline spacing (column spacing), beam spans e.t.c...on the strucutral drawings "because these are shown on the architectural drawings".

There are SOME design standards referenced in the Building Code (CANADA) where it is CLEARLY stated that the STRUCTURAL design documents should indicate the critical dimensions. Other design standards however do not specifically mention that the STRUCTURAL docs, should depict these dimensions.

I am concerned that if the architect were to make a dimensional change and not inform the strucutral engineer, then the engineer would have nothing to "fall on" as his drawings would not be indicating the (max. aloowable) design spans.

I am of the opinion (in this day and age with the help of CAD software), that the strucutral drawings SHOULD include the basic dimensions as these would also be required by the fabricators to prepare shop drawings.

Your thoughts for and/or against my argument are most welcome.

Thank you,

CVA1993

 

[whyun]

Typically, I am used to indicating plan dimensions (grid to grid and any structurally relevant dimensions such as columns not located on grid lines) on the foundation plan. On subsequent floor framing plans, the dimensions on the foundation plan are not repeated. Only dimensions shown here may be columns on a transfer girder that is not indicated on the foundation plan.

In the general notes, there would be a note indicating if conflict exists between structural and architectural drawings, contact the architect and resolve before proceeding with work.

Even then, things can get missed and cause much grief to everyone.

 

[JAE]

I work in an A/E firm where we directly link our drawings to architect's plans. We create a common grid-column plan drawing that both the Arch and the Struct reference. That way, all of the significant grids are common to both plans and the architects can't get away with moving columns without either we noticing it - or we allowing it (its our dwg file).

This can work also for engineers working with outside architects. Simply create a common Col-Grid file and share it for both disciplines.

As far as dimensioning - I do not see the logic in structural engineers not showing dimensions on their plans...as if this will some way help avoid liability or something. The structural drawings should be stand-alone sets of plans that are not dependent on others dimensions to build. See also AISC Code of Standard Practice Section 3.1.

 

[mrMikee]

I agree with JAE that the structural drawings should be a stand-alone set. If you defer to the architectural plans for important dimensions then you are giving the architect and/or their CAD people a way to change your design.

Regards,
-Mike

 

[JAE]

I do get the sense that a lot of structural engineers who work for architects many times are under a lot of pressure to get the project out as fast as possible - and this creates a temptation to just refer over the arch plans for the dimensional control of the building. This takes a lot of time off the plan and detail preparations and saves fee for other essential efforts.

 

[UcfSE]

We typically show dimensions that are relevant to the structural elements. This includes grid lines, dimensions to element not on grid lines, beam elevations and others that are necessary to locate structural members. Openings for doors and windows in walls are an example of what we don't typically show. We also typically have a grid line drawing as a stand alone that is externally referenced.

When I do specialty engineering I typically won't show dimensions but refer instead to the architectural or structural. By the time I get the drawings, half the time the best I can do is scale drawings to get dimensions and elevations. Because of this I don't feel comfortable putting scaled dimensions on my drawings and most of the time there is note saying not to anyway. I put maximum or minimum required lengths and let them go from there. It's more due to a lack of information rather than a steadfast belief that I should or should not put in dimensions.

 

[emmgjld]

When my technicians and Special Inspectors are having to chase around Architectural Drawings to come up with appropriate Foundation Dimensions, I hear all about it. This is not a matter of convenience, it can be critical.

 

[JAE]

UcfSE - I would agree with you that architectural elements such as window and door openings, cabinets, etc. should not be shown on structural drawings. But I also prefer to show out-to-out building dimensions and other face of brick, veneer, etc. dimensions just to tie down the structural dims with the overall architectural dims.

 

[WMO]

I understand that everyone involved in producing drawings is given the task with insufficient time to accomplish it.
However, it is not a steel detailer's job to dig that information out of the architecturals. The EOR's structural drawings should be a complete package.

My personal favorite is structural drawings showing section cuts with the all too familiar "see arch" label.
Unless that information is readily available in the architecturals, which it is probably not, then I, as a steel detailer with no time, have to rfi this and potentially delay your project. If the information is shown in the architecturals, I include that information clouded on approvals and ask for verification. If the approver fails to answer the clouded approvals then I am forced to rfi this information possibly further delaying your project. Some suspect that steel fabricators rfi trivial things in order to gain more time to create shop drawings. This is seldom the case. No one wants the job at hand detailed any sooner than the detailer that is working on the job. Lack of information in the structural package forces the detailer to either glean the information from the architecturals, guess, or guess and rfi in order to continue detailing the job. In any of these scenarios, it is you the architect or EOR, that will ultimately have to answer the rfi. This is, after all, a litigious society. Field repair costs increase exponentially because, often times, erectors view extras as billable at a gazillion time and a half involving a full crew. Someone will have to pay and everyone's stance is to make the other guy pay. Be thankful that someone took the time to RFI something instead of using incorrect information or guessing. Or better yet, put the information in the structural package.

Now, to cva1993r's comment regarding lack of gridline dimensions. I have also seen the opposite where the architecturals do not even show the gridline dimensions and I have also seen architectural drawings that did not even show gridlines.

Both the structural and the architecural drawings should show grid labels and grid dimensions. As JAE indicates, it is very simple to accomplish. Also, when it is apparent that a common grid dimension plan was not used, I typically compare the architectural gridlines with the structural gridlines looking for grid problems. That is a free check for the architect and EOR and has in my experience precluded many problems on many jobs.

I apologize for the rant but I just happen to be working on a job where this lack of information in the structural drawings is all too common. Cross referencing between the structural and the architecturals consumes what little time I have to detail this project. My interest in this project diminshes each time I have to unroll the architecturals.

 

[JAE]

It seems (it feels?) like the trend is heading toward a future where architectural, structural, electrical, etc. drawings will be developed within a total design/analysis program where the owner, desginers, fabricators, suppliers, and contractors will be able to all view and use for their respective jobs.

I think this is already happening to some extent in some big firms who can afford to write their own software (I'm thinking of the big power plant designers like B&V).

The trick will be how to separate the various entities responsibilities with regards to intellectual property and liability with a single "thing" called a comprehensive facility model. But my chrystal ball just got a bit fuzzy...maybe if I re-arrange these here rabbit ear antennae...

 

[Ingy]

JAE, I don't know all the particulars but the local ASCE just gave a presentation on the Lucas Art Center at the Presidio here in San Francisco. What was amazing was that they successfully utilized a multi-discipline 3D model. My understanding is that the owner took on the risk of any problems arising from using the 3d model, and once everyone realized they weren't going to be penalized, they relaxed and the system worked very well. I'd be interested if anyone else has had success in this area.

 

[cva1993r]

Thank you all for your responses.

I am noticing that there is a 'trend' for the strucutral engineers to omit these (critical) dimensions and rely on the architecturals.

I too have brought up the same issue that WMO brings up in that the steel fabricators have a hard time when the only dimensions provided are on the architectural drawings.

The design standards (not all) refernced in our Building Code, indicate that the STRUCTURAL design documents must show this information. I can't see how the EOR can ignore this !

I have heard the following (lame) arguments:

1. The dimensions clutter the strucutral drawings
2. There are extra costs as the draftsperson spends more time.
3. If there are discrepancies between struct. and archit. drawings, the contractor would be in a 'difficult' position to co-ordinate these discrepancies. We don't want to place the responsibilty on the contractor.

(I'm sure David Letterman could come up with at least 7 more excuses for a great TOP TEN list !!! LOL)


I am polling local strucutral firms to determine to what extent the dimension issue is indeed an issue.

I thank you all once again for your very respectful opinions.

cva1993r

 

[JAE]

OK, here's a top ten we can use:

10. Contractors usually just pace off their column lines, what’s the point?

9. Architects are too stingy with fees, I can’t even afford to by mag wheels for my new Mercedes!

8. Contractors can’t read, so why put more letters and numbers on the drawings…it would just confuse them.

7. My beams work at any span; so what’s the problem?

6. If I take responsibility for locating my columns, next they’ll have me calling out the type of toilets to specify.

5. I’ll show dimensions the day architects stop moving my columns around.

4. Dimensions show commitment. I hate commitment, its just so….committing.

3. I graduated from the Tawdry School of Minimalist Engineering – less is more!

2. With the earth flying through space, according to Einstein, and inch isn’t really an inch so why bother.

1. I’ve got a crush on that fabricator. The more he calls, the happier I am.

 

[BigH]

JAE - shuoldn't your fabricator be a "she"??

I opine that all drawings should be as complete as possible - there is then much less chance of error.

 

[JAE]

Well, I would hope so - just depends on the individual I guess.

 

[LPPE]

On my structural drawings, I try to dimension everything possible, down to the RTU frames. The way I figure it, my stuff is going in first, so the architect can work around me. That way last minute arch. changes are often desregarded, due to the change orders.

I often get the call "We moved your column line a little. It shouldn't affect you". OK, great, how much did you move it? 4 inches? 6 inches? "No, we moved it 6 FEET".

 

[samdamon]

I have the solution. In my spare time I have invented a special gizmo-tron. Its a combination of several used motherboards, cad and analysis software, an etch-a-sketch and a hair drier. Whenever the job dimensions change, you just have to push a black button, and the gizmo-tron whirs into action- it automatically redesigns all the affected framing, adjusts the dimensions correctly on the structural cad drawings, revises the details, and spits out corrected plots.
Just don't knock it accidentally during the work or you'll have to start over.

What do you think of my machine?

 

[HgTX]

That's all wrong. It should be a red button.

Hg

Eng-Tips guidelines: faq731-376

 

[whyun]

I agree with LPPE that structure goes in first. Therefore, providing dimensions on the foundation plan is critical. Contractors generally do not like to refer back to the architectural dimensions as they should. So, I agree with JAE that structural drawings, in general, should be sufficient to act as a stand-alone document.

Although it doesn't hurt to replicate the dimensions on subsequent upper floors, it carries little meaning because, columns are already placed from the dimensions indicated on the foundation plan. Only thing that need to be "dimensioned" at this point is any columns or elements that do not occur on the foundation plan. At least this system works for me so far.

As much as engineers would like to dimension everything, architectural changes are not predictable. More dimensions we actually put on CAD file, more we have to chase down when architects happens to change a few dimensions (we could miss some causing conflict).

I treat this similar to double-noting member sizes.

Various engineers have different philosophy about "amount" of information that goes in the drawings. Some say more is good (more chances of error) while others say less is good (less chances of error with increased chance of omission). I think the key is to find a happy medium which may also vary dependng on the individual.

 

[apsix]

Just to be different.
From my experience in Australia, building dimensioning is left to the Architect, unless the dimension pertains to the structure only. I can see at least 2 advantages.
1) The responsibility for correct dimensioning remains with the one party which produced the building dimensions in the first place.
2) It forces the fabricator's drafters (and contractor) to use both the structural and architectural drgs, ensuring they are fully aware of the structure and all the finishes, cladding etc.
I'm not saying that it's a better way, but it works, especially if it is the norm.