BIM and dimensions

[SteelPE]

I have a project that the architect is creating the drawings using BIM. The drawings are sent to us and we prepare our structural drawings. The problem I have is the fact that there are no useful dimensions on the drawings (besides the major grid lines). Every wall that is dimensioned is done to face of drywall not center line of CMU wall. In talking to the architect he states that all we have to do is overlay our drawings on top of his and pull the dimensions in AutoCAD ourselves. This makes it impossible to verify the dimensions without using a computer.

Now the drawings are complete and the shop drawings have been submitted for review. Usually we state that we are not responsible for checking dimensions during this review however, our drawings are the only drawings with useful dimensions… which makes us responsible for the dimensions.

Oh… and the architect will check our dimensions but says it is our responsibility to make sure any changes he makes to our dimensions are correct?????

It just seems like I now have a bit of added responsibility that I did not have before.

Has anyone else run into the situation? How have other people handled this situation?

 

[kslee1000]

The party who performed the structural design is responsible for the correctness of structural demisions/sizes..etc, unless you were hired to perform cadd drawings only (a technician task.

 

[Taro]

kslee1000, that's not universally true. In my experience, the engineer does not review shop drawing dimensions unless they are critical to the design. According to the AISC Code of Standard Practice, shop drawing approval constitutes a confirmation that the fabricator has correctly interpreted the design intent. The fabricator remains responsible for the accuracy of dimensions.

SteelPE, if the architect is the party responsible for setting and changing the dimensions, s/he should provide those dimensions to you instead of making you hunt for them. It's easy enough to do in BIM by creating a new view with dimensions included.

I have found that many architects in the "electronic age" are becoming increasingly lax in their coordination duties and shift the responsibility onto their consultants. In this case, I might take the approach that contractors use and send "design RFIs" to the architect and request that they confirm that your guesstimate of their dimensioning is correct.

 

[kslee1000]

I am from the old school, unless specifically waived, the designer is responsible to review shop drawings against his own design as part of contract obligation (the contract usually requires the contractors to submit structural shop drawings for review by the ENGINEER, not ARCHITECT). You are the one with full knowledge on how critical the changes, mark-up the discrepancies accordingly, it is your last defense before dragged into court for lengthy litigations.

 

[whyun]

Structural engineers are responsible for reviewing structurally relevant dimensions in the shop drawings. Architects are responsible for reviewing architecturally relevant dimensions on the shop drawings. Neither are liable for having missed a few errors in the shop drawings. Usually a shop drawing stamp will indicate this waiver.

Shop drawing provider is responsible and liable for accurately representing the dimensions on the construction documents. Exception to this "rule" is if there are missing dimensions or conflicting dimensions on the construction documents.

 

[Taro]

I don't think it is an "old school" issue. The established standard of care in the U.S. for many decades has been that shop drawing approval does not include a detailed review of dimensions or quantities. The standard contract forms (e.g. AIA A201 section 4.2.7) also include this same stipulation and it has been upheld in state supreme courts.

 

[JAE]

I'd agree with Taro (I don't know how old "old school" is but I started designing in 1979). Yes we check the shop drawings but no we do not verify every single dimension - only those that would be ultra sensitive to the design.

An example of a sensitive dimension might be the distance from a row of bolts to the weld of a tab plate where the connection has been designed based upon a set eccentricity. A change from a 3" offset to a 4" offset could have serious ramifications on a tab plate weld.

Now checking that the roof beam is exactly 23'-5 3/8" to fit into the wall properly isn't a sensitive dimension from a structural point of view. The beam size, whether the span is 23'-3" or 23'-8" probably isn't going to change.

 

[hokie66]

Interesting discussion, and one which has been around for a long time. Long before computer drafting. When I moved to Australia, I was surprised to find that structural engineers here do not dimension anything which can be derived from the architectural drawings. It is left to the detailers. Doesn't help your problem.

 

[SteelPE]

I was always told that we were to review the critical information only on the shop drawings. This would locations, sizes, spacing etc. This does not include dimensions.

This is the first architect that I have worked with who is using BIM. The job has masonry walls that the architect is placing drywall over. When he dimensions his drawings he is going to face of wall and not centerline of wall. Although it isn’t that big of a deal it does require us to show what I consider “architectural dimensions” (centerlines of walls) on our drawings that are not shown on the architectural drawings.

On another job I worked with a fabricator who needed some connection design done… both the architect and engineer did not show any dimensions on their drawings. This project was a platform for some large RTU’s (40’x12’). Don’t know how you can seal a plan that doesn’t show approximately how long your beams and bracing are going to be.

It seems like this is becoming more of a problem and I was wondering how other people handle it and how far my responsibility I have.