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BIM for reinforced concrete – From 2D to 3D for rebar detailing

Pawel Piechnik
May 31, 2017

Last year I published a blog post contemplating the value of BIM for Concrete, and discussing how the next generation of BIM tools for reinforced concrete are helping our customers in four main ways. I described these BIM-centric concrete benefits as:

  1. Combines the versatility of 2D documentation with the higher level of fidelity and accuracy of 3D modeling of steel reinforcement and concrete accessories, with minimal effort to produce both.
  2. Allows users to design and detail with clash prevention in mind to reduce clashes both in the preconstruction and site execution project phases.
  3. Enables the transition from design to detailed models while respecting both perspectives, following local code requirements, and automating the process of making changes so they are less disruptive to the design process.
  4. Increases transparency and quality of the model information being used from bidding to procurement by not only providing quantifiable information, but also enabling access to it in collaboration friendly environments.

I must say that it was great to hear your feedback from my last post, and see that so many of you are as excited by the future of concrete as I am! I’d like to continue the conversation I started with you, and spend some time discussing these four benefits and what they mean for the industry in depth. And by “in depth” I mean this in an engineering sense—I’m going to be thorough.

Since there’s A LOT to cover, instead of writing one long blog post on concrete that might bore you to sleep, I’m going to focus on one benefit at a time. For today, let’s talk about the benefits realized when moving from 2D to 3D.

Benefit #1: The BIM-centric concrete solution combines the versatility of 2D documentation with the higher level of fidelity and accuracy of 3D modeling of steel reinforcement and concrete accessories, with minimal effort to produce both.

We hear often that moving to 3D-based rebar design requires more work than traditional drafting. Many believe that creating a spatial representation of the engineer’s design intent and later installation reality is an extra step added to the effort related to drawings production. This is often followed by the complaint that obvious benefits of 3D (clash avoidance, accuracy, etc.) are for the benefit of general contractors rather than designers and detailers.

I want to challenge this.

While it’s true that 2D drawings, shop and lift drawings are still the primary deliverables nowadays serving as means of communication and instruction across broader teams, we’re also seeing these trends as well:

  • For communication, project teams across the are globe driving towards model-based communication and information handover, especially when it comes to the Design to Detailing transition. Customers like Norconsult are already using this approach effectively.
  • As a means of instruction, an undisputable benefit of traditional 2D detailing is the speed of drawings production and versatility. But the downside is the lack of precision leading to rebar clashes on site, compromises on quantities, and coordination with the formwork model.
  • Design changes also require drawings to be reproduced. The lack of consistency surfaces easily as drawings can be “adjusted” (“faked”, honestly speaking) and ultimately lose their connection to other sources of information like BOM, model data, IFC, ERP, etc.

Drawings and 3D rebar detailing in Revit

Let’s assume for a minute that by using a BIM-centric approach to rebar detailing we can still maintain a highly efficient and versatile process for drawing production, and incorporate the precision and information completeness that comes with 3D modeling at no additional cost. Well, that’s the idea for Revit.

For Revit we want to bring these two benefits of 2D to 3D together. How? This is where rebar detailers can leverage the traditional approach and perform 2D detailing “in canvas” of a section, plan or an elevation view taken directly from the concrete model, and have the rebar model created “for free” in the background. You can see this illustrated in this example:

Then, as the design/detailing evolves to a point where coordination is needed, detailers can focus on the rebar model editing directly and more comfortably in the 3D views. While in the 2D drawings space they can just easily add tags and dimensions to the rebar as a downstream part of the process since rebar is there, placed accurately, already.

What then makes a real difference is the accommodation of changes in the BIM process; there is no need to re-model or redraw rebar when that happens. The below example shows again how changes of concrete object sizes or rebar distribution parameters make all the rebar information adapt to changes and the submittals update instantly. Talk about a benefit for the detailers and designers!

A glimpse of the future

The ultimate proof of BIM-centric and fully model based reinforcement detailing efficiency can be recognized for projects dealing with complex concrete geometries such as water treatment stations, industrial structures, buildings with complex architecture, etc. Anywhere humans struggle to visualize the 3D structure in their minds when communicating instructions with only 2D drawings.

There are examples where using 2D drawings as layout instructions is nearly impossible. Check out this groundbreaking use case from Norconsult who is implementing a fully paperless process to construct this large hydro plant in Norway.

Additionally, use of these modern methods applied for complex projects is presented in a very interesting and recent master thesis from Pål Røe Larsen (Technical University of Denmark, Kongens Lyngby). Larsen’s thesis (you can download it here) includes several case studies and interviews with adopters from the industry, and draws attention to the new future of the concrete industry.

So, what do you think? Are you using a BIM-centric modeling approach for concrete yet? Are you seeing these benefits already? Stay tuned for more on this topic and let me know your thoughts in the comments.

For my next post, I’m going to talk about what I’ve described as benefit #2: allowing users to design and detail with clash prevention in mind to reduce clashes both in the preconstruction and site execution project phases.

Structural Precast Extension for Revit Software Overview

Revit 2018.1 New Feature - Free Form Rebar Distribution

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Pawel Piechnik

Pawel is the Sr. Product Line Manager for Structures at Autodesk. Having structural engineering background, Pawel has worked to apply computer software to this domain for around twenty years. Being with Autodesk for 9 years, he is looking after product strategies for structural authoring products supporting Steel, Concrete and Precast design to fabrication workflows. Find him on Twitter @piechnikp

2 Comments;

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  1. 123aint

    Hi Pawel, thank you for this interesting blog. We use Revit in the Bridge design space, and even though its a bit of a stretch for some of the more complicated geometries, we are still very excited about the advantages of bim. With reference to your 2D / 3D explanation above, I agree, but… a lot of our clients are still wanting to see rebar displayed graphically in a way we can’t do with Revit. This is to say, they want bars that are to be placed on top of each other in the real world, displayed at an offset to each other on the drawings.

    1. Pawel PiechnikPawel Piechnik (Post author)

      It’s a good point here you are bringing here. I hear the same and find this quite controversial as well. Some users desire such a behavior but for some this means opening a door for making documents becoming inconsistent with the model data.

      Drawings are instructions and they should ease the understanding of the rebar layout, so the point is valid to me. The question is what might be the best way to instruct site workers how to lay out rebar having new tools and new possibilities now. Spatial views with 3D annotations being added which might more naturally be aligned with human perception might be brought as an example. This is worth debating, I think.