Odorizzi - B2 BIM Handbook: Chapter 2 Parametric Modeling

The portion of the BIM handbook that was delegated to Group A was Chapter 2, titled “BIM Design Tools and Parametric Modeling.” I must confess that I did not find the 66-page-long chapter the most compelling of passages that I have had the pleasure of reading. I am going to attempt to pick out only the good parts to talk about, while giving a complete overview of the content in the chapter.

The focus of Chapter 2 is to bridge the gap from the 2-dimensional, autocad / hand drawing design experiences to the potential of designing with BIM using object-based parametric modeling. A major point that Chapter 2 drives home is that the “objects” being modeled are not represented with fixed geometry and properties, but are governed by parameters and rules such that the object has a behavior. These parameters and rules allow the object to update itself based on the context/connectivity of the object. For example, if the column layout of a building changes to increase the spacing between gridlines, moving the gridline will in turn cause the floor, walls, roof, etc to all move and adjust as well. Hence, BIM builds a series of parametric objects that relate each object to its surroundings, and also builds a database of properties to control the objects themselves. I typically find this idea to make the most sense when comparing to AutoCad - in AutoCad you draw lines, but in Revit (BIM), the lines that are drawn are representing an object with 3-dimensional properties.

Chapter 2 goes through the development of object-based modeling. I found the history rather boring. Major research on modeling 3D geometry started in 1960, and developed into a pairing of two 3D modeling techniques: Boundary representation (which stored modeling operations and arguments with the object) and Constructive Solid Geometry (CGS: which used algebraic formulas). Manufacturing and aerospace disciplines were the first to jump on board with these techniques. For example, Boeing spent over $1 billion when developing the parametrics for the 777 family of planes. The modeling process was estimated to save Boeing over 6000 change requests and reduce the spatial rework of the models by 90%.

The common thread with modeling in BIM is libraries of families, or more generically - libraries of objects. For example, Revit comes with families for walls, floors, beams, etc - and additional families can be downloaded from vendors online. Most importantly, specific families can be crafted by the user for specific instances in a project. These families store parameters that allow the user to gradually build a very complex model that holds very complete information. However, a common shortcoming of BIM is the size of model files (often multi-gigabyte), which can render the model impractical to use if the specs of the computer are surpassed.

The chapter proceeds to go through major BIM platforms available for use, including Revit, Bentley systems, ArchiCad, Digital Project, Vectorworks, Tekla Strutures, DProfiler, etc. Some of these platforms can be used for design only, others offer fabrication-level modeling. Typically, the common trend was that a more detailed model had a more complicated user interface and larger files sizes - such that the pros were “you can build a complete model” and the cons were “but there is a huge learning curve and it might surpass your computer’s capacity.”

A closing line in the chapter stated that the full potential of BIM will not be realized for at least another decade. Seeing that the handbook was written in 2004, we have passed a decade since the text’s writing. I know from experience that structural engineers are generally in favor of using Revit, or reserved about the process. I believe that it will be our generation of engineers that fully embrace the potential of Revit and BIM as we enter the industry, but I do not expect applications such as AutoCad to fall completely to the wayside. I have used Revit at Keast & Hood for the production of construction drawings very rapidly after carefully modeling the building first; or for exact coordination between MEP and structural Revit models; or for unusual designs to come into fruition after crafting a new family. I have also experienced the shortcomings of Revit with very slow user interfaces with big files, and I personally find detailing much easier in AutoCad than I do in Revit. However, to the point of the chapter, BIM undeniably has more power in its modeling capability and is a remarkable tool for storing and organizing vast quantities of information pertaining to each building object.

Source: C.M. Eastman.  “Chapter 2: BIM Tools and Parametric Modeling.”  BIM Handbook: A Guide to Building Information Modeling for Owners, Managers, Designers, Engineers, and Contractors.  2nd Edition., Hoboken, NJ: Wiley, 2012.  pp. 31-97

Comments:

To Dee Dee Strohl

I’ve had experience in Revit similarly to what Cody described above in his comment - on the structural side, relying on RAM for sizing, etc. Were you working simultaneously with architects out-of-house in the central model? That sounds remarkable! In the structural consulting firms I have worked at, we would always get an updated Revit model from the architect that we would link into our structural model, then we would have the worksharing you described with multiple engineers in-house working on the model simultaneously. We were never working on the same central model as the other disciplines, though. That sounds very efficient! Similarly for the contractors, I have never had exposure to allowing the contractor see the model while it is in progress. To me - that sounds like a negative aspect to collaboration, because I have experienced major changes happen to the model close to the deadline for CD’s. It would be counterproductive for a contractor to progress based on a model that is incomplete or susceptible to major changes.

To Jordan Shuster

One of the little stories that was included in Chapter 2 was about Boeing - and it rings true when you are discussing efficiency on a project through BIM. The handbook discussed how Boeing invested over $1 billion in BIM investments, modeling, etc for its 777 aircraft families, and it ultimately yielded 6000+ less change requests and a 90% decrease in spatial reworking when design was finished. I think your points about BIM bridging language barriers are very interesting. I find it on the same train of thought as the common expression, “math is the universal language,” but with pretty 3D pictures. However, one could argue that this benefit of bridging the language barrier is not new - it is essentially the same as scanning hand sketches and emailing them out. BIM is simply more refined and tech-forward, but they both rely on conveying ideas through graphics.

To Sherry Liu

I have only ever been on the design-bid-build process for projects over co-op. I think it is very interesting to think about the advantages a BIM platform serves for a design-build firm. I generally am reserved about involving the contractor in pre-construction phases of the model. I worked for a structural design firm for both of  my co-ops, and there was one instance where a contractor requested to see the 95% CD progress set of our drawings - from which he took the liberty to have his steel subcontractor develop the shops for all the column base plates. However - between 95% CDs and 100% CDs, the architect made some alterations that significantly changed the loading through the structure and changed all of the base plate sizes. My point is that the exchange of information with ALL affiliated parties throughout the entire design process can have its drawbacks as well. In my little story, the contractor wasted time and money to develop a wave of base plate shop drawings from incomplete drawings. Regardless, I believe the industry is learning and gaining efficiency with the use of BIM, and as our generation of engineers enters the work force, I think it will only continue to become more prevalent.