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.
