This
chapter provided a basic overview of how BIM defers from previous CAD modeling
techniques. With BIM systems, a set of predefined building cases are provided
from which the design can modify for their own use and needs. Compared to
earlier CAD modelling where a shape had to be defined and given properties,
with BIM systems, an object can update itself as the context changes. This is described
as the object’s behavior. The level of 3D modeling required, instead of
modification of objects, is what differentiates different BIM practices.
In
the beginning of 3D modelling, two methods competed which are B-rep (boundary
representation) and CSG (Constructive Solid Geometry). With B-rep, shapes were
created and Boolean operations were used to overlap, subtract the shapes and
other functions. This is called rendering. Extrusions and rotations of 2D
models could be used to produce 3D models. With CSG, shapes were described using
text strings. The two methods competed for years but modern “BIM models incorporate
both methods.” (Page 34) CSG is used for editing while B-rep is easier for
visualizing and measuring.
As
modelling evolved from CAD into parametric modelling, one factor that was
included in this evolution is the “recognition that multiple shapes could share
parameters.” (Page 37) The advantage to this is that if the size of the wall
changes, the other shapes in contact with the wall should be able to update to accommodate
for the change in the wall size. This has definitely made design easier and
more practical: designing a building with thousands and thousands of objects
without a system that allows for low-level automatic editing would time
consuming. It also makes the model more accurate if the designer can trust that
a change in one object will not lead to a gap/error in another part of the
building.
In
addition to discussing why BIM is important and the advantages of parametric
modelling, this chapter compared different BIM systems and discussed their strengths
and weaknesses. I was interested in the Revit and Tekla portions. Tekla is a
program that I have never used but was exposed to on a previous coop. The
program can be used for steel fabrication and allows for editing in the form of
trimming members for steel connections. Over time, the program has evolved to
include the design of precast concrete, reinforced concrete, and timber. Its
main strength is that it is able to model structures that incorporate a wide
range of building materials.
Through
this chapter I was able to acquire a deeper understanding of how far 3D
modeling has come from just using extrusions to create 3D-shapes, to being able
to monitor the development of different shapes in a building.
Comments:
Matt:
Great post Matt! It's great that you have experience with Revit and therefore are able to understand most of the handbook (which is more than I can say for myself). Your pictures are great as they explain in part what the handbook outlined. Maybe you can discuss other programs that were mentioned in the handbook such as ArchiCAD, Tekla and others. How do these defer from Revit in terms of BIM capabilities, in your opinion?
Stephen:
My coop was also similar in that there seemed to be a transition from from Autocad to Revit. There were two BIM modelers, their job required them to be Revit experts. They were also great at Autocad because most of the engineers were only proficient in Autocad and if they wanted to explain a connection, they would draw it in Autocad and send it to the BIM modelers.
Michael:
I agree that this chapter makes it seem really important to become more proficient with Revit. Like you, reading this helped me understand why BIM programs are so useful.
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