Guest editorial by Alexander Yampolsky
Several generations of builders over the decades failed to construct buildings whose commissioning would result in an industrial revolution. In such cases, errors were looked for in the design; below is an overview of what I consider as errors in BIM design.
Collaboration based on models; the death of drawings
BIM fans list numerous drawbacks to drawings and so call for a cultural shift by refusing to collaborate on the basis of drawings in favour of collaboration on the basis of models. Collaboration is based on understanding, and essentially the question is, “Which do we understand better?”
- Realistic photos -- the output of BIM-style programs; see figure below
- Conventional images and text in drawings -- "circles and sticks", i.e. linguistic references to knowledge (linguistic means of communication)
I am a structural analyst. I formalize analysis results as simple drawings because I am sure that it is possible to explain or understand something using only the language of drawings.
If someone requires the report as a 3D model, should I immediately attend training?
If you do not understand drawings (the professional designer language), it means that you don’t understand textbooks, building codes, regulations, and common instructions. If you see them only as “circles and sticks” then what sense is there in collaborating with you? The reason is that people who do not understand “circles and sticks” is that they left drawings and are not going to return to them.
Single model, single source of truth
Models sound attractive, but do not operate in practice. For example, the figure below illustrates an intermediate stage when designing a fixed-end arch.
The model comprises a pair of foundations and five units (of eight in total) of an arch body. Yes, the model is true in terms of the location and dimensions of these elements. But the intermediate model will misdirect us when we want information about forces at the points where the arch rests on the foundations. Based on the false information, we will construct foundations and end up with a dangerous structure.
The shape and dimensions of foundations correspond to real forces. Where did the designer get the correct information? Probably, the structural analyst created his own highly specialized model, even before creating the "single" model, then calculated the forces and configured the foundations. See the figure below.
The analysis model is a source of lies in almost all aspects and a source of truth only in one aspect: forces in its elements correspond to the real state of the arch during its operation.
The postulate about the single model does not take into account that any bounded system where all elements are interdependent) becomes the universal source of truth only after it is completely built, i.e., after completion of the design stage.
In the design stage, designers are forced to use many highly specialized, partial sources of truth. And this applies not only analysis models; the knowledge necessary may be obtained from reference books, standard construction practices, and similar projects.
Extracting drawings from models
Let's create the reinforcement field drawing in traditional way:
CAD Step 1. Draw a dashed outline, draw a bold line, draw a callout line, write text (diameter, steel grade, rebar spacing). The drawing is ready; see figure below.
Now do the same using new technology: create a model with BIM.
BIM Step 1: Select the command Reinforcing by Area, draw a contour, and specify properties (diameter, steel grade, direction, rebars spacing). The reinforcement field model is ready. Let's extract the drawing.
BIM Step 2. Adjust the view parameters, adjust the object visibility (only one rebar should be visible), draw an annotation (diameter, steel grade, rebar spacing)., draw an annotation. The drawing is ready. We arrive at the same drawing as in the figure above, but using much more resources and tools.
When comparing CAD 1 with BIM 1, we see that the designer entered the source data (parameters) in both cases following approximately the same approach to create the reinforcement field model. However, the source data are just saved as a drawing in case CAD 1 while they are processed and transformed into the reinforcement grid in case BIM 1. So, here is the algorithm of new technology:
- Source data entry by the designer
- Model generation based on source data
- Extraction source data from the model
If this is a breakthrough, then it is one that breaks through into the realm of absurd.
It would be easier to extract source data from the drawing, create the model, and calculate the specification -- and all of this can done automatically.
[This article first appeared on the isicad.ru CAD news portal. Mr Yampolsky also authored "A Third-generation 2D Editor" on WorldCAD Access and "Interpreting 3D Models from Formalized 2D Drawings" on upFront.eZine.]