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Everything You Always Wanted to Know About BIM But Were Afraid to Ask


Petri

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Q. Do you have to work fully in 3D in order to do BIM?

A. No. There are many stages and aspects where 3D is not necessary. There may even be entire projects which do not require 3D and yet you can produce a BIM.

Q. Should we nevertheless work towards implementation of 3D?

A. Yes. In future, at least some parts of your model need to be in 3D: primarily load-bearing structures and the overall envelope, not to forget internal, partitioning walls and any other aspects that are relevant to other designers and various permit etc. procedures.

Q. Is 3D difficult?

A. No. As long as you consider it as a design tool and don't get bogged down by irrelevant details, it is quite easy. Especially if you already have adopted the basic modeling approach, in which for each real-world object in the building there must be one and only one CAD-object.

Q. Oh enlightened guru, what is this BIM?

A. It is a way of thinking. Actually, it means that we can start to think in a natural way, instead of the complex and error-prone process of envisioning, deconstruction of our vision to less than perfect drawings and reconstruction to a distorted understanding of the intention. With BIM, we only need to produce pure data which then transcends to useful information in the way & at the moment required. You can let your spirit be free and just create great designs, instead of preparing drawings.

Well, here we go. Don't be afraid, but ask - the doctor is in. Better still, answer yourself.

Edited by Petri
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Q. In a BIM, are we supposed to model everything?

A. No. Only those aspects that are relevant. What is relevant varies from one project to another. In one, something like rafters (or whatever) need to be individually modeled, in the next one they can be considered as "implicit" and a part of the floor or roof structure.

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Q. Will drawings & drafting become obsolete?

A. No, but their role will change. The world-leading Finnish research project ProIT (initiated & funded, to the utter frustration of Australian carport extension specialist "architects", by the construction & development industry) has established that while plans and sections can (and should) in future be highly generalized as a "Product Model", details are still needed. Perhaps (my assumption) even more.

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Thanks again

How can rafters be implicit in one situation and require to be modelled in another ?

In the modelled scenario, is the rafter modelled once only ? If so, how are its multiples and various positions documented ?

I assume that the BIM Model is somehow less literal than a model one might make of a project using VW's 3d capabilities.

ptarmigan

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Q. How can rafters be implicit in one situation and require to be modelled in another ?

A. If you have a hectare or two of roof, a rafter, similar to every other rafter, can be considered as implicit, ie. a property of the roof structure. However, from the structural engineer's point of view, the rafters may be quite dissimilar. Thereby, some - or even all - rafters may be elevated to the exultated and jubilated state of Objects.

Q. I assume that the BIM Model is somehow less literal than a model one might make of a project using VW's 3d capabilities.

A. Not necessarily. One can create a BIM with unlimited level of detail. One may even end up with a very detailed model without trying, should eg. each and every truss of the two-hectare roof to be different to the Engineer.

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Q. In the modelled scenario, is the rafter modelled once only ? If so, how are its multiples and various positions documented ?

A. When the model is developed to "production stage" and tendering documents, previously "implied" rafters need to be quantified, but that can be done without placing them in the model. The latter may of course be easy enough.

The model is used for costing and similar exercises at various stages, with different levels of information in it.

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Q. Is it silly to model the sill of every window?

A. Yes, it is, unless every sill is different. At most, model the idea, but leave the details to the detail drawings. Give "them" a bit of credit: surely the contractors can figure out which detail is used where, if you annotate them, and can refer to detail drawings without the need of every piece of timber being shown in all 1:100 sections.

On the left of the attached image, we have a BIM-section. This we can, without bloating the size of the model, have for each of the 500 windows, but even that has some redundant aspects. On the right we have the detail - this we only need once.

http://www.imagehosting.com/show.php/1153141_Windowsection.jpg.html

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Q. Are details of wall sections and junctions to floors & the roof needed in a BIM?

A. No. They would serve no useful purpose, except supporting the fragile ego of The Architect.

On the left of the attached image, we have a BIM-section. This we can, without bloating the size of the model, have everywhere. On the right we have the detail - this we only need once.

http://www.imagehosting.com/show.php/1153163_Wallsection.jpg.html

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I'm not sure if VW can do this yet, but it isn't/shouldn't be too hard to get the image on the left to look more like the image on the right, w/ minimal extra time put in.

Simply imbed the higher-level detail in the object. So whenever, wherever you cut through that object, there is the corresponding detail.

There is still some extra 'connection' work to be done, this method just gets you that much closer.

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Simply imbed the higher-level detail in the object. So whenever, wherever you cut through that object, there is the corresponding detail.

There is still some extra 'connection' work to be done, this method just gets you that much closer.

I don't like this way of working at all. It causes too many workflow complexities and potential problems, one of the worst being that it slows down the revision of low-detail drawings/models (because you're having to simultaneously revise the high detail stuff.)

Why produce multiple instances of high detail information in a section when you only need to produce it once in a detail? And why mix high-detail information with low-detail information when you can keep it separate and easier to manage?

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I don't like this way of working at all.

Needless to say, neither do I. Sections of the entire building are "abstractions", not depictions of the actual conditions. At least the sections we know and love.

If one wants to model everything in high detail, where does one stop? Let's consider a stud wall. Does an architect really want to do "wall framing"? If he or she does, does the architect also model noggings and determine where they are higher, where lower? If not, then an arbitrary section may be incorrect: the chippie may have decided to build the wall differently. Perhaps the plastie has asked for a different way of placing studs.

OK - this may be reductio ad absurdum, but so it is supposed to be.

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WOW, settle down,

If it would slow down considerably the program, then it isn't worth it. The program that I learned to do this in, it wasn't a problem, it didn't slow it down. There isn't a huge amount of complexity involved. Simply applying the detail to the object. One plane/layer. It is projected through so that wherever you cut, you can see it. Not that difficult, not that complex, nothing to get worked up over. Like I said, not every nail, just a bit further than Petri showed. There are still more details that need to be added after cutting the 'simple' section. Degrees of complexity.

This brings me to another point.

I downloaded the 'BIM Best Practices' file from the NNA website. It ran incredibly slow. And there wasn't even any structural info in it. Is this file intended to be broken down and referenced multiple times (WGR), or is that it, a large clunky file? Am I missing something?

Here are my cpu specs using VW 12.5.2

Machine Name: Power Mac G5

Machine Model: PowerMac7,3

CPU Type: PowerPC G5 (2.2)

Number Of CPUs: 2

CPU Speed: 2 GHz

L2 Cache (per CPU): 512 KB

Memory: 1.5 GB

Bus Speed: 1 GHz

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