07 October 2013

What is the use of BIM Use

In my last post on LOD I touched on "BIM Use" as used in the [US]AIA E203 document. In that post I wondered why certain BIM Uses are not mentioned. But on reflection I now wonder what the concept of "Authorized BIM Use" is, and what it is trying to achieve.

What is "Authorized BIM Use" 

The obvious meaning of "Authorized BIM Use" is the use that elements in a BIM are "authorized" to be used for.

In the [US]AIA G202 document this is described as:
4.4 Anticipated Model Authorized Uses.
Indicate below the anticipated Authorized Uses of Models on the Project, which Authorized Uses will be agreed upon by the Project Participants and described for each LOD in G202–2012.
As you can see each "Authorized BIM Use" is associated with each LOD. So "Authorized BIM Use" is a requirement for properly describing an LOD. Note also that the assumption is BIM Uses are "agreed upon", so they are not necessarily imposed by the owner, but real Uses by actual participants.

It appears the idea is that when you select an LOD level that applies to certain elements, it is necessary to say what those elements can be used for.
I assume this is because the [US]AIA has decided that it is not enough to say that an element is "graphically represented in the Model with a symbol or other generic representation" (LOD100), but must add these definitions:
  1. Analysis. The Model Element may be analyzed based on volume, area and orientation by application of generalized performance criteria assigned to other Model Elements.
  2. Cost Estimating. The Model Element may be used to develop a cost estimate based on current area, volume or similar conceptual estimating techniques (e.g., square feet of floor area, condominium unit, hospital bed, etc.).
  3. Schedule. The Model Element may be used for Project phasing and determination of overall project duration.
  4. Other Authorized Uses. Additional Authorized Uses of the Model Element developed to this LOD, if any, including Authorized Uses identified or required by uses set forth in Section 4.4 of E203–2012, are as follows:

It seems to make sense

So apparently if you are defining the level of resolution or certainty of an element you also need to say for what purposes this certainty applies to.

And the act of defining "Authorized BIM Uses" means that if a BIM doesn't contain information needed for that particular use the BIM author can be forced to provide it via contractual coercion (assuming they signed up for it).

So there are two purposes for including "Authorized BIM Use" in LOD definitions:
  1. defining what information in a BIM can be used for,
  2. ensuring BIM modelling meets the requirements of others.

But is "Authorized BIM Use" rational?

Lets start with the fact that there is a separate BIM Use definition for each LOD. There are 5 LODs (6 if you include LOD350), times 4 BIM Uses for each equals 20 (or 24) separate "Authorized BIM Use" definitions as standard in E203. Possibly more if there are more "Authorized BIM Uses".  That is a lot of definitions.

The next issue is although LOD relates to elements and not the whole model, BIM Uses are usually deliverables that apply to the whole model. That is, for example, a use like Cost Estimating is not done as a continuous exercise, it is associated with project milestones. So strictly speaking there should be different BIM Use definitions per each LOD per each Project Milestone.
Or is this considered unnecessary because there is an assumption an LOD level matches particular milestones? (LOD100 = Concept estimate, etc). Surely not, that kills the concept of LOD not applying to the whole model.

And if a BIM has elements at different LOD levels at a particular time what does that mean for a BIM Use? If a thermal analysis is done and the floor is LOD 400, the walls are LOD300 but the roof is LOD100 what does the BIM Use definitions mean? There are three different BIM Use definitions applying to the analysis. How is that helpful?
Or is the assumption that for a particular BIM Use certain LOD levels must be met. So in the example above floor, walls and roofs must be LOD300 before the BIM is ready for thermal analysis. But doesn't that mean different milestones for each BIM Use will be required? If that is the case why associate BIM Use with an LOD level? Why not just associate BIM Use with a milestone?

So I really don't understand how BIM Use applied to LODs is supposed to work.  But more concerning is how are "Authorized BIM Uses" decided and what their implications are.

Problems with "Authorized BIM Use" in practice

There are a number of issues that arise when trying to apply "Authorized BIM Use" to the real world.

Insufficient Information

As I pointed out above the [US]AIA E203  document assumes project participants will decide what "Authorized BIM Uses" will be for a project. That is fine in theory but my experience with real projects is that not all project participants are on board when the BIM agreement is signed. The architect usually starts before anyone else, the quantity surveyor may be there depending on the contract type, then the consultant engineers, and the contractor doesn't appear till way past the time most have finished their BIMs. So BIM Uses are a guess as to what future participants may or may not want, or be able, to do. And of course there is no-one to offer any expert advice on specific requirements that those BIM Uses may require.

The assumption in BIM agreements is that the 'details' will be worked out later on when the BIM Execution Plan is done. But how do authors progress their BIMs if specific requirements are unknown when they start their BIM? How do they scope the amount of work that will be required so they can work out what their fee should be and how long it will take them?

Restricting BIM Use

There is an implicit assumption that by defining "Authorized BIM Uses" that other uses, i.e. those not explicitly defined, are NOT authorized. Why? Why can't anyone use a BIM for any purpose they like? Why do they need the BIM author's permission?

Certainly some-one using a BIM for their own purposes needs to be confident the information in it is accurate and complete enough for their purposes, but isn't that what an LOD level tells them?

What would the author know

And why would a BIM author (typically an architect or engineer) know what is required for some-one else's purpose? As an architect I have no idea if my BIM is adequate for cost estimating because I don't know what an estimator or their software requires. That is not my area of expertise. I can not warrant that my BIM is "suitable" for cost estimating, my Professional Indemnity insurance won't cover me for it. All I can say is I have modelled elements I am responsible for to a particular standard and they have a particular LOD level.

Other's requirements interfering with my requirements

The inference is that an author's BIM must be "suitable" for other people's particular BIM Uses. But what if the requirements of others prevents the author from using the BIM for their own purposes?
On a recent Linkedin group discussion on Correct Modeling Practices an estimator listed their requirements for a Revit model. One was to model floor penetrations as an "opening object", presumably so their software can extract accurate quantities. But we model floor penetrations with a component that cuts a hole in the floor. By doing this we can tag each penetration, embed what its purpose is in the component's data, and produce schedules of penetrations. All this greatly facilitates coordination, one of our responsibilities. Are we expected to forgo these benefits to fulfill our responsibilities under E203?

Allied with this problem is what if a requirement for one BIM Use conflicts with another Use? The estimator requires penetrations to be modeled as opening objects but the scheduler requires them to be modelled as shaft objects?

What is "Authorized BIM Use" really trying to achieve

Lets go back to the purposes of  "Authorized BIM Use":
  1. defining what information in a BIM can be used for,
  2. ensuring BIM modelling meets the requirements of others.
I believe both these purposes are misguided.

Is it really necessary to define what information in a BIM can be used for? Why do we think we need to restrict what a BIM can be used for? People are coming up with new and novel uses for BIMs all the time. Indeed there may be Uses that don't exist or are impractical when a project that goes for 2 to 5 years starts.

Ensuring BIM modelling meets other's requirements is not practical. Only the user can know what their requirements are, and quite frankly, their requirements may be unreasonable.

What is actually required is a way to ensure minimum modelling requirements are met. That the normal deliverables of an author is provided in BIM form that is known and consistent.
Recognition that it is the user of a BIM who has to work out how to utilize the information it contains, it is not the BIM author's responsibility to provide a "ready to use product".

And there is absolutely no need to tie this in with LOD definitions.  LOD may play a part but there are plenty of other ways to define minimum modelling requirements. Just look to the USACE M3 for a real life example.


"Authorized BIM Use" has no place in LOD. It is not necessary for the LOD concept to work in practice.

It is in fact an example of confusing Level of Development with Level of Detail, or degree of certainty with amount of information. "Authorized BIM Use" in the [US]AIA E203 document is an attempt to define minimum modelling requirements, which is a measure of amount of information, it has nothing to do with degree of certainty.

So what replaces "Authorized BIM Use"? - ways of defining minimum modelling requirements - an issue I think is becoming critical to practical use of BIM.
A topic for a future post.