Wednesday, August 8, 2012
Is your BIM score over or under PAR?
In golf we keep score relative to par; the number of strokes that should be required to complete a hole.In BIM I like to think of PAR as a breakdown of how valid our building model is, or can be, at any time in its development.
PAR for your BIM consists of three factors:
Let's break down the BIM game a bit and see how these three factors can help us achieve a better BIM score.
Precision; by default everything we model in Revit is precise. It is modeled full size using real world dimensions and those distances are measured precisely. Sure, we always have the option to round off values and display dimensions with less precision but internally the objects we place in our model can only be the size they are. We can create a beam in our model that is precisely the size it will be when delivered to the site.
Accuracy; the beam is precisely the size indicated but is it modeled in the correct location? Does it accurately reflect the actual size of the intended beam. That's the difference between precision and accuracy. If we model a W250 beam and create it with a depth of 410mm it won't be an accurate representation of the W250 beam. If we need to locate that beam in our model we can measure its location down to the mm but if we measure from the wrong point the location will not be accurate or may not meet the requirement.
Reliability; so now we have a precisely modeled beam accurately modeled and located. All that's missing is confirmation that it's the correct beam (size, strength, material, connections, fastenings, etc.) and that it's in the correct location (elevation, bearing points, not in conflict with other elements, etc.). This is where the reliability of our BIM comes into play.
Reliability can be attained only by making choices. The degree of reliability is in direct relation to the finality of those choices or the information at hand when the choices are made i.e. a decision! So how can BIM assist in improving that decision making process? Along the way, on every project, we will be required to make choices. Too often these choices might be based on limited or incomplete information. When that decision is required we try to choose the most likely option. By testing our models; for code compliance, for constructability, for energy utilization, our BIM can help inform us on what those options are and allow us to decide what may be the best choice. With a little forethought we can anticipate when those decisions might be required, include the appropriate information in our model and try to reduce the likelihood of needing to make decisions without sufficient information. If we do nothing until we have all the information we may never get anything done. The reality is we don't need all the information but we should always plan so we understand 'what is the least I need to know before I can make an informed choice?'.
Too often when we begin the development of a building model we jump to precision before we have any accuracy or reliability. Ideally BIM is most productive when it is undertaken as an additive process; beginning with what we know and leveraging the work we have done getting to where we are. The concept of placeholder elements does not require precision to inform or communicate intent. It should strive for accuracy and be the foundation for obtaining reliability. The earlier we can make our information reliable, the more accurate we can make our model. Once we have that reliability we can then add the appropriate level of precision. Over modelling is just an inappropriate level of precision (detail). So what defines inappropriate? If it’s not required to convey design intent or doesn’t contribute to the uses or value of the model then it’s inappropriate. Remember, a perfect solution that does not solve the problem or serve the purpose is still the wrong solution.
Just as in golf, you can achieve par more often when you make the right choices, minimize frustration and develop a good game plane to take advantage of the skills you have.