Mark Robison, P.E.

Summary: The following is a step by step introduction to designing and communicating ideas with 3D BIM.

There are many different ways to approach designing systems for a 3D BIM coordination model. I have found that the best way to create a 3D model is to start by designing in 2D, the way you normally would. Once you have the basic design in, all you have to do is add a third dimension. By breaking up the drawings by floor and by system you are giving yourself the flexibility to both have a 3D model which can be exported and a 2D plan which can be plotted. Splitting it up in this manner also helps with file size. Working with a model of the entire building will slow down all but the fastest computers. Another benefit to having both your 2D and 3D plans in the same drawing is that when you have to make a change, you only have to make it to one drawing.

The process of constructing a 3D model obviously begins with designing it, but at some point you are going to want to see how it fits together with everyone else’s models. The first step to is to export the 3D work on each floor of each system. If you are using Design Master you would click on the export 3D button. AutoCAD users can use the WBLOCK command to export their work. Next, you need to compile all the systems of each individual floor together into a single model. To do this I created a file for each floor of the building and started XREFing in the exported models which corresponded with that floor. Once this is done, you are left with a full MEP system separated into floors. The next step, is to go into each floor and adjust the orientation of the XREFed models so they all line up at the insertion point. Then adjust the ‘Z’ coordinate so the model is elevated to it appropriate location in the building. You should be left with a full MEP model for each floor, which, when compiled into a model of the whole building will snap together seamlessly.

One practice that is becoming quite common is group meetings between the different trades involved in creating a building coordination model. The building coordinator, who created a single presentation model comprised of each trades model, will share the model with all the designers involved in the project. This allows the different trades to see what each other have created and to work through conflicts in the design. The meeting can either be held in a single physical location or over the internet with a service such as GoToMeeting or WebEX. Either way, a projector is generally used to show the 3D model which is being manipulated in a BIM program such as NavisWorks JetStream. The participants in the meeting should also have 2D plans on the conference table for quick reference. If you are partaking in the meeting from a remote location you will need a speaker phone to join in the discussion.

Once the meeting is complete, you should have a list of changes you will need to make to your model before the next coordination meeting. This process will repeat until each trades model fits together without any conflicts. Then the physical building can be constructed.

Summary: Introduction to the concept of Building Information Modeling in contemporary engineering.

In the visions of the future, 3D-BIM starts at the concept phase and is carried through to the construction documents and beyond. That is the future, perhaps. For today, we still “design” using a range of tools including arm waving and architectural flimsy, you know, that tracing paper architects always have. I recall watching an architect working with a client over a set of plans. The architect grabbed some flimsy and drew a rectangle, laid it on the plans, and asked, “A room about this size?”. He then tilted the room at an angle and exclaimed, “In fact, this is how it should be”. The client nodded in concurrence and the design process continued.

Someday the computer will be as fast as flimsy, but it is not there yet. But as the design moves from flimsy to CAD, the process turns from “design” to “construction document” creation. And at some point it is appropriate to add detail to the elements toward being a 3D-BIM. I’m sure the creators of Revit and ArchiCad would cringe to hear me say anything but that the process should begin immediately, but that is why we have blogs, so people like me can share real life experiences.

The fact is that there is still both a culture of transition and a practical basis for that culture that does not match full 3D-BIM at the start of a project. I don’t think anyone should apologize for this condition. Don’t be thinking that you are somehow failing to keep up with technology just because you find it easier to think in stages. The human mind can only solve so many problems at once. In fact, don’t we often teach the concept of breaking a tough problem into smaller, easier problems, and solving each one separately. So rather than trying to think of door swings and egress path lengths at the start of a concept design, an architect draws big mass blocks and space planning diagrams. The door swing and lock set details would just get in the way of some really challenging issues. Likewise, working in 2D removes one dimension from the problem during a system layout. The third dimension can be added later after the engineer has the plane solution figured out. When you think of it in terms of dimensions, and time being the fourth dimension, you would never try to solve all four dimensions simultaneously. The fourth dimension is called “means and methods” for the contractor, and engineers are not suppose to address that issue. Of course, at some point it is good to think about that dimension, because sequence is of huge concern to the contractor. But even within design/build contractor organizations, there is generally a separation between the design phase and the shop drawing (third dimension) phase. And then further separation between shop drawings and project sequencing. (fourth dimension)