Tuesday, 17 January 2012

Enabling Better 3D Coordination

Not too long ago, some in the industry thought that simply by exporting Revit models into Navisworks meant they were performing 3D coordination.1 I firmly believe we are moving beyond this notion towards a more complete offering of coordinated inter-disciplinary model deliverables.

I was inspired to write this article from recent posts by Steve Stafford on RevitOpEd (“Designing Revit Content – What is Interference?”), and posts by Doug Bowers on Applying Technology to Architecture (“Clearance Zones in Revit Families – Part 1 and Part 2”). In their writings, Steve and Doug share some great tips and techniques for architects to generate more accurate clash detection results. Without reiterating their information on this blog, here are some of the key concepts:

  • Overlapping windows will not generate a warning in Revit
  • Know what families have 3D geometry and which consist of 2D linework
  • The door swing shown in plan is only a 2D symbol, unusable for clash detection
  • Clearance zones are not included in Revit door families because the rules can be different around the world

The main issue here is not necessarily about detecting interferences between 3D geometry, but one concerning model validation using implied spatial zones. I use the term ‘model validation’ because this type of checking has a range of uses including code compliance and maintenance clearance validation. Some facility owners are now starting to include such specifications in their BIM requirements. For example, writing the project execution plan for a recent project I found the following requirement:

“Clearances and access: All clearances and access to equipment, valves, etc. must be modeled in 3D and kept in a separate layer and labeled correspondingly.”

If your existing content library doesn’t include clearance zones, you might be in for some heavy duty family revisions as this project gets started.


As an alternative, an intelligent model checking platform can validate many of these rules (but not necessarily all of them). One such program in use at HOK is Solibri Model Checker (www.solibri.com). While this is worthy of future dedicated posts, the fundamental idea here is ‘intelligent model checking.’ What makes this tool intelligent? It utilizes IFC (Industry Foundation Classes) models that ‘understand’ the model parts. Navisworks does a great job in checking the raw 3D geometry, but the system cannot distinguish between various building elements - such as a wall and a door - without user interaction in the form of property search sets. In IFC, the data is generated from a compatible BIM platform and elements are classified according to international standards. As such, Solibri can understand a door and apply validation rules (ADA) to the door without the need to add them into the native door family.


Note 1: “3D Coordination“ is a defined BIM use in the “Project Execution Planning Guidelines.” Read more about BIM use definitions at the Penn State University website (bim.psu.edu). We also encourage you to follow a new blog by HOK’s Greg Schleusner: bimuse.blogspot.com

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