The Importance of AutoCAD in the BIM World
The Importance of AutoCAD in the BIM World
If you haven't been stuck under a rock or hiding in a cave you've probably heard about building information modeling (BIM) by now. According to Autodesk, “BIM is an intelligent model-based process that provides insight to help you plan, design, construct, and manage buildings and infrastructure.” But when you talk about BIM you're usually referring to software such as Autodesk® Revit®, ArchiCAD, Navisworks®, or some derivative thereof.
Although these are tools most often used for BIM, they are not the only tools. Many forget about the AutoCAD®-based modeling tools such as AutoCAD® Architecture, AutoCAD® MEP Fabrication, and the like. Then there's exporting to .dwg for compatibility between external team members. AutoCAD and .dwg, however, are not without their faults as there could be issues with object enablers and loss of information when passing through to a CAD format. We'll discuss AutoCAD's role as a BIM authoring tool, as a conduit for model pass-through, and some limitations of the .dwg format, all while citing tips and tricks along the way! (Throughout this article, you'll hear from our industry leaders who will share valuable insights on how they do things and what they think. Please keep in mind that these are their individual opinions and may not reflect the views of their respective companies.)
I know, I know... depending on your interpretation of BIM, your discipline, and what you're using it for, just about anything can be deemed BIM worthy, or nothing at all. Just take a look at this list of BIM applications and providers, courtesy of cad-addict.com
- Autodesk Revit Architecture
- Graphisoft ArchiCAD
- Nemetschek Allplan Architecture
- Gehry Technologies - Digital Project Designer
- Nemetschek Vectorworks Architect
- Bentley Architecture
- 4MSA IDEA Architectural Design (IntelliCAD)
- CADSoft Envisioneer
- Softtech Spirit
- RhinoBIM (BETA)
- Autodesk Ecotect Analysis
- Autodesk Green Building Studio
- Graphisoft EcoDesigner
- IES Solutions Virtual Environment VE-Pro
- Bentley Tas Simulator
- Bentley Hevacomp
- Autodesk Revit Structure
- Bentley Structural Modeler
- Bentley RAM, STAAD and ProSteel
- Tekla Structures
- Graitec Advance Design
- StructureSoft Metal Wood Framer
- Nemetschek Scia
- 4MSA Strad and Steel
- Autodesk Robot Structural Analysis
- Autodesk Revit MEP
- Bentley Hevacomp Mechanical Designer
- 4MSA FineHVAC + FineLIFT + FineELEC + FineSANI
- Gehry Technologies - Digital Project MEP Systems Routing
- CADMEP (CADduct / CADmech)
Construction (Simulation, Estimating, and Construction Analysis)
- Autodesk Navisworks
- Solibri Model Checker
- Vico Office Suite
- Vela Field BIM
- Bentley ConstrucSim
- Tekla BIMSight
- Glue (by Horizontal Systems)
- Synchro Professional
- Bentley Facilities
- FM:Systems FM:Interact
- Vintocon ArchiFM (For ArchiCAD)
- Onuma System
This is by no means a complete list (some entries may even be controversial), but hopefully it paints a picture of the different players involved that you may not have even considered. The question is, does BIM have to always be represented in 3D? What if you have a pipe that spans several thousand feet? Sometimes it make more sense to represent information in schematics such as P&IDs (Piping and Instrumentation Diagrams). What about details where it makes more sense to represent information two dimensionally? Take Garrett Hardy of Page, who says, "Currently we use CAD for a few different things. Depending on the scale and the complexity of our MEP flow diagrams and one line diagrams we will use CAD to develop and manage them. This is happening less and less now that our BIM template has views set up for these with legends for all of our fittings. We still use it for details, though, and ONLY on drafting views. Anytime we use an old detail we will convert it to Revit and change all the line types and clean it up. Then it will be put into our Revit details library file, then we archive the old CAD detail. So it is still being used to bring in details until we end up going through them all. That is about the extent of our CAD usage at the moment. I know that civil still uses CAD extensively in their BIM process but as for MEP and Architecture, we get farther and farther away from it with each release of Building Design Systems as they add features that reduce the need for CAD."
Construction is where we see other examples of AutoCAD-based authoring tools. The screen shot below (Figure 1) is an example of a federated model that consists of Revit components for the architecture, plumbing pipes, electrical conduits, and cable trays whereas the sprinkler lines and ducts were created in AutoCAD-based applications where each of the disciplines have their own methods of contributing to BIM and virtual design and construction efforts.
Speaking of MEP, Revit 2016 uses fabrication parts from AutoCAD Fabrication MEP in a sort of hybrid approach to further shorten the bridge between AutoCAD-based BIM (that's right, I said AutoCAD-based BIM) and full-blown BIM applications such as Revit. Speaking of hybrid, another widely used method for integrating BIM models has to do with the .dwg format itself.
In the federated model example in Figure 1, the different pieces had to be brought into clash detection software such as Navisworks and because different applications were used in the creation of the models, AutoCAD .dwg is a natural choice as it is most compatible with external applications. Although Revit can export straight to Navisworks via .nwc format, most deliverables also require a companion .dwg so that different trades can reference one another’s work (.nwc is a dead end as far as useful data is concerned.) during coordination efforts. When exporting from Revit to .dwg for coordination efforts, here are a few things to keep in mind:
Set solids export to "ACIS solids" to preserve the integrity of the object properties and geometry as much as possible. If you export as mesh geometry, you'll end up with individual facets for geometry, which are of little use (Figure 2).
Layers: you have the ability to modify and export objects to whatever layers you need or export to consistent layers for certain discipline specific components. To do this, modify the layer settings in the export options so that they may appear as consistent colors. Also make sure to not create any overrides (Figure 3).
The above steps will minimize frustration and extra work to get items represented properly for coordination processes. Then there's the issue with communicating between external team members during the design process. As Cesar Trevizo from PGAL puts it, "More often than not we’ve been using CAD as an export from Revit to share with consultants who use other applications." In these cases .dwg seems to be the most widely used and the most compatible format. Then there are the designers who may find that BIM software may not be the most conducive to a free-flow design process. "With Revit’s lack of user friendliness (the need of a large time investment to become a great modeler) for conceptual design with off-the-wall capabilities like either Dynamo and/or Rhino, which require just as big of a commitment to training as in Revit, it has the experienced designers in a quandary of either keep using CAD, or the large investment of time into software other than Revit for conceptual design. Thus the need for IFC conversion to Revit (even if Dynamo pans out to be a great workflow) as there are technological bounds that need to happen with designers that have been in the game the longest, " says Cesar.
It's great that we have the familiar format of AutoCAD to use as a common ground during the transition to BIM; however, there are challenges which we'll discuss next.
To use AutoCAD as a BIM authoring tool and as a conduit for model pass through are the positive aspects; however, it starts to cause problems when people don't change simply because it's "status quo." Perhaps this is why some feel that AutoCAD should be left out of the BIM equation. I sort of agree, having trained folks on AutoCAD/AutoCAD Architecture versus Revit, there's a common issue with adopting change. It is challenging to learn any new software, but the temptation to revert back to old behavior is too much for some to handle, especially with the pressures of a looming deadline.
However, if there are those who don't want to contribute to a BIM effort, it really causes issues for the entire project team. Take it from Michael Kennedy of Morris-Huitt Zolars, who says, "It is my opinion that the BIM process has little to no room for AutoCAD files. In an environment that is based on 3D and information-laden files, why would it? We are considering charging (reducing fees) for those consultants not engaged in a model as a deliverable service. It takes much more coordination and thereby time to work with AutoCAD files, which are often out of date as soon as we import/link them into our models. We are now seeing less drawings required as the contractors use the model to build from directly. It can be done and in some cases has to be done, but the ARC industry will be better off when all our teams and consultants are working in intelligent 3D files."
Aside from being a crutch for industry progression, there is the issue of preserving meta data when crossing different formats. There are enough issues between BIM applications and an agreement on formats such as IFC and COBie that when you add .dwg to the mix, it gets even more diluted. Looking at an example of properties for an object in a review application such as Navisworks taken from their native application (Revit in this case) versus .dwg export, we'll see that although there may be some information that is retained, much information is missing or lost in translation. This may not be that big of an issue if you're just interested in using the models for clash detection, but until this gets resolved there will continue to be issues with BIM and AutoCAD, not to mention the plethora of other applications out there. However, the advantages of having a common format far outweigh the issues.
When we talk about AutoCAD's role in the industry trends of the BIM world, it's evident that this is a transitional time for the industry and that it is commonplace for there to be a melting-pot of CAD and BIM models. After all, CAD is where it all started and it would be difficult to imagine not having AutoCAD in the BIM world. From BIM in construction, to design to analysis and engineering, there is not one-size-fits-all; however, there is one default format that all players can relate to: AutoCAD. Like it or not, AutoCAD and the .dwg format coupled with IFC standards with LOD specifications and the wide range of BIM authoring tools are what make up our building information modeling landscape today. In order to be successful we should find the best use for all these tools.