Integration of BIM with Structural Analysis Software: Some Cautionary Notes

Parag S. Kulkarni
Structural Design Engineer

Since the last few years, BIM (Building Information Modeling) is in the limelight in the architectural arena and is also making headway into the structural designer’s realm. Several BIM applications for structural engineering are available, including Revit Structure, Tekla Structures, and Bentley Structural. Since architects and planners are the ones at the top in the engineering food chain and they benefit the most from BIM, down-the-line structural engineering firms are almost coerced into adapting this new technology. If the project has to be made easily exchangeable between the architect/ planner and the structural engineer, it has to be on an interoperable platform for seamless information exchange.

Going by the latest software versions available today, I find that seamless BIM software integration with structural analytical software is part hype and part necessity. Let us see how. In the current scenario, BIM remains at the heart of the process, and in which structural analysis becomes an offshoot of the larger process. But on the other hand, for structural engineers, structural integrity is the most important aspect of all the project aspects that can be dealt with by using BIM.

Conceptually, the architect builds the model using BIM software, passes it on to structural engineer who runs it in an “external analytical engine.” The model is “updated” back in BIM, which is then used to take the project to completion. But there are caveats in the process. The integration of BIM with analysis tools does not run as smoothly, or in some cases, it does not run at all. In order to identify possible errors, one has to be aware of the inward-outward file sharing between the BIM application and analysis tool and vice versa. When information is sent out from a BIM application to an analysis tool, it is done by means of a “bridging” software. But a BIM model at any stage has numerous entities that are not recognized as they are not necessary in analysis. For example, masonry walls might be present in a BIM model but they are neither recognized by the analysis tool nor are they required to be modeled, as in most cases, masonry walls are plain line loads on the structural member.

In addition to elements not being recognized, distortions can also happen, such as the one shown in the illustration below.  The top image shows a Revit Structure model, which comes from one of the tutorials included with the application. The lower image shows the model distortion that happens when the model is opened in ETABS. The distortion is correctible, but is a distortion none the less. Perhaps as in medicinal advertisements that include warnings and cautionary notes, we also need to mandate warnings from our software vendors about the shortcomings in their applications. Any error that has gone unnoticed, particularly in a building structure, can put public safety at risk.

In the scenario illustrated above, the onus is on the structural designer for accepting or not accepting the model as it appears in the analysis tool. Careful scrutiny is most important and one way of verifying the connectivity is to see the model in wire frame mode. A second check could be to load the model and run it for excessive deflection which might be rooted in joint connectivity.

Here is a list of points every structural engineer should be aware of while integrating the use of BIM with structural analysis:

1. Trade apples with apples. That is, if the structural analysis tool is using an AISC library, do not export European beams from the BIM application to the analysis tool. It will be erroneous.
2. The same is true for export from the analysis tool to a BIM application. For example, if you have concrete columns sized 20"x38" and the BIM application does not have thus column type ready in its library, it is likely to substitute a W-shape in place of a concrete column.
3. Check for distortions. They are very likely in case of curved members, sloping members, etc. Double and triple check for distortions.
4. When possible, do not directly interlink the BIM and analysis models, just tweak the analysis model by itself.

The objective of this article was to make structural engineers aware of the potential problems with integrating BIM and analysis tools. BIM by itself is a revolution, but as structural engineers, we are responsible for the safety of society and we need to exhibit the same responsibility before we get overwhelmed by the current hype surrounding BIM.

About the Author

Parag S. Kulkarni completed his diploma in civil engineering in 1993, followed by a BS from Mumbai University, India in 1996. He worked as a civil and structural engineer for 10 years in government agencies and commercial firms in India, and is currently enrolled in a Master's program at Clemson University with a concentration of Structural Engineering. He is also currently working with a reputed structural engineering firm in Greenville, SC, and maintains a keen interest in civil/structural related softwares and emerging technologies. He can be reached at: paragskulkarni@gmail.com.