Revit / Analytical Interoperability

In the fast-paced environment we live in, many engineering firms look for faster, better ways to design, model, and produce documents.  Every major analytical application has its own method for integrating engineering models with BIM.  One such software developer is Bentley Inc., which first developed a product to integrate Autodesk® Revit® with their Engineering software, and has since expanded the software to start integrating with other non-Bentley applications.

What is Integrated Structural Modeling?

What if there were an application that could be used for everything that a structural engineer typically does on a project (Modeling, Analysis/Design, Drawing Development, not to mention those spreadsheets and custom formulas that we all have—either on the network or, heaven forbid, saved to a non-backed-up hard drive)?  Such an application sounds great, doesn’t it?  Unfortunately, an application like that would most likely be extremely complex and not very user friendly.

Well, the application discussed here may not be the one-stop-shop application we would all like, but it does help integrate multiple applications. Several years ago, Bentley developed an application to integrate their RAM Structural Systems software with the Autodesk Revit product.  As they further developed the product over the years, they have integrated it with multiple other products (both Bentley and Non-Bentley applications).  Tekla is just one of the first non-Bentley applications that has been integrated in the ISM workflow.

Figure 1: Overview of ISM Components 
(Bentley Communities: Integrated Structural Modeling, Feb 2017)

One of the advantages of the ISM product is that it gives you the ability to selectively choose what members are brought into the different applications (analytical or BIM).  So, if you change the framing to a single bay you can essentially modify just those members in the repository model.  This is also how you can efficiently round-trip models from Revit to Engineering applications.

Common Workflows

When it comes to the workflows, models can be started in a couple different ways.  These are the three most common workflows that people use to integrate analytical models with Revit (or vice versa).  There are three main steps to integrate Analytical and BIM models, as follows.

  1. Create the Repository model
  2. Import the Repository
  3. Modify / Update the model

One of the most common workflows is for the engineer to start the analytical model in an application such as RAM Structural Systems.  After the engineer has modeled the structure, added the load cases, assigned codes, and analyzed the structure, they will generate the ISM Repository.  Once the initial ISM Repository model is generated, the designer is ready to set up the BIM model by recycling the engineer’s model.  Being able to do this will save tons of time and money for the project team’s budget.  This will allow the team to develop the sheets, details, and sections much faster.  When using this workflow, it is very important that the analytical model is developed as much as possible to ensure a clean model is passed to Revit.  What this means is that when the repository model is generated it must have member sizes assigned so the designer can map basic sizes from the analytical model to Revit families. If sizes can’t be mapped to Revit families, then Revit won’t know what families to use when the repository model is brought into Revit.

The second most common workflow is to start the model in Revit and then generate the ISM Repository from the Revit model.  Once the repository model is generated, it can then be brought into the analytical application to generate load cases and analyze the structure.  After the engineer has analyzed the structure and made modifications, the ISM Repository model is then updated.  From there the designer updates the BIM model from the repository model.  When this process is done (this is called round-tripping the model), it is generally best to just select and bring in the modified members rather than to try pulling the whole model back into Revit.  This approach requires the most communication between the engineer and designer so the latest member information is updated to the BIM model.

The third method (the least common workflow) is a hybrid of the first two methods, where the designer starts the model in Revit, but only defines the grid and levels then creates the repository model for the engineer.  This can be done by either placing the grids and levels in the model or using the copy/monitor tools and utilizing what the architect has defined in their model.

The engineer then creates a new analytical model and transfers the data from the ISM Repository model to the Analytical model where the engineer can then start to build and analyze the model as they typically would do on any other project.  After the members have been sized initially, the engineer updates the ISM Repository model and has the designer update the BIM model.

There is no right or wrong method to setting up the integrated model between engineering and BIM models.  This is something that should be discussed with your firm’s BIM manager and develop best practices when integrating Analytical and BIM on your firm’s projects.

Integrating BIM and Analytical Models

For this article, let’s assume that going from RAM to Revit is the chosen workflow by the project team.  After the engineer has developed their analytical model and analyzed the structure, it’s time to generate the ISM Repository by exporting the saved model.  From the RAM application, the repository is created by selecting the File > Create ISM Repository from the drop-down menu and save it to your company’s standard file location.

One of the keys to successfully generating a clean repository model that Revit can utilize is to make sure that all the modules display green. If any of the modules do not display as green, Revit will have issues when the repository model is brought into Revit.

In the Revit model, clear out the levels that aren’t needed.  When the repository model is brought into Revit, the stories from the RAM model will generate the correct levels in the Revit model.

From the Bentley drop-down menu, select New from Repository from the ISM Revit Plugin CONNECT Edition toolbar.  This will load the interface to connect to the ISM Repository created from RAM SS application.

Locate the repository model on the network, and advance to the next dialog box where you will select the members that you wish to bring into the Revit model (this is the Structural Synchronizer viewer).  On the initial set up of the Revit model from the repository model you will select all members.  After selecting the members to bring into your Revit model, advance to the next dialog box.  This is where you will map RAM sections to Revit families for the conversion process. 

Figure 2: ISM mapping of parts

Once all the members are mapped, the repository model is ready to be brought into Revit.  Depending on the size of the model this may take a few minutes to finish processing. 

Figure 3: Imported repository model

After the model finishes the transfer, you are ready to start developing the project as if it had been modeled in Revit natively (development of sheets, sections, and details, etc.).

Some firms try to bring in the model one time, other firms like to do what is referred to as “round-tripping” the model between Analytical and BIM.

Capabilities and Limitations

With the development of any software there are always things that users expect to be able to do.  Bentley does a pretty decent job of documenting the capabilities and limitations of the ISM application.  Those capabilities and limitations can be found on the Bentley Communities wiki page:

From there you can do a search for the ISM 6.0 (for the latest list of Capabilities & Limitations).  This page will display the limitations of ISM with each of the Bentley Integrated applications.

Keys to Success

As you use the ISM tools more you will find little things to help you develop own best practices.  Following are a few key items that can help you be more successful.

  • Standardize your mapping table and store a copy of it with your firm’s standards.  In this mapping table make sure all categories are pointed to the families you use on typical projects.  This will help you get up and running a lot faster and will also standardize your firm’s process.
  • One would think that the shifting of a grid line would be a change to the model.  Unfortunately, at this time a grid line shifting in the model is not recognized as a change—even though members physically move and connecting members’ length changes.
  • The ISM plug-in was initially intended to be used to integrate the Analytical model with the BIM model.  However, with ISM capabilities in multiple analytical applications there is no reason that the ISM technology couldn’t be used to transfer models to other applications.  For instance, you could use RAM Structural Systems to develop the framing for a building and then use ISM to transfer the building design to RAM Concept to design slabs, or transfer the building model to RAM Elements to design the roof trusses.
  • Being able to round-trip the design model is the ultimate goal that most firms would like to accomplish with the ISM technology.  This is achievable with the Bentley ISM applications; however, there is one major rule that MUST be followed to accomplish this—that rule being that you can’t skip any steps.

Looking at this in more detail, if you started your model in RAM SS and then created the Revit model from the ISM Repository (like in the above example), the tendency of most would be that the framing for a bay is modified at a project meeting.  So the engineer opens the RAM model, re-frames the bay, and updates the ISM Repository model.  The designer then uses the ISM plug-in to update the model from said repository model.  When they update the model they tend to get errors and warnings as the model updates. 

The reason for this is that the team skipped an important step of updating the repository model from Revit.  The issue when skipping a step like this is that each element is assigned a unique ID number when it is initially brought into Revit.  That is how Revit keeps track of members’ placement and other important properties.  If the cycle is not broken, there is a much better success rate in round-tripping the BIM and analytical models.

  • When round-tripping models between Analytical application and BIM, make sure to keep the repository model name the same.  It is common practice for engineers to have multiple copies of a design (this is done to “test” different scenarios of their design during early phases of a project).  When the design is ready to be transferred to BIM, the same file name needs to be used to successfully round-trip models.  Probably one of the first best practice standards that your BIM manager and production team need to address when setting up a standard is the naming convention for round-tripping workflows.
  • Another key to successful round-tripping from BIM to Analytical (or vice versa), is for the engineer to run a “data check” on the model when updating the model from Revit.  This can be a frustrating and time-consuming process depending on the type of structure you are working on.  I have seen the round-tripping workflow work before, but it is mostly in a controlled project environment.  Projects that have typically had the most success in round-tripping the model were simple structures such as MOBs, hospitals, and office buildings.  Where round-tripping has run into complications are industrial facilities where members are slopped more often.  The reason is that the modeling techniques are different in Revit than they are in RAM.

Kenn Farr is the BIM Manager for Teasley Services Group and has more than 24 years of experience in modeling, development, and implementation of technology. 

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