When architects, structural engineers, and mechanical engineers collaborate on a building project, they often share information about the design, so that all teams are working with the same assumptions. By coordinating efforts across disciplines, the teams may avoid errors and rework. Using Building Information Modeling (BIM) tools can help aid in the collaboration and coordination efforts within the entire design team.
Structural engineers can use Autodesk Revit Structure while sharing building information between disciplines during a project. This article looks at the following specific tools: Revit’s two Coordinate Systems – the Project Coordinate system and the shared coordinate system, Linking Revit Files; and Revit’s Model Coordination Tools – Monitoring Changes, Coordination Review, and Interference Check.
Coordinate systems in Revit Structure
Revit has two types of coordinate systems that can be referenced in a model. The Project Coordinates are the primary coordinate location, and are located at the Internal Origin 0,0,0. As with other CAD programs, this fixed location is important when importing and exporting files for coordination. If the Revit Structure model needs to be relocated for coordination with an architecture or MEP model, it can be easier to move the coordinate system instead of moving the elements in the Revit model. In this case, a secondary coordinate location, called Shared Coordinates, can be used.
Both the Project and Shared Coordinate systems can be made visible by displaying the Project Base Point (circle symbol) and Survey Point (triangle symbol). Please note that if the shared coordinate system is not being used, the Project and Shared coordinates are at the same location.
Project Base Point (Project Coordinates) and Survey Point (Shared Coordinates)
The Project Base Point shows the location of the Project Coordinates. The Project Base Point also defines the center of what is known as the “2 Mile Rule,” where any elements modeled must be within a one-mile radius (2-mile diameter) of this point. Therefore, you should make sure to model your building near the Project Base Point.
The Survey Point is used to orient the building geometry in another coordinate system, such as the coordinate system used in a civil engineering file or architecture file. When a shared coordinate system is established, the Survey point is located at the shared coordinate system’s 0,0,0 location. If the Survey Point is moved later in the project, it will move the shared coordinate location. (see below)
If shared coordinates have been established, the project base point’s coordinate values will display the relative distance from the location of the survey point.
Linking Revit files
Linking a Revit file is similar to creating external references in AutoCAD. When the Revit files are linked to the Revit Structure model, any changes made to the original linked file will also be updated in the model. Linking files does not increase the size of the Revit Structure model, but it does require that the linked Revit file remain in the location where the link was originated.
When positioning linked or imported files, this can be done by selecting “Auto-Origin to Origin” relating to the Project’s Base Point, “Auto-By Shared Coordinates” relating to the Survey Base Point, “Auto-Center-to-Center” relative to the center of the current view, or by manually picking the Origin, Base point, or center within the project. (see below)
The location of the Linked Revit Model when it is brought into the Revit Structure model is based on the position that is chosen. For example, if the structural team has not yet started their Revit model, linking in the architecture model can be positioned by using the “Auto-Origin to Origin” option. This way the same project coordinates will be used between the structural and architectural Revit models.
However, if the Revit Structure model has already been created and the files were not started at the same location, one Revit file will need to “rule” as the primary coordinates for the project, while the other Revit models will have to acquire those coordinates. This can be done using the Shared Coordinate system. (see below)
The shared coordinates (Survey Point) can be automatically defined by “Acquiring Coordinates” from a linked file. As an example, if the architect’s Revit model has the primary coordinate system to be used for the project, the structural and MEP teams will acquire the coordinates from the architect’s linked model. Once the architectural Revit model is linked into the structural Revit model, one would move the linked architectural model so that the geometry matches up with the geometry in the structural model (in all three directions). When this is complete, the coordinates can be acquired from the architect’s Revit model. This will ensure that when the architect links in the structural model, the geometry will line up with their host file. Using the shared coordinate system based on the architect’s coordinates eliminates the need for the structural team to move their model. Once the shared coordinates are established, this process does not need to be repeated for this linked file.
The Revit Model coordination tools
Coordination tools can help keep your project consistent between the different disciplines’ BIM models. The Revit Model Coordination Tools include Copy/Monitor, where elements from linked models can be copied into the host project, automatically creating a monitored relationship, Coordination Review, which provides information about elements that have been moved or changed, and the Interference Check, which provides immediate feedback on component collisions. (see below)
The structural team can use the Copy/Monitor tool in Revit Structure to copy/monitor independently or just monitor elements that are being commonly used within the linked architect’s or MEP Revit models. For example, when it is used on a linked architect’s model, it will copy the elements from the linked model into the Revit structure model, and monitor those elements if any of them should change or move throughout the design process.
The elements that can be included in the copy/monitor process include: Levels, Grids, Columns, Walls, Floors, and Openings (Figure 1).
As an example, the structural team can Copy/Monitor the levels and grids from the linked architectural Revit model without having to add those elements individually to the structural Revit model. Any element that is being monitored will display with a monitor symbol, which looks like a break line, when selected (Figure 2).
Note that overuse of Copy/Monitor without thoughtful planning can result in performance degradation, so plan ahead as to which elements are the most important should any changes occur. It should be noted that it is possible to “Stop Monitoring” any element in the project once the monitoring is no longer needed.
When a change is made to a monitored element, Revit will display a list of warnings about the elements that have moved or changed. The actions that can be taken are:
- Postpone: take no action on the element
- Reject: makes no change to the element in the host file
- Accept Difference: Accepts that a change has been made between the monitored elements but no change is needed between the elements
- Modify/Rename/Move: If the element is renamed/moved, this option will rename/move the element to match the monitored element
Another tool that can help with model coordination is Interference Check. (see below) This tool identifies elements that interfere with one another in a project or between the host project and a linked model, and it can be used on all of the elements in a project or specific categories of elements.
As an example, by selecting the beams in the current project, and ducts in the linked MEP project, the interference report will identify any interference conditions between those elements. This report can be viewed in the Revit Project, or it can be exported to an HTML file. Once the situation has been fixed by either moving the beam or the duct work, the tool can be run again, and the interference will be removed from the report.
One of the benefits to BIM is being able to collaborate and coordinate with the entire design team. Software packages such as Revit Structure provide tools that can be used to collaborate and coordinate across all disciplines. While using BIM design applications will not prevent conflicts from occurring, they should allow the structural engineer to enhance their coordination processes.
Betsy Werra of Werra Consulting has been helping structural engineers and structural designers with Revit Structure since its first release in 2005. She can be reached at Betsy.Werra@LearnWithSEU.com. Lisa Willard, P.E., and Brian Quinn, P.E., are with SE Solutions, LLC. They formerly worked for a combined 21 years at RAM International/Bentley Systems and can be reached at Lisa.Willard@LearnWithSEU.com or 805-482-8436, and firstname.lastname@example.org or 616-546-9420, respectively. Visit their technology website, www.LearnWithSEU.com