Cadalyst Labs Review: Autodesk Revit Structure 3

Physical and analytical models link bidirectionally with third-party analysis software

Last year Autodesk introduced Revit Structure, a new tool designed to improve the way structural engineers, designers and technicians work. For those unfamiliar with the product, Revit Structure is Autodesk's BIM (building information modeling) application for the structural design team. Revit Structure is a multimaterial (steel, precast, cast-in-place concrete, masonry, wood, etc.) modeling tool for structural design, analysis and documentation. It integrates the physical model (for layout, coordination and documentation) with an independently editable analytical model and enables bidirectional linking with industry-leading analysis applications.

The physical model is made up of beams, walls, columns, slabs and isolated and continuous footings. The analytical model is a simplified representation of the physical model in which all the members line up, even if their geometries don't. The analytical model also contains the external loads input by the user as well as point, line and area loads or any load case, such as dead, live, snow or wind, that can be defined in Revit Structure. Users can also specify load combinations. The analytical model includes material properties and release conditions for the structural analysis.

Revit Structure's parametric change management system helps coordinate any analysis changes throughout the design and documentation process. When working in Revit Structure, a change anywhere becomes a change everywhere. For example, you can change the size of a structural member in a 2D model section or detail view, and the 3D model and schedules update accordingly. Make a change to the 3D model, and the 2D model views and schedules update.

This capability also means that you can model in 3D, create 2D model views and schedules, and send the model to your analysis software and bring the changes made in the analysis software back to Revit Structure with far fewer coordination problems. With Revit Structure, you can model from scratch, use 2D architectural backgrounds (AutoCAD, Architectural Desktop and MicroStation) or link directly to 3D models from Architectural Desktop or Revit Building. You also can work in any view that makes sense. For example, when laying out bracing, you can quickly create an elevation view to create your bracing, and those changes will be reflected in the plan and any other associated views.

Autodesk Revit Structure 3

Highlights of Release 3

Revit Structure is part of the Revit platform of products, and it shares several features with Revit Building and Revit Systems. Since its release a little more than a year ago, Revit Structure has rapidly added new capabilities and features.

Figure 1. Model in Revit Structure 3 and Robot. Revit Structure can link bidirectionally to several popular analysis applications.

Analysis tools and API. Revit Structure's greatest strength is that it creates a physical model and an independently editable analytical model that can be bidirectionally linked with third-party analysis software (figure 1). This bidirectional exchange of data with the analysis program ensures that the model reflects the most accurate structural data. Some third-party analysis applications already linked to Revit Structure include ETABS, RISA-3D, RISAFloor, Robot Millennium and RAM Structural System. Additional links are coming from other vendors as well. See "Structural Analysis Partners".

Structural Analysis Partners

Through the Revit API (application programming interface), Autodesk provides a means for third-party vendors and users to access the Revit Structure model database. The Revit API has undergone significant improvements from the previous release, with the focus on integration with analysis and visualization applications. Key improvements include the ability to access all elements, query and change element properties and create nearly all structural elements. These improvements enable Revit to track and report changes that were made in the analysis software.

With these API improvements, third-party developers will be able to create improved two-way interoperability with their links to Revit Structure. Because each third-party developer writes its own link to Revit Structure, features will vary from one analysis package to another. Depending on the analysis software that you use, you may need to adjust the analytical model in Revit Structure for use in your analysis software.

Figure 2. Unsupported objects are listed and highlighted in Revit Structure 3.

Revit Structure 3 includes new tools for member support and analytical consistency checks. The Check Member Supports tool can be used to find unsupported structural elements. Warnings display in a dialog box, and when you select an individual warning, Revit Structure highlights the object in the model. For example, in figure 2, a structural column is unsupported. The Check Member Support lists the unsupported column and, when selected, highlights the column in question. Similar to the Check Member Support is the Analytical/Physical Model Consistency Check (figure 3). This tool is used to find inconsistencies between the analytical and physical model or within the analytical model. These new tools help warn users of problems with their structural model before it's sent for analysis.

Figure 3. Potential problems with the analytical and physical model are listed and displayed.

I'm often asked if it's possible to start your design process in your analysis software. At the time of this review, ETABS and Robot allow this type of workflow. An improved link for RISA-3D is being developed that will allow you to start your Revit project using your analysis model as the basis for your Revit Structure model. But keep in mind that Revit Structure will make some assumptions during the import process, and they may require you to make changes to the physical or analytical model inside Revit. Other analysis developers are working on similar functionality in their links as well.

Modeling. My favorite new feature in Revit Structure 3 is sloped elements. Beams now have a new end dimension that allows you to offset them vertically while still maintaining relationships between beams and beam systems (figure 4). After you create your framing, you select a beam and specify a new offset dimension. As you change those offset values, the girders, beams and beam systems automatically adjust to the new dimensions. You no longer have to create additional reference planes to build these sloped elements. This system is much more flexible and simplifies the design process.

Figure 4. New beam offset dimension simplifies the process of creating sloped beams.

For those frustrated with the process of extending columns to an arbitrary point, a new attach and detach tool has been added to columns that allows you to select an object to attach to with a choice of attachment justifications. You can either cope or cut the column or cut the target, such as a slab above, to make a hole for the column. This new tool makes it as simple as using an extend or trim tool in AutoCAD.

Drafting and documentation. Revit Structure 3 has improved tools to create and deliver more accurate structural drawings with less effort. Drafting views can be saved to a library and reused from one project to another. Schedules, sheets and drafting views also can be saved to a library or copied from one project to another. You can also copy and paste details from one project to another.

Revit Structure's improved view management system allows you to create new views by importing or linking existing details. These details can be either AutoCAD files or files from any of the other supported CAD formats, including MicroStation. When you create a new view using an existing detail, the plan callouts can be linked to the view, and because of the relationships and parametric change engine, the view is automatically coordinated with the plan callout.

The process of importing and linking details is much simpler than in previous versions, but it's still recommended that AutoCAD details be converted to Revit families or files. If you must use AutoCAD details, linking them is the recommended method. Projects with numerous imported AutoCAD details increase file size and can make the project file unstable.

Advice for AutoCAD and ADT Users

Creating details gets a lot easier in Revit Structure 3. You create new views by defining the location of your section or detail in plan. The new view, based on the model geometry, is then created. Because the detail uses the model geometry, changes to the detail also update the model. All views, schedules, details and drawings in Revit Structure are live views of the building model. This system allows you to make changes in any view that makes sense to you, be it plan, section, detail or even a schedule. You then can use the annotation tools to detail your views as required.

Although it's possible to create fully detailed connections in Revit Structure, Revit Structure is not a steel detailing package. It can, however, export the Revit Structure model to CIS/2 format using a free plug-in created by Robobat. This tool allows all of the steel information contained within the Revit Structure model to be sent directly to any steel detailing software that can read CIS/2 files.

Coordination and interoperability. Revit Structure has added new functionality that allows you to control the way that linked files are displayed. For firms that work with architects who use Revit Building, the Copy/Monitor feature has been improved to monitor walls, floors and openings as well as grids, columns and levels.

Needs Improvement

Keynoting has been added to the Revit platform. It automates the creation of keynote legends so you can easily update the keynote definitions, which in turn update the notation throughout the whole project. You basically create a text file with your keynotes, and this file generally can be edited at any time. I encountered one limitation when I tried to edit the keynote item number. Changes to the keynote description definitely update in the project, but I wasn't able to change the keynote number—for example, from 10 to 12. You also can't add new items on the fly—you have to close and reopen your project for Revit to recognize changes to the keynote text file. This limitation affects the entire Revit platform, not just Revit Structure.

Autodesk Revit Structure 4

Other Additions

New to Revit Structure 3 are the ability to automatically display an obscured item as hidden, two-pick detail components and the entire detail component library from Architectural Desktop. Users now can control linked file visibility, raster images and work-plane hosted families. Dimensioning control is improved. Also new are sort order for details, tags with free leader ends that point in a user-selected direction, 3D snapping and area reinforcement.

Final Thoughts

Revit Structure and the Revit platform in general continue to develop at a truly amazing pace. Keeping in mind that Revit Structure is part of the Revit platform, I think the Revit Structure development team is responding to the wish lists of structural engineers, designers and technicians. I have only been able to scratch the surface of the tools and features that it offers to the structural design team. The value that Revit Structure brings to the table is something that designers should investigate. Highly Recommended.

Patrick Davis is a BIM manager for HNTB in Kansas City, Missouri. He has been a Cadalyst contributor since 1998 and also serves on the board of the Kansas City Revit Users Group. E-mail him at pat.davis@kcrevit.com.