Computer-aided design took a quantum leap forward in the 1980s when the Pro/Engineer parametric design program swept over the world of mechanical engineering. It has taken awhile, but that same change is now slowly taking place in building design.
Originally developed by members of the Pro/E development team and now sold by Autodesk, the Revit parametric building design program is currently going from being a cutting-edge technological curiosity to being the core design program at a number of architecture firms. Within the last year especially, the program has seen a dramatic growth in its user base, though exact numbers are not available, as well as being used on some high-profile projects.
For example, the program is being used by architect Skidmore, Owings & Merrill and its design-team partners to design the Freedom Tower at the World Trade Center site in Lower Manhattan. The Tower was modeled solely in Revit, and a schematic design set, including 132 drawing sheets, was released in September.
At an online presentation about the tower given last October by James Vandezande, an associate and CAD manager with SOM, nearly 30% of the attendees answering an online poll identified themselves as Revit users.
According to Vandezande, the SOM team of approximately 30 people are using Revit for all the structures in the subgrade, plus the tower's cores, structure, enclosure, and cable net structure on top. It's also being used as a documentation tool. Hardware requirements are simply a single-processor workstation with 2 gigabytes of memory. Total size for all files in the Revit models total just 220 megabytes.
"Our coordination meetings have changed from pinning up 2-D drawings on walls in a conference room to wheeling in the plasma screen with a workstation attached to it, opening up the Revit project model, navigating it, and resolving conflicts intelligently, sometimes right in place," says Vandezande. "It has vastly revolutionized the process of coordination and quality assurance in our office. And in terms of energy efficiency, we're using the [Revit] building information model to conform the design process, rather than taking [the design] off-line and waiting for the consultant's energy analysis results."
Overall, Vandezande's team has a "much greater understanding of the design and its constructability based in this virtual building model. At the schematic design level, we have a pretty good idea of how this building will be built. And that's in large part because we're working on the building, not on the drawings."
Last month Autodesk released Revit 8, now known as Revit Building 8, with a handful of important upgrades. New concept modeling tools create the building shell, then offer faces to create walls, roofs, floors, and curtain systems.
Another new feature of the program is an application program interface (API). Critics charged not having one was a shortcoming of the program that prevented third-party enhancements. Having an API gives access to all of the objects in a design. Add-on programs will be able to query properties, extract geometry, change properties, and perform limited additions to a design.
Also added to Building 8 is enhanced model linking, which enables teams working on large campus-style projects to directly link different Revit Building 8 models. Consequently, cross-scheduling between models has been strengthened.
The new worksets option can now divide a building into logical parts, allowing a team member to check out a part, work on it, check it back in, and have changes propagate throughout the entire model. Worksets are a better approach for modeling large, complex stand-alone buildings.
Interference detection, which scans models for conflicts between user-specifiable elements and systems, has been strengthened. And a new design options function allows multiple design alternatives to be developed during the schematic and design development phases. This enables users to substitute any option into the model for visualization, quantification, and other data analysis.
Revit Building 8 now also has the ability to publish 3-D Design Web Format files directly from a model, streamlining collaboration by bringing revisions and markups from DWF Composer back into a Revit model. It can also import and export AutoCAD ACIS 3-D solid models.
Coming later this year is the companion to Revit Building, the Revit Structure program, which is being beta-tested by a handful of users. Revit Structure produces a thorough set of construction documents directly from the structural model and interoperates with other Autodesk products, says Phil Bernstein, VP of Autodesk's Building Solutions Division.
Overall, the trend is that CAD systems are moving away from the raster and vector-based images to object-based information models, increasingly being referred to as building information models (BIM).
And while each of the major CAD vendors, including Autodesk, Bentley, and Graphisoft, offer increasingly sophisticated arguments as to why their latest offering is "the" definition of BIM, the dust has yet to settle on which version the industry will end up standardizing on, if any.