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Building Design

AEC From the Ground Up: The Building Information Model

31 Oct, 2004 By: AIA ,H. Edward Goldberg

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Is BIM the future for AEC design?

Computers and digital technologies have changed almost every aspect of society, but they've only just begun to have a major impact in reshaping the architectural and building industries. While manufacturing, industrial design, entertainment, and many other areas that rely on design and production have been revolutionized, the effect on construction practices has been small. We still rely on hand labor, work from drafted drawings, and generate schedules and work plans in traditional ways.

Figure 1. Autodesk Architectural Desktop 2005 outputs construction documentation in standard 2D format such as plans, elevations, details, schedules, and specifications.

Even BIM (building information modeling), a methodology for storing complete information about a building in a computer model that is lauded as the newest innovation, is based on a 30-year-old concept introduced by Chuck Eastman, Ph.D., of Georgia Tech College of Architecture and Computing: "Building information modeling integrates all of the geometric model information, the functional requirements and capabilities, and piece behavior information into a single interrelated description of a building project over its lifecycle. It also includes process information dealing with construction schedules and fabrication processes."

3D modeling, virtual buildings, single building models, and other ideas have been used during the last decade or so. These concepts focus on two areas: The generation or extraction of 2D drawings from 3D building models to improve productivity in documentation, and the use of data embedded in objects contained in the model for the purposes of generating schedules and lists of materials.

BIM (building information modeling) extends these ideas from drawing and schedule production to the creation, management, and communication of information about the building—specifically addressing the quality and consistency of that information. Certain inconsistencies are acceptable for drawing production, such as approximate vs. completely accurate area measurements, elements drawn graphically instead of modeled, and components duplicated one on top of the other. These inconsistencies are unacceptable in BIM, however, because they make the information unreliable for use by other team members and other software applications.

www.timberline.com

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Figure 2. Graphisoft ArchiCAD, in combination with the RCC database and Timberline Software (www.timberline.com), can produce a high-level construction estimate.

The building model excels in coordination between multiple design disciplines and in making building information available for use throughout the entire building cycle, including the design, construction, and facility management stages of a project. Depending on the particular need, data can be viewed as a 3D model, as traditional 2D construction documents, and as binary information for output to other programs for energy and structural analysis, estimating, and project management. BIM works on design, construct documentation, analysis, and implementation levels.

Design

Because BIM mimics a real building, some of the real benefits on the design side can be fully realized only when the architect or designer is the computer operator. This issue is getting attention from many of the large architectural firms that have traditionally used CAD as an electronic drafting tool and have structured their practices according to a hierarchy in which a project architect sketches a concept and the CAD operator acts as a scribe. One of the greatest benefits of using a BIM application at the design stage is the ability for the designer to understand the relationships of the building and its systems instantaneously in regard to aesthetic, performance, and program issues.

IN THIS ARTICLE

To be truly viable, a BIM software solution must contain a modeler capable of quickly and easily creating a 3D model. If it takes longer to create the 3D model than it takes to draw the model in three views, much of the design benefit of the software is lost. To this end, the major BIM options—Autodesk Architectural Desktop, Autodesk Revit, Bentley Architecture, and Graphisoft ArchiCAD—all include routines that allow easy modeling.

Analysis

Once a model is created, it can be analyzed for purposes such as structural member determination, electrical and mechanical loads, and, through gbXML, energy consumption loads. Autodesk, Bentley, and Graphisoft are all working to support gbXML with Green Building Studio (www.greenbuildingstudio.com). a free Web service that assists in the energy analysis of buildings in the design stages as well as with the selection of energy-efficient green building products and materials.

Another good example of this type of analysis is in structural engineering with Bentley Structural (www.bent ley.com/structural). or Tekla Structures (www.tekla.com). Both fully 3D parametric structural steel and concrete building modeling software packages that integrate with structural analysis applications. Bentley Structural even offers bidirectional links to analysis applications such as Staad Pro and GT Strudel—keeping the building model, analysis, and drawings all in sync.

BIM definitions

Construction Documents

Construction documentation is normally output in standard 2D format. It consists of plans, elevations, details, schedules, and specifications. Instead, data from the BIM appears as a traditional architectural drawing, but is actually planar views of the building model.

Once these views are placed on pages, interoperability between the different views is of paramount importance. Any changes to the model affect all the different views and, ideally, any changes to any of the views also reflect in the model and all the other views.

One of the top productivity features of BIM software is the ability to generate elevations and sections automatically from the model and have them coordinate and update whenever a change is made to the model (figure 1, p. 56). Another productivity feature now available in most BIM applications is the ability to create and maintain schedules for objects such as doors, windows, and walls. The most advanced BIM applications maintain these views directly as part of the building model, so that changes made in any view directly update the model and other views.

Implementation

The implementation level pertains to using the information contained in the building model. Once the model is created and construction documents are generated, it's possible to cull data from the model to use in special-purpose estimating, project management, and facilities management programs. For example, using ODBC export output, Autodesk Revit and Architectural Desktop 2005 can export information about all of their objects and transfer the information to programs such as Microsoft Excel and Access for manipulation.

Graphisoft ArchiCAD, in combination with the RCC database and Timberline Software (www.timberline.com can produce a high-level construction estimate (figure 2). Bentley's architectural, structural, and HVAC solutions integrate with programs such as Excel or databases so that users can manipulate information and make changes in either program, then synchronize the information with the building model. The AEC community expects to find the greatest gain at the implementation level. It's also in this arena that confusion exists as to who will own, distribute, and take legal responsibility for the building data.

In the Now

As noted above, the major options in the BIM arena for architects are Autodesk's Architectural Desktop and Revit, Bentley Architecture, and Graphisoft ArchiCAD. For engineers, Autodesk Building Systems and Bentley HVAC for MEP (mechanical, electrical, and plumbing) are available. All of these programs perform, to different degrees, those functions that classify them as BIM solutions.

The BIM concept has not been widely implemented, although a few clients such as Disney and the GSA are beginning to ask for BIM projects. However, BIM software is being used on projects around the world. Graphisoft's ArchiCAD was recently used to design the Eureka Tower, an 88-story tower in Melbourne, Australia, known as the world's tallest residential building. The architecture firm SOM is using Revit to create a building model for the Freedom Tower, which will be the world's tallest structure and overlook the World Trade Center site in New York City. Bentley's multidisciplinary BIM solutions are being used on the renovation of the Pentagon, the world's largest office building.

Many architects are still trying to figure out how to be compensated for the enmeshed data that exists in the model. They are reticent, at this time, to accept the liability that may exist if the owner and contractor rely solely on the exported digital data for material purchasing and project management. BIM is clearly being applied most quickly on projects where architects and engineers work for the same company, where a building owner values the building model for proprietary use, and in design/build projects where the liability is shared.

Gaze Into the Crystal Ball

Once all the legal problems are worked out, it's conceivable that the architect or designer could create only the virtual building model and have all other trades take the information they need directly from the model, thereby completely bypassing the construction document phase. For example, the concrete contractor would examine the virtual model for the necessary foundation components and send the quantity requests (over the Internet) directly from the model to the rebar and concrete supplier. The concrete contractor would then have the survey crew lay out the coordinates from the virtual model to the site through GPS-controlled instruments. Any questions could be resolved in the field by viewing the virtual model from any vantage point using portable computers and comparing the model with the actual building. The field personnel might also wear video glasses or virtual monitors so they could overlay the 3D model onto the building under construction.

The future possibilities are endless, but the foundation is centered on our ability to understand BIM.

H. Edward Goldberg, AIA, is a practicing licensed architect, industrial designer, and AEC industry analyst. Ed's book, Autodesk Architectural Desktop 2005: A Comprehensive Tutorial (Prentice Hall) is available now (www.prenhall.com). Ed is also offering real-time Web collaboration courses on how to use Architectural Desktop, VIZ, and SketchUp. You can reach Ed at ed.goldberg@cadalyst.com. His personal web site is www.hegra.org