2D or 3D: Do You Really Have to Choose?

The M/E Roundable in our May 2002 issue focused on issues of CAD development and usage. This Deep Link, supplied to us by the folks at Autodesk, offers their take on CAD development, focusing on the advent of "model-based design."

By Autodesk, Inc. May 17, 2002

The M/E Roundable in our May 2002 issue focused on issues of CAD development and usage. This Deep Link, supplied to us by the folks at Autodesk , comes from one of their reports on CAD development, focusing on the advent of ‘model-based design.’ This is an excerpt of that report.

Over the past 10 years, building design technology has been focused largely on an important transition, from automating traditional 2D drafting processes to the development of more sophisticated models as the basis of design. This transition has brought some valuable benefits to the building industry: improved coordination of drawings, speedier communication of design alternatives, and reduced field rework. Yet 2D and 3D methods need not be mutually exclusive, even in the context of a single project. Our most successful customers achieve this end by using a combination of methods in a technique that we call model-based design.

What Is Model-Based Design?

In model-based design, you create a data model of a proposed facility from which you generate work products such as massing models, space plans, space-planning reports, conceptual presentation models, design development drawings, and construction documents, which might include plans, elevations, sections, schedules, reports, and presentation graphics. Each of these deliverables is created from a central data representation of the building itself.

By employing model-based design methods, building industry professionals can create a more complete building model that includes important nongraphical data, 2D and 3D geometric data, and information about functional relationships, such as the association between a wall and the doors and windows that penetrate it. This improves coordination between the various work products and disciplines in the project. The digital design data that is generated from the building model not only supports design and construction phases but can also be used in downstream project phases to support the complete life cycle of a facility.

With a model-based approach, the amount of design information created is consistent with the design process stage. A wall representation, for example, may be a single line during schematic design, a double-lined wall of unassigned construction type during late schematic design and design development, and a fully detailed wall or partition type during construction documentation, without reentry or multiple inputs. The wall object in the model is simply modified to contain the level of design information detail consistent with the process stage. And the data model evolves accordingly; a design phase transition no longer means starting afresh with new drawings and deliverables. This evolution reduces the possibility of coordination errors, and makes graphic representation of objects consistent throughout the design deliverable set.

Benefits for Designers

For designers, overall project quality is enhanced by improved coordination not only among plans, elevations, sections, and schedules, but also between disciplines. For example, when the building model is shared across disciplines, 3D functionality can be used to easily identify interferences between electrical and HVAC systems. Since all disciplines are working from the same building model, interdisciplinary coordination is improved and potential problems are solved well before construction. The same design data, used in 3D, enhances visualization of the building design to better communicate with clients and others, helping to ensure that the resulting building satisfies client expectations.

To illustrate, let’s take an example. The Two Rivers Middle School, designed by DuBose Associates of Hartford, Connecticut, is a new science, technology, and math educational facility. The project is a three-story, 120,000-square-foot building on a challenging, irregularly shaped site. The design needed to resolve competing design objectives, such as providing sweeping views of the neighboring rivers and wetlands, maximizing natural light, and creating a flexible learning environment. A joint effort of five school districts, the project required swift and effective communication of various design proposals to a broad and diverse audience. By using the latest technological tools, DuBose executed the project successfully.

DuBose chose a model-based design approach using Autodeskr Architectural Desktop. The ability to coordinate with an extended project team, including four consulting firms, was a key factor in the success of this project. Kirk Johnson, Project Architect, commented that ‘The toolset in Architectural Desktop allowed us to seamlessly exchange data bidirectionally. Each firm utilized the same model file by overlaying their respective work onto our threedimensional floor models. The process was actually quite simple.’

In addition, the model-based design approach gave DuBose Associates tremendous flexibility in communicating design recommendations both to the project team and to the client and reviewing agencies. ‘Without the adaptability of the Autodesk Architectural Desktop modeling tools, we simply could not have effectively illustrated the building geometry and design features to our clients in a timely fashion,’ according to Johnson.

Benefits for Builders

Festival Place is af those encountered throughout the building design and construction industry.

Laing, seeing immediate advantages to a model-based approach, designed this project in Autodesk Architectural Desktop. ‘Using a complete building model allows us to alleviate spatial coordination problems because the designers and engineers are working within a single dataset at a 1 to 1 scale, ensuring a process where everything will fit together properly,’ says Richards. ‘Using a 3D model also makes it easier for teams during the design and construction review processes when revisions are more easily and cost effectively made.’

By leveraging model-based design, Laing has already demonstrated a 10 percent saving in total construction costs on previous projects (measurements carried out with government funding) and believes they could save 18 to 20 percent by solving problems before they get to the site. On just one staircase core portion of the Festival Place project, Laing has already seen a 10-to-1 return on investment through reduction of field changes that would have been required to resolve problems that were found by using model-based design.

Benefits for Owners/Operators

Perhaps the most significant opportunity for model-based design lies in the digital design data that can continue to support owner/operator activities throughout the facility life cycle. The data generated from the building model can be applied to short- and long-term systems maintenance, remodeling, resource management, environmental analysis, and a host of facility management functions. These are capabilities not offered by the ‘lines and circles’ of traditional CAD packages.

Process Support for the Total Facility Life Cycle

Autodesk’s current approach is carefully focused on improving design process–from conceptual design, through design development and visualization, to production of construction documents–with the associated goal of producing useful digital design data for downstream use throughout the facility life cycle. This approach enhances communication and collaboration among project stakeholders. But implementing this vision requires that building industry work processes move beyond drafting to model-based design. The larger opportunity to affect process improvements throughout the facility life cycle lies in using digital design data to facilitate the procurement, construction, and ongoing management of the facility.

Employing model-based design methods produces richer, more highly structured data that is useful beyond the design phase. Within this building model, not everything needs to be represented in 3D. A mixed media model will contain elements elaborated in 3D when necessary, but 2D will continue to play a significant role in critical areas, like construction details. The intent is to provide a variety of tools and options that let the user work in 2D, 3D, or both, whichever is more comfortable or appropriate for the desired result, and to support the building design process and overall facility life cycle.

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