The Importance of Parametrics in Building Information Modeling

The past year's discussion on building information modeling (BIM) has focused much attention on the information technology capabilities available for the design, construction and operation of buildings today. These capabilities are enabled by several key technologies, of which parametric design technology currently seems to be most in the spotlight. So let's take a look at why it's important, and what architects and engineers should expect and demand of their parametric solutions.

In their efforts to incorporate parametric capabilities into their practice and standardize on BIM, architects, engineers and facility managers might ask the following questions:

Where is the old base line?

Simple parametrics have been available for quite a while in tools like Autodesk's Architectural Desktop and now in Revit; Graphisoft's ArchiCAD; and, of course, our own Bentley Architecture, Bentley Structural, Bentley HVAC, and other discipline-specific applications. The ability to define and manipulate graphic and geometric elements, and to control the dimensional relationships between them based on the various parameters of those elements has, in essence, become a requirement in any computer-aided workflow. Most architects and engineers expect these basic parametric capabilities in their design applications, and have incorporated them into their practice.

These simple parametric capabilities have been available for years, continue to improve, and continue to provide great benefit beyond manual CAD for many practitioners in coordinating drawings and automating drafting tasks.

How does this relate to BIM?

So why is parametrics receiving so much attention now?

The growing adoption of the building information modeling (BIM) methodology has raised practitioners' expectations and overall awareness of the value of tools and technologies that offer more informed design experiences.

BIM has also, and perhaps more importantly, highlighted the value of integrating information and graphics within the building model. This value is often easily demonstrated when the integration involves information that directly affects the graphic presentation. For example, changing the value of a parameter for the thickness of a wall, the depth of a steel beam, or the dimensions of a duct will clearly affect the graphic presentation of that item.

Where BIM makes parametrics even more valuable is when the parameters represent more robust design information, and can more effectively inform the model, other elements and the graphic or alphanumeric output. True BIM moves the parametric dialog to the building design information parameters rather than just simple drawing parameters. These design parameters— such as the structural loads on a beam, or a beam's section name rather than just the distance between lines representing that beam on paper—are less abstract to the practitioner's thought process, and more relevant to the design process.

Interaction with these design information parameters, rather than just with drawing parameters, offers exponentially more benefit to the building design and delivery process. Continuing with that beam example, a change to the load conditions on a floor area would demand change to that beam's design parameters, which in turn could change the selected profile, which in turn will change the geometric parameters of that beam in the 3D model, and, of course, in the drawings. This type of benefit is even more profound in multidisciplinary teams where, for example, that beam change can automatically inform the HVAC engineer that her duct no longer fits under the beam.

Simply put, BIM elevates the parametric dialog from just the drawing graphics to the level of design information, resulting in a more effective interaction between the design and its representation.

So what's new and exciting in parametrics?

At Bentley, just as we view graphic parametric capabilities as a fundamental aspect of any CAD system, we view building information parametric capabilities as fundamental to any robust BIM solution.

To that end, Bentley introduces exciting new parametric capabilities aimed at enabling and encapsulating design intent. These technologies are available with the new 2004 Edition of our building solutions: Bentley Architecture, Bentley Structural and Bentley HVAC. These technologies have enjoyed notable success with early adopters over the past two years, and have already been successfully applied on BIM projects around the world.

These enhanced parametrics can be considered in three main areas of interest:

1. Parametric components

Parametric components enable the definition of characteristics, constraints, options and relationships within building components. This contributing technology is essentially focused on items—such as brick, steel, carpet or glass—and can include parameters such as sizes, weight, cost, colors and textures, specification values, drawing characteristics, acoustic properties, fire ratings, thermal properties, etc.

2. Parametric assemblies

Parametric assemblies enable the definition of the configuration, options and relationships within an assembly of building components. This contributing technology is essentially focused on the relationships of and between parameters within an assembly (or nested assembly)—such as doors/frames/hardware, curtain walls, louvers, cabinetry, ceiling grids, trusses, stairs, etc.

In addition, these assemblies have formative characteristics. Elements or nested sub assemblies can be automatically created, removed or even substituted, based on the design intent stored in the parametric assembly definition. The relationships between the elements and parameters within an assembly can range from simple associations to complex mathematical formulae as required to match the users' needs. These parametric assembly definitions can be easily created by users by simply modeling the assembly with our new parametric assembly tools, and capture design intent by automatically inferring relationships and behaviors within the assembly, or by the user explicitly describing them.

A simple example to visualize is a balcony handrail: Assume that balusters will be vertical bars at three inches on center, and that you must have a newel post at no more than every three feet. In a parametric assembly, as you stretch the length of the handrail, the number, layout and position of these components will change to comply with your design intent. Of course the constraints and options can be much more complex and involve many components and characteristics—including substituting components or assemblies, centering items, defining which dimensions are hard and which are soft—and can even include robust formulas and variables. The scale of an assembly could range from a single pane window to an entire prefabricated building.

3. Parametric controls

Parametric controls enable the manipulation of parameters based on robust design rules and formulas. This contributing technology is essentially focused on the use of rules to create parametrically derived geometry. The resulting components are generated by processing the defined rules to control their creation, characteristics, sizes, and placement and are generally of a higher order of complexity than the parameters within any given traditional assembly.

Parametric controls have enabled exciting exploration in form finding, and have been applied to evolve purely generative geometry or to manipulate form. An astounding range and complexity of form can be quickly explored, refined and revisited easily and dynamically within the building information model.

The control parameters can be driven by virtually any information source, such as in response to solar, wind or acoustic analysis, building program requirements and so on, to design the geometry, build evaluative tools, and integrate with digital fabrication.

In all the cases, these parametric definitions can be offered in managed catalogs of materials and building elements, and their parameters edited at placement time, or anytime thereafter. The editing of these parameters may change graphic characteristics such as dimensions, drawing color and style, or appearance in renderings, as well as non-graphic characteristics such as cost, construction schedule, or specifications information.

Who sets the available parameters?

At Bentley, we firmly believe that the definition of the parameters of interest in any given building information model for all components and assemblies should be at the discretion of the project team. Much of the parameter set is predictable and can be anticipated by a given solution, and, of course, it is the duty of each discipline-specific application to make these as accessible as possible in default behaviors and template components.

However, the potential scope of this information and the desired relationships is extremely vast, and as new building materials and systems continually enter the designer's vocabulary, this scope is ever increasing.

Therefore, we believe it is impractical to limit the potential scope to bounds set by those anticipated by the application or object model. The creation of new information parameters, assembly types, or control behaviors should easily support users' needs, and be bounded only by their imagination, and not those of the software provider.

All of these parameters must be stored in open file formats, and be accessible through published APIs to provide complete access and extensibility by the end user.

We don't need to start over, right?

One last thought: the capabilities of any exciting new technology are best appreciated when they are available within one's existing environment. Bentley is committed to the introduction of new capabilities and their underlying technologies without requiring any user to abandon any existing capabilities within our solutions. All of Bentley's BIM solutions, including these exciting enhanced parametric capabilities are available on our unifying platform, and work together.

So for our new baseline…

As BIM is becoming the standard of practice, the importance of parametric capabilities well suited for the BIM methodology is becoming increasingly important. Simple graphic parametrics will not suffice; BIM demands parametric capabilities that capture and empower design intent, support the hierarchical relationships common to building systems, and are open and extensible by the design team.

About the Author

Huw W. Roberts, AIA, CSI, is Global Marketing Director for Bentley Building, a group that provides technology based solutions to architects, engineers, contractors, owners, and operators of commercial and public buildings and facilities. After twelve years of highly successful architectural practice, and two years as director of technology for a leading international AE firm, Roberts moved to the software industry in order to more directly apply his skills and interests in the use of technology in design. Roberts has been a featured speaker at many major industry events worldwide on the best practices for integrating technology into the design, delivery and operational management of buildings, and has been frequently featured in leading industry publications as well. Roberts has also served on many industry committees, on work such as the National CAD Standards, Uniform Drawing Standards, Facility Information Council, and as chair of the AIA Technology in Architectural Practice PIA.

Note: The views expressed in Viewpoint articles are those of the individual authors and do not necessarily reflect those of AECbytes. Also, no advertising or sponsorship is accepted for Viewpoint articles.

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