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Modeling Technology for Building Engineers (AEC Insight Column)
1 Aug, 2008 By: Jerry LaiserinA specialized BIM workflow suits structure and building services.
Much of the initial attention paid to building information modeling (BIM) technology has focused on architectural design and the architect's workflow. It can be traced back to the earliest published work on the tools and methods that we now know as BIM, such as Chuck Eastman's 1975 architectural journal article titled "Designing with Computers Instead of Drawings." The concept then, as now, entails architects designing, documenting, and delivering their projects through internally consistent, multidimensional computer models rather than potentially inconsistent 2D paper drawings (or their digital/CAD equivalents).
As the architecture profession struggles to adapt to the radically different design workflows and business processes required by computer modeling, the engineers who serve architects and architectural projects face a different set of challenges. Whether engaged in structural design or building services design (mechanical, electrical, and plumbing, or MEP), building engineers' design and documentation workflow traditionally has differed from that of their architect colleagues.
Much of building engineering work starts with information imported from architects' design files, whether in the form of column grids for structural design or reflected ceiling plans and the like for MEP design. Building engineers then use the architectural information (primarily building geometry) as input for analysis programs (whether of structural loads, heating and cooling loads, or the like). The calculated results of these analysis programs typically are applied to the sizing of engineered components, whether structural members, heating and cooling systems, or other building equipment. Engineers then may aggregate loads and size connections such as structural joints and MEP distribution systems, then detail the actual elements in which the discipline-specific design is implemented, such as structural framing elements, ductwork, piping, and so on.
As practiced in the United States, several steps in this process might be performed by engineers working with or for construction subcontractors or fabricators.
Multiple Tools, Multiple Models
The notion of a single BIM modeling tool serving the needs of a building engineer, whatever discipline, simply isn't applicable in the same way that a single model-authoring tool can serve an architect's BIM needs. In most instances, especially in the Autodesk and Bentley BIM model-authoring suites, the structural modeler and the MEP modeler or modelers are software tools that serve more as containers or carriers of architecture-derived information used in engineering analysis. Although the transport mechanism of, say, Autodesk Revit Structure, may represent some degree of innovation over the traditional transmission of column grids by 2D drawings, the subsequent workflow surrounding analysis, sizing of members, and so on often is unchanged or only slightly changed from traditional practice. Ironically, many engineering analysis tools were model-based long before architects began to adopt model-based design for their own processes.
In fact, one of the key roles played by programs such as Revit Structure and Revit MEP is the reformatting of building information from the architectural model-authoring tool (Revit Architecture) into a an arrangement suitable for input to pre-BIM and/or BIM-adjacent engineering analysis tools.
In an architectural BIM model, for example, a column typically appears as a spatial object composed of the actual structural element (steel, concrete, or timber) surrounded by appropriate fireproofing and/or blast-proofing and its finish materials. In a structural analysis model, however, that same column most often is represented by its centerline as the basis for the application of loads and forces. Similarly, the representation of concrete in an architectural BIM model-authoring tool typically omits reinforcing steel within concrete elements and treats an entire concrete structure as if it were a single, monolithic element, rather than a composite assembly made of numerous lifts and pours.
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About the Author: Jerry Laiserin
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