1-2-3 Revit: BIM, Structural Engineering and Design

Coordinating structural engineering with the rest of the design team.

This month I examine how structural engineering firms can coordinate their design and documentation with the architect, leveraging digital representations from multiple design sources -- particularly AutoCAD and Autodesk Architectural Desktop. With the wide adoption of AutoCAD and more than 350,000 users worldwide of Architectural Desktop, structural engineers will find many opportunities to use Revit Structure to collaborate with architects using the DWG file format or the intelligent real-world building objects from Architectural Desktop.

Multiple Design Sources
One important aspect of a structural engineer's job is to share information with the rest of the design team, including the architect. To accommodate this requirement, Revit Structure offers a range of collaboration modes:

1. Importing/exporting standard CAD file formats (such as DWG and DXF)
2. Bidirectional linking to/from Architectural Desktop architectural models
3. Linking directly to an existing Revit Building architectural model.

Revit Structure lets firms import and link DWG or DXF files directly into Revit Structure. If you link the 2D CAD while importing it, it remains within Revit Structure as a background and you can refresh it if the architect supplies an updated version. You also can reference imported geometry or convert directly to create new structural components. For example, you can use the lines representing an architectural grid on a DWG file to create a new structural grid either by digitally tracing the lines (referencing end points, midpoints, etc.) or by selecting the appropriate lines and converting them directly to Revit Structure grid lines. Revit Structure will convert 2D wall lines directly to 3D structural walls in a similar fashion (using preset floor elevations to specify height).

Equally important is the ability of Revit Structure to export to these same 2D CAD formats -- not only because this format is frequently needed to communicate back to the rest of the design team, but also because some clients require the delivery of digital-based documentation sets in these formats. Autodesk Revit Structure can produce DWG deliverables just as AutoCAD software can, creating well-organized and layered DWG files using any layering standard the user wants.

Link with Autodesk Building Solutions
Autodesk Architectural Desktop and Revit Structure have an especially strong integration -- bringing added benefits to architectural and structural firms using these solutions together.

The structural engineer still starts with the architect's CAD files, and traces or converts geometry as described above. The structural firm can also import (and link) the Architectural Desktop model directly into Revit Structure, using the architect's model for design reference. And for improved coordination with architects, Revit Structure exports structural components as intelligent building objects native to Architectural Desktop. Structural components in Revit Structure that are not of a type supported in Architectural Desktop (and walls with structural characteristics) are exported to Architectural Desktop as mass elements. So you can share a structural model from Revit Structure directly with an architect using Architectural Desktop -- enabling the architect to review the structural design inside the architectural model and check it for interferences with architectural elements, directly inside Architectural Desktop (figures 1 and 2).

Figure 1 and 2. Structural engineers will find many opportunities to use Revit Structure (above) to collaborate with architects using the intelligent real-world building objects from Architectural Desktop (below).

Similarly, structural engineering firms using Revit Structure can also share models with MEP engineering firms using Autodesk Building Systems, since that software is built on the same technology as Architectural Desktop. Revit Structure can export structural members as intelligent building objects native to Autodesk Building Systems, as described above. When exported, you can use these objects directly in Autodesk Building Systems, enabling MEP engineers to layout their pipe/duct systems within the context of the structural model -- resulting in a better-coordinated design with minimal collision issues. Revit Structure can also import ACIS geometry and building objects generated by Autodesk Building Systems, allowing structural engineers to view the geometry of the building environmental systems within their structural model.

Using Revit Architectural Models
Structural engineering firms using Revit Structure also can share models with architects using the Revit Building software.

If the architect and the structural engineer are in the same organization (a large A/E firm for example) and both have access to the same network, they can work directly on a combined architectural and structural model. Alternatively, they can exchange and cross-link their respective models, much like cross-referencing an architectural DWG file into a structural DWG file, but with far more intelligence. The choice depends on their team organization and preferred way of working.

Cross-linking the architectural and structural models is the preferred means of sharing the models between architects and engineers if both are using Revit-based applications but are in separate organizations without access to a shared network.

The underlying Revit platform includes a monitoring and coordination tool that tracks all the changes that have occurred when a cross-linked model is reloaded or refreshed, and presents them to the engineer or architect in an orderly way for review. For example, the structural designer gets an updated version of the architectural model and is warned that the architect moved a column enclosure that is linked to one of the engineer's structural columns. The structural designer then can choose to respond to that design change directly in the model or to flag it for further action.

Summary
As I've discussed in my last two articles, the use of BIM gives structural firms an integrated modeling environment for analysis and documentation - helping to ensure that the structural design and documentation are always coordinated, consistent and complete. Leveraging existing architectural digital design information and sharing the structural building information model with architects and other engineers further coordinates the building design and documentation -- a winning combination for all parties involved in the design, construction and operation of a building.