BIM and Civil Engineering (1-2-3 Revit Tutorial)31 Aug, 2007 By: AIA ,Rick Rundell
Modeling for building design and civil engineering with Revit and Civil 3D.
Autodesk recently announced that the number of users of its 3D model-based software has passed the one million mark. Although 3D software for mechanical design, such as Autodesk Inventor, has been standard in the manufacturing industry for many years, the one-million-users milestone couldn't have been reached so soon without the growing adoption of 3D in the form of building information modeling (BIM) across the AEC industry.
With this growing adoption, architectural and engineering teams using BIM are seeking partners in related disciplines who can support this way of working. Take civil engineering, for example. The Revit family of products, purpose-built to support BIM for building design, doesn't directly support civil engineering design needs for building sites, subdivisions, roads, utility systems, and similar projects. How can civil engineering businesses best support design projects using a BIM workflow?
AutoCAD Civil 3D is the answer. Through an integrated, dynamic model that links design and documentation, Civil 3D delivers consistent, coordinated, computable information about civil engineering projects very much as Revit does for a building project. This month's "1-2-3 Revit" installment explores the synergies between BIM and civil engineering.
BIM and Civil Engineering Working Together
Model-based design isn't new to civil engineering by any means; consider the prevalence of coordinate geometry (COGO) and digital terrain model (DTM) applications. What is new is the concept of linking the civil engineering model environment (the design) and the drafting environment (the documentation).
Through this dynamic model, Civil 3D automatically coordinates the design and the drawings. When one aspect of the design changes, other related parts of the design -- including labels, annotation, and other documentation items -- automatically update to reflect that change. For example, when the elevation of the surface model changes, the contours and profiles for that surface update automatically, as do the contour labels, reporting, and spot elevations relating to that surface. This capability will be familiar to BIM adopters -- change management is at the heart of BIM.
Let's look at an example of a BIM workflow using Revit and Civil 3D: an office building project that could be potentially derailed by two major changes.
Revit and Civil 3D in a BIM Workflow -- Early Design
In our Revit and Civil 3D example, the architectural and the site designs are brought together early in the process -- enabling both firms to better visualize and coordinate their designs. Design data is exchanged between Revit and Civil 3D by using DWG files.
For example, the architect exports early conceptual building shapes from Revit in DWG format and sends it to the engineer, who xrefs them into the Civil 3D model. The resulting building envelope and preliminary site model is easily communicated back to the architectural firm for schematic design by sending the Civil 3D model (as a DWG file), which can then be imported back into Revit.
Design data is exchanged between Revit and Civil 3D by using DWG files. Above, a Revit model is exported to an AutoCAD DWG file. Below, a building model is xrefed into a Civil 3D model.
In our project example, the owner has an aggressive schedule for the new building and wants to fast-track the project, so the engineers create a preliminary design with all the site grading based on the location of the building envelope. The preliminary site design is nearly complete when the first major project change occurs. The owner needs to increase the building size, which affects both the building envelope and preliminary site design.
The architect using Revit revises the building information model, and all the documentation automatically updates. The revised building information is exported to a DWG file and sent to the civil engineer, who simply refreshes the xref to see the revised building and then updates the site model and grading design to accommodate the larger building. Like Revit, Civil 3D automatically coordinates the design and the documentation, and the affected drawings automatically update.
Civil engineering firms using Civil 3D can work in concert with a building team using Revit to quickly update and reconcile design changes, such as the increased building footprint shown here in this before and after sequence. Note the original building footprint is shown in blue in the top two images, and the revised footprint is shown in orange.
Revit and Civil 3D in a BIM Workflow -- Detailed Design
As the project moves into detailed design and then construction documentation, coordination between the architect and engineer becomes particularly important. The engineers create their construction documents using the architectural backgrounds and vice-versa. When the MEP engineers begin their work and need to tie the building mechanical systems into the preexisting town services (water, sewer, drainage, and electric), the coordination becomes even more critical. The high-fidelity model information from Revit and Civil 3D is easily shared among all these participants through the use of DWGs.
Remember that this project is fast-tracked, so the construction document (CD) set for the site excavation is issued while the rest of the project is still in design. That's when the second major project change occurs. Early site excavation reveals a large amount of contaminated material that must be removed and hauled offsite -- in more than 200 truckloads! But, the owner wants to forge ahead with this particular site, so the engineering firm decides to slightly lower the elevation for the whole site (generating additional excavation material so the owner doesn't have to purchase and haul in new material). Time is crucial at this point, as the contractor is charging the owner for downtime while the site is being reengineered.
The engineering firm uses Civil 3D to quickly rebalance the cut and fill for the site and calculate how much they need to lower the entire site. When the Civil 3D design model is updated, all the related objects and annotation are updated as well. All the contours, the spot elevations, the building's finished floor elevation, , the utility profiles, the pond volumes, and the earthwork volumes -- they are all updated without manual intervention, producing a consistent, coordinated site design and documentation set. In turn, that high-fidelity site information can be communicated back to the architect easily via a DWG file for incorporation into the building information model to vertically coordinate the architectural design on the revised site.
Revit and Civil 3D Together
The core concepts of BIM apply similarly to building design and civil engineering. Through the creation and use of coordinated, internally consistent, computable information, BIM is revolutionizing how technology is used throughout the AEC industry and transforming drawing-based processes to model-based processes. Civil 3D supports this way of working for civil engineering, resulting in faster design, higher quality, better coordination, and ultimately a better performing project.