CADENCE AEC Tech News #104 (August 28, 2003)

22 Aug, 2003 By: Lachmi Khemlani

In This Issue: BIM Solutions: Bentley Architecture--Part 1

  • Bentley's Approach to BIM
  • BIM Highlights of Bentley Architecture
  • The 2D/3D Choice
  • Relevant Links

In the last issue of the AEC Tech newsletter, I presented a selection of reader responses on the topic of Building Information Modeling (BIM), capturing the range of user perspectives on this new phenomenon in the AEC industry that is poised to take over CAD (see Issue #103: In this and the next issue, I will take a look at the BIM-relevant features of one of the leading software solutions in this space: Bentley Architecture, formerly known as Architecture for MicroStation Triforma. In subsequent issues, I will also explore other BIM solutions, such as Autodesk Revit and VectorWorks ARCHITECT. I have already reviewed ArchiCAD recently from a BIM perspective (see my review of Version 8 in the August 2003 issue of CADENCE at

Bentley's Approach to BIM

The BIM debate between Autodesk and Bentley earlier this year, which I wrote about in Issues #95 ( and #96 ( brought into clear focus Bentley's approach to BIM. The key aspects of this approach are as follows.

1. Bentley sees BIM as a superset of CAD and wants to provide its users with a "ramp" as a transition path from CAD to BIM, without abandoning current capabilities.

2. Bentley has a "federated database" approach to BIM, where all the data related to the building is not centralized in a single building model; instead, it is distributed across multiple applications and data stores in a coordinated fashion.

3. Bentley believes in "not starting over" with a new solution. Its individual discipline-specific BIM solutions--such as Bentley Architecture, Bentley Structural, and Bentley HVAC--continue to be built on top of its existing MicroStation platform and Triforma applications.

Let us now see how these key strategies are reflected in Bentley's BIM solution for architectural design.

BIM Highlights of Bentley Architecture

Based on Bentley's BIM strategy as a whole, I will outline the key aspects of the company's architecture-specific BIM application, Bentley Architecture. These can also be seen as the main aspects that differentiate Bentley Architecture from competing BIM solutions such as Autodesk Revit and ArchiCAD.

The concept of a ramp from CAD to BIM translates, in the case of Bentley Architecture, to a ramp from 2D to 3D. Officially labeled the "2D/3D Choice," this is a key new feature introduced in Version 8.1 that gives the user not just the traditional choice between 2D and 3D, but four different 2D/3D design modes. This feature will be described in more detail in the next section. Since the option to work only in 2D is also available, all legacy 2D content can still be used.

Since the building data is decentralized rather than maintained as a monolithic block in a single model, it lends itself more easily to distributed work processes and sharing of information among design teams in multiple offices. It also makes the application more efficient for large projects.

Since Bentley Architecture is built on top of the same platform as Bentley's building engineering solutions, building information is integrated and can be easily shared across various disciplines. Thus, the structural and HVAC components of a building, designed using the other Bentley applications, can be seen and intelligently queried in Bentley Architecture, without requiring the original applications to be installed. Similarly, the entities created in Bentley Architecture can be viewed and queried in the other applications and used as the basis for structural and HVAC design. This facilitates the multidisciplinary collaboration processes that characterize building design. A separate Interference Manager application is also available to detect spatial interferences within the entire model, including its architectural, structural, and HVAC components.

Bentley's evolutionary approach to BIM is not devoid of its share of challenges. Since Bentley Architecture is built on top of Triforma, which in turn is built on top of MicroStation, you have to install all three applications separately, even if you only want to use Bentley Architecture. This is inconvenient and tedious. The three-tier architecture of the application should ideally be invisible to the users; they should have to install only one application. I understand from my discussions with Bentley that efforts are underway to address this issue in the next product release scheduled for early next year.

Also, since the BIM functionality of Bentley Architecture is added to an existing CAD application, its interface seems more CAD-like than BIM-like, compared to the interfaces of from-the-ground-up BIM applications. The software designers do not have the luxury to start with a clean slate, which rules out any dramatic makeovers. CAD applications generally don't rate highly on ease of use (see my review of MicroStation V8 in the July 2002 issue of CADENCE:, and Bentley Architecture can't help but be plagued by the same shortcoming. For existing MicroStation users looking to transition to BIM, Bentley Architecture would be the easy and obvious choice. However, new users shopping for a BIM application would find Bentley Architecture complex and difficult to master.

The 2D/3D Choice

The new 2D/3D Choice feature in Bentley Architecture is an innovative approach to the basic 2D/3D conundrum that plagues building design software: how can the benefits of 3D BIM be provided, while still allowing users to work in 2D on entire projects or parts of projects, if that is what they want? The 2D/3D Choice feature gives users four different kinds of design modes to work in, briefly described below.

Drafting: In this mode, designers create 2D plans and other drawings only; a 3D model is not created.

Plan to Model: Here, designers work in 2D, but a 3D model is dynamically generated behind the scenes and can be viewed at any point for visual feedback. Any changes made to the model do not affect the plan. This one-way relationship between plan and model is intended to preserve 2D work safely in plan, leaving the designer to freely explore and learn 3D design.

Plan and Model: In this mode, there is a two-way relationship between plan and model, allowing designers to work either in the 2D plan or 3D model. The changes made to the 3D model can be used to update the plan.

3D Modeling: Here, designers work entirely in 3D mode. Any 2D drawings that are required need to be extracted from the 3D model. The model cannot be changed through editing the 2D drawings.

Work can begin in any design mode, by choosing the appropriate "seed" file when a new project is created. Subsequently, users can switch to other design modes as needed. Thus, a building project can be started schematically in 2D, and then switched to one of the 3D modes for detailed design development. Alternately, a part of a 3D model can be isolated and detailed out in 2D. The actual process of switching to another design mode is, unfortunately, not as simple as just switching an option in a dialog; it involves creating a new file from the appropriate seed file, attaching the original file as a reference in the new file, and then merging that reference file into the new master file. A one-click switching method would help to make 2D/3D Choice a lot more compelling.

It is important to note that regardless of the design mode, the tools that are used to create the building entities in Bentley Architecture are the same. Thus, the same Place Wall tool from the Architectural Modeling toolset is used to draw a wall in 2D or model it in 3D. The application uses a context-sensitive representation technology to determine the display of the object based on whether the context is a drawing or a model. This is common in other BIM solutions as well.

What is unique, however, in Bentley Architecture, is that 3D model objects exist separately from their 2D plan counterparts, and a sophisticated coordinated documentation technology is used to keep them consistent. It is this technology that allows the application to offer the four different design modes in 2D/3D Choice. In other BIM applications with the single building model approach, there is no plan independent of the model; the plan is simply one view of the building object while the model is another. Bentley Architecture certainly has to do a lot more work behind the scenes to maintain the synchronicity between the separate 2D and 3D entities. Its users, however, will appreciate the flexibility of the four different design modes, at least until 3D becomes commonplace and takes over from 2D as the de facto industry standard.

We will continue this exploration of the BIM features of Bentley Architecture in the next issue.

Relevant Links

Bentley Architecture: