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AECbytes Product Review (October 31, 2006)

Bentley Architecture and Bentley Structural V8 XM

Product Summary

Bentley Architecture V8 XM and Bentley Structural V8 XM are the BIM solutions for architectural and structural design respectively that are part of the Bentley Building V8 XM Suite, an integrated multi-disciplinary set of BIM solutions built on the MicroStation platform.

Pros: Powerful BIM solutions for architectural and structural design that are particularly strong when it comes to modeling large and complex projects and in distributed work processes; feature a solid and extensive repertoire of CAD and BIM features from the underlying MicroStation platform; provide the ability to model any kind of complex geometry using surface and solid modeling tools and to add BIM information to it; Bentley Structural has tight integration with leading in-house structural analysis tools such as RAM Structural System and STAAD.Pro as well as third-party tools.

Cons: Very complex, requiring a significant amount of time to master; distributed approach to modeling, which needs a lot more work in setting up the project, modeling it, extracting the necessary drawings, ensuring coordination, and managing all the component files and documents; limited amount of object associativity and intelligent behavior, making editing operations more difficult; no modeling constraints of any kind, which does not guarantee the integrity of the model for downstream analysis applications that need to work with it.

Price: List price for Non-MicroStation users is $5945 (includes MicroStation, Triforma, Parametric Cell Studio, and Bentley Architecture or Bentley Structural); MicroStation users can add Bentley Architecture or Bentley Structural for $750.

In the last AECbytes product review, we explored the main features of the Bentley Building Suite that is built on top of MicroStation Triforma, including the enhancements in the new V8 XM edition that are common to all its BIM applications, namely, Bentley Architecture, Bentley Structural, Bentley Mechanical Systems, and Bentley Electrical Systems. This review takes a closer look at two of these applications, Bentley Architecture and Bentley Structural, to see how they work specifically in their targeted domains. Since we have already looked at most of the new features in the last review, this review will focus on their overall functionality as BIM applications for architectural and structural design. (If you haven't read the last review yet, be sure to do so to get a more comprehensive understanding of these applications.)

How Bentley Architecture Works

This section takes a detailed look at the capabilities of Bentley Architecture for schematic design and design development. Other aspects such as drawing production, reports and schedules, and visualization that are common to Bentley Structural as well will be discussed in a later section.

Let's start with schematic design. One critical omission in the repertoire of most current architectural BIM solutions, including Revit Building and ArchiCAD, is a set of dedicated tools for programming, space planning, conceptual sketching, and quick 3D massing that work in an integrated fashion with each other and also tie in intelligently and efficiently with the subsequent design development phase. Bentley Architecture is no exception in this regard. It does have tools for tackling some conceptual design tasks, but on a piecemeal basis. There are no tools for space programming as such, except the ability to import Excel spreadsheets and place them in the drawing window, maintaining the link to the file so that any change made to the original spreadsheet gets automatically updated in the drawing. But the programming data in such a spreadsheet cannot be directly linked with the spaces that are created, which would have been useful in exploring various space planning options to determine the best fit for the program. The best that you could do is to create the spaces and then generate a report of the spaces to validate it manually against the space program data.

For the actual creation of spaces, however, there is a broader ranger of options and functionality. You could start experimenting with space layouts even prior to creating walls by drawing spaces of various shapes or selecting a 2D shape and converting it into a space. You can specify the actual area of a space prior to drawing it, in which case it will constrain the space to that area. You can also input the label and the targeted area of the space as listed in the program, and this information can be displayed in the space label along with the actual area. The area display in the label updates automatically if the space is modified. If you have already created walls, a flood method is available to create a space within an enclosed set of walls (see Figure 1). Spaces created by this method are associative, and update automatically if the enclosing walls are moved. You can also convert spaces to walls, which is a useful automated step going from space planning to detailed design. However, these spaces are not associative, and do not update if the walls are moved. A tool is available to show the area calculations for single or multiple spaces to validate their accuracy for code compliance. One current limitation of the space planning capability is that spaces cannot be filled with color, which is an important visual aid to the space planning task. But this functionality is expected to be available in an update release soon.

Figure 1. Creating spaces inside walls, whose attributes can subsequently be edited with the Edit Spaces tool. (Model courtesy of Gresham, Smith, and Partners,

While there are no sketching capabilities in Bentley Architecture, you can import a sketch—say, of the site—and use it as an underlay for developing 3D massing or detailed models. For massing, Bentley Architecture has the full gamut of solid and surface modeling capabilities—the advantage that comes from being built on top of MicroStation TriForma—which can be used to model any kind of regular or freeform shape. These tools, however, lack the intuitiveness and ease of use needed for quick 3D massing found in dedicated conceptual design tools such as Google SketchUp, which is why the recent SketchUp import capability is important as it fills a critical gap. Bentley Architecture does not yet have the capability to automatically derive the building shell—with intelligent wall, floor, and roof "BIM" objects—from the schematic massing model, whether it is created within Bentley Architecture or imported from another 3D modeling application. This means that the effort spent in developing a massing model cannot be effectively directed towards jumpstarting the detailed design process—you would pretty much have to start from scratch. You could, however, use the massing model as a reference while developing the detailed one.

It is in the actual detailed modeling of the building that one of the key strengths of Bentley Architecture as a BIM application lies. It has an extended toolset for modeling the site as well as different building components such as walls, curtain walls, doors, windows, columns, ceilings, floors, stairs, and so on. The Walls toolset, for instance, comprises several tools for different functions: placing walls, and placing and building wall assemblies; breaking, joining, and connecting walls; modifying wall geometry and wall type; cleaning up wall intersections and managing automatic wall unification in the 2D extracted drawing; making cuts in walls and creating wall pockets and recessed utility areas to accommodate other building design elements. When any building element is created, default settings are used for its type information, which can be changed later when required (see Figure 2). This allows the designer to focus on the design and its modeling without being burdened by specifying type information until necessary. It also keeps tool dialogs concise and easy to navigate. Type specifications follow industry standards, with higher-level categories called families containing several individual element types called parts.

Figure 2. Changing the type information of a wall element after it has been created.

For the modeling of non-regular building geometry, Bentley Architecture lacks the ease with which, for example, walls, beams, and columns can be slanted, curved in elevation, or given a custom cross-sectional profile in the new version of ArchiCAD. You can, however, create any kind of complex geometry using the TriForma surface and solid modeling tools and add BIM information to it. This will not make the object behave like a BIM object; so, for instance, a complex wall created using the TriForma modeling tools rather than the Wall tool will not automatically cut openings when doors and windows are placed in it. However, it will be recorded in the schedules and in quantity take-offs as a wall object. Spaces placed inside complex wall shapes do not automatically take on their geometry as they do in ArchiCAD, but remain vertical extrusions of the space footprint, which could be a limiting factor in analysis applications like energy and in HVAC design that need accurate volume calculations of spaces.

Let's move to look at the basic functionality of Bentley Structural.

How Bentley Structural Works

The basic functionality of Bentley Structural is similar to that of other BIM applications for structural design such as Revit Structure: instead of drawing 2D structural plans, sections, and elevations, engineers can use Bentley Structural to create a digital model of the building structure, which combines both the physical model as well as the analytical model. It can then be used for the different types of structural analyses engineers need to perform to design their structures, as well as to derive the construction documentation needed to build the structure. There is one significant aspect of Bentley Structural that makes it very different from Bentley Architecture, which is that the entire physical structure of the building has to be created in one model in Bentley Structural if it needs to be analyzed as a whole. If different parts of the building are modeled separately, then they also have to be analyzed separately. This is unlike Bentley Architecture, where most typically, different floors of the building are modeled in separate files and then assembled together by referencing within a master model.

For the physical modeling of the structure, Bentley Structural has a comprehensive toolset comprising column grids, columns, beams, bracing, studs, slabs and foundations, walls, joists, trusses, and so on. Multiple construction types are supported, with separate tools for steel, concrete, and timber members. The availability of a Structural Snaps option makes it easy to model structural elements in 2D as well as 3D by snapping on to the key points of other elements. Thus, for instance, a sloped beam can be quickly created simply by snapping on to the endpoints of two columns of different heights (see Figure 3). Automatic coping and end trimming is available for steel and concrete members respectively, where the ends of the members are correctly cut based on how they connect with other members. Any change in the structural configuration automatically adjusts the coping and trimming. Bentley Structural has dedicated tools for creating larger structural assemblies such as framing, joists, and trusses, making it possible to put together a detailed structural model relatively quickly.

Figure 3. Creating a sloping beam by snapping to the endpoints of two columns of varying heights.

Just like the elements in Bentley Architecture, the elements in Bentley Structural belong to individual element types called parts that are categorized at a higher level into families. Each member inherits various attributes from its parts and families categorization including size, material, orientation, drafting attributes, labeling, and even specific customizable notes such as paint color, cost, or manufacturer's name (see Figure 4). One key size-related aspect for a structural member is its section, and to this end, Bentley Structural provides over 20 different section tables containing industry-standard sections used across the world. The XM edition has the ability to load multiple section files, allowing large lists of sections to be reduced to more manageable lengths. Also, these are now in XML rather than ASCII format, allowing them to be more easily edited by the user. All of the structural tools have the option to select a section for the structural member before placing it (see the Place Steel Beam dialog in Figure 3), as well as the ability to modify the section after it has been placed.

Figure 4. Viewing the attributes of the beam element created in Figure 3.

Analysis is the core of the structural engineer's task, and one of the biggest benefits of a BIM application like Bentley Structural lies in its ability to automatically create a fully associated analytical model of the structure that corresponds with the physical model, and then link it bi-directionally to popular structural analysis tools for performing different kinds of analyses. The ability to create the analytical model is optional, so if a model is being created for documentation or other purposes only, this option can be turned off to reduce the file size. If the analytical model option remains active, the analytical members are created at the same time as the physical members, and can be reviewed in various ways: the analytical model superimposed on the physical model, a single-line analytical model only, etc. The application allows you to modify analytical members and physical members separately, so that you can tweak the analytical model for correct input to an analysis program, without affecting the physical model. Additionally, various structural information such as nodes, boundary conditions, loads, and so on can be added before exporting the model to an analysis tool. You can choose to send the entire analytical model or only a portion of it for analysis.

Bentley Structural links with a number of analysis tools including GTStrudl, RAM Structural System, SFrame, and STAAD.Pro, of which RAM and Staad.Pro were acquired by Bentley last year and which therefore feature better integration. Bentley Structural also supports the import and export of CIS/2, IFC, SDNF, and MIDAS file formats, which allows interoperability with other analysis and detailing applications. The link with the supported analysis tools is bidirectional, which means that you can export the analytical data to the program, do the analysis and make any necessary changes within the analysis tool, and then import the results back into Bentley Structural (see Figure 5). The application provides you with a summary of the import, listing the analytical program's suggested changes, which you can then choose to accept or reject. If a change is accepted, both the analytical as well as the physical model in Bentley Structural are modified according to that change. The Design History capability which comes from the base MicroStation platform makes it possible to visually review any changes that are accepted.

Figure 5. Interoperability between RAM Structural System (top image) and Bentley Structure (lower image). (Courtesy: Bentley)

Other Functionality Common to Both Applications

In both Bentley Architecture and Bentley Structural, drawings are section cuts that are extracted from the model using the Drawing Extraction Manager utility that comes from the base MicroStation Triforma platform. The basic procedure is to define the section cutting plane, identify the forward view, adjust the settings that control the output, and name and generate the drawing. Different "drawing definitions" can be specified for different types of drawings, such as floor plans, sections, structural framing plans, and so on, which will be used to guide the elements that will appear in a specific drawing type as well as the symbology (color, level, style, weight) of that element (see Figure 6). This means that if all the drawing definitions are well established, little work will be needed to touch up the drawing, apart from the necessary dimensioning and annotation. The extracted drawing can be placed in a separate DGN file or in the same master file that contains the model from which the drawing is extracted. Due to the separation of 2D and 3D objects that comes from Bentley's federated database approach to BIM, as described in the last review, a change in the model does not automatically update the extracted drawing. But because of the association, the change is detected and the drawing is recognized is being out-of-date when it is opened, giving the user the choice of updating it. If the update option is chosen, the necessary changes are made to the drawing, while still preserving any dimensions or annotations that may have been added to it after extraction.

Figure 6. Generating drawings based on preset drawing definitions in Bentley Architecture (top image) and Bentley Structural (lower image).

As mentioned in the last review, both Bentley Architecture and Bentley Structural inherit the full range of MicroStation's capabilities for documentation and presentation, including a vast array of dimensioning and annotation tools for creating drawings and details; a Quantify tool that can extract needed information from a 3D model and export it in the form of spreadsheets, databases, or word processing files; the DataGroup feature which is not only used to manage objects but also generate schedules and other needed reports; as well as powerful visualization and animation capabilities including full-blown radiosity that can create highly photorealistic renderings and animations (see Figure 7). A related new feature in the XM edition is the ability to locate the project in a specific geographical location and create animated solar studies, which allow architects to study the impact of solar light and subsequent shadows on the building during the course of the day and at different times of the year.

Figure 7. Some examples of rendered images from the project shown in the top image of Figure 6.

Strengths and Limitations

Both Bentley Architecture and Bentley Structural are powerful BIM solutions for architectural and structural design that are particularly strong when it comes to modeling large and complex projects and in distributed work processes. By virtue of being built on top of MicroStation TriForma, they inherit a solid and extensive repertoire of CAD and BIM features that have been honed over years of development. With the ability to create any kind of complex geometry using surface and solid modeling tools and to add BIM information to it, they pose relatively few constraints on the form of building they can handle.

In the context of individual disciplinary requirements, Bentley Architecture provides full support for the actual detailed modeling of the building but lacks a set of dedicated tools for programming, space planning, conceptual sketching, and quick 3D massing that work in an integrated fashion with each other and also tie in intelligently and efficiently with the subsequent design development phase. This is a critical omission that all architectural BIM solutions, not just Bentley Architecture, need to address. The space element, in particular, needs to be overhauled in Bentley Architecture with accurate volume calculations that take into account features such as canted walls and sloping roofs.

Bentley Structural, in contrast, is not hampered by any such disciplinary omissions. Not only does it provide a comprehensive toolset for structural modeling that includes both the physical and analytical components, its tight integration with in-house structural analysis tools such as RAM Structural System and STAAD.Pro as well as third-party tools make it a very compelling choice for structural engineering.

As I pointed out in the last review, the most critical limitation of Bentley's BIM solutions is complexity—they are extremely hard for new users to learn and use without proper training. The interface enhancements in the XM edition make it easier to find tools and access files, but the basic operation of the individual tools remains complex and not very intuitive, making it difficult to even get started without referring to the documentation. Extensive training would be required to master the applications. This is more so with Bentley Architecture than with Bentley Structural, which is better defined and has a more logical workflow. Also, the federated database approach of these applications, while facilitating distributed work processes, requires a lot more work from the user in setting up the project, modeling it, extracting the necessary drawings, ensuring coordination between them, and managing all the component files and documents.

While a large part of the complexity of Bentley Architecture and Bentley Structural comes from being built on top of the MicroStation TriForma CAD platform, it is intensified by the limited amount of object associativity and intelligent behavior. For example, if you draw a closed set of walls in Bentley Architecture and create a space inside it, moving one of the walls will correctly update the area of the space. But if you now draw a second set of enclosed walls overlapping with the first set, the application is not smart enough to detect that the area of the first space has been reduced, even if you create spaces inside the new set of walls (see Figure 8). It continues to show the first space with the original area. And in Bentley Structural, there is no kind of associativity between objects at all—if you model a beam connecting two columns, then moving one of the columns does not automatically modify the beam to maintain the connection. You will have to use a Fence Stretch command to do this, which is a geometric transformation rather than one that relies on built-in relationships between objects. But if the angle of the beam changes with the move, the copings do clean up and adjust accordingly.

Figure 8. A simple example showing that if a space is created that overlaps with an existing space, the application does not detect that the area of the first space has been reduced.

Associativity is an aspect I always discuss in my reviews of BIM applications, because it is important in two primary ways. First, associativity makes it much easier to edit a building model as elements maintain the relationship and don't need separate editing to re-establish the relationship. Also, associativity is helpful in maintaining the integrity of the model, which is another critical aspect I discuss (see my recent reviews of Revit Building 9, ArchiCAD 10, and Revit Structure 4). Not only do Bentley's BIM solutions lack associativity for the most part, they do not impose too many modeling constraints—walls can overlap with other walls, doors and windows can be moved out of walls, doors and windows can overlap with each other on the same wall, and so on. While this does allow a great deal of flexibility and freedom in modeling, it also renders the application incapable of guaranteeing the consistency and integrity of the model, which would be critical for downstream applications such as energy analysis, egress, fire safety, circulation analysis, and so on to work with the model and provide results that can be trusted. Model integrity will become a critical issue in BIM going forward, as the focus will increasingly turn to analysis and simulation rather than on generating construction drawings and visualization.

Turning to the documentation accompanying both applications, this can be rated as fair. The content that is provided is well explained and illustrated, and in Bentley Architecture, it is accompanied by many animated movies illustrating specific tasks and features, which are very helpful. The only downside to the movies is that they are not accompanied by a voice-over, which would have enhanced their usefulness. A Tracking feature can be enabled in the applications that automatically opens up the documentation related to a tool when you select it. In Bentley Architecture, this integration works both ways, where you can click on a tool in the documentation and it takes you back to the application and opens the tool. On the flip side, a significant portion of the documentation, including the movies, has not been updated for the new version. Also, the documentation is not comprehensive and does not cover all aspects of the applications, so users will have to rely on other training material, such as that available through Bentley's SELECT and LEARN programs, to learn the applications fully.


As I discussed in the last review which explored the main features of the Bentley Building Suite, what differentiates Bentley's BIM solutions most from competing BIM applications is that they have a federated database approach where all the data related to the building is not centralized in a single building model contained in one file, but is instead distributed across multiple files in a coordinated fashion. Interestingly, however, this does not always hold true for Bentley Structural where the entire physical structure of the building has to be created in one model if it needs to be analyzed as a whole. It is possible that Bentley Architecture will also have to follow this centralized approach if an architectural model is to be analyzed as a whole, once architectural BIM applications are expected to provide more support for analysis. This might perhaps make Bentley eventually re-think its federated approach to BIM, which would also go a long way towards reducing the complexity of its applications.

About the Author

Lachmi Khemlani is founder and editor of AECbytes. She has a Ph.D. in Architecture from UC Berkeley, specializing in intelligent building modeling, and consults and writes on AEC technology. She can be reached at

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