Autodesk Revit Building 8/8.1

Starting in March 2005, Autodesk Revit officially became a platform rather than a single product. This was when Autodesk released version 8 of its BIM application for architectural design, now known as Autodesk Revit Building rather than just Autodesk Revit. This was followed in June by the first release of Autodesk Revit Structure, a BIM application for structural engineering built on the Revit platform. A third Revit-based application for MEP engineering is currently under development. By expanding the scope of Revit from architectural design alone to a platform that can support collaborative multi-disciplinary building design, Autodesk has successfully addressed what has been one of Revit's biggest limitations so far. (See my reviews of Autodesk Revit 6 and Autodesk Revit 7.) Revit can now realize the full potential of BIM in enabling cross-disciplinary collaboration, with architects and engineers using the same building model and the same modeling tools for building design.

Last month, Autodesk released updated versions of both its Revit platform products: Revit Building 8.1 and Revit Structure 2. The main enhancement in these two releases is that they are interoperable with each other, allowing architects and engineers to work in a more integrated manner.

AECbytes is publishing back-to-back, consolidated reviews of both these products. The current issue looks at the new features in the main Revit Building 8 release and the updated 8.1 version, while in the next issue, we will look at Revit Structure 1 and the new integrating capability in Revit Structure 2.

Main Improvements in Revit Building 8

Several modeling operations have been enhanced in Revit Building 8. Wall sweeps have three new parameters that provide better control over how the sweep interacts with the building model: Cuts Wall, which cuts the sweep geometry out of the host wall if there is an overlap; Cut by Inserts, which cuts the geometry of inserts such as doors and windows out of the sweep; and Default Setback, which sets back the sweep from each intersecting wall insert by a specified value (see Figure 1-a). A new Continuous Footing tool is available in the Structural tab of the Design Bar, which lets you place continuous wall footings along structural walls while in plan or 3D view (see Figure 1-b). Formerly, the footing had to be separately modeled as a wall. When creating new stairs, you can now select the railing type before completing the stair sketch. The Roof tool has been enhanced by the ability to create true conical roofs (see Figure 1-c), which can also be segmented by simply setting the segmentation property of the base arc to the desired value.

A few editing enhancements for modeling have also been provided. You can select multiple elements and flip all of them at the same time by use the Spacebar. When you select a chain of walls or lines, controls are displayed at the coincident endpoints, which you can drag to new positions while still preserving the joins between the elements. On a potential chain of walls or lines, when one element is selected, the TAB key can then be used to toggle between the selection of the whole chain and the partial chain.

On the representation front, a noteworthy improvement is the ability to use overrides to control the appearance of cut edges of walls, roofs, floors, and ceilings in plan and section views. For this to work, the Detail Level of the view must be set to Medium or Fine so that the individual layers of the compound structure can be seen. You can then select the Cut Line Styles option in the Visibility properties of the view and specify required line weights, line colors, and line patterns to each layer: Structure, Substrate, Thermal/Air Layer, Finish 1, and Finish 2. In addition, you can specify the appearance of edges that are common to adjacent layers of differing functions. Figure 2-b shows a plan display with the cut line styles specified in Figure 2-a. As you can see, this ability makes it possible to make the structure read bolder graphically as well differentiate more easily between materials, and will be especially useful when creating detail views. To apply the same settings across multiple views, they can be saved from one view in a view template, which can then be applied to other views. Another related improvement in Revit Building 8 is that it allows you to apply a view template to several views at the same time. And this in turn is related to yet another enhancement on the interface front, which allows you to use basic Windows functionality (Shift/Select or Ctrl/Select) to select multiple items, such as views, in the Project Browser.

Working with families has been improved significantly in Revit Building 8, streamlining the workflow for using them within a project. Families can now be edited directly within a project, and can be reloaded immediately into the project after the modifications are made. This also applied to nested families. If multiple projects or families are open, a dialog displays allowing you to select which projects or families you want to load the family into. This is a marked improvement over the earlier method of editing families, which required finding the location of the family file, editing it within the family editor, saving it, and then returning to the project to reload it. The Project Browser has a new right-click option for reloading a family. Another critical improvement is the option to convert a nested family into a family consisting of shared subcomponents. This allows each subcomponent to be separately selected, tagged, renumbered, and scheduled, and this information is retained even when the project is exported to ODBC. It is also possible to add the individual subcomponents into the project independent of their original family. Figure 3-a shows an example of a 'conference table with chairs' family, which was converted from a single unit to a shared family, and subsequently appears listed as shown in Figure 3-b, with all its individual chairs and tables in a furniture schedule.

Improvements along the documentation front include the ability to add dimensions within legends, being able to create a chain of references and obtain the total length of the chain with the Tape Measure tool, and the option to create expanded or condensed text with a new Width Factor parameter for text. It is now possible to hide an unreferenced view tag for views that have been created just to assist in design and are not placed on sheets, which is a useful enhancement for printing.

Revit Building 8 features several improvements in import and export. 3D DWF files can now be published, which can subsequently be viewed and queried in Autodesk DWF Composer. Sheet views can be exported as 2D DWF files, which can then be marked up in DWF Composer and linked back into Revit Building, allowing a digital review process similar to that introduced in Autodesk AutoCAD 2005 and 2006. (For more details on how this works, see my review of DWF Composer). Revit Building also features better integration with Buzzsaw: you can publish a Revit Building drawing set directly to Buzzsaw in either dwg or dwf format, as well as save Buzzsaw locations. DWG export enhancements include new options for file naming, as well as the option to export as a single file without creating Xrefs. Revit Building rooms can be exported as closed polylines in DWG format with attached room data, which can be used as input to facilities management applications. Revit Building 3D geometry can be exported as ACIS solids in the SAT format, as ACIS solids or polymeshes in DWG or DXF format, and as polymeshes in MicroStation's DGN format. (The ability to import ACIS solids was made available in version 7.0, and was critical to the Building Maker functionality described in my review of Revit 7.0). The long-promised IFC export feature is available in Revit Building 8, as well as the first public Revit API (Application Programming Interface), which is supported through the Autodesk Developers Network (ADN) and will allows third party vendors to develop tools that extend the capability of the application. The API enables all objects to be accessed and queried, geometry extraction, modification of properties, and some limited object creation. Future versions of the API will allow plug-in tools broader functionality to create objects.

Last but not the least, Revit Building 8 introduces the concept of interference checking in the form of an Interference Check tool which can find intersections between the geometries of selected elements or all elements in the model. The check can be run across a single model or several linked files, allowing for better coordination between different disciplinary models such as architecture and structure, architecture and interior design, and so on. As shown in Figure 4-a, you can select specific categories of elements for the interference check, such as structural columns and architectural columns, structural framing and walls, and so on. In fact, the selection of specific categories is recommended since an open-end interference check would take a long time to process. All the interferences detected are displayed in a report, and can be reviewed in the graphics window when selected, as shown in Figure 4-b. After fixing all the problems, the report can be re-run to verify that there are no conflicts.

Main Improvements in Revit Building 8.1

Considering that it is just a point release, Revit Building 8.1 packs a surprising number of new features. To start with, it enhances the Building Maker functionality for conceptual design mentioned in the previous section by enabling the import of NURBS surfaces from other applications in the form of DWG or SAT files. These can be turned into mass objects in Building Maker, after which you can create roofs, walls, floors, and curtain systems from selected faces (see Figure 5-a). A separate but related ability is the creation of non-vertical walls from massing components, created within Revit Building or imported from other applications (see Figure 5-b). These non-vertical walls behave like the regular walls: you can place doors and windows in them; they can be joined to other walls; they appear properly cut in plan views; they are correctly listed in schedules; and they can be exported along with their information to ODBC and other formats. Considering that Revit Building lacks a good set of freeform modeling tools, these new capabilities make it easier to bring conceptual massing models created in other applications into Revit Building and convert them into building models rather than having to start from scratch.

Curtain walls, sloped glazings, and curtain systems in Revit Building 8.1 are easier to create with the new type-driven curtain element layout. This allows you to pre-define parameters such as horizontal and vertical spacing and layout as well as mullion types in the Properties dialog of the wall type, so that when a specific instance of the curtain wall is placed, it already has panels, grids, and mullions based on the specified rules (see Figure 6-a). More options have been provided for selecting specific panels and mullions of a curtain wall for modification, and mullion joins can now be made continuous or broken as required. Another modeling enhancement is the ability to create shaft openings with the Opening tool that cut through several floors, roofs, and ceilings simultaneously, useful for modeling ducts, elevator cores, and stairwells (see Figure 6-b). In previous versions, the openings had to be cut separately for each level. If the shaft is moved in one view, it moves in all other views as well to maintain the vertical continuity of the opening. The Opening tool has also been enhanced with the ability to cut rectangular openings in a straight or curved wall.

There are two critical enhancements which will improve Revit Building's ability to be used in large projects across distributed teams: the ability to create comprehensive schedules that work across all linked files, as opposed to creating separate schedules for each file and then manually collating the information together; and enhanced element borrowing, which allows unowned elements to be automatically borrowed without explicit permission from the application. Also, a file can now be opened independently from the central file and send to clients or other interested parties without relinquishing all worksets and borrowed elements.

Other improvement areas in Revit Building 8.1 include snapping, where doors, windows, and openings can be centered on walls by using the Midpoint jump snap; dimensioning, where a new dimension type is introduced that allows vertical and horizontal dimensions to be created between angular elements; DWG export, where hidden lines can be exported on user definable layers and collinear wall lines can be merged; 3D DWF export, which now supports linked files; site modeling, which allows toposurfaces to be created from a comma-delimited points file; and the API, which continues to be further refined and expanded.

From an interoperability standpoint, particularly with Revit Structure, the most critical new feature in Revit Building 8.1-which operates in conjunction with a similar feature in the new Revit Structure 2 release-is the Coordination Monitor. It currently works only for key elements such as grids, columns, and levels and allows you to copy these elements from a linked project, say a structural model, into the current (host) project. The copied elements are automatically related to the original elements. If you attempt to modify a copied element, a warning dialog box is displayed. Similarly, if any of these elements are modified in the original linked project, say by the structural engineer, the Coordination Monitor issues a warning about it in the host project. You have the ability to approve or reject changes and attach comments for review. We will explore this feature in more detail in the forthcoming review of Revit Structure to see how well it works for coordinating the architectural and engineering models.

Strengths and Limitations

Revit Building 8 and 8.1 include several new features and enhancements which add to the core strengths of Revit that I have highlighted in my previous reviews: relative ease of use, particularly in comparison with other BIM applications; automatic generation and coordination of all views and documents and the instant update of all views when any change is made to the model; parametric building components; built-in associativity that intelligently propagates changes to all associated elements; the ability to define custom relationships between elements; the display of temporary dimensions that can be written over to resize a component while it is being created; the immediate availability of 3D views that provides instant and critical feedback on design decisions and helps expedite client approvals; and the ability to automate many tasks related to drawing setup and coordination. The improvements in editing families, the ability to import NURBS surfaces and convert them to building elements, being able to create schedules that collate data from linked files, the ease of creating curtain walls with panels and mullions based on specified parameters, the improved integration with DWF Composer and Buzzsaw, and the host of other enhancements all continue to make the application smarter and easier to use.

Revit is also starting to address two of the main interoperability-related limitations of previous releases: IFC support and an API. It has received Phase 1 certification by the International Alliance for Interoperability (IAI) for meeting the IFC2x2 code checking view for architecture, and is currently in the review process for the final, Phase 2 certification. This code-check certification is a pre-requisite for compliance with Singapore Building and Construction Authority's automatic plan checking system, CORENET e-Plan Check system (which will be subject of a separate article in AECbytes next month.) It is important to note that this IFC certification for Revit has been achieved for the code-checking view only, and does not guarantee that an IFC exported file from Revit will work with all applications that use the IFC format. But it is still a good start. The same can be said for the API, which is still quite limited in the functions it allows access to. However, it definitely paves the way for a full-fledged API in the future.

With regards to the Coordination Monitor that is designed to allow better coordination between the architectural and structural models, it may be premature to judge it without an indepth look at Revit Structure. However, it seems a little convoluted at this point, requiring you to make copies of the elements of the linked file that you want to monitor within the host file. This step seems redundant. Ideally, the application should automatically detect how the architecture and structure fit together and enable a more seamless workflow where the models can be coordinated without any extensive setup by the architect or the engineer.

Revit's lack of freeform modeling tools and the awkwardness of its massing tools, which I have pointed out as a limitation in previous reviews, has been somewhat mitigated by the ability to import ASIC solids and NURBS surfaces and convert them to building elements. A single application cannot do everything, and Revit seems to be wisely focusing on better interoperability with other applications rather than attempting to improve its capabilities along all fronts. In the past, I have also found that Revit's native rendering capabilities fell far short of the sophisticated renderings that dedicated 3D visualization programs can produce, but I recently received some rendering examples done in Revit out of the box, which shows that experienced renderers can, in fact, create very good quality visuals in it (see Figure 7). It allows Revit to be used as an efficient presentation tool even as a project is being designed.

The poor quality of documentation in Revit Building currently stands as its biggest limitation, forcing users to rely on professional help for learning the program. The online help has an overabundance of text that is not sufficiently illustrated, and while the tutorials accompanying the application are good, they are again all text-based and rather long-winded. There is no easy way to learn all the new features of the application: the tutorials cover only a few of them, and the listing of new features in the Online Help is not very helpful. At a time when video tutorials for applications are so common (see my recent review of SketchUp 5), it is surprising that a leading vendor like Autodesk has not invested sufficient time and effort into providing better tutorials for Revit Building. Even for a newcomer, there is no easy way to get started with the application other than plod though the Getting Started booklet that accompanies the application CD. It would be so helpful to new users if at least that section was illustrated interactively.

The old adage that "the more you have, the more you want" seems to be particularly true with regard to technology. Revit already has an abundance of smarts that sets it apart from competing BIM applications, but I still found that it is not yet as smart as it could be. This was highlighted particularly when I used its new interference checking capability. I found that the application allows you to perform "illegal" operations such as moving furniture into walls, elevators out of their cores, and so on, without even a warning (see Figure 8-a). You have to run interference checking to detect these errors. It is also inconsistent with enforcing other constraints. For instance, while you cannot create a door or window that overlaps with another door or window, once you have created it, you can move it so that it does overlap with another opening (see Figure 8-b). Thus, Revit by itself does not ensure model integrity. While this may not be an issue right now, it will be in the future when we use more analysis tools that will expect a fully accurate building model. There is certainly a trade-off between ensuring accuracy versus flexibility of modeling, and applications like Revit will have to figure out where the balance lies. An example of a BIM application that ensures model integrity by not allowing, for example, furniture to cut into walls, is VisionREZ (see my recent review of this application). But VisionREZ is specialized for residential design and is therefore easier to build such constraints into. The challenge before general-purpose BIM applications like Revit is to build more constraints that ensure the accuracy of the model-so that you don't have to run geometry-based interference checking to spot errors-without detracting from the user experience. It's a tough challenge, but not an impossible one.

Conclusions

With the new release of Revit Building and the launch of Revit Structure, Autodesk Revit has taken a dramatic leap forward towards strengthening its position as a BIM solution that can be used not only by architects but by structural engineers as well, with MEP engineers not too far behind. BIM can only achieve its full potential when it is used by all the disciplines involved in the design, construction, and operation of buildings, and the expansion of Revit from a single application to a platform for multi-disciplinary design will be a critical step in speeding up the transition of the AEC industry from CAD to BIM. While many challenges lie ahead for BIM applications in general, such as those discussed in the previous section, Revit has done extremely well so far and its users can remain confident in its ability to continue innovating and improving with each subsequent release.

Stay tuned for the upcoming review of Revit Structure, where we will also see how well it coordinates with Revit Building.

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 lachmi@aecbytes.com.

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