Dr. Frame3D

In Cadence AEC Tech News #59, I discussed different types of structural design software and pointed out how few tools were available for conceptual structural design. A small company named Dr. Software pretty much had a monopoly in this area, with two real-time structural analysis tools: Dr. Beam for modeling beams, and Dr. Frame for modeling frames and trusses. The focus of both products was on direct manipulation—the ability to draw the structure, specify support and loading conditions, and see the resulting analysis feedback graphically right away. Such tools for simulating and visualizing behavior in real time, using a simple graphic user interface, allow the architect or structural engineer to easily and quickly run through a number of iterations before finalizing the design of the structure.

Dr. Software recently released one more product in its engineering tool lineup based on the same philosophy and approach, of using direct manipulation and interactive modeling to study the behavior of a structure. While both the earlier products had a 2D interface, the new product, Dr. Frame3D, allows users to build and test 3D truss and frame structures while receiving real time visual and numeric feedback to evaluate structural behavior. This review takes a detailed look at Dr. Frame3D to find out how it works, and should be of interest to structural engineers as well as architects.

Interface

Dr. Frame3D has a simple, functional interface with a concise toolset, which makes it easy to learn (seeFigure 1). All the tools for creating and manipulating structures and modifying viewing parameters are located in the two toolbars running on the left and top of the application window. The rest of the window is divided into panes: the main modeling and visualization pane used for creation, manipulation, and inspection of the structure; the results pane below, which provides basic numerical results summaries in tabular format; and the property inspector pane on the left, which lists the properties of the selected object and allows them to be directly edited. In addition, the loading conditions for the structure can be manipulated with options located above the visualization pane, and the status bar running along the bottom of the application window provides useful information concerning objects, views, and tools.

The visualization pane is essentially a 3D space demarcated with an axis and grid in which the structure is created and manipulated. The size of the grid, its spacing along the X, Y, and Z axis, as well as the location of the origin can all be set as required. The space is lit, and a subtle shadow effect allows the 3D structure to be more easily visualized. All the common 3D viewing options such as Zoom, Pan, and Camera Orbit are provided; in addition, quick shortcuts to the plan and elevation views are also available. The perspective effect can be toggled on and off, allowing various 2D views of the structure to be generated. It is also possible to view only selected elements and hide the others. Thus, it is easy to isolate parts of the structure for detailed design and analysis. Value labels can be added to the members to show numerical results, and the units for length, displacement, force, stress, and other structural quantities can be set as required.

How It Works

The first step, naturally, is to create the structural model. The primary means to do this in Dr. Frame3D is to use one of three commands: Auto Frame, Auto Truss, or Auto Beam. Each command is accompanied by a dialog box in which various parameters of that particular type of structure—frame, truss, or multi-span beam—can be specified. For example, choosing the Auto Frame command brings up the dialog box shown in Figure 2-a, where the number and dimensions of bays and stories of the frame are specified. It also allows you to select how the background grid should relate to the frame's dimensions. The frame resulting from the settings shown in Figure 2-a is illustrated in Figure 2-b.

This basic structure can now be further refined by deleting portions of it, by transforming the position of other elements to alter bay and story dimensions as required, and by adding new members. Members can be selected for transformation individually, by groups, or by using the area selection option. Transformations such as translation, rotation, and reflection can be carried out precisely using a dialog as shown in Figure 3, or by graphically moving selected elements in the visualization pane. New members can be added to the structure with fixed ends or free ends, depending upon how they need to relate to their neighboring members. To start with, all the members of the structure will have identical properties based on the default settings. Subsequently, the properties of the individual members can be set as desired using the property inspector pane. This is demonstrated in Figure 3, which also shows how the preliminary frame of Figure 2 has been modified to quite a different configuration by deleting several members and transforming others.

While there is no dedicated option to import structural models from other CAD applications, it is possible to open a simple script in XML format that describes the basic geometry and connectivity of a structural model. A DXF file containing a line drawing of a structure can also be opened; however, the model has to undergo extensive transformation and rotation to be correctly oriented and located with respect to the grid in the visualization pane. Moreover, this ability is still so recent that it is not even mentioned in the documentation. Essentially, most users would rely on the three Auto commands to create the model in Dr. Frame3D, in the absence of more convenient ways to import the model.

After the model has been defined, the next step is to specify the loading and support conditions and watch the structure respond to these actions. Three different kinds of loads can be applied: point loads, distributed loads, and moment loads. All three are demonstrated in Figure 4. Individual loads can be aggregated into load sets designated as live load, dead load, wind load, and so on. These individual load sets can, in turn, be aggregated into load combinations using different factors. One example of such a load combination appears in the dialog in Figure 4. As the loads are manipulated, the structural displacements can be interactively visualized. In addition, a number of other feedback options are also available that can help evaluate the structure, including moment and shear diagrams, axial forces, reaction forces, and so on. Figure 4 shows the displacement of a structure under the applied load.

With regard to supports, the following types are provided: fixed supports; pinned supports; translational (multi- and unidirectional) and rotational springs; internal hinges; and line and plane roller supports. Supports can be created in the structure by clicking at the desired location with the appropriate tool. The location, settlement, and orientation information for a support can be manipulated graphically or with greater precision in the inspector pane. In Dr. Frame3D, joints are created automatically at the junction of elements and/or supports, and are automatically removed when their associated members and/or supports are deleted. The fixity and constraint conditions of joints are automatically defined by the members and supports framing them. Joints can, however, be selected and relocated graphically or through the inspection pane.

The final structural element that can be modeled and analyzed in real time in Dr. Frame3D is a shear wall. You specify the desired parameters of the wall in a dialog, and then graphically create the wall by selecting a starting and ending joint, support, or member point. The stress fields and displacements for the wall caused by the applied loads can then be observed interactively, just as with any of the other members.

Rounding up the repertoire of the application are visualization buttons that allow the viewing scales of feedback options such as displacements, loads, shear diagrams, and so on to be quickly adjusted; various display options for members such as lengths, section IDs, axial force values, and tension/compression coloring (see Figure 5); the ability to define and maintain multiple view states for a given structural model and use these views to generate customized multi-page reports of an analysis or series of analyses; various plotting options that allow different ways of viewing structural response; support for up to 10 levels of undo/redo, which is useful in exploring the effects of varying modeling assumptions; the ability to perform nonlinear analysis in addition to basic linear analysis without any significant increase in analysis complexity or overhead; assistance in design checking by the ability to display values and plots in terms of percentages of each member's relevant capacity; and finally, the ability to export the results and the geometry of the structure in XML format and the screenshot of the visualization pane in JPEG format.

Strengths and Limitations

The greatest strength of Dr. Frame3D lies in its interactivity and ease of use. It provides a single environment within which users can quickly explore structural behavior and the effects of varying loads, support conditions, geometry, topology, material and cross-section properties, and so on, all in real time. This is in sharp contrast to traditional structural engineering software where the modeling of the structure is done in an independent tool or module and then exported to a complex analysis program for determining various aspects of its performance. Changes cannot be interactively explored; the structural representation has to be updated and exported again to the analysis program to see the results of the changes.

Other pluses are the reasonable price of the software ($899), and its very modest system requirements. It is cross-platform, and supports Microsoft Windows 95 and up, as well as Apple Macintosh 8.6 and up, including OS X. An educational license is available for $99, making it an excellent choice for architectural and engineering schools to teach basic structural engineering concepts by demystifying them and hiding their mathematical complexity.

From a professional standpoint, the biggest limitation of Dr. Frame3D is that it is a closed application with limited import and export abilities. Buildings are currently being designed in architectural and engineering firms using a wide variety of CAD and BIM applications using different file formats. Without the ability to read even basic CAD file formats like DWG and DGN, you would essentially have to create the model from scratch in Dr. Frame3D. Conversely, if you create a detailed model in Dr. Frame3D and refine it using the analysis tools, you cannot take it back to your CAD or BIM system. Thus, the application can only be used in isolation and does not form part of an integrated workflow and design process, which is critical for long-term success in the AEC industry.

Another limitation that is rendered more acute in the absence of an import option is the lack of flexibility in creating complex structural configurations. The three Auto structure generation commands for frames, trusses, and beams, along with the ability to delete, modify, and add members can only take you so far—it would be very tough to model, for instance, a pyramidal or spherical shaped structure.

A minor limitation is the quality of the documentation, which could be more comprehensive and better written to capture the manner in which the application would be used rather than by focusing on the description of individual features. What is completely missing are tutorials that can walk you through actual modeling and analysis examples. These are essential in an application that is otherwise so well suited to education.

In Conclusion: The Architecture-Structure Divide

In my training as an architect, I was required to take several courses in structural engineering and while I mastered those with ease, I wasn't really taught structural design in conjunction with architectural design. I have seen this to still be true in the way architecture and structural engineering are currently taught—as two independent disciplines rather than as an integrated one. The same is true for current professional practice and the tools used by architects and structural engineers—they barely talk to each other, let alone work in an integrated fashion.

Ideally, both the architecture and the structure of a building should be designed in the same application and be represented in one model, so that the architectural requirements automatically determine many of the loading conditions and constraints of the structural system. This will reduce much of the tedium of remodeling the structural system and specifying the loads—of essentially starting from scratch. With an application that affords integrated architectural and structural design, the architecture and the structure can be created in tandem and will result in a much more coherent building. Hopefully, a structural design tool such as Dr. Frame3D, which is simple and intuitive, will eventually be integrated with an architectural design tool and provide this unified design capability.

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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