There have been major changes to the analytical model in Autodesk® Revit® 2012—changes so drastic that you actually have to forget everything you know about the anaytical model from Revit 2011 and before. The changes are as far reaching as visibility of the analytical model, adjustments to the analytical model and linking with structural analysis software. This article will discuss how to use these new changes to help create and modify the physical Revit model.
The analytical model in Revit has been something of a mystery. It has gotten a bad reputation over the years. It is there whenever you create the physical model, so there is no escaping it. Figure 1 shows the difference between the analytical and physical models.
Figure 1: The analytical and the physical model.
Revit Architecture users hated it because it is always visually getting in the way. Revit Structure users hated it because it cannot be changed easily. In Revit 2012, these problems have been solved.
The biggest change is the ability to edit the analytical model. One element added to the edit model is the reference point or analytical node shown in Figure 1. The analytical node now controls the ends of the analytical beam lines. The analytical node or reference point, as it is called, in the mass family editor is the most powerful modeling tool Revit has to offer. This article will discuss how to take advantage of this very special “gift” that was given to all users in Revit 2012 and how to edit the analytical model and then apply those changes to the physical model. Before we do that, let’s first take a step back and examine what changes have been made to the analytical model in Revit 2012.
Visibility Control Changes
Revit users will rejoice over the new changes that have been made to the visibility controls of the analytical model. To find out about all these changes please check out “What’s new in Revit Structure 2012” by Phil Russo in the April 2011 issue of AUGIWorld. In summary, visible representations of the analytical model are now completely separated from the physical model elements. Before Revit 2011, isolating the analytical model was cumbersome and each element had to be toggled and turned off element by element. Now with one button click in the view display toolbar, you can toggle or isolate the entire analytical model from the physical model as shown in Figure 2.
Figure 2: The view display toolbar.
Adjusting the Analytical Model
To activate the analytical edit model, first select an analytical element and click on the “Analytical Adjust” button. This command can also be found under the Analyze tab as shown in Figure 3.
Figure 3: The Analyze ribbon commands.
Note: The procedures described in this article for adjusting the analytical model is limited to Revit Structure. However, these methods may be used on Revit Architectural and MEP models if opened in Revit Structure.
Let’s discuss what happens to the relationship of the physical and the analytical models when the analytical model is adjusted. Let’s take the one-story framing example shown in Figure 1. If one end of the middle analytical beam is moved 2’-0” away from its physical beam end and the physical beam end is later moved, the relationship or “offset” remains the same as shown in Figure 4.
Figure 4: Relationship of physical and analytical models.
Adjusting the Physical Model
The analytical model is always adjusted from the physical model; however, there is nothing preventing you from adjusting the physical model to the analytical models location. The rest of this article will describe how to use the powerful adjustment tools for the analytical model and then adjust the physical model to match the analytical model’s location. Until the developers give the same editing tools to the physical model that are now part of the analytical model, we have to take matters into our own hands. To adjust the physical model to match the adjusted analytical model, follow the steps below.
Consider the new location of the beam on the physical model in Figure 4. Go to the roof/second floor plan view> select align > select adjusted analytical beam > select physical beam. The beam will align to the location of the analytical beam however the analytical beam will also auto adjust to the same offset as described in Figure 4. To correct this, select the analytical beam > select analytical adjust> select analytical reset. The results are shown on Figure 5.
Figure 5: Physical model adjusted to match the adjusted analytical model.
Analytical Edit Mode
The analytical edit mode is activated when you toggle the “adjust analytical” command. The analytical edit mode has some features that are helpful when adjusting the analytical and, ultimately, the physical model. You are allowed to add dimensions that only exist in the analytical edit mode. As mentioned earlier, the analytical node is only available in the analytical edit mode. This is helpful when adjusting the physical model to the analytical model for complex geometry.
Unique Characteristics of the Analytical Node
Now that the basics of how to use the analytical model to adjust the physical model have been presented, it’s time to examine how to use these new tools for more complicated structures. The analytical node shown in Figure 1 has some powerful and unique characteristics. The analytical node has pull handles; in global coordinates that can be adjusted easily, as shown in Figure 6.
Figure 6: The adjustment handles on the analytical node.
Also, analytical nodes can be hosted onto other elements including analytical beams. A hosted node will appear as a small sphere while a non-hosted node will appear as a large sphere as shown in Figure 7. Contrast this with the end of a physical beam. There is no way to tell by looking at the end of a physical beam if it is hosted to its supporting girder.
Figure 7: Hosted and non-hosted analytical node.
Another unique characteristic of an analytical node is the ability to set the hosted node’s location based on a relative location along a hosted curve as shown in Figure 8. It is not possible to do this with the end of a physical beam. In the example in Figure 8, the node/end of the analytical beam is half the distance from the end of the analytical girder.
Figure 8: Hosted analytical node location relative to host curve/analytical beam.
A Complex Adjustment
Let’s use what we just learned and what was illustrated in Figures 7 and 8 on a real example. Consider the following girders in Figure 9.
Figure 9: Curved girder framing example.
If, for example, you wanted to place three physical beams at the ¼ points of a curved girder that was made up of a spline curve, how would you do it with only the physical model? You could cut sections at each location in plan along the ¼ points, but this would not be accurate and it would be very time consuming. The better solution is to use the “adjust analytical” command. Follow the steps below for the solution.
Draw the three physical beams in plan. Make sure to start and end each beam on the curved and straight girders as shown in Figure 9.
Turn on the analytical model line and click “adjust analytical.” Select the analytical nodes of each beam and select the “pick new host” command as shown in Figure 10.
Figure 10: Adjusting the analytical node via Pick New Host command.
Place each analytical node at approximately the ¼ points of both girders, if they are not already located there. Select each node point and change the dimension parameters in the properties box, as shown in Figure 8, to “measurement type = normalized curve parameter” and normalized curve parameter = .25, .5, and .75 accordingly. This will set the beams at exactly at the ¼ points along the girders length as shown in Figure 11.
Figure 11: Adjusting the analytical node to the ¼ points.
Note: Make sure that each analytical node of the ends of the analytical beams are hosted and appear small. If you have trouble placing the analytical nodes on the curved girder, place the nodes first at the end of the end segment of the curved beam.
Finally, adjust the physical model to match the analytical model.
Figure 12: Adjusting the physical model to align with the analytical model.
Go to the 3D view> select align > select the end of adjusted analytical node > select the end of physical beam as shown in Figure 12. Repeat these steps for each end of the beam that frames into the curved girder. Ignore the “unjoin element” message. Also adjust in plan each end of the physical beams that frame into the straight girder. The resultant framing is shown in Figure 13.
Note: As shown in Figure 4, the analytical model moves relative to the physical model so you may find it necessary to click the “analytical reset” command for each analytical beam.
Figure 13: Final physical and analytical beam locations.
Based on these examples, it is clear that using the analytical model to create/adjust the physical model is very helpful. Only two examples were presented; however, these methods may be applied to all types of structural framing.
Marcello Sgambelluri is the BIM Director at John A Martin & Associates Structural Engineers in Los Angeles, CA, USA. He has been using Autodesk products for over 15 years including AutoCAD, 3ds Max, and Revit Structure. He is a member of hte ASCE-SEI BIM committee and speaks at structural professional conferences across the country. Marcello teaches classes at Autodesk University that focus on free-form modeling in Revit and he beta tests the yearly releases of Revit Structure. He can be reached at email@example.com.