Free Form Rebar Basics
Have you noticed that building footprints have become more complex with fewer 90-degree angles and straight lines? With the increase in the complexity of buildings and the need to model rebar in the concrete foundation walls, footings, etc. The “Free Form Rebar” function has been added to Autodesk® Revit® 2018 to help users better define the reinforcement in their structural model.
The Definition of Free Form Rebar
Before we begin to model Free Form Rebar we first need to understand the definition of Free Form reinforcement, so here it goes.
Free Form reinforcement can have any geometry, either planar or 3D, and can be used for modeling and detailing rebar in complex 3D structural elements. Free Form Rebar is part of the structural rebar category and will have all the properties associated with it. Like regular rebar, you can place Free Form Rebar in single bars or sets. This allows this rebar type to be easy adjusted for a specific need.
The First Step
So you have modeled some structural concrete elements with some more complex geometry. This will be the perfect opportunity to use this new feature, so let’s begin.
To get started you will want to create a 3D view of the element to which you want to add the reinforcement. You can do it a few different ways. I suggest using the Selection Box, which will allow you to quickly isolate the object or objects to which you want to add reinforcing.
For this article I have created a 3D view of a wall footing with an arched profile.
Figure 1: 3D view of arched wall footing
Now that we have created a 3D view of our footing, we are ready to begin placing rebar, but before we get started let’s learn how the Free Form Rebar tool works.
Where to Go
Now that we are ready to add rebar let’s find the proper Revit tool to do so.
Click the Structure tab ► Reinforcement panel ►Rebar.
Next click Modify|Place Rebar ►Placement Methods panel ►Free Form Rebar.
Note that the Modify|Place rebar ► Rebar Set Type Panel ► Surface Distribution is selected.
Make sure the Modify|Place Rebar ► Multiple Selection Panel ► Select multiple is not selected.
Figure 2: Free Form Rebar tool locations
Understanding the Properties Palette
When you start your layout you are going to want specify the rebar type in the Properties palette.
Figure 3: Properties palette
Some important information resides within the Properties palette such as Rebar Size, Type, Layout Rule, etc. Knowing what resides within this palette will help you tremendously in laying out the rebar as rebar contains a lot of important parameters that are found within this area.
Now that you are more familiar with the Properties palette, let’s get started.
Let’s select a layout type. You have five choices for layout styles: Single, Fixed Number, Maximum Spacing, Number with Spacing, and Minimum Clear Spacing.
Each layout offers its own benefits. I personally like to use the Maximum Spacing layout tool, but I suggest you try them all. The more you are familiar with the options, the more versatile you will be.
Now that we are ready to place some rebar let’s get started. The first thing you will be prompted to do is to select a Host Surface. This is the surface that will host the Free Form rebar.
Figure 4: The host surface
You can keep selecting host surfaces, but in this case we don’t want to, so we will hit the space bar to switch to the next selection option we will need to make.
You will now be prompted to select the Start Surface, which will dictate the start of the rebar path.
Figure 5: The Start Surface
After selecting the start surface we will now need to dictate the end point of the rebar run. Hit the space bar and it will switch to your next selection type, which will be titled the End Surface.
Figure 6: The End Surface
Let’s Finish the Layout
We have now made all the required selections for this particular rebar layout. Hit the green check to finish. You will now see the results of all your selections.
To make the rebar show up properly in your 3D view, you will need to select the rebar you just placed and select the View Visibility Parameter in the properties box
Figure 7: The “View Visibility” settings
You will need to check the View as Solid box in your “3D View” view type. Doing this will make your rebar show up as a solid as shown in Figure 8.
Figure 8: The end results
Editing the Constraints
Free Form Rebar will adhere to the cover settings in your model, but you might need to edit the settings for your newly placed rebar, so let’s understand the constraints.
Figure 9: The rebar cover settings
Select the rebar you just placed. Doing this will bring up the rebar settings you are accustomed to seeing such as Layout, Spacing, etc. Along with those common settings you will find the Edit Constraints command.
Figure 10: The Modify Rebar settings
Once you select the Edit Constraints command you will now have the option to modify such settings as end cover, top cover, and even the slope of the rebar path. Familiarize yourself with these settings and how modifying them affects the rebar appearance.
Figure 11: An overall look at the constraints
Here I covered the basic flow of the new “Free Form Rebar” tool that has been introduced in Revit 2018.
In my opinion this has been a great advancement. With the advances in materials and design, Autodesk is taking the steps to make sure Revit Structure keeps up.
This was just an example of what you can do with the new Free Form Rebar feature. Play around with the new feature yourself and become comfortable as the reinforcement capabilities have become almost limitless.
Figure 12: An example of the possibilities (Image courtesy of Autodesk)
Jason Lush is a long-time veteran of Structural Drafting and Design. He is a Structural BIM Specialist with Warehaus, based out of York, Pennsylvania. Jason also currently serves as the Revit Structure Content Editor for the AUGIWorld. Jason can be reached at email@example.com.