A Promising Option for Truss Design
Three popular truss layout and design programs in use today are MiTek 20/20, Alpine, and Key Frame. I’m familiar with MiTek 20/20, having used it for more than five years. For this article I will focus on a comparison of MiTek 20/20 and Autodesk® Revit® plus an extension from tools4revit called Truss+.
Truss Design in MiTek
Before we review how to lay out and design trusses in Revit, let’s take a quick look at the workflow process in MiTek 20/20. The traditional process is one where the engineer/architect or the builder will submit a set of architectural drawings to the truss manufacturer for production. The truss manufacturer then needs to reproduce the footprint of the structure and place the roof and ceiling planes on top of it.
From there the manufacturer produces the truss layout by placing the trusses in the most efficient positions. Next, the manufacturer exports the truss to the engineering side of the MiTek 20/20 program where they check loading and optimize the truss webbing, size the 2x members according to span and loading, and generate the plate for the truss. When this is complete, they send it to the shop for manufacturing.
Figure 1: In this figure we see the walls with the overhangs placed in MiTek E-frame.
Figure 2: In this figure we see the roof planed in on the walls.
Figure 3: A 3D look at the roof plan of a simple hip roof.
Figure 4: The trusses are inserted using the roof planes to shape the profile of the truss.
Figure 5: A 3D look at the roof trusses for this hip roof.
One of the problems of performing this work process through MiTek 20/20 or any of the other programs is that the designer has to reproduce the architectural footprint of the structure along with the roof and ceiling planes. This takes time, and in production, time is money.
In addition—and this is critical—no one can use these programs unless you purchase their products or equipment to manufacture the trusses. Because their software program is only given to those who resell their products; architects, engineers and builders are out of the game due to lack of access to these tools.
Another Option within Revit
So you may ask yourself, “How can I design my own trusses?” In my humble opinion, the solution is tools4revit Truss+. This affordable tool allows architects, engineers, and builders to get ahead of the game by laying out their own trusses and by generating truss profiles with the truss layout directly inside Revit Architecture or Revit Structure.
tools4revit Truss+ is easy to use with the proper training. You can lay out your trusses in much the same way as you saw in the previous MiTek examples by using model lines and truss grids.
I’ll show you what I mean. I will use a simple hip roof for this example.
Figure 6: In this figure we insert the walls in Revit Architecture.
Figure 7: Next, we insert the roof plans in Revit with the proper pitch and overhangs.
Figure 8: Finally, we insert our truss hip grids by picking the end walls first, then the left and right side walls. This is a tools4revit truss+ function. Each truss grid is placed one at a time. Each grid is selected one at a time for truss generation. You can also place a truss grid by model line or place each truss by model line.
Figure 9: In this example we see all of the trusses generated in 3D.
Figure 10: In this example you see the truss layout in plan view.
After this has been completed, you can produce your truss layout with dimensions and truss tags or labels for the truss manufacturer, along with all the truss profiles. This entire process is done in Revit. This saves truss designers time when they produce the truss engineering drawings from the information you give them for professional seals and manufacturing.
Truss Optimization and Analysis
You can see how this process compares to MiTek 20/20 when it comes to the truss layout process. The only difference is that Truss+ does not at this time produce any analytical process; however, this is about to change in the very near future. I am glad to announce that AGA-CAD, the developers of tools4revit Truss+, will have analytical processing in the next release. You will also be able to optimize the truss webbing and panel points. Please note that truss plating will not be a part of this next release.
There are a lot of factors in truss design with regard to the analytical side of the process. By analytical process I mean loading, lumber sizing, lumber grade, plating, and so on, as well as truss connections. Just the span of the truss itself can affect all of these areas. The next tools4revit Truss+ release will allow for even more versatility with truss design.
Truss+ Tips and Tricks
Despite my previous example’s simplicity, you can produce complex roof truss systems such the roof system in Figure 1. In this example, the Revit roof was not planed in from the walls, so the conventional truss grid process would not work. In this case, you must either place the grid by model line or simply use model lines to place the trusses, as I did here. You can use simple commands such as Array, Copy, and Mirror to set the trusses. You can also use the Trim and Extend command to adjust the truss length.
Figure 11: Complex truss design.
Refer to Figures 12 and 13 for some tips and tricks to better utilize the tools4revit Truss+ tool. How you place a model line is important. Whatever the length, the model line will become the length of the bottom chord of the truss. Also, make sure that you have your work plan placed at the truss bearing point at the top of your walls or beams. Trusses also center up on the model lines so in the case of hips offset your model line accordingly.
- The hip you see in the two Figures has a setback of 7’-0”.
- The hip girder truss and the first mono truss have a Model Line offset of .75” so the trusses do not overlap.
- When placing mono trusses, start the model line from the bearing wall and draw it inward or the truss will go in backwards.
- When setting grids by model line set the model line on the outside edge of the wall for hips and gables. You can also set valley trusses by model lines by placing a Reference Plane on the outside sloped surface of the roof, and then you simply set your Model Lines.
- You can Trim or Extend the Model Line to the proper length by trimming to the edge of the roof face.
Figure 12: Model line placement.
Figure 13: Hip corner after proper model line placement.
Refer to Figures 14, 15, and 16. These are just a few examples of what you can do with tools4revit Truss+.
Figure 14: Showing the work plane on the roof slope.
Figure 15: Showing the model line being trimmed back the edge of the roof face for valley trusses .
Figure 16: Shows the model line placed on the outside edge of wall for hip grid placement.
In some of my recent Truss+ support-related conversations with individuals who have downloaded the evaluation version of Truss+, it seems that the designers are trying to create trusses for major commercial roof systems like the one shown in Figure 1 before getting a grasp of how Truss+ works in the first place. My advice to people that are evaluating the tool is to use the help material provided on simple roof systems and to learn how the tool works prior to trying to tackle a major roof truss job. CAD Training Online offers one-on-one training to support your needs.
Also, turn off all unnecessary elements on the drawing by going into view section of Revit and then visibility graphics. All you need are the walls, roof planes, structural framing, and load bearing beams. Set your roof to Transparent so you can better see what you are working on. By doing this you should have fewer problems selecting all the elements you need to create your truss layout.
Most architects, engineers and builders use AutoCAD® to create a 2D truss layout and produce truss profiles. Truss+ eliminates this tedious and time-consuming process by doing most of the work for you, as well as giving you a very nice 3D view of your truss system. This 3D view is invaluable as it helps you solve truss design problems in your truss layout.
There is a lot more that you can do with Truss+, so please visit YouTube and watch a 16 minute video on the entire Truss+ process and see additional examples of what Truss+ can do to save you time and make you far more productive.
If you wish to learn about truss design please visit the Structural Building Components Association (formerly the Wood Truss Council of America or WTCA) website. You will have to pay for the SBCA dues, but it is your best source of information on truss design, practices, and principles.
Stephen Young has been a designer for 30 years, specializing in truss design, architectural drafting and design, and machine part and component design in various industries. He has used Autodesk products for all of his engineering CAD work since 1989.
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