Friday, April 1, 2011

Structural Trusses with the Revit Truss Tool - Simple Truss

So the Revit Truss tool universally gets a pretty bad wrap, I would agree that it isn't living up to its expectation. But like a lot of tools in Revit if you are not using it you are missing out. But for some reason people are happy to miss out..

I have spent a lot of hours with the truss family, and here are some of the things I have learnt

Firstly make sure you understand what you want, and how you want to flex it
  • What is the geometry of this truss
  • Will the truss be a one off
  • If not, will it need to flex and adjust geometry as multiple instances
  • How do you want the truss to display in the project, are you going to detail the truss to a high level with 3D isometrics at connections etc.
The answer to these initial questions will generally send me down 3 paths
  1. A simple non-parametric truss which is prebuilt to approximate dimensions in the truss family
  2. A parametric truss family with in-built parameters and arrays
  3. A framing family which acts like a truss, but is actually a parametric beam/frame
 Path 1 - Non-Parametric Truss

This is the easiest option, and will be suitable for most trusses that dont require the ability to flex and update number of verticals

Truss Example
 So lets consider an example, in the situation above, we could use a parametric family, but if we dont need to flex the bays, there is no point wrestling with formulas and arrays

The first thing to remember with trusses in Revit, is we don't need to build the angle into the truss, Revit already allows us to sketch the angle in the project, and even lets us attach the top chord to the roof plane

I have made a quick video of the steps required to model a truss like this




Finished truss

But the key points for this are
  • No need to constrain the truss linework in the family, the lines will follow the built in reference planes and each other
  • Set the truss length and truss height to approximately the dimensions you require in the project, there is no point building this thing to 20m long if your project actually needs a truss 4m long and 0.6m high
  • Use equalized dimensions to your advantage, you could also easily add an additional reference plane at a third point for example to create an additional setout point with equalised bays in between
  • Once you load the family into the project, make sure you add member types in the type properties first before placing the truss. Revit does funny things if you try and change it afterwards
  • Think about the best way to place this truss in the project, in the example of created a reference plane to setout the bottom chord, and then attached the top chord to the roof. You can also attach trusses to floors, you cannnot attach them to ref. planes, but you can sketch the top chord by editing the profile as well

Well that is a simple non-parametric truss family, next post I will go through a simple parametric truss family





3 comments:

  1. That is cool, I have been looking into what the truss companies here in Chicago IL actually do. It is kind of nice to have a better idea.

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  2. Thank you very much for making this video, I appreciate the time and effort.
    Best

    ReplyDelete