Mastering Parametric Trusses

Transcription

1 Class Description With the introduction of the Truss Tool into all streams of Revit now is the time to understand how to build your own parametric truss families. This Lab Session will go through the steps required to build up a custom parametric truss Menzies Building, Monash University Clayton, Melbourne About the Speaker: Ben is a Structural Draftsman with 10 years experience with early experience in 3D modelling of structures. Ben is the Technical Drafting Leader with Irwinconsult, a multidiscipline full service engineering firm with offices in Melbourne and Darwin. Ben has been using Revit since 2006 working on projects including the Royal Children s Hospital in Melbourne, a $1 Billion project

2 Class Example 1 Top Release Truss Page 2 of 2

3 Class Example 2 Support line 1 Support line 2 Truss with internal set-out constraints Page 3 of 3

4 Class Example 3 BEYOND Façade truss Variable start and end offset Page 4 of 4

5 Notes: Before you start: Before you even open Revit, you need to make sure you understand exactly what you require from your model. The best way to think it though is to get out the pen and paper. Sketch down what you need, from there you can then start to think about what is required in your family to achieve what is required Some Key points to consider How will your truss be setout? Top Chord, Bottom Chord? How will it be triangulated? Does the triangulation have intermediate setout? Is this truss a once off instance or will it be used in multiple instances with varying lengths? Example of working sketch Page 5 of 5

6 Building the Truss Family Starting a new family you will select the Metric Structural Trusses.rft template When you initially open the fresh truss template file, the initial reference planes and parameters in the file are hard locked into the template and cannot be removed. Particularly the centre line might not be required for your truss but it will have to remain as it cannot be removed Example of clean template file Page 6 of 6

7 Setting the bones - Reference planes The first step to building a truss family, much like any other parametric family is creating what is often called the bones, or skeleton for the geometry No family is this more important than for trusses Following what you have hopefully planned out, create reference planes for each setout point of your truss Example of truss skeleton Page 7 of 7

8 Making it Parametric You can easily make your truss your truss length parametric, but what if you want to be able to extend your truss and maintain a minimum spacing for your verticals? You need to setup some simple formulas with your parameters which you can then use to drive an array First you will need to set a truss bay width parameter, you can either make this parameter an instance or type parameter depending on what you require I would generally call this parameter MaxPanelWidth TIP:Don t forget parameters are case sensitive, and although it is tempting, avoid using symbols as much as possible as they can conflict when used in formulas Page 8 of 8

9 You can now calculate the number of bays with the formula NumberPanels =(Truss Length / MaxPanelWidth) + 1 You then then need to create another parameter for actual bay width ActualPanelWidth= Truss Length / NumberPanels You now have all the parameters needed to create a simple array Model the first vertical and first diagonal/s roughly to the length required with the web layout line Add a dimension from the vertical to the diagonal end and for the height of the vertical carefully choosing the end points of the vertical not the top/bottom chord or reference plane Page 9 of 9

10 Now you can array the typical bay, the truss layout lines need to part of the array group as they will disassociate from the reference planes once arrayed You can then set your number of panels parameter The next step is constraining the array to the truss length, in the case below you would align and lock the first vertical to the left reference plane, and align and lock the bottom corner of the last diagonal to the right reference plane Repeat for the bottom reference plane to lock in the vertical direction Example of truss array Page 10 of 10

11 Testing Do it or suffer the consequences! If there is one thing you will learn, it is that you will not always get it right the first time with parametric familles. Before you think about loading it into your project, flex the key parameters to ensure your formulas are working as expected and that you have constrained the geometry correctly Testing is particularly when it comes to arrays, once you array a set of elements it can be very difficult to remedy a unconstrained array group once in place. Truss gone wrong Groups have lost their constraints Page 11 of 11