Elements from the Structural Framing category, where the “Material for Model Behavior” parameter is set to Steel, Precast Concrete or Wood (in the family) used to have family instance parameters “Start Extension” and “End Extension”. You know, the parameters that were calculated using negative dimensioning trick. These parameters threw some confusion in the use of the beams when connected to other elements. Besides, the analytical model didn’t respond to the change of shape (cfr. Article from Village BIM).
What has happened with those refreshed and simplified families now?
Well, the family parameters are replaced with built-in instance parameters “Start/End Extension” in case of non-joined beam (i.e. cantilevered beam end) and “Start/End Join Cutback” in case of joined beams (i.e. beam-column connection).
How to use “Start/End Join Cutback” ?
The possibility to extend the beam ends is essential for detailed design of steel structures in Revit. We all know that the “Join Cutback” is measured from the bounding box of the connecting element (i.e. Structural Column) to the shape of the beam, once a beam is automatically “joined” with the column.
In this image the “Start Join Cutback” is set to 12.7 mm (default value). The Cut Length of the beam is influenced directly by this value. When scheduling steel beams, the calculated length will not reflect the one you need in your construction quantification. In that case it’s better to lengthen the beam with the “Start/End Extension” or “Start/End Join Cutback” parameters.
Some customer cases have proved that the difference can be up to 6% of the total weight of the structural beams ! Next question: Who is willing (read: has time) to measure the distance between the bounding box of the column and his web edge? So that you can fill in the correct negative Join Cutback value, in order to lengthen that beam? …
In the video below you can see how to assign the cutback graphically, by using the align function on the shape handle of the beam.
This method used to work in Revit 2013 too, but you needed to use TAB key to select the Shape Handle of your beam in plan view. Now in Revit 2014 the shape handle shows up immediately. The shape handle is basically visible when applying instance parameters on two ref planes in a family. For structural framing the shape handle is generated programmatically. Besides this method now also works in 3D view.
This only works in Revit 2014 – Update Release 1
(You can download UR1 using one of the links below)
Direct download links – UR1