Steel Weight - A Conversation, Further Thought and Another Method

• A Conversation

Mike: "So, the Revit weight schedule calculates using volume?"


Me: "Yes"


Mike: "So when you put a service hole in a beam, it subtracts it from the volume?"


Me: "Yes"


Mike: "But when you buy steel, it doesn't come with holes in. Shouldn't the weight takeoff reflect this?"


Me: "Ahh... Good point"

• Further Thought

In order to overcome this, the weight can be calculated using kg/m multiplied by length. In my mind, this presents a couple of issues:

1. How to get a steel length from a column
2. How to make it multi-category, so it all appears on one schedule

Fortunately, our families all contain cross-sectional area figures 'A', calculated automatically by formula based on the parametrics of the profile. The kg/m value 'M' is calculated from this:

• Another Method

The solution to both problems is to introduce a new shared parameter, 'Section Length' to all the steelwork families. This is set to 'instance' and set as a reporting parameter. A dimension is then run from one end of the beam/column to the other and is set to this parameter. Because it is a reporting parameter, whatever length the beam/column is, its value is fed back to 'Section Length'. This can then be used to calculate the weight. The following video demonstrates this concept

Steel Weight - A Method and Some Thoughts

There are a lot of bit and pieces online regarding steel weights in Revit Structure. The aim of this post is to pull some of it together and to add my own thoughts. The video goes through the procedure for creating the schedule and the information below discusses the finer points

• Before You Start, Content is Critical

We abandoned the OOTB steel families early on and generated our own family content. This allowed us to take a much more holistic approach to the content. In the video example, there are 'Universal Beam' members of both 'Structural Column' and 'Structural Framing' Categories. These families are driven by identical parameters, profiles and most importantly, Type Catalogues. All our steelwork families contain two parameters, 'Section Type' and 'Section Name'. These are only ever used in Steel Families and they allow us to isolate steelwork in schedules. In the case of the example, the values of these two parameters are consistent in both 'Universal Beam' of 'Structural Column' and 'Structural Framing' categories. This allows us to consolidate all 'Universal Beam', regardless of family category, together in a multi-category schedule

• Some Points on Volume
  
  In the 'Material Take-Off' schedule, the parameter 'Material : Volume' is used to calculate the weight. The material parameters in Revit Structure are only available for the following family categories:
  

• Revit will calculate volume based on the medium level of visibility. Another reason we abandoned the OOTB families is that for all rolled sections, the root radii are omitted in the medium level of detail, so the weights were coming out incorrect. Hence our content shows a full profile for both medium and fine detail to get the correct volume.


• The calculated value in full is Volume multiplied by Density. The syntax is:
  (Material : Volume/1)*7.85
  
• The parameter 'Material : Volume' must be divided by 1 to neutralise m³ to a number to avoid an 'Inconsistent Units' error.
  
• 7.85g/cm³ is the metric density value of mild steel (in old money, this is 0.284 lb/in³).
  
• Elements must have physical material applied to them in order to appear in the schedule. I'd recommend that a generic steel material is applied in the family by default so they will show up regardless
  

So that pretty much sums it up. Hopefully this will be of some help