there are two kind of column/beam structural families in Revit content:
- Standard structural steel element. The Section Shape type property of a steel framing element specifies a section shape. A defined set of Structural Section Geometry parameters exists for the element.
- Custom steel element. The Section Shape type property of a steel framing element is Not Defined. The geometry parameters required for generating steel connections are not defined.
(source: https://knowledge.autodesk.com/support/revit-products/learn-explore/caas/CloudHelp/cloudhelp/2018/EN...)
Each have a different parameter for weight:
- Custom steel element - W - it is nominal weight/foot. Can be used in schedule
- Standard structural steel element - doesn't have a weight parameter that can be added to schedules. It has the Nominal Weight type parameter.
Weight parameter (not to be confused with the Nominal Weight from element type parameters list) can be used in schedule just in the case when the steel fabrication data is attached to the beam. In this case, in the schedule, the value takes into consideration the cuts made by holes or bolts, but considers the cuts made with steel modifiers. It is a read-only value.
(for more details about steel fabrication shape you can fin here: https://knowledge.autodesk.com/support/revit-products/learn-explore/caas/CloudHelp/cloudhelp/2018/EN...)
(more info about how to calculate the exact weight for the custom families can be found here: https://knowledge.autodesk.com/support/revit-products/learn-explore/caas/sfdcarticles/sfdcarticles/S...)
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