topic Re: Modify Moment of Inertia of Sections in Revit in Revit Structure Forum

Modify Moment of Inertia of Sections in Revit

Ryan.sulistian — Tue, 16 Nov 2021 10:20:12 GMT

Hi, I made a model from Revit and sent it to Robot to be analyzed but I forgot to reduce the moment of inertia of the members.

The sections were predefined in Revit. Is there a setting to edit a section's moment of inertia in Revit?

Re: Modify Moment of Inertia of Sections in Revit

RPTHOMAS108 — Tue, 16 Nov 2021 10:41:04 GMT

They are defined in the type properties in Revit (if the section profile is set and they have been populated). Can likely be changed in Robot also.

Would suggest they are reduced in Robot if the change is for a temporary purpose.

Re: Modify Moment of Inertia of Sections in Revit

dhepi2311 — Mon, 28 Feb 2022 09:41:48 GMT

@Ryan.sulistian @RPTHOMAS108 Do we have any options to calculate Moment of inertia automatically in Revit family without entering the values or formulas.

Any possible while creating the element it automatically calculate its moment of inertia.. like area, volume similar to that..

Re: Modify Moment of Inertia of Sections in Revit

RPTHOMAS108 — Mon, 28 Feb 2022 22:03:32 GMT

No you'll have to add an idea for that.

In UK we would use values taken from the blue book anyway for rolled sections, so in that instance these could be added to type catalogue from the blue book. Obviously it is geometric property so we could have a formula that works it out directly but designers tend to recognise the values that come from the tables. If you see some overly precise value worked out by formula that doesn't match the table value you tend to wonder if it is exactly correct. Also is is appropriate to use a value with a greater precision than is commonly used in design manually for these kind of things? Some would argue that the precision used to describe properties of things in design tables is the precision you should use for those things in design calculations (I would agree with that).

For plate girders and other sections not noted in the blue book we would work out the second moment of area via combination of second moment of areas for individual parts of a section via parallel axis theorem (combinations of 'I' values for rectangular parts and corner fillets etc.).

This process leads to some simplified formulas for certain section types which I'm sure would be commonly available somewhere online.