topic Re: What defines the "Top" of a beam? in Revit Architecture Forum

What defines the "Top" of a beam?

nmcmahonTW94C — Fri, 13 Dec 2024 14:41:13 GMT

Having issues with swapping beam families while trying to retain their Z position.

As we can see below both these beam families have their Z justification set to Top with offsets of 0.

The right hand beam "Top" appears to be somewhere just above the refplane of the beam. Not as I had imagined it would be the top of the geometry. I had planned to have a reporting parameter give the value of extra top encasement and use this to offset the beam so that the beam itself in the same spot.

The reference planes in the family are all the same (I duplicated the original family and just added encasement and coordination zones.

Any pointers would be appreciated.

Re: What defines the "Top" of a beam?

RDAOU — Tue, 17 Dec 2024 05:22:17 GMT

@nmcmahonTW94C

It is logical for it to be the top of the geometry unless the plane above the geometry is referential. If the Geometry is modeled in the family or nested into it, the software assumes it is part of the beam.

Nonetheless, whether the top justification is to the top of the metal beam or top of encasement should not be an issue. If it is the top of the beam what should control the encasement, you can still control it using the same formula either in family parameters or global parameter. instead of subtracting the offset add the offset

Re: What defines the "Top" of a beam?

nmcmahonTW94C — Mon, 16 Dec 2024 08:55:28 GMT

That was my assumption but the reason why I've posted is that that is not the case.

The top of beam in the encasement family is somewhere in the middle of the beam. It not a reference plane, its not the top of geometry.

Re: What defines the "Top" of a beam?

RDAOU — Mon, 16 Dec 2024 09:13:55 GMT

@nmcmahonTW94C

It is the top of the geometry and at my end it works as expected and you can see the gif in the previous post where I added a nested encasement/plate above the beam...maybe you have an issue with the family you modeled. If you wish you may upload it to have a look on what is happening at your end

Re: What defines the "Top" of a beam?

nmcmahonTW94C — Mon, 16 Dec 2024 09:28:40 GMT

Hi Please find the beam attached.

Re: What defines the "Top" of a beam?

RDAOU — Tue, 17 Dec 2024 05:32:43 GMT

@nmcmahonTW94C

Functioning as expected...See initial reply. You have set the planes as weak references so Revit is assuming they are to be taken into consideration when inserted into the model (for instance an offset between the encasement you have placed and some other building element it might clash with)

If it is not what you are trying to do, select the top most plane and the bottom most one and set to "not a reference"

Re: What defines the "Top" of a beam?

nmcmahonTW94C — Tue, 17 Dec 2024 11:01:02 GMT

Apologies, Sent the wrong family. Please see this one.

My findings indicate that reference planes have no bearing on Beam Top or origin Justification points.

Re: What defines the "Top" of a beam?

RDAOU — Wed, 18 Dec 2024 08:53:26 GMT

@nmcmahonTW94C

When you select the beam in the model and see that the top/the center and the bottom are not where they are supposed to be, it means the reference planes and family origin are not set up properly.

It has two essential things to fix and one option...open the Left view:

There is the reference plane at the center - Select it and check the option defines origin
There is a reference plane at the bottom and the top of the upper encasement panel - set to Not a Reference
Set the reference plane controling the Coordination box/zone to weak reference considering it might extend further up if clearance from the encasement is required. (Not necessary but a neat good practice to avoid using geometry edges for alignment in the model)

And now it should work like this (Notice how the origin changed?)

Re: What defines the "Top" of a beam?

nmcmahonTW94C — Wed, 18 Dec 2024 15:16:02 GMT

Thanks RDAOU for your efforts, Although I don't think it's quite correct.

What sets the origin seems to be the Ref plane of the Beam and not the plane ticked Origin. And I really wanted the ability to set the "top" to somewhere I'd like. However...

Your selection of weak reference plane to define "Top" works if it's outside of all geometry but as soon as you place that Weak reference plane within the geometry the "Top" is now the top of geometry.
The position of the origin ref plane in relation to the Ref Level affects the positioning of "Top". For instance If I place ref plane "Origin" 25mm above Ref level. The "Top" is now 25mm below the top of geometry (See first Pic). If I move that origin ref plane 50mm above Ref level, the "Top" is now 50mm below top of geometry.
Changing the Origin reference plane from "Weak reference plane" to "Top" doesn't affect positioning but does move the reference plane see pic 2+3

Pic2 - Green original ref plane set to weak Ref.

Pic 3 - Origin reference plane set to "Top" (Green line is Reference level, dim is to Origin Ref plane)

It's like discovering a new species. My guess is that this isn't exactly desired functionality but quirks of the system. And therefore not really documented.

It would be nice if Autodesk could chime in with some facts. Not being a structural engineer I might be missing something.

Re: What defines the "Top" of a beam?

SeanSpence — Fri, 31 Jan 2025 16:54:26 GMT

I came here looking for help, for me the issue with the offsets top and bottom ended up being related to the OTB family framing template. In the beam extrusion there are 4 reference planes. I wasn't using them, didn't give them a thought, I applied the profile and closed the extrusion. Once I deleted them everything showed up the way it should. This may help others looking for reasons why their families extents aren't correct.

Re: What defines the "Top" of a beam?

nmcmahonTW94C — Tue, 27 May 2025 15:35:16 GMT

Hi Sean, thanks. I think the simple long and short of this is that Reference plane don't define as they should. The beam takes it top as the modelled geometry top. I've yet to see a beam that has a top below the geometry. Happily corrected if someone can show me one.