Rebar constraints for straight shape automatically changed

[longt61]

I have a straight standard bar that snap to the bar segment of a set of stirrups. The strange thing is that if I use the default bar type, the constraint for "bar segment" of the standard bar is set correctly. However, whenever I change the bar type to a bar with greater diameter, the bar segment handle of the standard bar is automatically set to other constraint.

The other funny thing is that I find it only happens if the shape of the standard bar is straight (M_00 by default of Revit). Please take a look at the images to see what I mean.

[ovidiu_paunescu]

Hi @longt61 

Standard bars with a single segment (00 shape) can automatically connect to the stirrup corner.

This happens when the bar is in range (at a certain distance, based on the bar diameter) of that stirrup corner.

When you're changing the diameter to a larger value, the bar will be constrained to the corner and snap.

If you edit the bar constraints and manually set the target as the top face, that becomes a preferred constraint, and the bar no longer snaps to the corner.

More info here

In your example, you can see that corner constraint highlighted in orange.

[longt61]

@ovidiu_paunescu 

Thank you for your explanation, I have already figured out the rebar constraints at the time I ask the question.

The thing is that according to the document (Revit and Revit API docs) the default value for snap distance is 0 and it is based on the distance between the surface of 2 rebars. How come that the standard bar can snap to the stirrup instead of the top surface of the beam if there supposed to be distance between them (about 10 mm if I am correct)?

P/s: yes I am working with Revit API too and have posted the same question on API forum. The rebar was placed there by API without any modifications to the default snapping distance. I tested it again manually in a new Revit project and the same thing happened. This, I would like to understand this as a Revit user, not as a developer.

[longt61]

Further more by while we are on the topic, is there anything that I should be aware of about rebar snapping if the beam is joined to other element that it may not have its own face?

For example, I add rebar to the beam, then create a floor or a wall that joined to beam. Will something like this happen?

[ovidiu_paunescu · Accepted solution]

@longt61 

It's because the stirrup corner constraint has a higher priority with respect to the automatic constraint set to the concrete face.

If the constraint is manually set (set as preferred), than that has a higher priority.

Snapping to the stirrup corner means that both the Bar Plane (the start of the set) or End Plane (end of the set) as well as Bar Segment 1 connect to planes positioned like in the picture below.

The "0" offset means that the bar is exactly next to the stirrup corner, even though the bar constraints are referring to perpendicular planes of each available corner constraint (you can see the dots when editing the bar constraints, while the bar is in range of that corner)

See the example below where I have a 3 bar set with the first bar constrained to the middle point of the stirrup corner (2 - highlighted orange). 1 and 3 are also available, and selecting any of them as the target would reposition the set such that it is aligned.

In case the end bar is in range of the other stirrup corner, the Out of Plane Extents (end of the set) will constrain similarly to that corner.

This behavior allows the correct placement (no clashing) of longitudinal bars in beams and columns with respect to the stirrups, in plan, elevation or section views.

In Revit 2020, there have been some improvements to the automatic snapping behavior, to not have the bars snap if they don't go through the stirrup (or are in range of it).

Regarding your other question, faces of elements resulting from cut and joins to other elements are a bit more special.

There is currently a limitation in displaying or picking them as manual constraints.

If you have a beam joined to a column (such that the column is cutting from the beam and producing a cut face) and you place some stirrups in that beam, the set will correctly expand to the cut face, it will follow that face if the beam changes.

You cannot, however, see that face when you're editing constraints, or be able to manually select it.

That face is not representing formwork (the side of the concrete element) and has no cover.

Let me know if you have any questions.