modeling depressed slabs

[trialbyfire]

How are you modeling depressed slabs? For example, where you have a 6" slab, and want to show a 2" depression for tile at a bathroom, etc. (I'm not worried about modeling the slope for any drains - I usually just detail line that part).

Modeling a 6" slab with a hole in it, and then modeling a 4" slab separately at that area is a drag because every time it needs adjusting (which is often) twice as much editing is required.

I was thinking there was a way to create a partial void that I could embed just a little bit into the slab (model the slab full thickness and then just 'void' out the depressed area), but everything I'm seeing cuts out the entire thickness of the floor, not just the top two inches.....?

[cdatechguy]

How your doing it is how we do it currently....have heard that some people will add a void to floor based family....but it can be tedious if you have an irregular shape...

[david_peterson]

One trick is to align and then lock the 4" slab to the opening in the 6" slab. I've gotten this to work in the past. However you may run into issues with over-constraining. Also the model may have performance issues when editing the slab.
Using 2 slab and joining them is the only way I've heard off. It's also the easiest and least likely to cause major issues in the end.
Of course the other option is to not model it. In the end the floor is going to be flat. In your detail you could simply mask the void. But this gets into that whole question of model sharing. I wouldn't know there was a void there if I just had your model linked. So I guess it's users choice. I've had to many MEP consultants use the excuse "Well they'll just adjust that in the field and I don't have time to redo all my piping routes so....we're just going to leave it where we have it now." Damned if you do, damned if you don't.

[lzaras]

Ditto to your two separate slabs.
Ditto to David's suggestion of locking the edge of the 4" slab to the hole in the 6" slab.

Lucky for me, most of my depressions have been pretty rectangular so far so I haven't run into any "over-constraining" issues.

[trialbyfire]

That spawns another question I have about locking elements (which I've addressed in another thread).

Thanks all for the input!

[m20roxxers]

I use a face based void family so it cuts into the floor, but does not generate a new Structural analytical element. For edge like this they are quite easy to move since you do not modify the skecth and break any specific join conditions.

[trialbyfire]

Is that a custom void family with depth parameters added to it? Revit's built-in face based opening tool just cuts through the whole element with no thickness or depth adjustment (or am I doing something wrong?)

[m20roxxers]

Yes it is a custom floor based void family.

Be aware if won't affect concrete beams or framing members but will cut through floors. Keep all parameters as instance properties.

[Steve Mintz]

I don't like the idea of modeling two different floors. It has a number of downstream effects that may adversely affect model updating and structural analysis.

In a few of my AU classes, I walk through how to create a slab depression family. It also hatches itself for construction documents.

I think the most complete tutorial is found in this class:
http://au.autodesk.com/?nd=e_class&session_id=5234

[trialbyfire]

Thanks Steve!! In looking at the lab info, I think I saw the presentation version in AU Virtual at one point. I was only on my first or second Revit project at the time, so I had bigger fish to fry than slab depressions, but it was a great presentation.

Your solution works great for most of my situations. Before I even try, is it possible to make a similar void family that would be sketch based, so you could outline complex shapes? I see that you can hook multiple rectangles together, but I have a couple depressions with angles, 17 corners, etc.

[m20roxxers]

Not sketch based unfortunately. The only addition I have to this is a triangular option that has some basic trig for offset corners. between those I can usually create the area I want. If it's really complex then I will use another floor since that is faster then having families for all situations.

There's a limit to tools like this, before it becomes to cumbersome for them to be fast and useful.

[Craig_L]

From a structural drafting standpoint, I hate voids for set-downs. It's just an extra problem.
The reason I hate them is - more often than not, set down areas have a slab fold where the set down area overlaps with the upper slab, causing a "fold", this is something architects rarely model correctly, and something that is required to be shown in structural documentation, voids do not handle this issue.

[m20roxxers]

I don't have this issue, but my voids are for wet area's mostly.

[Steve Mintz]

travis - Most of my irregular depressions in a project have been the same (usually for bathrooms), so I will copy the family and "hard code" the shape. If I have a number of different irregular depressions, I might resort to inplace families.

(From an engineering standpoint, I usually prefer to question why we have this number of irregular depressions, and if the contractor can actually achieve them).

karalon - Agreed - I dislike them. For slab depressions (a 1" to 2" decrease in fill thickness, I've never needed to show any special details). For depressed slabs (where the metal deck drops in addition to the fill), I've added detail components to my depressions so that when cut in section, they add most of the drawing information for the "fold". For these cases, I also consider it appropriate to model a separate slab (because structurally that is how it functions and how it will be built).

Just my $0.02 :-)

[Baghera]

It's a shame you can't put a reveal in the floor. That's what I do for beam pockets

[nafsc10351180]

I'm bringing this thread back to life since I am currently trying to do this in my current project (Revit 2012). The link to the tutorial that was posted by Steve Mintz is no longer active. Does anyone have another tutorial on how to create a slab depression family?
Thanks

Nic

[mburke.54112]

We don't model too many slab depressions in our projects, so we use a "model in-place" component.
I've created directions for how we do it:
To create an “Model In-Place” Component for a Slab Depression:

- set Workset & Work Plane to correct level (the level that the slab depression is to be modeled)
- {Home} tab / WorkPlane
- {Home} tab / Component / Model In-Place:
- Family Category = Floors
- Enter a name for slab depression (ex: “Slab Depression”)
- {Home} tab / Model Line:
- draw outline of slab depression (KEEP IT WITHIN A FLOOR SLAB)
- {Home} tab / Forms / Extrusion:
- {Properties} box:
- Start = 0”
- End = (the depth of depression as a negative number (ex: -1 ¾”))
- Solid / Void = Void
- {Modify | Create Extrusion} tab /Draw
- pick lines of outline just drawn
- Finish edit mode
- {Modify | Void Extrusion} tab /Geometry / Cut
- pick Floor Slab
- pick Slab Depression
-{Modify} tab / In-Place Editor
- Finish Model

Drawing the depression two times (model lines & create extrusion) will ensure that you can see & pick the slab depression for future editing.
Hope this helps.