Monday, December 15, 2008

Revit - Modelling balcony slab with sloped edges

Here's an interesting modelling challenge set by one of my colleagues in the London Office. She wanted to quickly produce a balcony, based on the sketch below, for a large high rise residential scheme. In reality this is reasonably straight forward modelling, but it may not seem that obvious on closer inspection, especially to those that are new to Revit.


You will see from the diagram above that the majority of the balcony is 450mm deep and is flat as indicated by the blue area. The balcony then falls away on three edges to only 150mm thick. You will also notice the balcony is not rectilinear as indicated, with three sides at different angles.There are a number of different ways to tackle this.... create a family, an in-place family? All have their merits, but at the concept stage of a project you don't always have time to produce what in essence is actually a rather complex family to create. So the easiest way to create the balcony is in four separate elements.

So start by sketching out a few reference planes to define the extent and shape of the balcony.

Next create a new floor slab type which is 450mm thick. Edit the type properties of the construction of the floor slab and set the structure "variable" radio button is ticked. This will ensure that that slab is flush on the underside after you have edited the slab.


Next model four separate slabs based on the reference plane sketches.

4 slabs

You can then slab edit the edges of the three slabs which need to slope away using the sub-element edit tools. Select one of the floor slabs you created and the sub-element edit tools will appear in the options bar.

sub edit

Next select the edit points/edges tools, then select the outer edge of the slab you want to edit and alter the elevation from 0mm to -300mm; this will drop the whole edge of the slab and it will slope as required.

edge edit

Now do this for all the other edges which need to fall away.

dropped edge 

For extra finesse, use the join geometry to clean up all the floor slabs.

result  result

One could argue that this is not a purist approach to the BIM problem because you end up with four slabs rather than one, but at that concept stage where you want to convey an idea, this approach is ideal.


Gig said...

David, it does seem to be an easy modeling endeavour at first glance, but it isn't that straightforward! In fact this is predicated on how accurate to the processes of BIM you'd like to be. I agree with your modeling technique given the goal desired, but just for experimental purposes modeled the balcony using two different methods:

a) an inplace floor family with a combination of voids, swept blends, sweeps and extrusions. (when I schedule the floor though it reports the incorrect area and after some investigation it seems that it is only calculating the area of the first sweep I created. This is one that I haven't yet been able to figure out)

b) creating a variable floor and then using the floor editing tools. I then created ridge lines that denote the 450mm area and followed your technique of adjusting the elevation of the balcony edges to 150mm high. (However, since this is one slab and we're modifying it in this manner, Revit creates additional lines to connect vertices on the floor) This approach seems the most "BIM" like although the creation of the additional lines is not desired.

Any ideas on what else one might try?

David Light said...

Gig - I too tried the second option you described, but I also got the additional lines and edges. Which was not ideal for what we were creating. Agreed, its the most BIM friendly option. Only other options I guess it to create a family and extract the areas and volumes of this with some calculated formula.

aireq said...

If the slope of the taper is perpendicular to the slab you can create a custom slab edge that adds a tapered section to the edge of a flat slab.
Here's a screen shot of an example I just made.
If the taper is not perpendicular to the slab edge you can also create a single slab as you have been doing with the varying slab height but use the line work tool to remove the extra diagonal lines that are created in plan.
Here's an example of that as well:

ab0apm said...

This was a great help as I was looking for a quick method of modelling exactually this. However, I also have balconies which taper on the upderside, flat on the top, any ideas?