RAILING IN PLACE

Way back in October last year, before any of us had heard of Covid19, I worked on a staircase that was causing problems for one of our Revit teams.  The stair tool is great most of the time, but sometimes the railings won’t join nicely.  In this case, the strings were twisting out of vertical as they curved around.

When setting out difficult geometry I often find that the best approach is to start with 2d drafting in plan and section views.  We tend to take orthographic views for granted in our excitement about the 3d aspect of BIM.  But descriptive geometry was actually a big breakthrough in graphic technology, more abstract in its conception than the perspective constructions that preceded it.

So I started with drafting lines in a plan view, and rationalized the geometry as far as I could.  My first instinct was to use point world (conceptual massing).  But then I realized that Swept Blends would work, modelled in place.  The paths are drawn in a plan view, picking the 2d drafting lines of my setting out.  Then the two profiles are given vertical offsets.  

I like to rough things out “by eye”, so I can quickly see how the overall shape is developing.  Later I can fine tune the heights of the various profiles in a section view to follow the curve of the nosings more closely.

I realized that I could copy-paste these elements to “the same place”, an option which always confuses beginners, but is perfect for this situation.  Take each segment of this second copy and swap in a different profile.  Very quickly you can create the glass balustrade and tubular handrail following the same, twisting path as the strings.  Now combine a quick render with a shaded view and do a bit of cleaning up in Photoshop to disguise the imperfections.  

This image was placed on a sheet as a jpeg, along with various live views of the model, and shared with the client and structural engineer.  First iteration.  

Coming back in the new year, we had some feedback.  The strings had to be more substantial and we needed to smooth out the transitions where the runs meet the landings.  This meant resorting to point world after all.  Maybe I could use the swept blends as a guide, picking along one edge to create a 3d spline that would host profiles.

That’s one approach. But I got more control by creating profiles with a built-in offset parameter.  These could be aligned to my 2d setting-out curves and inherit vertical offsets from the swept blends ... all except the “transition” profile which was raised a little to force that smooth transition.  Then you create a single loft, instead of 4 separate swept blends which share a profile where they meet each other.

When I talk about “profiles” in a Point World context, I mean Generic Model families with a closed loop of model lines.  In this case they are drawn on a vertical work plane, with reference planes and labelled dimensions to create type and instance parameters in the usual way.  The width and height of the profile are type parameters.  The offset needs to be varied for each instance.  The notch on this profile is to allow for a soffit, most likely a stretch-fabric ceiling.

Let’s wrap this up.  Lots more work went into refining the design, especially the various junctions with floor slabs at each level.  I was using short enscape video clips to communicate the design as it developed … several clips per day.  Eventually I was asked to model the underlying steelwork to guide the structural engineer/ specialist fabricator … another interesting challenge. 

PART TWO

We’re in lockdown now, and an old friend contacted me with a “scan-to-bim” problem.  Turned out to be a stair handrail with a difficult geometry. “Aha” think I, “an opportunity to build on that work I did before, starting with some drafting in a section view (masking regions).

The first bit of String I built could have been done with swept blends.  Actually I think I had forgotten that’s what I did before, so I went straight for point world.  Just as well, because there are some portions that really need to be done as lofted forms defined by 4 or 5 profiles.

The profile is a Generic Model family, similar to the one I used before, with a somewhat fancier shape on top.  It may be that we should take a notch out of this profile where it fits over the edge of the floor slab.  Easy enough to do by editing the family and reloading.   

The string is an in-place Mass family.  I gave it an instance Material parameter so it could become red to stand out against the point cloud.  The next portion to model is quite a complex curve in 2 dimensions, formed from 5 profiles.  Each portion is sharing one profile the next piece the whole serpentine form.  So far, all the shapes have been roughed out.  There will need to be some fine tuning later on to smooth out the transitions and adjust more closely to the point cloud.

To figure out the bend where one storey meets the next. I copied the in-place family up to the next level. Changing the colour of the second copy to yellow, it is possible to turn the head of the "red serpent", up-and-around to bite the tale of the yellow one.  It seems that the floor-to-floor distance varies quite a bit, so once a typical floor is completely modelled it may be necessary to make adjustments for subsequent levels.

Now for the metal balustrade panels. The easiest one is going to be the straight portion along the landing, so let’s start with that. There is an “H” shaped extrusion, modeled directly in the host family. Next an “S-shape” created as a nested family and arrayed across the centre.  At the ends, two more nested families.  Top and bottom, in the middle, two copies of a circle family.  Nothing parametric in any of this, it would be easy enough to add some parametric capability should that seem helpful, but for now I don’t see the point.

This whole thing is going to be passed on for further development.  I just wanted to do enough to point the way.  The last piece of the puzzle in terms of tackling typical situations is a corner panel.  This is quite tricky, but can be done by setting up a diagonal reference plane to host one side. This is a loadable family and my approach is to repeatedly “have a go” ... then reload and check ... “have another go” … closer and closer.  

It requires a sharp eye and the ability to visualize 3 dimensional relationships, but can you really expect to “do BIM” without those skills?  

So there it is.  Something different after a year "slaving away" on Project Notre Dame.  I enjoyed myself.  Model in place.  You can go for weeks without using it, but sometimes it's the only way.

This "starter file" contains 3 in place mass families (in need of further refinement) There are two Generic Model "profiles" and three "rail panels". The corner panel is only half-done and there are another 3 or 4 very tricky panels to be attempted.  Good luck :)