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Monday, 20 April 2015

Weird Revit Railing Stuff - part 4 - Handrail Terminations


Staircase on Kukulkan Temple at Chichen Itza, Mexico

Railing Termination Visibility

The great temples at Chichen Itza (Mexico) were built well over a thousand years ago.  The Mayan/Toltec architects and engineers who designed them created some grand staircases.  They didn't have the same building regulations and OH&S concerns that we have today, so their concepts of railings and balustrades was a bit different.  However, they did love to put grand terminations at the base of their balustrades - in this case, representations of Kukulkan, the feathered serpent deity:
Kukulkan Serpent balustrade terminations

Of course they didn't use CAD, let alone BIM to help them design the stairs - they were brilliant mathematicians, who probably worked it all out in their heads.  The angles of the stairs were not designed to make it easy to climb up or down them - it was more about astronomical significance and perfect acoustics so that massed crowds at the base could hear the leaders speaking from the top of the stairs.  The Toltecs also practised human sacrifice of a rather gruesome nature.

At around the same time on the other side of the world, another culture was also creating impressive architecture with similarly steep staircases - at Angkor Wat in the Khmer Empire (now Cambodia).  They went in for some pretty substantial stone railings, with elaborate terminations in the form of seven-headed serpents (Nagas).

Angkor Wat railing terminations
What has all this to do with Revit?  Well, in version 2013 a new feature was added to the railing functionality:  Top/Hand rail 'terminations'.  The developers probably did not have in mind representations of serpents heads - but there are plenty of modern day uses.


Revit Railing Terminations

First a quick description of how to create rail terminations in Revit, as it is very convoluted.
Step 1 - Termination Family
  • First you have to create a termination family from the '(Metric or Imperial) Railing Termination' template.  This has an inbuilt 'Extension Length' parameter.
  • Once loaded into a project, this family has a category of 'Terminations' and could be placed on its own (but you would not normally do so).  In the family browser it is listed as a subcategory of Railings (with whatever name you give it).
Step 2 - Adding a termination to a Railing 
  • Terminations cannot be added directly to railings - you have to define them as part of either a 'Top Rail' or 'Handrail' (both new features in v2013);  these can then be selected as part of a railing.  So, they can only be used if your railing has one of these new features.
Top rail type properties
Railing type properties
  • The termination will be added to the end of the top rail (or handrail), perpendicular to the rail.  Normally it will be on the end of the rail but some strange behaviour can go on there - to be described later.

  • Terminations can be used in combination with 'Extensions' - another new feature in v2013, which are a property of Top Rails and Handrails.
 
  • You can add an extra tread length at the base of the stair, which maintains the railing slope
  • You can also add a further extension length, which would typically be horizontal if you already added the extra tread
Extra tread plus 300mm extension as per Australian BCA

  • The 3D view of the railing will display whatever you have modelled - my ambitions for scaring people were quite modest compared with the Mayans/Toltecs/Khmers, but might be appropriate for renovating a Gothic mansion or the bat-cave.

Rail Termination Visibility

Within the family editor,  you have typical controls as expected:
  • Revit will not allow you to create subcategories, which is to be expected, as the termination is itself a subcategory.
  • None of the family Category settings make any difference to the behaviour of the family in the project, except the category itself

  • Rail terminations have standard Revit visibility settings (Plan, Front, Left; coarse, medium, fine) for selected 3d forms within the family.

The problems start once you get into the project environment:
  • Rail Terminations are visible in 3D, section and elevation - but terminations are not visible in plan.  It makes no difference what view settings you use, they are just plain invisible.
 
  •  If you hover the cursor over the railing, you can see the termination there
  •  Select the railing, and there it is, plain as day, but it disappears as soon as you deselect the railing
This is a bug that has been in the software since Terminations were introduced in v2013.  It has been reported to Autodesk by various people and documented elsewhere (18 months ago).  There are several references to this in various forums, but they remain unanswered by Autodesk.

Terminations Terminated

The upshot of this bug is that Terminations are effectively useless to us if we want to document anything in plan.  The industry has not yet achieved the goal of supplying 3D models for final information to contractors, so we still rely on 2d documentation.
There is another bug to do with extensions and terminations in combination, which does not help matters either.
It is technically possible to use newel posts (balusters) to achieve this end, but they have all sorts of other issues - not the least of which is the difficulty of keeping them on the end of the rail, at the correct angle.

What would the ancients have done?  Well, they probably managed to build their serpent terminations without 2D plans, but they would not have been impressed by the lack of attention to detail shown by modern day software developers.  The Mayans and Khmers might have let them off with just a severe scolding.  But I'm not so sure about the Toltecs?  Did I mention that they introduced human sacrifice?

Antonio Gaudi probably would not have been very impressed either.
Staircase termination by Antonio Gaudi, Barcelona

Naga handrail terminations - Wat Hanchey, Cambodia

More about top rails:
Top Rail Properties in Revit Railings
Weird Stuff in Railings - part 1 - Top Rail Transitions
Weird Stuff in Railings - part 2 - Railing Extents
Weird Stuff in Railings - part 3 - Rail Offsets 
Weird Stuff in Railings - part 5 - Rail Extension Length

2 comments:

  1. Funny conclusion, Tim.
    :)

    Striking that the good guys from Autodesk still have not found the time to fix up their "Grand Fix" to railing and stairs from 3 years ago.

    jan

    ReplyDelete
  2. because theyre prob working on stair&railing suite, $1800 annual subscription

    good articles, thank you

    ReplyDelete