Sunday, November 20, 2011

GHERKIN TAKE 1

The mind is a strange thing. It loves to wander randomly making unexpected associations and diversions.  Perhaps this is the key to the emergence of artistic expression often dated to around 40 thousand years ago.  Whenever I'm sitting at my laptop working away on some urgent deadline, part of my brain is wandering off on it's own.  Seems like it takes the adrenalin shot associated with serious physical danger to focus our attention narrowly on the task at hand.


So despite having several more urgent tasks on my list, I found myself modelling the Gherkin this weekend.  They used to say that if your want to understand something, draw it.  There is freehand drawing, T-square drawing, CAD drawing and BIM drawing.  These days I find the best way to get deep inside a building's soul is to make a Revit model.  For 30 St Mary Axe I set up 40 levels with a typical floor to floor of 4.2m  I set the first floor at 8.7m on the basis that the crossing point of the diagonals is about a foot (300mm) below floor level.  These are all "intelligent guesses" but I don't think they are far off.


I had a source saying that the diameter at ground level is 50m, increasing to a maximum of 57m at level 17.  So I went into in-place mass mode and placed these 2 circles using reference lines.  Looking carefully at the finished form you can see that the radius gets progressively smaller over the last few floors, so I placed 3 more circles towards the top, selected all 5 and hit "Create form".
Because they are Reference Lines, the circles still exist inside the form, you can select them and change their offset levels and radii.  So I did just that, and tweaked the form till it looked right. 



Next stage is to select the surface and divide it.  There are going to be 2 masses, one slightly smaller one for the large white structural grid, and the bigger one for the glazed skin which is framed in black mullions.  Both of them are Rhomboid (Diamonds) and the structural grid is 4 times as big as the skin.
The structural grid is 11 diamonds high (4 storeys each), with 18 diamonds around the circumference (20 degrees each)  So the glazing grid is 44 diamonds high (including a double height ground floor and triple height top) with 72 modules around the full circle )5 degrees each.

In Revit, the Rhomboid grid is derived from 4 squares, so you need to double up all the numbers. But the mass comes in two halves, so the U/V grid numbers end up being 22/18 and 88/72.  I did it by trial and error.


Now we need a curtain panel.  The structural members are also diamond shaped in section, so I made a profile for this.  Host it on a point in the Rhomboid template, make form and you have a sweep. 


I decided to use the same family for the glazing so I added a glass surface with a visibility control and linked the profile dimensions to parameters in the panel family. 


Once this was loaded into the project and applied to the mass, a couple of problems cropped up.  The sharp corners were sticking out at every joint right at the top everything was distorted and spiky.  I just deleted the top 2 rows on the basis that the structure changes up there in real life. For the other problem I added a void in the family to cut the corners off.  There's still a bit of overlap at the join, but I decided to move on.


For the glazing I made a second mass with circles offset by half a metre.  By the time I had this kitted out with panels everything had slowed down.  No problem with normal working, but as soon as you change any parameters affecting the curtain panels, be prepared to make a cup of tea.


Next complaint is to do with changing individual curtain panels.  Had to delete a whole bunch at the bottom to make the entrance etc.  There seems to be no alternative to selecting one by one. With the delayed response it was taking me 5 or 6 seconds to delete each panel.  Not good.  Ideally I would have selected hundreds of panels going up in spirals and changed them to a darker coloured glass, but I didn't have the patience.  There has to be a better way.


I started to put in floors and explore the geometry of these spirals.  There are light wells/ventilation shafts behind the dark glass: triangular voids that rotate by 5 degrees (one glazing module) from one floor to the next.  Some of these are 2 storeys high and some link 6 storeys.  I need more time to work this out in the model.


Did some trial renders on the entrance and compared the result with a picture I took 2 years ago.  In the end I couldn't resist compiling a render, a shaded view and the photo into a composite image.  The live photo is only used around the entrance area.  It adds the subtlety of the internal lighting and the realism of the street lights and the taxi.  I masked out the structural frame and the glazing, so this is all from Revit, but the dark glass is faked by drawing a selection around those areas and adjusting levels.



6 comments:

  1. Hi, Great job there, is it possible to share the link to this model? Because i am doing a school project and everyone else uses simple regular building and my group decided on the gerkhin, we are unable to build it without a 3d cad model.

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  2. Hi, I am an architecture student in Pratt Institute, the U.S.. My project assignment is to rebuild the structure. The drawings and details online are quite limited.
    You have very precise information about the structure. Could you send my plan, sections and the detail drawings? Or if possible share it on this website.
    I really appreciate the great work you shared on this website. It is amazing!

    My e-mail: slix11@pratt.edu or lisihui1992@gmail.com

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  3. Thanks everyone. There will be a series of posts on the Gherkin over the next few weeks and I will be sharing Revit files etc. This will be targeted at Architecture Students around the world who have chosen to study this fascinating building. Get yourselves signed up for your student copy of Revit 2014 and follow along with my explanations & sample files. Stay tuned.

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I've been getting a lot of spam so had to tighten up comments permissions. Sorry for any inconvenience. I do like to hear from real people