topic Re: Gateway to the West Arch in Modeling

Gateway to the West Arch

Anonymous — Thu, 14 Jan 2010 20:23:43 GMT

I am creating an arch similar to the Gateway to the West Arch in St. Louis, Missouri, only not quite on the grand scale the gateway is.
How would I do this in archicad?
I have tried a few features only to stopped at dead ends so far.

Thanks

Timothy Green
Instructor
Howard College
Big Spring, TX

Re: Gateway to the West Arch

Erika Epstein — Thu, 14 Jan 2010 23:20:02 GMT

For those not familiar with the Arch it was designed by Eero Saarinen.

Arch website

Do you have any of his drawings to know the geometry? Or are you 'eyeballing' the model of it?

And is some data on the Catenary Arch. Scroll down and it talks about the St. Louis Arch.here

Re: Gateway to the West Arch

Anonymous — Fri, 15 Jan 2010 02:37:08 GMT

I am planning on just eyeballing it. It doesn't really have to be to exact mathematical calculations.
I was hoping to plug in some sizes or radii or etc. and see what it looks like - sort of a 'trial and error' until I get the right look.

Re: Gateway to the West Arch

David Collins — Fri, 15 Jan 2010 06:44:25 GMT

A variable triangular section following an elliptical path....?
I would build it flat on the ground and lift it up. Isn't that what Saarinen did?
(Just joking: I got my M.ARCH at Wash U. in St Louis.)

1) Paste in a photo of the St. Louis arch and trace the elevation outline in plan with a polyline.
2) Create a mesh using the magic wand on the polyline. Use "Linear Segments" Tracing method to create nodes at regular intervals. (The actual arch is segmented, too.)
3) Keep the inside nodes at 0. Raise each outside node to 1/2 the trianglar section height at that location. Ask Pythagoras for help. That should give you the top half of the arch.
4) Save as 3d object, with view in 3d window from top of the arch.
5) Place the object. Mirror a copy to complete the arch.
6) Viola! (joke, old, ArchiTalk)

For extra credit, drag and drop the mesh into GDL, mirror the mesh using MULz -1, use CUTPOLYA to eliminate the unsightly line at join, rotate up into place. Create 2d symbol, with museum entry shown.

Re: Gateway to the West Arch

Ralph Wessel — Fri, 15 Jan 2010 10:32:05 GMT

tgreen wrote:
I am creating an arch similar to the Gateway to the West Arch in St. Louis, Missouri, only not quite on the grand scale the gateway is.
How would I do this in archicad?
I have tried a few features only to stopped at dead ends so far

Try modelling this with OBJECTiVE. I've modelled a quick example - although it's bent to a regular arc rather than an inverted catenary, you could achieve a similar effect by placing 3 or more segments rather than one. It all depends on the effect your after. With OBJECTiVE you could:

1. Draw the shape of the arch in plan (as if you were looking down on it) with the fill tools, and use the menu OBJECTiVE > Component > New Profile to construct a profiled object from it. Set the type to 'Elevation'

2. Elevation profiles have a bending hotspot at the midpoint. If you grab this, you can loft the arch to the required height.

3. The finished arch.

Re: Gateway to the West Arch

Erika Epstein — Fri, 15 Jan 2010 17:52:00 GMT

Tim,
I noted that you are on the faculty, Objective is free for educational licenses, correct Ralph?

Re: Gateway to the West Arch

Ralph Wessel — Fri, 15 Jan 2010 18:09:39 GMT

Erika wrote:
Tim,
I noted that you are on the faculty, Objective is free for educational licenses, correct Ralph?

Yes, correct. Just download from http://www.encina.co.uk/sw-download.html and install - no registration is required for educational users.

Re: Gateway to the West Arch

Anonymous — Fri, 15 Jan 2010 18:13:54 GMT

Hello Ralph,
I notice that your arch has a rectangular cross section.
Can Objective make a tapering equilateral triangle cross section
like the gateway arch ?
Thanks,
Peter Devlin

Re: Gateway to the West Arch

Erika Epstein — Fri, 15 Jan 2010 18:32:25 GMT

Just to see what I could do in archicad,
I. drew in floor plan window with lines and arch an eyeballed Catenary arch.

2. Magic wanded a Polygonal wall into the area of the arch. I used the wall tool as thin slabs are not easily trimmed using the trim to roof function. I did not want to SEO as cumbersome for this exercise.

3. placed a roof on the top of the wall. in 3D window I adjusted the slope and trimmed with top of wall.
4. Dragged a copy of the roof down and put a minus sign in front of its angle to reverse the slope and then trimmed bottom of wall.

5. Saved trimmed wall as a library object and stood it up.
Crude result; If I had made a true Catenary arch in plan it would have been much better.
Time: ~10 minutes

Re: Gateway to the West Arch

Anonymous — Fri, 15 Jan 2010 20:03:07 GMT

Here's my quick and dirty arch. It's made with one profiled wall sandwiched between two slanted walls. No SEO necessary. They clean up automatically.

This was very easy. Just a couple of minutes depending on how much you want to tweak the curves. The triangular section of the original would be much more difficult.

Re: Gateway to the West Arch

Steve Jepson — Fri, 15 Jan 2010 20:10:54 GMT

Thanks for posting that technique Matthew.
I like it! I can use it for several things I have been doing the hard way.

Re: Gateway to the West Arch

Ralph Wessel — Fri, 15 Jan 2010 20:15:49 GMT

Peter wrote:
I notice that your arch has a rectangular cross section.
Can Objective make a tapering equilateral triangle cross section
like the gateway arch ?

Not directly, although you can SEO one OBJECTiVE profile from another to achieve that affect. Refer to the attached image. Took less than 1 minute to make.

Re: Gateway to the West Arch

Ralph Wessel — Fri, 15 Jan 2010 20:31:10 GMT

Peter wrote:
Can Objective make a tapering equilateral triangle cross section
like the gateway arch ?

Sorry - triangular section this time

Re: Gateway to the West Arch

Anonymous — Fri, 15 Jan 2010 20:44:42 GMT

Hello Ralph,
Thank you. That is quite impressive.
Peter Devlin

Re: Gateway to the West Arch

Anonymous — Fri, 15 Jan 2010 21:39:53 GMT

As usual, objective rules!

Re: Gateway to the West Arch

Anonymous — Sat, 16 Jan 2010 00:40:04 GMT

Dang,

I guess I didn't know ArchiCAD as well as I thought.

Thanks for all the help ya'll

Timothy Green
Howard College
Instructor
Architectural Drafting
Big Spring, TX

Re: Gateway to the West Arch

Anonymous — Sat, 16 Jan 2010 02:19:28 GMT

Hello Tim,
If you don't want to use an add-on but want to model
an arch like the gateway arch entirely within Archicad,
I would suggest the method outlined by David Collins
except constructing a catenary curve for the entrados
or extrados of the arch rather than tracing as David
suggested, though you could use the image to get
the proportions of the catenary . Your topic is an
intriguing problem in drafting and modeling.
Peter Devlin

Re: Gateway to the West Arch

Anonymous — Sat, 16 Jan 2010 03:38:27 GMT

Try this. It should be fairly close to what you want.

Please note that it's still a *little* buggy when you start adjusting the sizes of things, and you may find it disappears completely! This is because the tube used to form the section is right on the limit before it self-intersects. If anyone wants to see if they can make it work better, please go ahead!

It works by throwing out some tubes in a parabola, then it places a similar version slightly lower with a negative shaped section then cuts one away from the other.

See the GDL Cookbook 3 p165-166 for the various codes for arches.

Hope it helps.

Re: Gateway to the West Arch

Anonymous — Sat, 16 Jan 2010 03:41:16 GMT

Here's a picture -