Previous megastructure efforts

However, their results seem to me to have been rather dismal.

As far as I can tell, few of them have displayed much understanding of how to construct large enclosed structures.

• Buckminster Fuller was one of the first to design large domes. His 1,500 meter diameter [Old Man River City] clearly illustrates a geodesic dome. The even larger proposed [Manhatten dome] is also described as a geodesic dome.

  Though Fuller invented aspension roofs, his most famous proposals for creating large spans seemed to primarily employ compression-based structures that transmitted forces in their surfaces directly down to the ground - just like an arch does.

• Frei Otto once proposed a [dome covered Antarctic city].

  This was to have been an air-supported structure - and from the pictures, it clearly has no exterior tensile supports.

  Since 1971, large air-supported structures have gone completely out of fashion - with the subsequent discovery that large tensile structures are practical without the need for air support.

• After making the first practical cable network domes, David Geiger pointed out how well his structures scaled up:

  Geiger quickly reported that the diameter of his domes could be expanded indefinitely with little additional weight or expense per square foot of roof.
  - http://www.columbia.edu/cu/gsapp/BT/DOMES/SEOUL/intro.html

  Neither the weight nor the cost increases significantly with increase in span [...]
  - http://www.columbia.edu/cu/gsapp/BT/DOMES/SEOUL/s-desig.html

  Geiger was being optimistic here, and his statements must be regarded as being inaccurate.

  His design places large vertical load-bearing masts at regular intervals across the interval being spanned - something no self-respecting large-span bridge designer would do, due to the weight involved needing to be supported by other members all the way out to the edge of the structure.

  Geiger's design is better than one based on an arch - but it is no match for the patterns based on large-span bridges when it comes to covering large areas.

• More recently, a group called [XanaDome] has produced a structure which it claims is suitable for covering large spans.

  [http://www.xanadome.com/Xanadome%20Image%20L5.html] has a reasonable image of one of their patterns.

  Originally, the site claimed:

  Larger clear spans are possible than with any other type of structure
  - http://www.xanadome.com/structure.htm

  They now seem to have toned down their rhetoric a bit - though the claims made for the structure remain rather overblown and inaccurate - e.g.:

  Xanadomes use less material than any alternative
  - http://www.xanadome.com/Technical%20C.html

  Their proposed structure is based on an arch, formed into the pattern of a hexagonal geodesic dome - using a pattern of radial cables rather like the cells in the ASM dome.

  Structures based on arches in compression are fundamentally inferior at spanning large distances - when compared to cable stayed structures - and in particular suspended structures.

• Horst Berger writes on the subject of large spans in his tensile structures book, as follows:

  Although arches, respecially in combination with cables, still prove to remain the most powerful means of covering super-large spans, they also have a place in short-span structures.
  - Horst Berger, in "Light Structures, Structures of Light", p. 150.

IMO, those who deserve credit for pioneering the most scalable large span technology are probably those responsible for large cable-stayed structures - such as the Millennium Dome in London - and the Muna reservoir cover in Saudi Arabia.

Links

Dante Bini's tower city
Shimizu's proposed tokyo pyramid