Hexagonal Geodesic Domes - Isometric Struts

Using struts of equal length

While this essay doesn't contain a proof of the hypothesis - or even much concrete evidence favouring it - it does contain some suggestive drawings - which illustrate that it's possible to at least get pretty close to struts having equal lengths in hexagon-based domes.

From the perspective of building domes, this is probably good enough: the question of whether you need a few odd-length struts sometimes - if you want the dome to avoid all deviations from the surface of the sphere - can be largely left to future theoreticians.

This leads to the question of whether using equal-length struts in domes is desirable:

Advantages

• Fewer resources spent on cutting strut material - sometimes;
• Less wasted strut material;
• Avoidance of the issue of long struts being more prone to buckling;
• Struts can more easily be recycled in subsequent structures;
• The resulting panels may be of more uniform area;
• Structural strength is more evenly distributed over the dome's surface.

Disadvantages

• Panes covering the surface are less flat - possibly a problem if glazing is being used;
• Hubs become more variable - possibly increasing hub costs;
• Forces in struts become more variable - possibly increasing the required strength of the strut material;
• Existing works on dome buliding are not quite so relevant to the new structures.

Hub types

However the second type of hub makes using a mitre saw much more desirable - and if you have to saw the ends of the struts anyway, using struts of the same length doesn't save you as much effort.

On balance

The other issue with using isometric struts is the fact that the panels deviate from all being in the same plane more than they do with a conventional structure. If you are using a flexible covering, this may not be an issue - but if you have plans to cover the dome with something rigid - such as glass - then these deviations from the plane may well be a problem.