Hi Jackson,
@jackson said:
The guywires in the skp model make it pretty much impossible to build anything on top of the trusses and lateral guywires (as in the image) make it extremely difficult to design anything other than a series of unconnected towers with fairly small footprints. Can you clarify please?
Can you provide a screenshot of the horizontal radial wires? It sounds like an error but I don't see them anywhere.
For an example of how a design can look without interfering too much with the lateral wires, take a look at the sample design: Images and SketchUp file (which is still being polished).
@jackson said:
Why aren't the supporting legs/columns at the corners? Not only would that create a much more stable structure, but the trusses would then form a square frame around the perimeter making it far easier to design an efficient layout for any added structures. After all, oil production platforms follow this format and they know more than anybody about living off-shore.
I've never seen guywires used at this scale in above-surface marine structures (other than ships' masts of course). Guywires tend to be used to brace very slender structures which have high compressive strength, but little lateral rigidity. The pillars and trusses in the skp model however are extremely deep/broad in comparison to their length/height so it would seem more logical to provide the bracing in the form of rigid connections at their intersections. I'm no marine engineer, but it doesn't seem at all logical that the trusses aren't structurally connected to the columns other than (presumably) within the flat "raft" base. Why not design it as a single connected structure? If marine engineers did design it they appear to have gone against generally accepted practice in a number of rather inexplicable ways.
I send your question to our staff and the marine engineering company, which made the design. Please see the following initial answer to your question from our staff:
*"Putting the legs at the corners results in a larger span, that is, more cantilevering, and thus requires a bigger truss which wastes materials. Right now, the largest span is 200', which means the furthest cantilevering is 100'. If spars were at the corners there would be a 400' span and thus 200' cantilevering.
As for wires vs. trusses, materials are generally more efficient in tension than compression. Hanging things saves on materials - see the work of Buckminster Fuller."*
And more details from the engineering company:*"Semi-submersible columns are in general connected at the top (by beams under the deck, and at the bottom, using large pontoons. We're not, so increasing the separation makes it difficult for the structure to wistand the "hogging" and "sagging" modes due to wave loading. Moving structure outside the column also helps in distributing the load directly above the column center , and minimizing the offset moment, again because we only have one connection point.
The cables are there to reduce weight and redistribute the weight again above the buoyancy.
Why not design as a single structure? Mostly because it would be too large for most shipyards in the world, and we want the flexibility to use smaller fab yards, and improve economics, in the assembly and integration scenario.
Lastly, this is not an oil and gas platform. The design basis requirements are different, and there is a coolness factor that needs to be included. We're trying to combine an more efficient structure, a larger footprint, an optimized payload, good motions, without increasing cost."*
I hope this answers your questions satisfactory.