I would expect flexible connections, between modules.
For the purposes of this Guide, long-span floor systems are generally spanning greater than six metres for reinforced concrete systems or eight metres for prestressed systems. Some systems are effective below these arbitrary limits and their full range is included herein for completeness.
The aim of this Guide is to provide designers with an appreciation of the factors that should be taken into
account in selecting a floor system for a particular building.
It is emphasised that the graphs are not design charts but aids to enable designers to quickly identify
appropriate floor systems to carry the applied loading for the desired span, and thus provide approximate
dimensions for the preliminary design.
A serviceable long-span floor is one that has sufficient strength to carry the permanent and imposed actions
as well having adequate stiffness to limit deflection and vibrations.
An economical long-span floor is one that optimises the material and labour costs. Minimum weight does
not necessarily result in the lowest cost. Structural designers should review the design progressively as it
proceeds to ensure the structural design is integrated with other aspects of the design of the building, eg
building services, and no significant errors have been made. The accuracy of structural design theories,
applied actions and material properties is such that there is no point in determining actions or member
sizes to an excessive degree of accuracy.
Formwork for insitu concrete and propping of precast is a major consideration as it can directly affect the
architectural appearance of the project and the construction cost and schedule. Formwork can be
50–75% of the direct cost of a floor. Generally, a specialist designer, employed by the contractor, will
be responsible for formwork design. It will take into account the requirements of the specification and the
construction process, eg construction loads, stripping, back propping, and specified finishes and formwork
To simplify formwork, member sizes should be rationalised consistent with structural economy, eg
band-beam widths of 1200, 1800 and 2400 mm will enable standard plywood sheets to be used. Similarly,
drop panels in flat slabs should be dimensioned to suit plywood and timber sizes.
Because of the high cost of site labour, making soffit formwork on site is often avoided. Formwork is usually
designed to have a number of reuses and to facilitate easy stripping and re-erection to keep the overall floor
construction period as short as possible. Sophisticated table and flying forms have been used on multistorey
projects, while, to minimise costs, precast floor units are sometimes preferred
Reinforcement details should be as simple as possible to facilitate fixing, reduce the risk of errors
and to simplify checking. Cogs and hooks should be limited to those that are essential. Mesh should be
used where possible, while consideration should be given to using stock length bars for larger projects,
and to using alternative bar sizes to distinguish column strips from middle strips.
Ribbed floors consisting of equally spaced ribs are usually supported directly by columns Figure 12.
They are either one-way spanning systems known as ribbed slab or a two-way ribbed system known as a
waffle slab. This form of construction is not very common because of the formwork costs and the low
fire rating. A 120-mm-thick slab with a minimum rib thickness of 125 mm for continuous ribs is required to
achieve a 2-hour fire rating. A rib thickness of greater than 125 mm is usually required to accommodate
tensile and shear reinforcement. Ribbed slabs are suitable for medium to heavy loads, can span
reasonable distances, are very stiff and particularly suitable where the soffit is exposed.
Slab depths typically vary from 75 to 125 mm and rib widths from 125 to 200 mm. Rib spacing of 600 to
1500 mm can be used. The overall depth of the floor typically varies from 300 to 600 mm with overall spans
of up to 15 m if reinforced, longer if post-tensioned. The use of ribs to the soffit of the slab reduces the
quantity of concrete and reinforcement and also the weight of the floor. The saving of materials will be
offset by the complication in formwork and placing of reinforcement. However, formwork complication is
minimised by use of standard, modular, reusable formwork, usually made from polypropylene or
fibreglass and with tapered sides to allow stripping. For ribs at 1200-mm centres (to suit standard forms)
the economical reinforced concrete floor span ‘L’ is approximately D x 15 for a single span and D x 22 for
a multi-span, where D is the overall floor depth.
Precasting offers the advantages of off-site
manufacture under factory conditions and fast
erection on site. When combined with prestressing,
additional benefits of long span and high load-capacity
can be obtained. A number of different systems are
■ Hollowcore planks, either with or without a
■ Composite flooring using precast permanent
■ Composite flooring using precast beam and infill
■ Solid slabs either reinforced or prestressed
■ Single and double T-beams.
True- a lot remains to be determined about the anchoring/connecting system. I am leaning toward spuds (temporary piling or gravity base) in the Cay Sal implementations. Thus each hex provides its own anchor points, doesn’t need space outside its own footprint for anchor lines, doesn’t swing about in a “watch circle”, and doesn’t move with tide or wave action, has connections to neighboring hexes, and the aggregate provides a great deal of stability. The spuds can be contained in thickened wall sections or internal buttresses at the 6 points of the hexagon.
I envision a hinge-pin type connection with very rigid shock absorber pads (vulcanized rubber or the like, perhaps up to a foot in thickness) above and below.
Ok, one more comment:
Just kind of thinking out loud.
The hexagons can be built in multiple circles.
Multiple circles of hexagons are staggered to each other.
That would allow gradual wave breaking of domes on the water surface.
Multiple circles of octagons are not staggered.
Hexagons win for now.
I think of the Pacific ocean and floating.
Can’t really make a radially symmetrical shape with octagons, which means at some level it limits your direct connection points and requires open space between them. That may be a design feature, not a bug, but I think it complicates the engineering.
Hexagons are still wining.
I stand corrected. That is four symmetrical radiants, I was thinking 8 symmetrical radiants, which is not do-able. Each set of two is flat on to each other, so you have more of a rounded square than a circle, but close enough for our purposes of wave attenuation, aesthetics, and biomimetic atoll emulation.
I no longer have a copy, but there was a very informative video on the making of the Atoll from Waterworld, and the engineering, mooring and all of the platforms. The whole thing was later disassembled and towed from Hawaii to California, to become part of one of the Disney parks. I only vaguely remember it… Movie Magic was the video series.
A “hexatoon” was proposed here at TSI around 2009. It was also designed and a prototype was produced.
Octavian! I am happy to see you.
I liked the concept back then. I just don’t feel that scaling down that small is useful.
I guess at heart, I’m more of an artificial island proponent than floating seastead. I try to provide useful input to both camps.
I just looked and the hexatoon, despite the prototype, still doesn’t seem to be available for purchase anywhere. Sometimes, things that seem like a reasonable idea just don’t work out. The original criticisms that the design narrow attachment to the inside hub probably have something to do with it.
I agree. For seasteading purposes it should have been 4-5 times bigger and there where to many “slots” in it (that could have been easily fixed). BUT, he did mention that it was designed to fit into a standard container, which indeed would have made shipping the hexatoon much cheaper.
It’s not available because they never mass produce it. They were trying to work out a deal w/TSI at the time but it didn’t happen…
This is my inaugural post. I have been giving some thought to the idea of how to construct the main structures to handle storms. I feel like I have some good ideas that could benefit from some input from others.
The idea is basically that we should gimbal the structures to allow some movement. We would restrict or arrest movement using a counterweighted cable system similar to those used on aircraft carriers (These could also be used as wave motion generators). The gimbaling would effectively be an outer structure that goes around the main platform to create a skeleton of sorts. The skeleton would be hard fastened to the skeleton of other platforms but connected by a webbing of cables to the inner section of the platform. There would need to be rubberized expansion plates or joints of some type on the skeleton as you still wouldn’t want it to be perfectly rigid. The cables would be on spools attached to the inner section that would turn a generator as the cable spooled in and out. It would also increase resistance as the center platform moved further from the center or the “0” position. The idea comes from the way a tree sways in the breeze or how a spider’s web stretches in the wind.
I haven’t drafted a graphic yet but in my head it looks like the hexagonal structures posted below with an extra outer layer.
"Floating Island" design in the news
There are a lot of parts in that design so it’s going to be expensive. Semi submersibles are the benchmark here. They are likely to cost 2-3 times as much as a basic pontoon
Guess that depends on multiple things. A semi-submersible is a bit more complex, so, of necessity, it will cost more for an otherwise identical pontoon boat.
One of my threads has a smaller couple-scale semi-subs, based off a known working design…
Not sure what you mean by cable systems used on carriers? Do you mean the system meant to trap and slow aircraft using tail hooks? I’m not sure how that applies to stabilizing floating structures without further description.
Generally, I would look for less moving mechanical parts and more stability thru shape of displacement, static ballast, etc.