The biggest single mountain on Earth is Mauna Loa of Hawaii. (see link). Note what it says about the vast mass of the mountain depressing the sea floor. A big pile of solid rock can be expected to do that just about anywhere. For example, the 27km-high Olympus Mons on Mars, even though it is 540km wide, still manages to depress the surrounding area of Mars by about 2 km (see link).
However, a constructed building is mostly hollow, and so its total mass is rather less. We can expect a really large building to depress the Earth's surface somewhat, but this can be reduced by spreading-out the base of the structure. Some of such a thing has been suggested already here in the Half-Bakery, under "Pyramid Skyscrapers". It may be impossible to construct a really really big building without it looking something like a wide cone or pyramid. Various steel alloys are plenty good enough for, say, a mile-high building having ordinary-skyscraper proportions, but if want something 50 miles tall, then you can bet it MUST have an appropriately wide load-distributing base. On the other hand, if we use moderately exotic materials, a somewhat narrower width-to-height ratio is possible. I'm thinking about steel tubing filled with reinforced concrete, where the rebar is titanium instead of steel. Concrete is actually an impressive substance with enormous vertical-load-bearing "compression strength" and approximately the same density as, of all things (!), aluminum. Appropriate reinforcing means the concrete gains the "shear force resistance" it needs to be used as diagonal and horizontal beams, such as will exist in vast numbers in a "Space-Scraper".
So, if the goal is to build a SpaceScraper and not merely a skyscraper, then we first need to find a place big enough to put the thing. Since it is likely to have a base-width on the order of 100 kilometers or more, we need to find that much landscape (100x100=10,000 sq km) which can be put to this use without destroying a vast chunk of the biosphere. Deserts such as the Sahara seem to qualify, big enough and uniform enough that life-forms in one area probably do not make a uniqe "niche".
Ok, so now the construction begins, sinking millions of support-piles all across the chosen landscape. At any level of the overall building, the cross-linked structural members have the task of spreading the load from above to the wider area below. Initially, however, the work of just building the first few storeys will all by itself be a huge and hugely expensive undertaking. It absolutely MUST be built in comparatively small (say city-block-sized) sections that can be finished completely and rented/sold. Appropriate power facilities obviously must be built also, and since we are using a desert site, solar power may be a significant part of that. Also, a vast reservior must be built to hold water pumped in from the nearest ocean, for initial desalination and later recycling. We also will probably have to cover vast tracts of landscape with partially-mirrored-glass greenhouses, to grow food (and keep the water from getting away).
An "arcology" is defined as entire city inside a single building. A SpaceScraper will be so big that every one of the lower storeys would qualify as megalopolis-class cities. (This is why water recycling is absolutely essential, to maintain a steady supply.) Since any arcology is such a huge thing that can only be built in affordable sections, the overall construction time is likely to stretch out for a couple centuries or even more. Still, with global population increase, we will soon start needing arcologies, anyway, which means that people will be available to be buyers. (Already Japan, with limited room to grow, is seriously considering several arcology-scale projects.)
Finally, while contructing a SpaceScraper as an arcology allows the thing to be built in an affordable way, that is not the real purpose of this Idea. A certain percentage of the funds from sales/rentals of finished-arcology space should be devoted to extending the STRUCTURE of the building, faster than completing saleable/rentable sections. And some sections might might deliberately be finished out-of-obvious-order. For example, at the 7-mile or 11km level, some holes in the side of the building can be left open, perhaps 50 storeys high. This is stratospheric altitude, and arriving jets can fly straight in and park, and later fly straight out again, without needing to waste time and fuel descending to low altitude (or ascending again later). Anyway, it should be possible to finsh the overall structural-member construction (say 50 miles or 80km high) within a few decades, even though "filling in" the space between girders is a job that will take many more decades of work. Well, once the girders are done, the main use of the building can now be started. On the OUTSIDE angled surface we constuct vacuum-filled tubeways. The exits of these tubes are above 95% of the planet's atmosphere, and so it will be really easy to use electromagnets to launch payloads by the thousand into orbit and beyond.-- Vernon, Aug 09 2005 Mauna Loa http://www.skimount...F.php?name=MaunaLoaAs mentioned in the main text [Vernon, Aug 09 2005] Olympus Mons http://www.answers.com/topic/olympus-monsAs mentioned in the main text [Vernon, Aug 09 2005] Some deserts http://www.factmons.../ipka/A0778851.htmlAs mentioned in the main text [Vernon, Aug 09 2005] Concrete http://www.roymech....atter/Concrete.htmlAs mentioned in the main text [Vernon, Aug 09 2005] Exotic materials http://www.bohemian...rials%20science.htmAs mentioned in the main text [Vernon, Aug 09 2005] More about concrete http://www.nibs.org/MetricNews/4qtr99.PDFAs mentioned in the main text [Vernon, Aug 09 2005] One proposed arcology in Japan http://www.emporis....en/wm/bu/?id=103142It says this is the tallest building ever envisioned. Not any more! [Vernon, Aug 09 2005] Plasma Valve http://www.bnl.gov/...003/bnlpr052803.htmThis is needed at the mouth of each vacuum-filled tubeway, to keep the air out. See, if left open, even thin air at high altitude will fall down the Earth's gravity well, in a vacuum tubeway, and eventually fill the tube with air at the same pressure as exists outside the tube. [Vernon, Aug 09 2005] Pyramid Skyscrapers pyramid_20skyscrapersAs mentioned in the main text. Link is also at upper-right of this Web page. [Vernon, Aug 09 2005] More info on arcologies http://www.arcology.com/Lots of links. [Vernon, Aug 09 2005] About Light Pipes http://www.sea.vic....I/VSII%20Sheets.pdfIn section 6 of this document; other solar ideas are here, too. [Vernon, Aug 10 2005] Umbilicals for passengers boarding/leaving jets http://static.howst...port-terminal2a.jpgAs mentioned in an annotation [Vernon, Aug 10 2005] Elesorter, for mining anything Elesorter_20(and_20Isosorter)As referenced in an annotation [Vernon, Aug 11 2005] IKECE IKECEA hypothetical way to increase the efficiency of radiant-cooling, as mentioned in an annotation. [Vernon, Aug 11 2005] Landscpe's Enemy Nuclear_20waste_20tombi don't think there's enough space on the web for both this linked idea, and the Space-Scrapers [sweet, May 24 2006] I had a similar idea of staged building (No where near this scale). I was thinking that with a pyramid form you could put the heaviest foundation supports inside the perimeter of the initial built and sold units.
At the place I worked last my boss tested post-tensioned high strength grout inside steel tubes & found them to be very strong. He applied for a patent, but I thought I heard later that he didn't get it.
I wonder if you could use the wind at high altitude to remove some of the gravity load by designing "wing" shapes into the building allowing sections to "float".-- Zimmy, Aug 09 2005 The model here seems to be to finance a long-term space program by renting living areas as it is built. This would seem to require that conventional living space become really crowded, unpleasant, dangerous, or expensive to make the alternative of living in a vastly expensive manmade mountain in the desert attractive.
Perhaps a more effective financing plan would be to initially build a great weapons platform, then extort the additional construction costs from the low-lying populace. This is a time-tested pattern and would no doubt attract more venture capital. ;-)-- dhill, Aug 09 2005 I don't actually have enough time to read all of this (Promise to return later). It seems big and clever so I'll give it a pre-emptive bun.
Edit: Yep, big and clever.-- hidden truths, Aug 09 2005 [Vernon], While I'm intrigued by the idea of a building which has aircraft landing fields installed at stratospheric levels, won't the breathable atmosphere at these heights and above be rather rarified? Presumably, you must be planning to pressurize all levels of the building above the two and a half mile level, or so, for the physical comfort and convenience of the building's inhabitants. Or will visitors to these levels wear space suits? Perhaps your references to vacuum-filled tubeways and plasma valves are meant to address this basic component of comfortable living, but it's not clear to me as you've explained it.-- jurist, Aug 09 2005 [dhill], ideally, an arcology is supposed to be a pleasant place to live. In practice, of course, the ideal may not be achieved, but if the developers won't TRY, then obviously they won't be making very many sales. One thing that occurs to me is that as soon as, say, the 200th storey is built (roughly at the half-mile mark), the VIEW is likely to attract buyers for the outer living suites. And the view only gets better as the next 49 1/2 miles are built. Next, a city isn't just a residential block; it needs industries, all of which should be located well away from the outer regions of the structure. In-between, "light pipes" can bring daylight to many many dwellings that aren't quite at the outer surface of the building, especially in a bright place like the Sahara desert.
[jurist], yes, the living space and connecting corridors all need to be pressurized above a certain altitude. (And yes, I know that different levels must be pressurized separately; if all were connected vertically, and the uppermost level was presurized to be breatheable, gravity would pull that down to the lower levels and the pressure down there would be ridiculous.) For jets, well, "umbilicals" for passenger entry are already used at most big airports; they just need to be a little better designed to seal against the jet doors and maintain pressure.-- Vernon, Aug 10 2005 I saw arcology in the name; there was only one possible poster.-- david_scothern, Aug 10 2005 //roughly at the half-mile mark), the VIEW is likely to attract buyers // The view of what? More desert? An immense building site and road/rail network? A salt-water lagoon and industrial park? Even at the 200th level, someone living near the middle is going to be tens of kilometres from the edge - what is the incentive to live there?-- coprocephalous, Aug 10 2005 Indeed. The ratio of surface area to volume won't be good, when compared to a single storey building on the ground surface. Consequently, there won't be much natural light to share between all the occupants. That's not a big objection, though.-- david_scothern, Aug 10 2005 [coprocephalus], the view does depend on just exactly where in the desert the thing is built, doesn't it? How about near the edge of the desert? (OK, so two sides still don't get such a good view. The construction of living suites on those sides don't have to be done first, either. Next, because the reservior is in the desert, it would be kind of stupid to put it above-ground where it would evaporate quickly and need constant refilling with (not cheap) desalted seawater. The reservior would have to go underground. Next, any "industrial park" would actually be inside the building; it is supposed to be a complete self-contained city, after all. Finally, NO, even if the exterior of the building sloped at 45 degrees, the 200-floor level (half-mile mark) would not hardly be tens of kilometers from the edge. (At 45 degrees it would be exactly as far from the edge as it was high off the ground.)-- Vernon, Aug 10 2005 It's definitely an interesting idea and reminds me quite a bit of the space elevator mentioned in a number of science fiction novels (Red Mars springs to mind).
I don't think I've seen it combined with an arcology before though. My concern would be that such a solid structure would be adversely affected by high altitude weather. If you used the pyrimidal structure as a base for a more linear and flexible 'space scraper' then it might be more effective.
Bun, this one's typically verbose but very readable.-- madradish, Aug 10 2005 //I don't think I've seen it combined with an arcology before though// 3001: The Final Odyssey. Arthur C Clarke-- coprocephalous, Aug 10 2005 Similar to this is Poalo Solari's attempt at arcology.Although, I must say all this does sound rather anti-ecocolgy.What with all the concretes and aluminium- the embodied energy (especially when being taking to the sahara desert) will be enough in itself to be labelled a total wreck to the earth's health.-- chocolateraindrops, Aug 10 2005 [madradish], No space elevator is attached to this building. It is a launching site. (Also, to attach a space elevator, the building has to be located on the Equator. It happens that there are not many deserts on that line...)-- Vernon, Aug 10 2005 // It happens that there are not many deserts on that line...)// Unless you could consider the sea itself as being a desert, which again raises several more interesting considerations and economies.-- jurist, Aug 10 2005 How would you deliver raw materiel, despatch product, dispose of waste? A 400km base perimeter could not service such a volume with ground transport. Heavier than air tranport is too expensive, zeppelins could not lift enough.-- TheBearMadeMeDoIt, Aug 11 2005 [Pa`ve], yes, I'm aware that high speeds are required at high altitudes. However consider this building in a little more detail. If it slopes at 45 degrees from a 100-km-long base, then at the 11-km altitude the width of the building is still 78km. PLENTY of room for landing high-speed jets!
Regarding using up the world's production capacity, NAAAH! That's only true if you are impatient. If you are willing to build/sell it in sections, then you can also progress at whatever rate can be accommodated by the good old Law of Supply and Demand. Remember they used to take hundreds of years to build old Gothic cathedtrals....
A modest rate of construction also answers the problem of bringing in the stuff. Ordinary construction rate means ordinary transport is all that is needed.-- Vernon, Aug 11 2005 /Finally, NO, even if the exterior of the building sloped at 45 degrees, the 200-floor level (half-mile mark) would not hardly be tens of kilometers from the edge. (At 45 degrees it would be exactly as far from the edge as it was high off the ground.)/
/If it slopes at 45 degrees from a 100-km-lon base, then at the 11-km altitude the width of the building is still 78km. PLENTY of room for landing high-speed jets!/
You can't have it both ways. If it's 100 km wide at the base, then it's possible, at ground level, to be fifty kilometres from the nearest edge. If it's 78km wide at the 11km mark, you could be up to 39km from the edge. That, to me, is tens of kilometres. You can only sell the view to people in the very outermost apartments, or those within a sensible distance of viewing galleries.
[edit, in case of confusion] The edge that I think coprocephalous was referring to was not the ground-level interface between arcology and sand, but rather the sloping outer face of the arcology at the 200th floor, from which the view can be seen.-- david_scothern, Aug 11 2005 Why thank you [d_s] - you saved me an anno there.-- coprocephalous, Aug 11 2005 [david scothern], your math is right but your assumptions are wrong. First, the 45-degree angle is just a convenient way to make some quick estimates regarding such things as how wide the building is at the 11-km height. Obviously if it was a 60-degree angle, a fair number of kilometers of width at that altitude could still be expected -- even if the base was smaller than 100km wide (a worst-case estimate). I do not know just what slope the building has to be, to properly distribute the loading to the ground while reaching an 80km height. Of course, the steeper the slope, the less of the view will consist of the building.
Next, you seem to have missed the point that most of the interior of the building is supposed to be used for industries (like power plants and waste recycling) and businesses, not residential suites. (Heh, one way to build the thing faster is to construct construction industries inside it, including mining and ore-processing and metal-fabrication, remembering that about 20% of igneous rocks (deep bedrock) consists of iron, aluminum, magnesium, titanium, etc. See my "Elesorter" Idea.) Anyway, you know that most people don't want to live next door to stuff like that. A good internal mass-transit system will be crucial, of course.-- Vernon, Aug 11 2005 I recognise that you're going to put industry and the like in the core; that's only logical. My point was simply that there's not a lot of surface area relative to the volume of the structure, and that therefore there will be many people who have to live some distance from any view of the outside world. That's not necessarily an especially important point.
More relevant is the problem of power supply to this building. The low surface-to-volume ratio suggests that solar panels on the exterior aren't going to be enough, especially not if you want anybody to be able to see out. You could surround the building with more panels, but you'd need many times the footprint of the building to generate sufficient power. A fusion plant would fulfil requirements nicely, when they are finally available.
With all this power supply, we need an adequate way to dump waste heat. Near the edges, low down, we can exhaust hot air to atmosphere. Nearer the core we hit more of a problem. I'm not certain whether a massive chimney up the centre would be the way to go; maybe a kilometre-wide chimney with lifts climbing up its edges for real sci-fi images.
Higher up will be much colder, and there the problem will be keeping warm. Perhaps that waste heat from lower down might be useful at height.-- david_scothern, Aug 11 2005 Let's face it. Nothing this big will ever be built. If you consider that buildings the size of the Sears tower cost upwards of one billions dollars, and what you're proposing would be at least 10000 times as large, you're looking at a project cost measured in annual US GDP's. Not in our lifetimes or the forseable future. But I don't understand why the building has to be filled up inside. Something 100 km wide by 50 km tall would be large enough to fit several planets worth of people inside (my geometry tells me we are looking at around 170,000 km^3 in volume, which is obnoxious) Couldn't it just be a very large structure with a very low density of human inhabitants, where 99% of the volume is just scaffolding for the superstructure? The idea of a building with a massively distributed construction in order to achieve great heights is a good one, and has been turned over several times. How about the tower is just as large, but is such that the main use is having people live only near the surface area, and to have big tubes running up the sides for launching things into space. These things could be parts for giant solar panels in space, which could in turn provide power for the people down below.
Also, how long do you suppose steel and concrete constructure could last? Anything less than 1000 years would be a terrible investment. Another nice thing about these scales is that they would be very difficult to destroy with conventional terrorism. The building would easily fit a Hiroshima bomb's blast radius and the people on the other side of the building wouldn't feel a thing.-- estreet, Aug 11 2005 OK this seems like the long annotations idea of the year. This is very unlikely to ever be baked unless absolutely necessary, as it would be political suicide. As [Vernon] himself put it. The building would be centuries in construction. No government would want to be spending billions in public money to fund a project that would be many decades from being of any use.-- hidden truths, Aug 11 2005 [david scothern], yes, I also had thought about the waste heat problem, and indeed am aware that there will need to be power plants on the inside of the structure. One feature the Sahara offers is quite-cold nights, even in summer, due to the dryness of the air (both humidity and clouds work as greenhouse-heat-containment). Which means a large area might be set aside to receive and store waste heat generated in the day, to be exposed to Space, radiantly, at night. (see my IKECE idea for more madness along that line).
[estreet], that is a good point, about how long the thing can last. Time for another Idea! How about the thing be designed/built in such a way that every girder is accessible and removeable? (As in, "put in temporary strut, unbolt, remove, refurbish, replace".) As technology improves, embedded sensors can be added to indicate when some particular girder has aged or fatigued enough to need replacing.
Next, I was thinking that since people would only be using living suites in the first few kilometers from the surface, the total population need not be as large as you have hinted (but still very large, admittedly). You can't have the structure (even part of it) ONLY used for living space, because where are those people going to work, if not also right there in the building?
Finally (and also for [hidden truths]), I was not trying to say that Government should be responsible for building this thing. Private enterprise is quite capable, provided that some sort of long-term plan is adhered-to. That's specifically why I repeatedly said that the thing has to be built in rentable/saleable sections. THAT'S a plan that can indeed work for centuries!-- Vernon, Aug 11 2005 It is interesting to consider the likely politics of a city-state-size building, larger than Singapore, for example. Especially one built in a remote, inhospitable location (desert below, space above). Would it be prone to autocratic rule? Several life support facilities would probably be centralized, and anyone who seized them would have the populace at their mercy. As it approached an operational state, it would have to be prepared to defend its space launching asset.
Also, I guess people would come from all over the world. Would there be an attempt to integrate everyone or have separate cultural areas?-- dhill, Aug 11 2005 /Would it be prone to autocratic rule? Several life support facilities would probably be centralized, and anyone who seized them would have the populace at their mercy/
Law enforcement would have to be more efficient. Roll the legislature, police, the courts, and the penal system up into one governing body.
The members of this body (call them Judges)would have ultimate power to enforce the LAW. Give them really big motorbikes (Lawmasters), and really big guns (Lawgivers).-- TheBearMadeMeDoIt, Aug 12 2005 Could you build this on top of a very large mountain or plateau? Or could you put the foundation of each girder on a different peak in a mountain range? Then the building would effectively "hang" above a valley and provide a very large covered area. Building on mountains would help reduce the volume and cost of materials.
Or, you could mine out the mountains for resources, use the tailings as filler in concrete, and use the empty mineshafts as more real estate.-- discontinuuity, Aug 12 2005 The original suggestion - put it in the sahara - is going to need some interesting foundation design... it's got to support a building 100km tall without subsiding, yet the surface is notoriously mobile. Out of interest, how deep is the sand in the sahara?-- david_scothern, Aug 12 2005 [rasberry re-tart], this thing COULD be put just about anywhere, but I was specifically looking for places where the ecologoical impact would be minimal. The SHADOW of an 80-km-high building will be deleterious to plant life -- except there is so little plant life in places like the Sahara. However, one possible alternative is the Gobi desert, which is, I think, on a fairly hight plateau.
[david scothern], note the mention of "millions of pilings" in the main text. I assume you know that the purpose of pilings is the place the load onto bedrock, regardless of what lies above the bedrock. Still, there are large areas in the Sahara where there is essentially no sand, just as there are other places where the sand is tens of meters deep. Expecially if you are on top of a dune. It is my understanding that radar from space has identified a major westward-going dry river channel under the sand; I think the sand could not be more than a hundred meters deep for such probing to work. OK?-- Vernon, Aug 12 2005 Scoop up all the sand and use it in the cement, or melt it down for glass or silicon chips. But really, as Vernon says, there are many places in the Sahara where the bedrock is free of sand.-- baconbrain, Aug 14 2005 The view at the half mile mark would be awesome. Desert stretching away, ever changing, peacefull. The world below looks like something from another planet. At night the building is alight with thousands of stars, as is the expanse above you. Work, everyday life with all its petty problems is the furthest thing from your mind. Look at those little ants, scurrying around...
People would want that kind of view on the same bases that people want a penthouse on top of the highest skyscraper.
The housing problem might be less if you'd employ a rotation schedule. In the beginning most people living there would be the constructors and their families. The workers currently on shift would sleep in the 'inner ring' those not, return to their 'outer ring. As you go higher there should just be an outer ring for living and maybe a few levels of shopping areas. I'm thinking that it could be created along the lines of Maslovs pyramid .
I like this Idea very much Vernon. Very big bun.-- Susan, Aug 14 2005 [baconbrain] and [Susan], thank you.-- Vernon, Aug 15 2005 [Vernon] yup... I'd be surprised if the sand was as deep as 100m myself.
The critical thing about the material you use is its compressive strength to weight ratio, as I'm sure you appreciate. The limiting height is the height at which the total weight of the building causes compressive yielding in the foundations. Hence we need very strong, light materials.
The interesting thing is, maximum height is actually independent of the slope angle of the pyramid. Increasing the area of the base will also increase the areas of higher floors by a proportional amount; the ratio of total building weight to floor area will remain the same.
It is also important to realise that this is an essentially two-dimensional problem. If 50% of the plan area of a level is taken up by structure, and 50% of the level above and so on, with the rest being accommodation, then for the purposes of calculatin a maximum height we can factor out all of the accommodation and pretend it is a solid pyramid. This approximation actually works in our favour, as a solid pyramid will not be susceptible to buckling failure (occurs when a beam is too long and narrow, at a much lower load than compressive yielding).
So now we have a solid pyramid with an arbitrary slope angle. Its volume is 1/3 x base area x height.
The pyramid will collapse when the pressure it exerts equals the yield stress of the material. Pressure = load / area, and hence is equal to 1/3 x base area x height x density x gravity / base area
Hence yield stress = 1/3 x height x density x gravity
and maximum height = yield stress / (density x gravity x 1/3)
As gravity and 1/3 are constants, the tallest pyramid will be built from the material with the best yield stress to density ratio.
I went looking for high performance materials and found one relevant example; with the very low density of 500kg/m3 this high performance concrete exhibited a yield stress in compression of 70MPa. Putting that into the equation above gives a maximum height of 42km, if all of the mass of the building is structural (nobody living in it!) and we have no factor of safety against structural failure - one snowflake lands on it, and the whole thing collapses.
If instead we assume that 1/3 of the mass of the pyramid is useful (accommodation, equipment, people, etc) and allow a factor of safety of 2, the limiting height drops to 14km. Still plenty tall enough to make a visual impact, especially with aircraft landing half way up.-- david_scothern, Aug 15 2005 [david scothern], thanks for the analysis. I think I must disagree somewhat about the slope of the pyramid not mattering. Consider the cone of sand in the bottom part an hourglass, for example. Consisting of loose grains, it still piles up, maintaining a fairly constant slope ("the angle of repose"). You seem to be saying that no matter how wide the base, the height of this pile of loose grains can never exceed a certain amount, that the angle of repose must change to an ever-shallower slope as that height-limit is approached. I'm not saying this cannot be true; the height-to-base ratio of Olympus Mons might indicate such a thing, despite the lesser gravity of Mars. But I do have doubts -- and if a pile of loose grains can Scrape Space, then an equivalently-sloped solid structure should be able to do the same.
Meanwhile, there is one somewhat exotic material that recently became manufacturable in interestingly large sizes -- although I doubt they've thought about sizes like THIS, heh -- which has a much better steady-compression-strength : weight ratio than concrete. Diamond....-- Vernon, Aug 15 2005 I'm saying that the average ground pressure at the base is related only to height, and I'm sure you can follow through my analysis to see that that is in fact the case. Obviously the stress state will be more complex than this, but that will accurately give the mean.
Your analogy of a pile of grains is entirely different. It is not a structure, and is already totally collapsed. It's equivalent to building this pyramid up beyond the height at which the base starts to collapse, and then just continuing to add height. The pyramid will grow upwards, sure, but the lowest floors will be crushed flat.
I suppose that in the case of the solid tower, the stress state near the centre of the base will be close to hydrostatic, so there will only be a net downward force on the material and while it might sink, it won't deform significantly. It will exert huge sideways pressure though, so the outer edges of the structure will be prone to squeezing outwards.
As soon as you start incorporating voids into the structure (living quarters, for example) that hydrostatic case no longer exists, and the structural members will collapse into the accommodation.-- david_scothern, Aug 15 2005 [david scothern], OK, now we come to the nifty thing which is composite-materials design. Note in the original main text where I mentioned the possibility of "steel tubing filled with reinforced concrete". The steel isn't there to handle the vertical load, it's there to handle the sideways pressure of the loaded concrete. Yes, the tubing might need rather thicker walls than I originally envisioned (inverse analogy: pressure hull of submarine).-- Vernon, Aug 15 2005 Such details are interesting and necessary, but until the fundamental problem of massive structural overload is solved, they're secondary (For your information, the above calculation carried out with steel produces a limiting height of about 9km, suggesting that the extra tensile strength of steel to take the hoop stresses would be more than offset by its higher density).-- david_scothern, Aug 15 2005 ldischler, I went looking for high-performance concrete and found low-density stuff with a yield stress of 70MPa and a density of 500kg/m3; this compares favourably with steel (rough yield of 210Mpa, density 7000kg/m3). I've no idea what its other properties are like, but its strength-to-weight is better than steel so I used it as an ideal-case scenario.
Where I have difficulty with this is that the basic maths doesn't work; over 42km height, the base _will_ collapse, even if the tower is purely designed to support itself and nothing else. Consequently, more complex analysis won't help; the back-of-the-envelope stuff tells us that.
As regards encasing the columns in steel, I think it is reasonable to suggest that as you add material with a lower strength-to-weight ratio (steel), so your structure's maximum height will decrease.
Let me explain something about composites (he said, rather patronisingly) Typically they are composed of a fibre (eg carbon fibre, or rebar) in a matrix (epoxy, or concrete). Under load, the strength of the material is the average of the strength of the fibre and the strength of the matrix. Similarly the density is the average of the deThat is to say, composites aren't going to buy you any improvements in structural strength.
Where they do help is with bending stiffness; the matrix transfers loads between the fibres very efficiently.
However, the load here which we are having difficulties with is the direct load. In that case, we should use either 100% fiber (steel structure) or 100% matrix (concrete structure), depending on which has the best strength to weight ratio.
In practice, you're going to need some reinforcement to resist shear when taking loads from floors to walls, but that's not immediately relevant.
I think what I'm trying to say is, resisting those hoop stresses with steel is good (hoop stresses are tensile, where concrete is poor) but it doesn't allow us to make the building any taller. It just highlights that the very high performance concrete I found wouldn't deliver as much as it promises (lower str-to-wt steel is needed to resist tensile stress), and that the final height of the building will be smaller than the rough analysis predicts.-- david_scothern, Aug 15 2005 I take it back. There is an exotic concrete with compressive strength to 200 MPa, about half that of a good steel. (Of course, you'd have to use a large safety factor--ten or so.) As for column collapse, you'd build it in the form of a pyramid (or Eiffel tower).-- ldischler, Aug 15 2005 I went concrete-hunting again and found Ceracem with a compressive yield of 200Mpa, but its density was five times that I was using. It was the material of choice for the Millau Viaduct, incidentally, so perhaps it would have been a better choice for these numbers.
I had to look for exotic stuff and work with minimal factors of safety to demonstrate that even at the outer boundaries this isn't feasible. The Eiffel Tower shape, with its curving walls, may well represent an optimum as it means that the stress is kept constant all the way up the structure. Of course, if we're not working with a solid tower, then that curve could be incorporated instead by increasing the amount of habitable space vs solid structure higher up the tower. I haven't worked out how much of an improvement this would give us though.
As regards building it as columns, or a tower or pyramid etc, that is important for resisting buckling failure, which occurs at a much lower load than total compressive failure. Even if we assume an ideal structure in which buckling does not occur, we still can't get the height we need with the materials we have.-- david_scothern, Aug 15 2005 [david scothern], I do understand. However, what I meant by "composite materials" was simply that even ordinary reinforced concrete qualifies as a composite material. You probably noticed that I mentioned using titanium rebar instead of steel, because I knew (as you probably know) that titanium has the same strength of steel at half the density. It was only because of fire-related aspects of titanium that I didn't suggest using it as (exposed) tubing, also. I also could have suggested beryllium instead of titanium (possibly should have, for the rebar), but again as exposed tubing beryllium is problematic (toxic). Well, be that as it may, what height do you get if diamond instead of concrete is used?
Also, with respect to "getting the height we need", even 14km may be sufficient. Think about what percentage of the atmosphere is below the 14km mark, when considering an electromagnetic launcher sending ablative-protected payloads from an evacuated accelerator through a plasma valve into the air, toward orbit....-- Vernon, Aug 15 2005 Yup. It's a Vernon idea.-- DesertFox, Aug 15 2005 //Yup. It's a Vernon idea// How long before it reaches 14km in length?-- AbsintheWithoutLeave, Aug 15 2005 [Vernon], I ponder the abililty of "Skyhooks" to reduce the wind load on your structure. Skyhooks as I imagine them would be high tech (ha!) kites that would be tied into guide wires and "pulleys".
The guide wire would zoompk down to an appropriate fulcrum point at which it would be pulley tensioned to backside stress the tower against the wind load.
To further describe the kites or Skyhooks: They will require supierior flight/navigation tech. When the wind blows, & at thier altitude, it should, They will curcuitly close off the majority of their "sails" and pull to counter-act the wind load on the structure they are programmed to love. When blows the wind beyond design specs, the Kites will open breach points in their sails to break the force.
I wish I could really describe what I want to say, & I hope someone can understand. (sorry folks).-- Zimmy, Aug 16 2005 [Vernon], that's very true. Or alternatively, I saw a suggestion somewhere for attaching a space elevator to the top of a tall man-made mountain on the equator; I think that this would qualify quite neatly for the role.
[edit] or would, but as you say above, there's not many deserts on the equator, and 10,000 square kilometres of farmland, villages, towns etc is gonna set us all back a bit. Maybe just the launch site, instead.-- david_scothern, Aug 16 2005 [Zimmy], wind-loading against a pyramid is usually ignorable. For an ordinary skyscraper, of course, the tower can sway in the breeze. But a pyramid has too big a base for that.
[david scothern], if we cannot build higher than 14km, then assuming a 45-degree slope, the base of the building would only be 28km squared, and not 100km squared. Less environmentally problematic, fits more places easier, less expensive to build, and faster to build. However, the stratosphere airport gets a lot smaller, too: 6km. May still be enough. Certainly could be enough if some aircraft-carrier take-off-and-landing technology is employed.-- Vernon, Aug 16 2005 You could slope the runways. Not to the slope of the building face, maybe, but that was my first thought. Land uphill, take off downhill, and have the top end rounded to a level platform. I've flown off two grass strips like that, on hillsides, and much prefer them.
One of the recent James Bond movies shows such a runway in the opening sequence. It doesn't show passenger jets landing on it, of course.-- baconbrain, Aug 16 2005 This is too big for a pyramid - and i am only using earth maths - olympus mons' shape is due to its massive size, it is like a slice of a sphere but bloated at the base.
If you really want to get this big, I think you will want to go dome - with an even larger base spanning, perhaps, a continent(australia - they need shade), industry and accomodation can be built into the support struts with a massive launch pad/solar grid/airport complex at the top. More efficient than the (oh so stone age) pyramid the dome would be tricky to design but look way cooler.-- Trodden, Aug 16 2005 Is the pyramid/dome completely enclosed, or are there occasional openings that could allow for some outdoor deck space on the first thousand levels? And is there an altitude at which meteors might become a concern (the probabilities involved may be inconsequential...I'm not sure)?-- sleeka, Aug 20 2005 [baconbrain] a friend told me of just such an airstrip, high in the mountains in India. Terrifyingly though, landing was downhill and takeoff uphill. Why the direction was not reversed, he couldn't say. Maybe there was the small matter of a mountainside getting in the way; I'm not sure.
[sleeka] interesting point about meteorites. If you could actually build it to the 100km mark then I think that they might be a concern; a strike would result in decompression, for one thing. I don't think the height is feasible though, and consequently I doubt meteor strikes would be a risk either. Are there any reports of meteor damage to aircraft? The probability of a meteor and an aircraft colliding is small, but if meteors do get low enough, at sufficient size to be dangerous, you'd think that a few reports would be out there (I don't know if there are or not; I'll look). A quick search seems to suggest that there are no reports as yet, but that the possibility has been noted.-- david_scothern, Aug 20 2005 [sleeka], one reason why I suggested an 80km structure is because it's pretty close to space, but has 20km of high atmosphere to stop the micrometeors (they would have some sort of long-term erosion effect). The bigger ones that get deeper in the air can mostly be stopped with the same sort of shielding that is on many satellites. That is, some layers of foil are placed a few centimeters from the thing you want to protect. The small meteor's impact with the foil destroys it (vaporizes it) and the vapor-blast cannot hurt the next surface. That spot of foil it hit is also destroyed, but it also is not likely to be the impact spot of the next small meteor.
Anything big enough to do significant damage will be fairly rare, and I've already indicated that various levels of the building have to be separately pressurized. It would be reasonable to have a set of pressure doors around the perimeter of each level, through which retreat would be possible when needed.-- Vernon, Aug 20 2005 Fair enough. [david_scothern] yes, I wouldn't think much would make it down to aircraft height (<15km), but a golf-ball size meteor might make it to at least the 50 km mark. So I suppose the realistic height is the question, and I see from previous discussion that it’s substantially lower than 80 km. Although I wonder what type of super-materials corporations could develop in the next 50-100 years, considering how many zeros could be involved in the potential monetary windfall. //Anything big enough to do significant damage will be fairly rare// extremely rare, for sure. But maybe your ‘mega-pyramid’ stands for well over a thousand years: as long as you are in charge of the "upper-atmospheric protection council”, and not Bruce Willis, it should work out well.-- sleeka, Aug 21 2005 Last time we tried building a tower up to the heavens, god gave us loads of cool languages to use. Let's do it again and see what we get this time.-- wagster, Aug 21 2005 [wagster], I seem to recall reading that that other tower was built as an act of defiance or challenge or something like that. NOT the goal here....-- Vernon, Aug 22 2005 funny how Jacob got away with it, though.-- Zimmy, Aug 22 2005 I think the best shape for this project would be a cone like the arcology proposed for Tokyo Bay. You would have an open truss structure supporting several "layers" of about 50 stories each, with passages for wind in between. You could even shape each layer's cross section like an airfoil (or a frisbee disc)at higher levels so that the wind would support some of the load.-- discontinuuity, Aug 22 2005 There's no way private capital will invest in this unless all the better land is taken. I also seriously doubt there is enough concrete in the world to build this, and without cleaner energy there's not enough power to haul the raw materials around.
[david_scothern]- I'm curious whether concrete columns could hold beyond their yield stress if they are also compressed from the sides- ie if you push on the sides hard enough, the columns can't crack and expand outward. Thus, it seems like with an arbitrarily large base you might be able to go beyond the limit you suggest.-- sninctown, Apr 06 2006 [sninctown], you can increase the bearing capacity of concrete columns by increasing confinement. There are a number of products in the market for this specific application (I am familiar with the design and installation of a polyaramid, carbon fibre and glass fibre composite). I am not sure whether you could increase it past the yield point of the materials.
Of course, a project like this is madness, but very interesting madness.
One more for the road: We have assumed that the bedrock can withstand the load. At these levels, we need to start thinking what is below it.-- methinksnot, Apr 06 2006 Viven los biodomes!-- wakeNbake, Apr 07 2006 [methinksnot], one reason for a pyramid design was exactly to reduce the load on the bedrock. Also, keep in mind that this thing is a building, not a solid lump. Its mass would be much much greater if it was a solid lump, and not full of rooms and corridors and atriums and so on.-- Vernon, Apr 07 2006 I understand your point [Vernon]. My comment stems from the fact that this Goliath, whether hollow or not, is big enough for us to be considering the compression yield point of concrete because the vertical loads are so great. We have to transfer these loads to the substrate, which will not have infinite bearing capacity.Even if this rock substrate is strong enough to withstand the pressure, it, in turn, will be transferring the load to what is below it.-- methinksnot, Apr 07 2006 Whats a little lava? Hot rock, right? If it cracked the substrate, we could power the thing with geothermal power.-- DesertFox, Apr 07 2006 I like the idea, may I suggest a bootstrapping/ incremental approach where is started with building smaller pyramids , immediate put to use to generate money, resources (hydrogen for example) and energy that will allow for the integration of groups of smaller pyramids into larger pyramids, for instance exercise the following scenario:
LOCATION: Western Sahara
A desolated arid area you generally don't want to be, but heavily squabbled over by the Morrocans and the Polissario for its natural mining resources.....
PHASE 0, THE SEED PYRAMID: There is some pretty large scale iron-ore and phosporus mining by the morrocans in the Western Sahara, so lease some komatsu bulldozers from the local mining company and,
near the coastline, construct from sand , earth and rubble a rough pyramid or zigurat approximately 1 km high, use the mountainsloped version of the australian solar tower concept generate copious amount of electricity, all four slopes of the pyramide are utilised and slopes covered with black material (locally produced concrete slabs and dark iron oxide paint?) that will adsorp heat and prevent the wind from blowing away your little sandcastle.
PHASE 1: ENERGIZE & CREATE SUPPLY/DEMAND As part of the leasedeal, start delivering electricity to the local mining company that equipped you with the diesel bulldozers, also provide a nearby costal town with electricity to start recover costs for building the pyramid. Next start building some railroad track along the coast that can be powered by electricity, will bring added economic value to the region and will aid you in the construction of more pyramids
PHASE 2: CLONING, SCALE UP THE POWER GRID start building neigbouring pyramids along the coastline to create some kind of sharkteeth shaped wall. Start using electrical powered cranes/bulldozers as the pyramids will provide the energy to build the next one. With about 10-20 pyramamids you will soon run into the problem that the local goat-trading economy simply cannot handle all those Gigawatts of power you are offering for rock bottom prices, so ink a deal with the relatively nearby highly developed/touristic spanish canary islands , a huge undersea power cable will make the canary island less dependable on fossil fuel imports.
PHASE 3: FILL IN THE GAPS & INCREASE HIGHT OF THE WALL
Fill up the gaps between the sharkteeth so that one has one 10-20 km long and 1 km height wall, increase the wall height to 2 km, great now we capture a lot of clouds/moisture on the westside of the wall (incidentelly the western slopes of the morrocan Atlas mountains receive 5 times as much rain as the country avarage) and still maintain our solarthermo bussiness on the eastern slope, now with lots of water and enegy in place a lucious green tourist Riviera can be constructed, generating income as well as extensive farming , growing crops etc. Don't forget to build some electrolysis based (since electricity is really cheap) hydrogen plants as well to support your upcoming spaceport....
PHASE 4: PEAK ECONOMY Once the cash is flowing, you can pay for constructing really large (solid) pyramids / higher walls, some spots peaking out at 12 km to accomadate your:
- stratospheric airfields - observatories especially the new infrared telescope generation that will benefit from the cold up there (less heat "noise" signals) as well as some huge visble light telescope large baseline arrays that have pretty unobstructed view. - your sloped electromagnetic railgun launchassist, relatively near the equator (natural sling effect), if not for sporting a topnotch spaceport, than do it for becoming a rogue nation and instill fear in the hearts of the infidels with your supergun ;-) - all the other things that people can dream up with huge megalomanic structures.
Actually i think that many people here have very valuable ideas contributions for space arcologies and as such it would perhaps deserve its own orionarms like website as a melting pot of inspiration in a collabarative project to build a virtual space pyramid....-- jvanguts, May 24 2006 But - I don't WANNA live in North Africa.-- sleeka, May 24 2006 <sorry to act like the drunk party chick, but>Bigger, Higher, Wider, Cooler. I love it.
I can only picture one can literaly be with it's head in the clouds. And LIVE there. </staltdpcb>
Only hope nuclear waste won't be a problem tll these babies are born <link>-- sweet, May 24 2006 If you don't want to live in N-Africa, build another wall in the states, consider the lake yellowstone proposal, where a huge stratospheric protective wall encircles the park and is partially filled (100 m depth or so) with water to apply pressure and keep the supercaldera from destroying western civillisation.
Incidentally i believe maps of the Jetstream show the jetstream freuqently run nearby Wyoming overhead, so a stratospheric wall could sport extreme windturbines and naturally you'd have an instant allied C&C Weather control device 'cause one can manipulate the jetstream. For instance one could optionally divert the jetstream more to the south to blow away any hurricanes that approach from the carribean, probably the hurricane will end up in backyard of Hugo Chavez and Fidel Castro, wich would make it a big plus for the neoconservatives.
One could erect huge long range lasers as means of missileshield taking advantage of low air density. Several other niche places in the usa could be thought where a huge wall could be put to use (how about the mexican border ;-) One would need oxygen masks and snow boots to illegally cross the border. naturally in stark contrast luxurious decadent sking ressort would be put on the usa side of the slopes....
Other interesting places on earth would be resource/energyhungry China, the Gobi dessert, to stop duststorms while capturing energy in the process and the outback in Australia.-- jvanguts, May 24 2006 electromagnetic energy from the sun => differences in temperature along the globe => winds with kinetic energy, which cleverly used by THE WALLS with a lot higher efficiency than solar cells
this is the prettiest global energetic solution I’ve ever seen-- sweet, May 24 2006 Regarding a linear accelerator: up the sides is far from optimum. *Much* better to have a ridge along the top: the most efficient way to get to orbital speed is applying force horizontally. As far as getting the vehicle/cargo up there, a plain old elevator would suffice.
Regarding shape of the structure... Eiffel Tower ? Isn't there a generic shape where you can increase the size without increasing the load per sq.ft ? (edit: no there isn't: increasing 3d means an exponential increase in 2d so ... "Eiffel Tower")-- FlyingToaster, Aug 03 2012 Suddenly, Dubai makes sense.-- Phrontistery, Aug 04 2012 you'll need to seal off the atmosphere by level with airlocks every mile or so, otherwise the air will simply fall to the lowest levels.-- Voice, Aug 04 2012 random, halfbakery