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Old November 15th, 2013, 08:54 PM   #2261
droneriot
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Look, I'm as far from being an engineer as you can get, I'm a total layman, so I'll put this is super-layman's terms:

An 800m building is really heavy, dude. And without a central core to hook up to, or mechanical floors to distribute the weight, the entirety of that weight is carried by the prefabricated steel sections of the first floor.

Also, at a few meters up it gets really windy, dude. And this building is literally as aerodynamic as a brick.
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Old November 15th, 2013, 08:57 PM   #2262
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Quote:
Originally Posted by patrykus View Post
Wrong analogy People get tired fast, and as we know from construction sites speed of construction doesn't change much for repetitive floors during timeline of the project. Actually it's often the opposite. Construction speed increase in later phases as logistics gets simpler at the base. And for this particular shape it's rather obvious that for the same amount of cranes even if lifting will get a little bit longer on later phases decreasing floor space at upper levels will compensate for that.
Not quite true.
You are assuming that the lifting is always from ground to top. At that height, one does not lift from ground to top but rather it's it staged at regular points. Same goes with all super tall constructions.

I do realize that there are many who are pessimistic that this building can be erected. I am personally quite sure that the Broad Group knows exactly what they are doing and they will demonstrate in due time how this can be done.
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Old November 15th, 2013, 09:14 PM   #2263
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I know that. But you can investigate it on real construction sites. Just look how fast last phases of construction at shanghai tower regular floors were. Much faster than at the base. The act of lifting alone isn't actually that long. When I mentioned logistics I meant more the traffic at the base because this is what slows construction sites down the most. And lastly as I said before however construction can be slowed down it still will be faster by an order of magnitude from everything else. There is no doubt about that.
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Old November 15th, 2013, 09:14 PM   #2264
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yes droneriot, we are all pretty optimistic all the time, because this indeed is a dream we all like to dream
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Old November 15th, 2013, 11:33 PM   #2265
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Just for fun I made some very pessimistic estimate according lifting times for the section of the tower from the picture below. It is the worst section of the tower because it's tall and still quite wide. One floor consist of 48 prefabricated "pieces". Now if we assume there are four cranes (one on each wing) under disposal and each package needs even as much as one full hour to be lifted it would still be enough to build two floors a day. And if they would go for 6 months schedule (instead of 3) 12 hours per day would be enough to lift all the sections they need. And of course as we go taller even less parts are needed to be lifted in a day.

So once again. Lifting times are not going to slow down this technique significantly. If the workers can install it so fast at 200m there is no reason to believe they can't do it at 600m.

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Old November 15th, 2013, 11:43 PM   #2266
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Quote:
Originally Posted by droneriot View Post
A few months ago I mentioned in this thread that I find the idea of a 700-something-meter box withstanding wind pressure and its own weight without a solid core very unrealistic, and I got a massive shitstorm in response, "OH NO, YOU'RE WRONG, THEY DID TESTS!!!" Now I come back to this thread and everything is still the same...
You're not the only one, I've made that argument too, with the same reaction received
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Old November 15th, 2013, 11:50 PM   #2267
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And yet they bought steel for the tower and moved heavy machinery on construction site
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Old November 15th, 2013, 11:59 PM   #2268
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Why do I have a feeling that in this thread technology of that skyscraper is supported only by people who don't have a clue of fundamental rules of statics and material properties? It is amazing how many people advocate this 50+ years old technology of prefabricated construction as new and revolutionizing ...

I have also feeling that this tower is delayed not because some mysterious forces of classic skyscraper building technology but that the statics of proposed building is fundamentally flawed and cannot be proven safe enough. Just a humble opinion of an unimportant civil engineer ...
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Old November 15th, 2013, 11:59 PM   #2269
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Quote:
Originally Posted by patrykus View Post
And yet they bought steel for the tower and moved heavy machinery on construction site
And what would that prove?
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Old November 16th, 2013, 12:19 AM   #2270
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That plans for this tower are real instead of being just an publicity stunt as some suggest. If the plans are real they have to have model for this tower that works. I'm not saying this technology makes super strong super safe tower, but it looks like it is stronger than old wtc towers and with pyramidal four wing shape could indeed reach the height they claims to reach. Old wtc towers looked even more fragile than this and yet they stood 400m without even single setback. Maybe they weren't jumbo-proof but is that really necessary everywhere?



Doesn't broad structure looks stronger to you than this?
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Old November 16th, 2013, 12:42 AM   #2271
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Quote:
Originally Posted by patrykus View Post
That plans for this tower are real instead of being just an publicity stunt as some suggest.
As I said before:
Quote:
Why do I have a feeling that in this thread technology of that skyscraper is supported only by people who don't have a clue of fundamental rules of statics and material properties? It is amazing how many people advocate this 50+ years old technology of prefabricated construction as new and revolutionizing ...
Doesn't broad structure looks stronger to you than this?[/QUOTE]
No.
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Old November 16th, 2013, 12:47 AM   #2272
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Well that wasn't very constructive..

I guess the time will tell if this technology will prove itself or not.
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Old November 16th, 2013, 01:30 AM   #2273
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Sorry I'm not here to teach you statics. Read again previous posts of @droneriot and @crriss, especially this one:
Quote:
Originally Posted by crriss View Post
The picture from the post above is very useful to discuss about this controversial construction method, if is possible or not. I am not Structural Engineer, but EE, and I studied a bit of mechanics and I can say that I understand what happens in the picture above. At a first impression that crane has at least 30-40 tonnes without any load lifted. there are complex forces which act from crane support mast to building structure, both static and dynamic. first is a vertical component with a value almost equal with the weight of the crane plus load then there is lateral force which either pull or push the upper support depending on the position of the crane boom and if there is weight lifted of not. then is a shear force at the upper support created by the weight variation from load/unload condition. added to this there are forces caused by wind, weight lifting, load or unload as well oscillations of the mast, counterweights and the whole assembly.
All these forces are huge, with order of magnitude within 300-600kN or probably more in the worse case conditions. Suppose that the building from the previous post is made of prefabricated materials and no concrete or very little must be poured, it has to rise in record time and concrete takes at least few weeks to settle and gain it's default strenght, usually 28 days but we don't have that time, as we can see the building is rising few floors per day or per week ? then the floor slab seen on the trailer truck as well as underneath supporting beams are way too thin and fragile to be have enough tensile, bending and twisting strength to support the crane which is fixed on the outside wall. even the exterior wall which carries the vertical component of the weight might not be strong enough. It has probably thick steel piles but even so the structure is not robust enough because the upper side is unfinished yet and there is no closed polygon for return forces...
If I'm missing something, please someone clarify.
And yes: WTC had a central core with 47 steel columns, what has Sky City for holding that great load?
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Old November 16th, 2013, 02:18 AM   #2274
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It has:

1. Outer perimeter structure (green - 60 steel columns )
2. Inner perimeter structure (red - 32 steel columns)
3. Structural walls going inside the building (blue - 12 steel columns)
4. Steel trusses inside each floor
5. Pyramidal more stable structure.



I don't know if that is enough but that doesn't seems much less than what wtc have had and I'm simply giving it a chance. Btw crriss's main argument was the crane wouldn't hold on that structure without concrete floors and core. And as we know it actually did showing even seemingly week structure can actually be quite strong.
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Old November 16th, 2013, 02:26 AM   #2275
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I can at least understand why China, with its rapidly urbanizing population of 1.3 billion, would want to build something that tall. Ultimately extremely high density building will allow for more suburbs amd green spaces surrounding their cities. Meanwhile the only reason Saudi Arabia (with its population of just 28 million) would want to build the Kingdom Tower is to flaunt its oil wealth through an irresponsible white elephant that will always stay half empty and will never turn a profit, in an insecure Gulf state contest of "whose prick is bigger"...

I am of course, like everyone else, concerned first and foremost with the safety, security, and structural integrity of something as huge as SkyCity, and when I hear "prefabricated" I automatically think of cheaply made materials. I sincerely hope the Chinese reputation of making "cheap" and easily-breakable products doesn't apply here. I really think they shouldn't rush to build something like this in less than a year just to show they can. There needs to be meticulous analysis for safety.
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Old November 16th, 2013, 07:59 PM   #2276
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broad at least claims they have done all tests to assure it is indeed safe. china does now have to confirm this and approve the building and this is why it takes longer time now, because the chinese government is the least to want a building like that to collapse, because they are the ones who will get the blame in the end. just think of the high speed train incident, people died, the government had to take the blame and they reacted by shrinking all speed limits although the accident was not because of any speed limits. if something horrible would happen in a project like this it would be the last to use the technology and better a good testing phase and approval so that nothing could possibly go wrong indeed is a good thing even with the delays it brings.
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Old November 17th, 2013, 11:51 AM   #2277
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Quote:
Originally Posted by patrykus View Post
It has:

1. Outer perimeter structure (green - 60 steel columns )
2. Inner perimeter structure (red - 32 steel columns)
3. Structural walls going inside the building (blue - 12 steel columns)
4. Steel trusses inside each floor
5. Pyramidal more stable structure.
You cannot compare small building to megaskyscraper. It is not comparable at all.
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Old November 17th, 2013, 01:05 PM   #2278
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You asked me what this tower have so I answered. This model is cut out section from the final design of the tower.
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Old November 17th, 2013, 01:15 PM   #2279
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should the status be changed to on hold?
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Old November 17th, 2013, 01:19 PM   #2280
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I would think so. Strange nobody ever noticed that. I guess ssc doesn't see too many "under preparation" projects going on hold too often.
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