Obviously, most of this is prefab...so I wonder how much time was spent building all the individual pieces before the official ground breaking?
With 220 floors and 104 elevators...that's more than 2 floors and 1 elevator a day. I imagine just the fitting/assembling in place process per floor is enough to fill up a third of a day on its own...so is this basically a huge vertical jigsaw puzzle in which the pieces have been made and just need to be moved onto site?
That was one of the questions I was wondering about. I recently looked at a new factory in the bay area of prefab houses (http://www.youtube.com/watch?v=UmpRRoNqsDI)and one of their claims is they can put up a house in 7 days. But of course it isn't that they start with dirt and 7 days later there is a house, there is a time to build the foundation, and the house is built in a factory, but once the foundation is ready and the house manufactured, it only takes 7 days to install and unfold it. Which is still pretty cool.
So one way this headline could be strictly true is if all of the floors of the building were fabricated off site, once they were ready the company might be able to assemble the final building, in a prepared foundation, in 90 days. That is the only interpretation I can think of that works.
Concrete can take 4 weeks to get to 90% strength [1], so if you didn't do the prefab route you would have to spend more than 90 days just waiting for the lower levels to cure so that you could build the upper levels.
I am interested in what they are trying to do though, it sounds like an interesting challenge.
>"Concrete can take 4 weeks to get to 90% strength [1], so if you didn't do the prefab route you would have to spend more than 90 days just waiting for the lower levels to cure so that you could build the upper levels."
Concrete made with Type III portland cement achieves most of its strength within seven days (concrete made with normal (Type I) cement reaches its design strength in 28 days).
When one needs significant strength more quickly, the mix can be adjusted to provide a higher ultimate strength than is required for the intended loads during the normal life of the building and accelerants added . This results in adequate capacity for construction to continue in as little as a few hours.
The general rule of thumb is 75% of 28-day strength in 7 days. Most concrete mixtures reach their design strength well before 28 days due to the fact that any particular batch of concrete will be mixed such that its 28-day strength is higher than the design strength by a few 10s of %s. This is due to the fact that failing a compressive strength test for any one test or any 3 averaged consecutive tests (guidelines are set forth for failure criteria in ACI) requires remedial action in general.
There's always a lead time. But the pace at which prefabricated items can be built in a factory is significantly greater than that at which items can be site built. The constraints on an urban site are a significant logistical problem - site fabrication requires lots of different trades arriving through city traffic at the same time because there isn't much space in which materials may be staged. Every trade adds to the traffic through which other trades must transport their materials.
Conversely, prefabricated units can be built virtually anywhere and shipped economically over long distances...i.e. fabrication can occur at a factory in a rural location and assemblies can be moved by rail or barge.
I worked on a Low Income Housing Tax Credit project where the developer had granite countertops and solid wood cabinets shipped from China for roughly the same cost as standard economy cabinets and commodity laminate countertops.
What made it practical was the specifics of LIHTC funding. A significant amount of the funds had to be spent upfront on materials and/or labor or it would have been lost. This made the long lead time beneficial because early stages of construction such as clearing and grubbing are relatively inexpensive whereas finishes are relatively expensive.
With 220 floors and 104 elevators...that's more than 2 floors and 1 elevator a day. I imagine just the fitting/assembling in place process per floor is enough to fill up a third of a day on its own...so is this basically a huge vertical jigsaw puzzle in which the pieces have been made and just need to be moved onto site?