RussianJet
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Demolition - Huge Buildings In City Centres

Tue Aug 07, 2012 7:45 pm

I was watching a programme about the tallest buildings around, how they were made etc., and got to thinking. If you were to take an example like the CN Tower, how long is it expected to last, and how on earth would you demolish something that tall without damaging the surroundings? Would you literally just have to disassemble most of it piece by piece? That seems incredibly laborious. Sorry if the question is simplistic, but I am curious about the issues involved with such things. Are there any major examples of incredibly tall buildings in built-up areas being demolished? I imagine that any super-tall buildings are no where near old enough for it to be an issue yet.
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Aloha717200
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RE: Demolition - Huge Buildings In City Centres

Tue Aug 07, 2012 8:13 pm

The basic idea is to control the detonation of specific charges in such a way that the building implodes onto its footprint. How to do this depends on the building's structure and expected center of gravity. A lot of math goes into building demolitions that are controlled by explosives.

Here is a video of what happens with miscalculations...the final clip is the way you do it properly:

http://www.youtube.com/watch?v=5wwDF58Hw9M&feature=related
 
aloges
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RE: Demolition - Huge Buildings In City Centres

Tue Aug 07, 2012 8:17 pm

Just wait a couple of hours until a programme about demolitions goes on the air! 

Anyway, I suppose you would disassemble the metal structure of something like the CN Tower and then hire a very renowned demolition company to blow up the remaining concrete - if it can be made to collapse without affecting too large an area.

If you can't or won't demolish it, you have to make sure that it doesn't decay or that the decay doesn't threaten anyone. The latter is the fate of many above-ground bunkers in Germany.

or, in short:
you hire these guys: http://www.controlled-demolition.com/
not these: www.youtube.com/watch?v=Diw2PS3FEuA

[Edited 2012-08-07 13:26:57]
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kaitak
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RE: Demolition - Huge Buildings In City Centres

Tue Aug 07, 2012 9:15 pm

We're likely to be facing the same problem in Dublin, where the tallest building in the city - Liberty Hall - is due to be demolished in the near future; although it is Dublin's tallest building, it is a bit of an eyesore. It is, however, in a central area and quite close to a rail line, so demolishing it is going to be quite a challenging process. I think quite a few streets around the area will need to be closed and nearby buildings protected.
 
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Aesma
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RE: Demolition - Huge Buildings In City Centres

Tue Aug 07, 2012 9:26 pm

New buildings are thought out with their ultimate fate in mind, not so much old ones. I'm guessing in the future the currently new towers will mostly be "deconstructed" rather than demolished.
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MD11Engineer
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RE: Demolition - Huge Buildings In City Centres

Tue Aug 07, 2012 10:18 pm

You take out the load bearing structure and let gravity do the rest.
It is a bit difficult to explain without a drawing, but to cause a building to collapse inwards, you´ll need to cause the core to break down first, a few fractions of a second before you fire the charges in the outer walls, so that the core, through the floors, will pull the outer walls towards the inside. You also remove everything within the building before the big blast (sometimes through separate demolitions), which might cause an imballance. Sometimes you´ll even have to brick up windows or doors to get an even load.

I´ve learned this job in a German civil defence engineering unit (imagine military engineers without the guns) and used to have a licance for this kind of work.

Jan
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ltbewr
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RE: Demolition - Huge Buildings In City Centres

Wed Aug 08, 2012 12:50 am

The 55 story Bankers Trust/Deutsche Building just south of the original WTC site and badly damaged in the 9/11 attacks is probably a good example of what may have to be done to demolish a large building where explosive demolition is not practical. As far as I know, NY City will not allow the use of explosive demolition so dismantlement is the only way to remove an obsolete building.

Basically after a long decision period, it was determined that the building had to be dismantled floor by floor, from the inside with assistance with elevators and cranes from the outside. This Wikipedia article in part discusses its dismantlement.
 
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RE: Demolition - Huge Buildings In City Centres

Wed Aug 08, 2012 6:06 am

The use of explosives to remove large buildings is now very much out of fashion in western Europe, high reach demolition excavators can now reach beyond 50 metres and can safely nibble away at both concrete and steel from the ground. Beyond that smaller excavators are craned onto the buildings to remove the upper floors first. Some are remotely operated. I was recently in the US and was interested to see on the news that buildings are still regularly imploded, complete with dust clouds and the leaving of huge tangled heaps of debris, which still has to be cleared with excavators anyway.
 
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nighthawk
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RE: Demolition - Huge Buildings In City Centres

Wed Aug 08, 2012 7:37 am

This very situation just happened in London. In order to build the Shard, they had to remove the existing building Southwark Towers. Due to the proximity of other buildings (one of which was a hospital), they couldn't use explosives. Instead they had to dismantle it piece by piece.

Here is a video with some photos of the demolition: http://www.youtube.com/watch?v=qEYONTG3_Yg
 
kl671
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RE: Demolition - Huge Buildings In City Centres

Wed Aug 08, 2012 8:30 am

Here is how to bring down a chimney stack wihout using explosives. I suspect however this method may not be appropriate for bringing down huge buildings in crowded city centres.!

http://www.youtube.com/watch?v=0L1WOnR2KBY
 
Superfly
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RE: Demolition - Huge Buildings In City Centres

Wed Aug 08, 2012 8:41 am

Quoting Bongodog1964 (Reply 7):
I was recently in the US and was interested to see on the news that buildings are still regularly imploded, complete with dust clouds and the leaving of huge tangled heaps of debris




...and pretty cool to watch.  
I was at this demolition standing near the camera man in this video.
This is an abandoned dormitory (Verducci Hall) at San Francisco State University.

http://www.youtube.com/watch?v=0JQZM5nA-l0
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MD11Engineer
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RE: Demolition - Huge Buildings In City Centres

Wed Aug 08, 2012 11:14 am

Quoting Bongodog1964 (Reply 7):
The use of explosives to remove large buildings is now very much out of fashion in western Europe, high reach demolition excavators can now reach beyond 50 metres and can safely nibble away at both concrete and steel from the ground. Beyond that smaller excavators are craned onto the buildings to remove the upper floors first. Some are remotely operated. I was recently in the US and was interested to see on the news that buildings are still regularly imploded, complete with dust clouds and the leaving of huge tangled heaps of debris, which still has to be cleared with excavators anyway.

Often the people involved in the decision making process don´t have a clue what you can do with modern explosive techniques. They are prejudiced by Hollywood and also by American demolishers, who like to go for the big, sectacular bang and dust cloud (which would be a major show stopper here due to environmental rules).
Then we also have much stricter laws on explosives handling and transport due to security reasons, which give headaches to the people involved.
The basic rule in using explosives for demolitions is to use the minimum which can be used to get the job done safely (unlike military engineers, who use whatever is required to remove the obstacle plus some more to make sure).

One drawback of using hydraulic hammers to demolish massive concrete structures is that it causes lots of multiple low frequency vibrations, which can cause damage to neighbouring structures. In such a case the one big shock from the mass of a falling building is less harmfull. Also think about the continous noise going on for weeks while a big structure is being nibbled down (I´ve seen a company removing a concrete bombproof aircraft shelter at our airport using an excavator with a hydraulic hammer and "nibblers". It took them several weeks to get it done. I would have demolished the structure like an arch of a concrete bridge and cut it at the same time with explosives into neat lumps to be fed right into the breaker to separate concrete from the rebar. It probably would have taken a week or so to drill the about thousand shotholes and a day to load them with small charges, and another week to clean up after the blast. I would have made full use of the millisecond delay effect to both reduce the vibration shock and to cause massive fragmentation of the concrete, while keeping flying debris low, which´s flying away I would have prevented using special blast matts).

Another option for a massive building is to demolish it inside out with multiple small blasts, keeping the outer walls in place until the end to act as catchers for debris and dust. Not very spectacular, but efficient and clean.

Jan
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planeguy727
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RE: Demolition - Huge Buildings In City Centres

Wed Aug 08, 2012 12:05 pm

Quoting LTBEWR (Reply 6):
As far as I know, NY City will not allow the use of explosive demolition so dismantlement is the only way to remove an obsolete building.

Correct. Here in NYC buildings are taken apart.
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Geezer
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RE: Demolition - Huge Buildings In City Centres

Fri Aug 10, 2012 4:47 pm

Here's what concerns me; there were already several VERY tall buildings; (Taipei 101); then the Burj Khalifa was built;
it's beautiful, but I wouldn't want to spend a whole lot of time in it ! My point being..........you can build a building just "so tall"...........beyond that, it's either going to topple while you're building it.......or do so later on; either way, people are sure to be killed. In spite of all of this, there is always someone who just MUST have the tallest building in the world ! I shudder to think of the "next one" that exceeds the necessary 2,600 feet to out-do the present record holder !

Does anyone think the Burj Khalifa will be the "last one" ? ( Personally, I hope it is ! )

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RE: Demolition - Huge Buildings In City Centres

Fri Aug 10, 2012 6:37 pm

Quoting GEEZER (Reply 13):
Does anyone think the Burj Khalifa will be the "last one" ?

I think it will be for a long while. Their have been larger proposals in Dubai like the Al Burj and the Nakheel Tower but they have been canceled both exceeding 1,000 meters in height and projects slightly shorter than the Burj Khalifa like the Pentominiom and the Burj Al Alam both just over 500 meters are on hold if not outright canceled. Other supertall projects in the Middle East like the Mubarak Tower, and the Kingdom Tower both at 1 kilometer in height are currently paper projects. For the future of skyscrapers, China is where to find new projects but don't expect to see new building rise far above 2,000 feet or 600 meters anytime soon.
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RE: Demolition - Huge Buildings In City Centres

Fri Aug 10, 2012 10:56 pm

Thanks to this topic I just spent hours of reading about old airports... ATL and FBU   At least work went by fast...hahaha
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