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How Do We Destroy Big Buildings?

Written by Kevin Jennings

https://commons.wikimedia.org/wiki/File:Demolition_of_Tesla_Hloub%C4%9Bt%C3%ADn.jpg

Buildings are mankind’s oldest enemies. For thousands of years, the population growth of buildings across the entire globe has gone unchecked. Thanks to advancements in technology, we have finally developed several methods of various levels of sophistication with which to dispense with our greatest foe.

            There are a few main reasons that buildings are demolished. While some structures like the ancient pyramids have withstood the test of time, modern buildings are generally built with a specific lifespan in mind, perhaps 80-100 years. Once the design life of a building is over, the building is no longer consider safe to occupy, and may even be a danger to surrounding buildings. Even if a building is not at the end of its design life, older buildings may be replaced with new ones. A building may need to be destroyed as a result of some structural damage or other instability. Or, they may simply want to tear down a small building to pave way for a much larger one.

            Whatever the reason for demolishing a building, safety is paramount. Buildings are big and heavy, and simply trying to topple one to the ground could result in massive damage to property and loss of lives. Depending on how the offending building was designed, its location, and its distance from surrounding buildings and city infrastructure, there are various different forms of demolition that may be employed.

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Small Scale Demolition

            While these days the idea of demolition conjures up images of controlled explosions sending a building instantly to the ground, it is by no means the only form of demolition. In fact, for smaller buildings it would be extremely inappropriate. There are various non-explosive methods that can be employed depending on the scope of the project.

            For the smallest projects, nothing beats a good, old-fashioned sledgehammer. For taking out a single wall or column, this is the perfect tool for the job. It’s important to remember that not all demolition projects are the complete tear down of an entire structure. There is also selective demolition in which only specific parts of a building are being removed.

            In addition to sledgehammers, excavators can be used both in selective demolition and in dismantling entire buildings. Though many people mainly think of them as used in smaller projects, excavators can be fitted with high reach arms equipped with various tools on the end to allow for precision dismantling of a building. While many of these high reach arms are built onto the body of a standard excavator, there are also models specifically designed for this purpose.

            In recent years, Caterpillar released their 6015B, the world’s tallest excavator. At over 70 meters (230 feet) tall, this machine is able to demolition tall buildings in urban areas where other, more intrusive means may not be viable. In case you were wondering how on earth the operator can see what they’re doing from such a long distance, naturally these high reach arms have cameras at the end to help them maneuver the various tools into position.

            Though extremely rare these days, Miley Cyrus would be very disheartened if I didn’t at least give mention to the wrecking ball.  Before high reach arms made them largely obsolete, the wrecking ball was a mainstay of larger scale demolition projects. Wrecking balls range in weight from 1,000-12,000 pounds (450 kg-5,400 kg). These massive steel spheres are attached to a crane and either swung at the target or elevated above an area and dropped.

            Unfortunately, the wrecking ball is not terrible efficient at what it does. You’d think that a massive ball that size would cause some serious damage to a building, and you’d be correct, but excavators are simply safer and more efficient. Among the safety concerns are the somewhat unpredictable nature of how the structure will respond. More importantly, though the swinging of the ball into the building can and must be carefully controlled, once it makes contact with and bounces off the building its trajectory cannot be controlled until the system is reset for another swing. One bad bounce could have catastrophic consequences.

            Finally, while we’re on the topic of small scale demolition, let us not forget the beautiful simplicity of a bulldozer. If there’s a house that needs removing, just drive a bulldozer straight through the thing! Okay, it’s not quite that simple to do it properly, but a bulldozer can still make short work of an ordinary home in about an hour.

Implosion

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            Implosion is one of the most common forms of demolition. Although the earliest attempts at this method date back to the 1700s, it didn’t really take off as an industry until the 20th century. Jack Loizeaux is regarded as a pioneer in this field, and by some even as the founder of building implosion. He began demolishing buildings with explosives in 1947, and in 1960 he founded Controlled Demolition Inc. His wife “Freddie” coined the term implosion as a gentler term for what they did, even if it is not an accurate use of the word.

            While the demolition itself is over in a matter of seconds, preparations can take months. The blueprints of the building need to be carefully studied to determine the precise locations where explosions should be placed, and multiple tours are taken of the location to inspect it. Time is also spent clearing out load bearing walls and other nonessential materials to make sure the event goes smoothly.

            Each building is different and explosive locations and timings will vary, but the general principle is the same. By using small explosions to damage the building’s central supports, the outside of the building will collapse inward towards the center. This material will fall down and crash into the floor below it with enough force to bring that floor down as well; the explosives are just the catalyst, and it is actually gravity that does the bulk of the demolition. These explosive charges will be set on various floors throughout the building, and the entire structure will fall inward on itself in mere seconds. In the above example, it’s important to ensure that all of the explosives on one floor and detonated simultaneously. If one charge goes off before the others, the building will begin to fall in that direction instead of towards the center.

            It is a very difficult and sophisticated process, and there are few companies that will attempt to take down a building in this fashion. Because of the complexity, it is usually only done when necessary, like in heavily urban areas where a building would need to fall into its footprint. Not only is the process highly technical, it is also extremely impressive, and building implosions are typically big spectator events. The demolition of the Sears Merchandise Center in Philadelphia was able to draw a crowd of 50,000 spectators and vendors.

            Though not always practical, a much easier way to destroy a large building is to make it “fall like a tree”. This is also considered a form of implosion, despite being even further from the actual definition of the word. In this scenario, explosives are placed on the bottom levels of the building on one side. Once detonated, the building will fall like a tree in that direction. This is the expected outcome, but just to be safe there will often by steel wires attached to the building as well to help guide its falls in the intended direction. Obviously this requires a large amount of space for the building to fall, but it is the preferred method when the location will allow for such a demolition.

Bottom-Up Demolition

london-bottom-up-demolition by CamCanary https://flic.kr/p/2wQEJX

            This type of demolition only works on buildings with a very specific architecture. It was most noticeably performed on the P&O Building in London in 2007, and pictures of the unusual demolition can frequently be seen online.

            In this instance, the exterior walls of the building provided no structural support. The support all came from a concrete core at the center of the building. On top of the core were huge support beams from which the other floors essentially hung. Because the floors were hanging like this, if the building was going to be demolished without the use of explosives it would have to be done from the ground up.

            One by one, each of the building’s fifteen floors was dismantled was dismantled. A platform jack was placed underneath as a support, and as each new floor was removed the jack was elevated to prevent the hanging floors from plummeting to the ground. Once all of the floors were removed, the massive supports on the top of the building were dismantled and the concrete core was demolished from the top down.

            It is a slow process, and while it lacks the instantaneous visual bang of an implosion, a bottom-up demolition is still an impressive sight to behold. Unfortunately, very specific architecture is required for a building to be dismantled in this way, but it may have served as the inspiration for our final method.

Kajima Cut and Take Down Method

            Named after the Kajima Corporation in Japan who first implemented this method in 2008, the Cut and Take Down method is the newest innovation in building demolition. Traditional demolition projects tend to be extremely noisy. Implosions involve explosives, so naturally they are loud, but even manually tearing down a building from the top down creates an obtrusive amount of noise. Furthermore, these options create an excessive amount of waste both in the form of massive clouds of dust and materials that are too damaged to be recycled. Implosions also risk damaging surrounding buildings, and both other methods have a high chance of injury as well; demolition is much more dangerous than your average career.

            When it came time for one of Japan’s oldest and largest construction companies to demolition one of their own buildings, they had all of these issues in mind. But what if they could reduce dust, maximize recyclable materials, minimize noise, increase safety, and allow the entire demolition process to be done from the ground floor? Kajima figured out a brilliantly simple way to accomplish this.

            In the Cut and Take Down method, the bottom floor of the building is completely gutted. Temporary supports are built next to the building’s existing supports, and then the original supports are destroyed. A number of large hydraulic jacks are then placed to support the weight of the remainder of the building. Once the temporary supports are removed, the hydraulic jacks lower the building back down to the ground, and the second floor is now the ground floor. Keep repeating this process, and eventually the entire building will be gone.

            Traditional methods of demolition have a recycling rate of around 55%, but this new method has a recycling rate in excess of 90%. The details start to get a big more technical, but with the top of the building no longer connected to the foundation, measures are taken to ensure the building remains stable while on jacks in spite of high winds or even earthquakes. With improvements to safety, conservation, and noise, it seems like this may be the number one way for tall buildings to be demolished in the future. So what’s the catch?

            The only real downside of the Cut and Take Down method is cost. The costs associated with this new method are about 5-10% higher than traditional methods, but it may be worth the cost. Not only are there the benefits we’ve already mentioned, but, seemingly against all odds, the total time of demolition is actually about 15% less than other methods. The Kajima head offices that were demolished were a pair of buildings, one was 20 stories and the other was 17. From start to finish, the demolition project took nine months. That might seem extraordinarily long compared to implosion which is over in nine seconds, but don’t forget that’s only the actual detonation. There are months of planning and gutting the building, then after the implosion there are more months of cleaning up the rubble.

            There’s one other advantage of the Cut and Take Down method, and that’s the videos. Building implosions are impressive and all, but they’re old hat. We’ve had the better part of a century to get used to them, and it’s time for something new. For buildings using the newer method, time lapse images of the site show what appears to be a building sinking into the ground until it finally vanishes, and that’s pretty cool to watch.

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