Как работают строительное конструкции при взрыве здания. Сейсмоизоляция

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Как работают строительное конструкции при взрыве здания США
How Building Implosions Work
By: Tom Harris
https://science.howstuffworks.com/engineering/structural/building-implosion.htm
The Barkway Court Towers in London, England: The building was blasted
by Controlled Demolition Group, Ltd. in February 2000.
PHOTO COURTESY IMPLOSIONWORLD.COM
You can demolish a stone wall with a sledgehammer, and it's fairly easy to level a
five-story building using excavators and wrecking balls. But when you need to
bring down a massive structure, say a 20-story skyscraper, you have to haul out the
big guns. Explosive demolition is the preferred method for safely and efficiently
demolishing larger structures. When a building is surrounded by other buildings, it
may be necessary to "implode" the building, that is, make it collapse down into
its footprint.
In this article, we'll find out how demolition crews plan and execute these
spectacular implosions. The violent blasts and billowing dust clouds may look
chaotic, but a building implosion is actually one of the most precisely planned,
delicately balanced engineering feats you'll ever see.
The Bigger They Come, the Harder They Fall
The basic idea of explosive demolition is quite simple: If you remove the support
structure of a building at a certain point, the section of the building above that point
will fall down on the part of the building below that point. If this upper section is

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heavy enough, it will collide with the lower part with sufficient force to cause
significant damage. The explosives are just the trigger for the demolition.
It's gravity that brings the building down.
The Reading Grain Facility in Philadelphia, Pa., was blasted by Controlled
Demolition Group, Ltd. in the winter of 1999.
PHOTO COURTESY IMPLOSIONWORLD.COM
Demolition blasters load explosives on several different levels of the building so
that the building structure falls down on itself at multiple points. When everything
is planned and executed correctly, the total damage of the explosives and falling
building material is sufficient to collapse the structure entirely, so cleanup crews are
left with only a pile of rubble.
In order to demolish a building safely, blasters must map out each element of the
implosion ahead of time. The first step is to examine architectural blueprints of
the building, if they can be located, to determine how the building is put together.
Next, the blaster crew tours the building (several times), jotting down notes about
the support structure on each floor. Once they have gathered all the raw data they
need, the blasters hammer out a plan of attack. Drawing from past experiences with
similar buildings, they decide what explosives to use, where to position them in the
building and how to time their detonations. In some cases, the blasters may
develop 3-D computer models of the structure so they can test out their plan ahead
of time in a virtual world.
The main challenge in bringing a building down is controlling which way it falls.
Ideally, a blasting crew will be able to tumble the building over on one side, into a
parking lot or other open area. This sort of blast is the easiest to execute, and it is
generally the safest way to go. Tipping a building over is something like felling a
tree. To topple the building to the north, the blasters detonate explosives on the
north side of the building first, in the same way you would chop into a tree from the
north side if you wanted it to fall in that direction. Blasters may also secure steel
cables to support columns in the building, so that they are pulled a certain way as
they crumble.

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Sometimes, though, a building is surrounded by structures that must be preserved.
In this case, the blasters proceed with a true implosion, demolishing the building so
that it collapses straight down into its own footprint (the total area at the base of
the building). This feat requires such skill that only a handful of demolition
companies in the world will attempt it.
Blasters approach each project a little differently, but the basic idea is to think of
the building as a collection of separate towers. The blasters set the explosives so
that each "tower" falls toward the center of the building, in roughly the same way
that they would set the explosives to topple a single structure to the side. When the
explosives are detonated in the right order, the toppling towers crash against each
other, and all of the rubble collects at the center of the building. Another option is to
detonate the columns at the center of the building before the other columns so that
the building's sides fall inward.
The Hayes Homes, in Newark, N.J.: The 10-story housing project was
demolished in three separate phases, over the course of three years. Even
though all the buildings had exactly the same design, blasters handled the
implosions differently for each phase. These towers were blasted
by Engineered Demolition, Inc. in the summer of 1999.
PHOTO COURTESY IMPLOSIONWORLD.COM
According to Brent Blanchard, an implosion expert with the demolition consulting
firm Protec Documentation Services, virtually every building in the world is unique.
And for any given building, there are any number of ways a blasting crew might
bring it down. Blanchard notes the demolition of the Hayes Homes, a 10-building
housing project in Newark, New Jersey, which was demolished in three separate
phases over the course of three years. "A different blasting firm performed each

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phase," Blanchard says, "and although all of the buildings were identical, each
blaster chose a slightly different type of explosive and loaded varying numbers of
support columns. They even brought the buildings down in different mathematical
sequences, with varying amounts of time factored in between each building's
collapse."
Generally speaking, blasters will explode the major support columns on the lower
floors first and then a few upper stories. In a 20-story building, for example, the
blasters might blow the columns on the first and second floor, as well as the 12th
and 15th floors. In most cases, blowing the support structures on the lower floors is
sufficient for collapsing the building, but loading columns on upper floors helps
break the building material into smaller pieces as it falls. This makes for easier
cleanup following the blast.
Once the blasters have figured out how to set up an implosion, it's time to prepare
the building. In the next section, we'll find out what's involved in pre-detonation
prepping and see how blasters rig the explosives for a precisely timed demolition.
A Real Implosion?
Strictly speaking, an implosion is an event where something collapses inward,
because the external atmospheric pressure is greater than the internal pressure. For
example, if you pumped the air out of a glass tube, it might implode.
A building implosion isn't truly an implosion -- atmospheric pressure doesn't pull or
push the structure inward, gravity makes it collapse. But the term implosion is in
common use for this sort of demolition. In this article, we use the word this way.
READ MORE
Detonators and Dynamite

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The Frank Leux Building in Birmingham, Ala., was demolished by Engineered
Demolition, Inc. in the spring of 1997.
PHOTO COURTESY IMPLOSIONWORLD.COM
In the last section, we saw how blasters plan out a building implosion. Once they
have a clear idea of how the structure should fall, it's time to prepare the building.
The first step in preparation, which often begins before the blasters have actually
surveyed the site, is to clear any debris out of the building. Next, construction
crews, or, more accurately, destruction crews, begin taking out non-load-bearing
walls within the building. This makes for a cleaner break at each floor: If these
walls were left intact, they would stiffen the building, hindering its collapse.
Destruction crews may also weaken the supporting columns with sledge hammers
or steel-cutters, so that they give way more easily.
Next, blasters can start loading the columns with explosives. Blasters use different
explosives for different materials, and determine the amount of explosives needed
based on the thickness of the material. For concrete columns, blasters use
traditional dynamite or a similar explosive material. Dynamite is just absorbent
stuffing soaked in a highly combustible chemical or mixture of chemicals. When
the chemical is ignited, it burns quickly, producing a large volume of hot gas in a
short amount of time. This gas expands rapidly, applying immense outward
pressure (up to 600 tons per square inch) on whatever is around it. Blasters cram
this explosive material into narrow bore holes drilled in the concrete columns.
When the explosives are ignited, the sudden outward pressure sends a powerful
shock wave busting through the column at supersonic speed, shattering the concrete
into tiny chunks.
Demolishing steel columns is a bit more difficult, as the dense material is much
stronger. For buildings with a steel support structure, blasters typically use the
specialized explosive material cyclotrimethylenetrinitramine, called RDX for short.
RDX-based explosive compounds expand at a very high rate of speed, up to 27,000
feet per second (8,230 meters per second). Instead of disintegrating the entire
column, the concentrated, high-velocity pressure slices right through the steel,
splitting it in half. Additionally, blasters may ignite dynamite on one side of the
column to push it over in a particular direction.

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Concrete columns (on the left) are blown apart with conventional dynamite or
a similar sort of explosive. Steel columns (on the right) are sliced in half using
a high-velocity explosive called RDX.
PHOTO COURTESY IMPLOSIONWORLD.COM
To ignite both RDX and dynamite, you must apply a severe shock. In building
demolition, blasters accomplish this with a blasting cap, a small amount of
explosive material (called the primer charge) connected to some sort of fuse. The
traditional fuse design is a long cord with explosive material inside. When you
ignite one end of the cord, the explosive material inside it burns at a steady pace,
and the flame travels down the cord to the detonator on the other end. When it
reaches this point, it sets off the primary charge.
Blasting caps are used as a catalyst to set off the explosives loaded in support
columns.
PHOTO COURTESY IMPLOSIONWORLD.COM
These days, blasters often use an electrical detonator instead of a traditional fuse.
An electrical detonator fuse, called a lead line, is just a long length of electrical
wire. At the detonator end, the wire is surrounded by a layer of explosive material.
This detonator is attached directly to the primer charge affixed to the main
explosives. When you send current through the wire (by hooking it up to a battery,
for example), electrical resistance causes the wire to heat up. This heat ignites the
flammable substance on the detonator end, which in turn sets off the primer charge,
which triggers the main explosives.

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Columns are fully loaded with explosives and hooked up to blasting caps and
fuses.
PHOTO COURTESY IMPLOSIONWORLD.COM
To control the explosion sequence, blasters configure the blast caps with
simple delay mechanisms, sections of slow-burning material positioned between
the fuse and the primer charge. By using a longer or shorter length of delay
material, the blasters can adjust how long it takes each explosive to go off. The
length of the fuse itself is also a factor, since it will take much longer for the charge
to move down a longer fuse than a shorter one. Using these timing devices, the
blasters precisely dictate the order of the explosions.
Blasters determine how much explosive material to use based largely on their own
experience and the information provided by the architects and engineers who
originally built the building. But most of the time, they won't rely on this data alone.
To make sure they don't overload or under-load the support structure, the blasters
perform a test blast on a few of the columns, which they wrap in a shield for safety.
The blasters try out varying degrees of explosive material, and based on the
effectiveness of each explosion, they determine the minimum explosive charge
needed to demolish the columns. By using only the necessary amount of explosive
material, the blasters minimize flying debris, reducing the likelihood of damaging
nearby structures.
A test blast is performed on a concrete column in the RCA Victor Complex in
Camden, N.J. The building was demolished in the summer of 1997.

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PHOTO COURTESY IMPLOSIONWORLD.COM
To further reduce flying debris, blasters may wrap chain-link fencing and geotextile
fabric around each column. The fence keeps the large chunks of concrete from
flying out, and the fabric catches most of the smaller bits. Blasters may also wrap
fabric around the outside of each floor that is rigged with explosives. This acts as an
extra net to contain any exploding concrete that tears through the material around
each individual column. Structures surrounding the building may also be covered to
protect them from flying debris and the pressure of the explosions.
When everything is set up, it's time to get the show underway. In the next section,
we'll find out what final steps the blasters must take to prepare for the implosion,
and we'll look at the implosion itself. We'll also find out what can go wrong in
explosive demolition and see how blasters evaluate the project once the smoke has
cleared.
Becoming a Blaster
Brent Blanchard, an implosion expert with Protec Documentation Services, says
that countless implosion enthusiasts ask him the very same question: "How can I
become a blaster or demolition expert?" There is no "blaster school" or organized
demolition instruction program in the world, Blanchard says, so the only way to
become a demolition expert is learn on the job. Prospective blasters will work at an
established blasting company until they know the field inside and out. Then, they
can either stay on with their boss or venture out on their own and compete with the
blasters who trained them.
Clients are understandably cautious about building implosion, and they tend to hire
a demolition company based on the jobs it has pulled off in the past. For this reason,
Blanchard says, it's very difficult for a young demolition firm to land major
implosion jobs. Almost all major building implosions in the world are handled by
about 20 well-established companies. In many of these companies, blasting is
passed on from generation to generation. Parents teach their children the skills, and
the children then raise little blasters of their own.
READ MORE
The Big Bang

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Click here to see a video of the Holly Street Development, blasted in 2001
by Controlled Demolition Group, Ltd..
VIDEO COURTESY IMPLOSIONWORLD.COM
In the last couple of sections, we looked at everything blasters do to prepare a
building for implosion. In addition to these measures, the blasters must prepare the
people in the area for the blast, assuring local authorities and neighboring
businesses that the demolition won't seriously damage nearby structures. The best
way blasters can calm down anxious authorities is by demonstrating the firm's
success with previous implosions.
Animation courtesy ImplosionWorld.com
Two towers in the Holly Street Development in London, England, were
demolished in March 2001. They were a formidable challenge for the blasting
firm, Controlled Demolition Group, Ltd.. One tower had to be rigged so it
would fall over on its side, away from a gas line, while the other had to collapse
perfectly into its own footprint, to avoid damaging neighboring structures. The
demolition went exactly as planned, with no damage whatsoever to the gas
lines or the neighboring buildings.
To help the blasters work through this process, a blasting company may bring in an
independent demolition consulting firm, such as Protec Documentation Services.
Protec uses portable field seismographs to measure ground vibrations and air-blasts
during an implosion. Brent Blanchard, an operations manager for the company, says
that they also inspect surrounding structures prior to the implosion, so that they can
help assess any damage claims following the blast. Additionally, Protec's
staff videotapes the blast from multiple angles so that there is a record of what
actually happened. Using data collected from previous blasts, the company's
engineers can predict ahead of time what level of vibration a particular implosion
may cause.

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Once the structure has been pre-weakened and all the explosives have been loaded,
it's time to make the final preparations. Blasters perform a last check of the
explosives, and make sure the building and the area surrounding it are completely
clear. Surprisingly, implosion enthusiasts sometimes try to sneak past barriers for a
closer view of the blast, despite the obvious risks. With the level of destruction
involved, it is imperative that all spectators be a good distance away. Blasters
calculate this safety perimeter based on the size of the building and the amount of
explosives used.
On occasion, blasters have misjudged the range of flying debris, and onlookers have
been seriously injured. Blasters might also overestimate the amount of explosive
power needed to break up the structure, and so produce a more powerful blast than
is necessary. If they underestimate what explosive power is needed, or some of the
explosives fail to ignite, the structure may not be completely demolished. In this
case, the demolition crew brings in excavators and wrecking balls to finish the job.
All of these mishaps are extremely rare in the demolition industry. Safety is a
blaster's number-one concern, and, for the most part, they can predict very well
what will happen in an implosion.
The Wolverine Hotel in Detroit, Mich., was blasted in early 1997
by Engineered Demolition, Inc.
PHOTO COURTESY IMPLOSIONWORLD.COM
Once the area is clear, the blasters retreat to the detonator controls and begin the
countdown. The blasters may sound a siren at the 10-minute, five-minute and oneminute mark, to let everyone know when the building will be coming down. If they
are using an electrical detonator, the blasters have a detonator controller with two
buttons, one labeled "charge" and one labeled "fire." Toward the end of the
countdown, a blaster presses and holds the "charge" button until an indicator light
comes on. This builds up the intense electrical charge needed to activate the
detonators (this is similar to charging a camera flash to build the necessary
electrical energy to illuminate a scene). After the detonator-control machine is

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charged, and the countdown is completed, the blaster presses the "fire" button
(while still holding down the charge button), releasing the charge into the wires so it
can set off the blasting caps.
Two types of blasting machines, a traditional rack-bar and a modern
electronic control box
PHOTO COURTESY IMPLOSIONWORLD.COM
Typically, the actual implosion only takes a few seconds. To many onlookers, the
speed of destruction is the most incredible aspect of an implosion. How can a
building that took months and months to build, and stood up to the elements for a
hundred years or more, collapse into a pile of rubble as if it were a sand castle?
Following the blast, a cloud of dust billows out around the wreckage, enveloping
nearby spectators. This cloud can be a nuisance to anyone living near the blast site,
but blasters point out that it is actually less intrusive than the dust kicked up by nonexplosive demolition. When workers take down buildings using sledgehammers and
wrecking balls, the demolition process may take weeks or months. In this time, a
significant amount of dust is being kicked up into the air every day. When the
building is leveled in one moment, on the other hand, all the dust is concentrated in
one cloud, which lingers for a relatively short period of time. Nearby residents with
allergies can leave the area for that one day and avoid the dust entirely.
The Scudder Homes in Newark, N.J., blasted by Engineered Demolition,
Inc. in the summer of 1996
PHOTO COURTESY IMPLOSIONWORLD.COM

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After the cloud has cleared, the blasters survey the scene and review the tapes to see
if everything went according to plan. At this stage, it is crucial to confirm that all of
the explosives were detonated and to remove any explosives that did not go off. If a
demolition consulting crew was on hand, the blasters review their vibration and air
blast data as well. Most of the time, experienced blasters bring buildings down
exactly as planned. Damage to nearby structures, even ones immediately adjacent to
the blast site, is usually limited to a few broken windows. And if something doesn't
work out quite right, the blasters log it in their mental catalog and make sure it
doesn't happen on the next job. In this way, job by job, the science and art of
implosion continues to evolve.
For more information on building implosion, check out the links on the next page.
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