Kind: captions
Language: en
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for more than 50 years the peva bridge
stood as a landmark in the city of
Genoa it was a
masterpiece and everybody knows it was a
masterpiece it was one of the most
famous bridges in
Italy the toward was the bridge of the
future the bridge was really
beautiful but on August 14th
2018 disaster
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strikes a huge 800 ft section of the
bridge carrying four lanes of TR traffic
collapses 27 Vehicles plummet into the
valley
below 43 people
die it is one of the worst roadbridge
collapses in Europe for more than a
century and yet there was no
warning why did this seemingly sound
Bridge suddenly fall
down and is anyone to
blame in the last 10 years more than 60
Bridges have collapsed around the
world how many more are about to give
way in the United States over 47,000
bridges are classified as structurally
deficient we have had over two dozen
Bridges fail in the United States since
2000 can Engineers guarantee the safety
of our aging Bridges before it is too
late why Bridges collapse right now on
[Music]
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[Music]
Genoa one of Italy's busiest
ports over 6,000 ships a year carry 54
million tons of cargo through here
nearly all of it placed on
trucks the trucks fan out in all
directions
but many end up on this highway the
e80 it's a critical link between the
south of France and Rome shuttling more
than 70,000 cars and trucks past Genoa
every
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day August 14th
2018 firefighter David Capello drives
his SUV along Route e80 heading east
towards
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Genoa
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John LCA ardini a foreman for a
Furniture Company heads in the opposite
direction along the e80
highway
both John Luca and Dav are heading
towards the pev bridge locally known as
the mirandi
bridge this iconic Landmark connects the
two sides of
Genoa at 11:36 a.m. the world in front
of them begins to come
apart
for oh de oh de oh
de
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oh
a massive 800 foot section of the bridge
carrying four lanes of traffic
collapses John Luca's truck plummets
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27 Vehicles fall with the
bridge this is David capello's
SUV it falls 100 30 ft and lands inside
a cavity formed by a section of the
bridge
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across from David's car trapped inside
the remains of the collapsed Bridge
Tower Rescuers make a shocking
Discovery hanging inside this truck is
John Luca
ardini
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firefighters begin the precarious job of
rescuing him from the mangled
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cab it takes 40 minutes to cut John LCA
free and carry him to
safety 400 firefighters from all over
Italy arrive with specialized equipment
most often used to rescue people from
earthquakes sniffer dogs search for
survivors after 4 days firefighters
finally recover the last
body the collapse of the pev bridge
kills 43 people and injures
15 it's far and away Italy's worst Road
Ridge
disaster the catastrophe sounds a
chilling
alarm Engineers around the world want
answers why was there no
warning what caused the sudden
collapse and most important how many
other bridges are at
risk the stakes are huge
if the bridge failed due to age that
could mean disaster for thousands of
other bridges built at the same
time all products of a highway
construction boom that began more than a
half a century
ago across many countries the second
world war destroyed thousands of roads
and
bridges
in the years that followed Engineers set
about rebuilding the bridges while also
constructing new Superfast
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highways this was the dawn of the golden
age of the car and nowhere more so than
in the United
States in 1956 President Eisenhower
signed the federal aid Highway Act to
create 41,000 Mi of Interstate highways
as far as the eye can see in almost
every city concrete and asphalt are
changing the patterns of land and land
use soon traffic will flow smoothly in
around and between every major city and
town in
America today in America just as in
Europe many of these concrete bridges
are growing
old about 2/3 of our interstate highway
system Bridges were built in either the
1960s or 1970s so a number of those
structures are coming to the end of
what's called their useful design
life the United States has more than
600,000 Road
bridges over 47,000 of them are
classified with the term structurally
deficient what that means is that when
the bridge is inspected one of the key
structural elements is rated uh in poor
or Worse condition
so it means they're bridges that need to
be
repaired are these Bridges located all
across America and the world ticking
time
bombs and particularly if they share the
same faults as the pev bridge in Genoa
then lives could be at
stake within hours of the disaster in
Italy the site becomes the focus of a
major
investigation Engineers need to find out
what caused the bridge to
collapse Camilo NTI is an independent
engineer who worked on the Italian
government inquiry into the
disaster one should be very cautious
before removing
anything obviously you have to remove
the debris but then be very very careful
because you have to take the pieces then
try to understand if there was failure
somewhere if there was failure you
should find those pieces
broken finding those pieces is a
daunting challenge sifting thousands of
tons of debris investigators need to
identify the Single part of the bridge
that failed and triggered the
disaster they move any suspect pieces to
this secure
Warehouse the operation will take months
so at the same time they pursue a
parallel line of
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inquiry they turn their attention to the
way the bridge was
built and its original
design the planning of the pev bridge
began in the early
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1960s its designer Ricardo mirandi was a
star engineer of Italy's post-war
reconstruction
boom his work included astonishing
modern
structures like this aircraft hanger in
Rome and dozens of
bridges
he was the best bridge design engineer
in Italy there is no Italian engineer
who built what orandi
built to construct the pev bridge in
Genoa Morandi faced a huge
challenge the bridge had to span the pev
river multiple railway lines and four
apartment
buildings
his plan was to build three enormous
trestles each with a tower nearly 300 ft
High then to hold up the road deck he
would use giant supports called cable
stays made of steel and
concrete when complete the vast Bridge
would be over half a mile
long to build it mirandi used a
relatively new method of construction
one that he had helped
develop before this time most concrete
bridges used simple steel
reinforcement but by stretching steel
cables threaded through Hollow guides in
the concrete Engineers found they could
build longer
spans the tension in the wires acted to
compress the concrete making it less
likely to Bend and
crack this was called pre-stressed
concrete and mirandy relied on it for
the pev
bridge in his design he does something
radical in most cable stay Bridges the
road deck is supported by many cables
spread out across the
span
but to support his deck mirandi bunches
all the cables together to create
massive cable
stays each one made of 52 steel cables
wrapped in concrete to protect them from
corrosion the technique was a novelty we
put just four cables for H Pier but it
were incredibly strong
cables after four years Construction in
1967 Italy's president opened the bridge
to an enthusiastic
reception the Morandi Bridge was the
most important bridge in Italy the
biggest the more beautiful the most the
most famous
absolutely it was a Masterpiece and
everybody knows it was a
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masterpiece but 50 years later the
bridge fails
catastrophically did Mandy's pioneering
design play any role in causing it to
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collapse to find out what caused the
disaster investigator need to discover
which part of the bridge failed
first they look for CCTV cameras in the
area that would have recorded the moment
the bridge
collapsed rain obscures the view in
almost all the
cameras but in this scrapyard they find
a video that captures the disaster from
beginning to
end the record in is part of an ongoing
criminal investigation and is
impounded Franchesco koty is the state's
prosecutor in charge of the criminal
investigation
sources familiar with what happened have
provided clues that allow a
reconstruction of the probable sequence
of the bridge
collapse at just after 11:36 a.m.
something happened that caused the
southeast cable stay on pylon 9 to
break unsupported that side of the road
deck
sags this unbalances the whole structure
and increases the load on other
components beyond their breaking
points this sends the road deck
plummeting to the
ground and causes the giant Tower to
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collapse it looked like the unthinkable
had happened
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some of the steel cables mirandi had
embedded in concrete to protect them
from corroding had
snapped but
why the bridge had stood firm for over
half a century carrying millions of
Travelers so what caused it to fail the
very moment it
did like most Road bridges built during
the building boom of the 1960s and70s
the pev bridge had been experiencing
steadily Rising traffic
loads by 2009 it carried four times as
many vehicles as 30 years
earlier over 25 million Vehicles crossed
it each
year could the weight of traffic on the
bridge have brought it down
like all major bridges in Italy the pev
bridge was designed to carry the load of
a convoy of heavy military
vehicles this meant it should have been
able to carry the weight of modern
traffic but a small error in design or
construction can have catastrophic
consequences as happened to this bridge
in the United States
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on August 1st 2007 Kelly kayy was
driving towards the i35w bridge in
Minneapolis it's rush hour traffic 6:00
I'm going north and we get right on the
interstate all of a sudden there's a
rumbling and then all of a sudden the
bridge in front of me far in front of me
looks like it rose up and it almost
looked like it was
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oscillating looking back on it I can see
that we were on a point that was failing
and we were starting to
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fall this is Kelly's Car it narrowly
escaped plunging into the
river I climbed onto the hood of the car
and and skimmed onto this concrete
Island and just looking around and
seeing other people kind of getting
their wits about
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them 111 Vehicles were on the bridge
when it gave way 13 people
died 145 were
injured when investigators reassemble
the pieces of the collapsed Bridge their
attention focuses on a part known as a
gusset
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plate gusset plates are flat plates of
Steel that hold the girds of a truss
Bridge
together the key pieces of the i35w
bridge have been
preserved these pieces are all connected
to the the single gusset plate that
failed uh when the bridge collapsed
during the collapse this folded in on
itself and was completely mangled uh by
the weight coming down on top of
it at the time of the collapse workers
were preparing to relay the
road trucks had dumped piles of sand and
gravel on the closed
Lanes there were 800,000 lb of
construction equipment on the top of the
bridge as well as over 160 people uh in
cars because it was the very end of rush
hour that day that combined load proves
too much for one of the gusset
plates the gusset plate split along a
line of rivets you can see that it's
completely torn
apart the bridge was
overloaded but its designers had also
made a
mistake the guzet plate was uh only a
half an inch thick and it should have
been one inch uh so it should have been
double the thickness that it that it was
and that's what led to the failure
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did genoa's pev Bridge collapsed because
of a similar fault a failure to make it
strong enough to carry heavy
loads when mirandi planned the bridge he
designed it to support a lot of weight
the ideas of Morandi was let's build a
bridge with very very strong cables it
was over designed very much over design
so the design was incredibly safe for a
time when the bridge was built the cable
stays were capable of carrying over
twice the weight of the vehicles on
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it the bridge should have been easily
strong enough to carry the light traffic
on it when it
fell
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what is well known is that the total
load that the bridge could support was
well be beyond the loads that was on the
bridge so if the weight of the vehicles
on the bridge didn't cause it to
collapse what
did experts sources suggest that the
southeast cable stay snapped near the
top of the
pylon if it was this cable stay that
broke first something had gone seriously
wrong this is the kind of fault that all
Engineers
fear it's known as a single point
failure when one component breaks and
brings down an entire Bridge
it's a lesson driven home by an earlier
disaster in 1928 the people of Point
Pleasant in West Virginia celebrated the
opening of their new bridge over the
Ohio
river and it was a really exciting day
there was 10,000 people in town there's
pictures that show the bridge is
completely covered with people
they were very proud of it you know to
have a nice big shiny Bridge like that
well it was a talk of the talk of the
are in the east coast you know the
Silver
Bridge it was nicknamed The Silver
Bridge because of its shiny coat of
aluminum
paint but unknown to the people that
used it its design contained a serious
flaw on December 15
1967 Peggy hooer was driving towards the
Silver
Bridge traffic was heavy it was Friday
and near Christmas time I got behind a
dump truck and it was moving so slow it
stopped right at the light where the
bridge was and I was behind it and um I
had uh reached down to turn the radio
dial and I heard this awful noise and
when I looked up uh the bridge was just
like a tinker toy waving and it just
fell it just sounded like a bunch of
metal it was very
loud it collapsed I think 458 so it was
a busy time there was 31 vehicles that
there the collapse killed 46
people it Remains the worst Road Bridge
disaster in American
history to find out what had caused the
bridge to fail investigators searched
the riverbed for
wreckage they brought in a whole bunch
of divers and they would bring pieces up
and of course they would examine all of
it and see if it fit in any
way the bridge was an iar suspension
bridge giant bars up to 55 ft long with
a hole called an i at each end were
linked together with steel
pins crucially each link of the
suspension
chain contained only two eye
bars and they finally found
one of the eye bars that was broken
split and when they examined it they'
found that there had been a a hairline
fracture in
[Applause]
it nearly 40 Years of corrosion in the
steel had triggered a fracture that
ripped the eyear from its
pin the weight of the bridge proves too
much for the remaining eyear pulling it
with an extreme force that tears the
link
apart the failure of this single point
triggers an unexpected domino effect
causing the entire bridge to
collapse in the United States alone
around 18,000 Bridges have been
identified as fracture
critical this means if one component
fails part or all of the bridge would
probably collapse
many were built in the 1960s and70s
during the rush to complete the
interstate highway
Network today Engineers aim to design
Bridges so that if a single component
fails it won't bring down the whole
structure modern cable stay bridges are
built with a fan of cables to spread the
load this design is very different to
that of morandi's pev bridge in
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Italy mirandi bundled all his cables
together and covered them in concrete to
create single giant
stays his design was meant to protect
the cables from
corrosion but he inadvertently made the
bridge vulnerable to a single point
failure if just one of the huge stays
broke the result would be
disastrous sadly mandi's design was
completed a few years before the Silver
Bridge
disaster luckily it has not been widely
copied other Engineers realized the
potential problems and only a handful of
similar Bridges were ever
built the pev Bridge was routinely
inspected maintained and
monitored for it to collapse something
must have gone seriously
wrong but
what 4 months after the disaster workers
remove the last of the
debris forensic Engineers now have
several key pieces of
evidence their initial inspections
reveal that some of the steel cables
that were supposedly well protected
inside the concrete covered stays have
suffered from
corrosion some cables appeared broken
when there is corrosion the corroded
cable are brittle so if you just bent
them you break them which is not usual
for steel but when you have corrosion
this may happen very
easily
the investigators identify 17 key
sections of the bridge for further
investigation their Prime
Suspect is part number
132 this is believed to be the part of
the cable stay near the top of the
bridge that
broke they shipped the pieces to a
laboratory in
Switzerland where investigators will
attempt to find out what caused the
steel cables to
corrode when mirandi covered the cables
with concrete they should have been
protected concrete is very alkaline the
opposite of
acidic this produces a thin layer of
stable iron oxide around the
steel and should almost completely
prevent the steel from rusting
thousands of bridges rely on this
protection in most cases it works
fine but just occasionally it goes badly
wrong
London the Hammer Smith fly
over it's one of the city's busiest
Bridges how Smith flyover is critical to
the London Road Network it provides one
of the main routes from Heathrow Airport
into Central London and it's also one of
the major routes out to West London in
itself in December
2011 just months before the 2012 London
Olympics Engineers discover this vital
bridge is at risk of
collapse the overpass was built built in
the early 1960s from giant concrete
sections the problem lay in the way they
were held
together to build the Hammersmith
flyover construction Crews use a form of
pre-stressed concrete made using a
technique called post
tensioning they hoist giant
pre-fabricated sections of the bridge
into
position then thread 64 steel tendons
through holes in the
structure they then stretch and tension
the wires to hold the concrete sections
of the bridge
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together to prevent the steel cables
from corroding workers cover them with a
concrete
grout like mirandi the engineers of the
Hammersmith flyover thought the concrete
would prevent the cables ever
rusting
but in the early 2000s inspections
reveal they were
wrong water is seeping into gaps in the
concrete grout causing the steel tendons
that held the bridge together to
rust as you can see here they're all
encased in grout and that means it's
very difficult for the water to escape
um and it's also very difficult for us
to inspect the tendons and make sure
that everything's
okay unfortunately the concrete grout
that was meant to prevent rust trapped
water in cavities and hid any corrosion
that did
occur Transport for London calls in
structural Integrity engineer John
Watson to try to identify where the
corrosion is
worst he installed stalls over 500
microphones inside the
bridge we put a microphone about every 3
m along the structure to missing out for
anything that's distinct like a wire
BR each of the cables buried in the
concrete contains 19 separate strands of
wire the cables themselves are built up
of individual wires when these wires
corrode a small crack grows in the wire
eventually the wire snaps with a very
distinct snapping sound
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and it's this energy this sound wave
that's detected by the microphone on the
structure that enables us to determine
the position of the wire brake on the
cable
itself over the period of 3 and 1/2
years of monitoring we detected in
excess of 1,100 wire brakes so typically
one or two a
day within a couple of months we were
able to determine exactly where the hot
spots were where most wire brakes were
occurring this told Engineers where the
corrosion was most severe allowing them
to focus their
inspection we were able to break out the
grout around full sections of those
bundles of Highly stressed steel cables
to see just how deep the corrosion had
penetrated those
cables what they discovered was
alarming the bridge was at risk of
collapse although they thought the risk
small to be safe they decided to close
it to repair the bridge they attached
four miles of new cables to the
outside and stretch
them just like a supersized version of
the original post
tensioning it's estimated that this
rescue operation has extended the
Bridge's Life by 60
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years the close shave with the
Hammersmith flyover shows how cables
buried inside concrete can
rust so did a similar problem with
corrosion caus the pev bridge in Italy
to
fail in Switzerland
scientists examine the pieces of the
bridge brought from
Genoa they need to find out what caused
the steel cables that held up the bridge
to
corrode like the Hammersmith flyover the
pev bridge relied on post tension steel
cables they held the road deck together
and gave the cable stays their
strength back in the 1960s to construct
each stay workers cover its 52 cables
with steel
ducts then cast the concrete around
them once this sets Engineers stretch
the cables to post tension the
stay finally they inject a concrete
grout into the ducts to cover the cables
and prevent the steel from rusting
when scientists examine the steel cables
inside the stays they also carry out a
forensic examination of the
ducts in some they find
cavities places where the grout is
missing leaving the steel cables
unprotected once moisture entered these
cavities the steel wires would
corrode become brittle and
break investigators have not yet
announced the cause of the Bridge's
collapse but one theory is that
corrosion of the cable stay played a
major
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role
Auto Strada the company that managed the
bridge maintains that a failure of the
cable stays was not the primary cause of
the
collapse it says that with the amount of
corrosion the Zurich laboratory found
the cables would still have had enough
strength and would not have broken
It also says the ducts were present and
doing their job of containing the cement
grout if the Bridge's collapse was in
fact due to its poor condition could
Auto Strada have detected that it was
about to
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fail corroded steel is easy to see if it
is
exposed but when steel is embedded in
concrete it's very hard to check that it
isn't
corroding concrete is very difficult to
inspect
non-destructively it's very difficult to
detect actual wire brakes and really
quantify the extensive
corrosions on the pev bridge Engineers
used different techniques to assess the
level of corrosion of the cables inside
the concrete
stays one one they appear to have relied
on heavily is called reflectometric
impulse measurement technique or rimp
for
short this method aims to detect
corrosion by sending short electrical
pulses up the steel tendons and
recording the reflected
signal at the beginning everybody was
very optimistic with this method in 1994
95 some technicians from
autostrada published some papers where
they say oh the method is fantastic you
can find
everything but in
1997 independent scientists conducted a
study and found that rimp could not
reliably detect
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faults part of the prosecution case is
likely to question the use of the rimp
method Auto strata says that since 2000
Engineers have used a new version of
rimp called rimp
2 it says this is completely different
and does enable experts to accurately
assess corrosion and that its
reliability has been verified by
multiple International scientific
studies
rimp 2 is not widely used in the
industry in
2017 autostrada submitted a detailed
plan to replace the cable
stays but before the work could
start the bridge
collapsed the p chevra bridge is one of
the worst Road Bridge disasters to hit
Europe in over a
century it raises troubling and pressing
questions about how our aging bridges
are inspected and
maintained the highway building boom of
the 1960s and70s has left us with
thousands of bridges that are growing
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old and we don't know how many contain
hidden flaws that have yet to reveal
themselves pre-stressed concrete Bridges
with their concealed steel wires are now
a particular
concern Berlin
Germany this is the elen bridge it was
built in the mid
1960s in the summer of 20 2018
inspectors find a 90 ft long crack in
its concrete
span fearing that some of the steel
cables inside the bridge have corroded
and snapped they restrict
traffic many aging pre-stressed concrete
Bridges have similar
problems some like the Hammersmith
flyover can be saved by retrofitting
external cables
others like the elsen bridge will have
to be demolished and
replaced so How likely is another bridge
collapse like the one in
Gena you know it's hard to say How
likely a collapse like that would be but
we have had over two dozen Bridges fail
in the United States since 2000 for
various reasons so there are concerns
these are bridges that we have a number
of them that need to be repaired and
replaced I think we have a significant
challenge uh we have underinvested in
our transportation system for
decades but safety has a
price we could probably double or triple
what we're spending uh across all levels
of government to really make those
repairs that need to be
made maintaining this aging
infrastructure is a huge
challenge but engineers are rising to
it modern cable stay bridges are
designed so that the cables can be
removed and replaced one by
one and Engineers have even developed a
solution to one of the most challenging
problems in Bridge
maintenance the main cables that run
between the towers on suspension bridges
are extremely difficult to
replace so what do engineers do if they
discover that these cables are
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corroding Pittsburgh
Pennsylvania it has been called the city
of bridges as it has over
400 Richard Connors manages some of them
including the city's Philip Murray
Bridge
well this fridge gets about
177,000 Vehicles a day it's very
important this is a major physical asset
in the
city the bridge depends on its main
cables which are over 85 years old this
cable is about 13 in in total diameter
it's made up of
4,864 individual wires steel wires that
were installed in 1933
three this film of San Francisco's
Golden Gate Bridge shows how the
Pittsburgh Bridges cables would have
been
made individual wires were stretched
across the river bundled together then
wrapped inside a waterproof skin to
prevent moisture seeping
inside but when Engineers opened up the
cables of the Pittsburgh Bridge in 2009
they found that water had gotten
inside we noticed upon inspection of the
main cable there was significant
corrosion there was much as uh 21 to 23%
loss in certain
sections most of the corrosion was at
the center of the bridge at the lowest
point where the water would just sag to
the low
point to stop the corrosion Engineers
first seal the cable in a new waterproof
skin
then they install a dehumidifier to blow
dry air through the
cable this should reduce the humidity
inside the cables to less than
40% below this level steel won't
rust the dry air travels up to the top
of the main cards and then it's blown
through the cable with very low pressure
1 to 2 lbs per square in and the dry air
collects moisture along the way inside
the cable the moisture comes out right
here removing the moisture from the
cables will stop them corroding and
hopefully extend the life of the bridge
for years to
come this ingenious system prolongs the
life of suspension
bridges Engineers are using other
techniques to help preserve structures
built of pre-stressed concrete
Innovative Technologies like these
should enable our aging Bridges to
remain safe into the future if their
faults are spotted in
time the sudden collapse of the bridge
in Genoa is still felt in the city the
loss of this vital transport link
continues to cause traffic jams and
delays to get the traffic moving again
planners are racing to build a new
bridge
its designers have a big advantage over
previous generations of
Engineers they have had the chance to
learn from earlier
mistakes Bridges now are rarely built
with components that are prone to single
point
failure regulations on designing gusset
plates now require Engineers to
calculate their Str
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strength and when building post tension
Bridges greater attention is paid to
ensure cavities can't form in the
concrete
grout we may never completely design all
weaknesses out of the structures we
build but every disaster is a lesson we
can learn from to make Bridges safer in
the
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future
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[Applause]
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