How To Stop A Colossal Bridge Corroding

– When it opened in 1981,
the Humber Bridge was the longest single-span
suspension bridge in the world. More than 1,400 metres of road, weighing 17,000 tonnes, held up by cables that weigh thousands
of tonnes themselves. Those cables are made up
of more than 14,000 individual wires, all anchored into concrete
foundations on the shore. And those cables, and the
whole structure in turn, is held up by these enormous towers. The bridge is so wide and so tall that, while both towers are vertical, they’re just a couple of centimetres
further apart at the top because of the
curvature of the earth. Nearly 40 years after it opened, this bridge is about a third of the way
through its design lifespan, and it’s time for a checkup. – Back in the ’90s, in the United States, bridge engineers started to unearth severe cable corrosion in
their early structures. So, they were building
suspension bridges in the ’30s. The way that the cables were
designed to be kept watertight was, once the wires had been spun and formed a cable and compacted, the open wires were
coated with lead paste, which is lead and linseed oil. Wrapping wire was then added around the outside of the cable,
trapping the lead paste and effectively keeping
the cable watertight, and it was thought that
would be sufficient. Inspections in the United States demonstrated that moisture
was still penetrating and gathering in the main cables and causing significant corrosion, because, inside here was its
own mini climate, in effect, so it was affected by
external temperatures, day, night, winter, summer. – This is a brutal
environment for the cables. We’re near the ocean, for a start, and down by the road there’s
engine exhaust and spray. Remember, the cables aren’t
one sold piece of metal. They’re made up of thousands
of individual wires. And while they’re packed tightly, they’re cylinders, so there will always be
a slight air gap between them, and that air gap is the solution. – Water-based corrosion of steel or iron cannot occur below 40% relative humidity. There’s approximately 15-20% open space in this compacted cable. If you can keep that volume below 40%, then effectively corrosion is halted. Inside the main deck of the bridge, there are plant rooms that
produce dehumidified air. That air is then pumped
up to the main cable and injected into a stainless steel sleeve that surrounds the main cable. The relative humidity of the
air blown into the cables is low enough to have an
affinity to collect moisture as it travels through the cable, drying the cable and exhausting
the moisture to atmosphere, and that is a continuous,
24-hour cycle, 365 days a year, essentially for the rest
of the bridge’s life. So, the Humber Bridge Board
first inspected their main cables in 2009, and then deployed dehumidification
the following year, 2010. Here we are, 10 years later in 2019, reinspecting the main cable
to ascertain the effectiveness of that dehumidification system. What we do is, with a sledge hammer, we drive the wedges in to form
an open wedge in the cable. From each wedge line,
the consultant engineer will select a wire, and then
our guys will come along and sample that particular wire and remove approximately
a five-meter length to then take the data that they need
to collect from the cable. We then select a five-meter length
from the drum of the new wire and splice that in with ferrules
and then remove the wedges, and that wedge line is then finished. That is then repeated seven more times
around the circumference of the cable, and then that effectively
is the inspection complete. With 100-ton hydraulic
jacks in each corner, we compress the cable back
to its original diameter. – The idea that the wires
are slightly corroded could be worrying, but it’s well, well
within design tolerances, and it’s been noticed
early and dealt with, and they’re keeping a
watch on them just in case. But bridges elsewhere in the
world that aren’t inspected, where infrastructure isn’t
maintained, where cutbacks mean that this isn’t happening? Those should give you just
a little cause for concern. The Humber Bridge is doing just fine. That works?
All right. We’re going to go for the drone shot.

100 thoughts on “How To Stop A Colossal Bridge Corroding

  1. "Hey, Tom, do you want to go up the Humber Bridge?" Yes. Yes I do. And I'm amazed that I got access to the actual corrosion test gantries, because they're understandably sensitive about that!

  2. Sometimes I wonder what my life would be like if it was as interesting as Tom's.
    And then I get exhausted and have to go for a wee lie-down.

  3. when tom was on the bridge that i can legitimately see outside my bedroom window because i live really close to it…

  4. Why not to build stone bridge? it would last at least 1000 years and you would not have to check on it. roflmao

  5. Moisture may not be penetrating. It could be condensation, so in that case the cables should be opened air to get at them and dry them out. Sealing them is a bad idea.

  6. How to cancel a colossal crossing construction’s mini climate caused cable corrosion with carefully crafted moisture collection

  7. Tom Scott nowadays: "How to stop a colossal bridge corroding"
    Tom Scott in 2013: "10 illegal things to do in London"

  8. When I clicked on this video, the last thing I expected the answer to be was "by air conditioning the inside of its cables".

  9. I'm having a hard time figuring out a scenario where your helmet would be of any help in case of an accident.

  10. Glad i live in a place where we are not afraid to invest in maintaining and upgrading infrastructure.

    When i look at places like the US i start to worry though, very little seems to be spent on maintaining and upgrading infrastructure unless there is money to be made from it.

    They won't see the problems that will cause until it is too late, and many times as much will have to be spent.

    Plenty of bridges that could collaps like that one bridge in Italy, extreme weather countermeasures not being maintained etc.

    Not just maintaining, but upgrading infra like internet infrastructure, public transportation, bicycle accessibility and for those insisting to stick with cars: the roads themselves…
    (which seems to be getting to the point where regular non-selfdriving cars are getting driven around in self driving cars in tunnels to supposedly alleviate congestion, witch confuses my European brain)

  11. I love the little glimpses we get into Tom’s process with the extra sound bites at the end of some of his videos: like in this video him saying what shot he’s going to get next and saying he’s happy with the take. Just a simple thing about Tom’s videos that I always enjoy. Keep up the good work as always Tom!

  12. A decade ago, engineers found the Humber Bridge had the same problem as many of the world's suspension bridges: unexpectedly fast corrosion. Here's how they fixed it, and how they're checking that it's staying fixed.
    Thanks to all the team at the Humber Bridge board, at Cleveland Bridge, and Visit Hull and East Yorkshire, all of whom spent a lot of time and effort getting me up to the towers!

  13. I've loved my whole life not far from this amazing structure. We've books and photos/ all media pictures of it throught the family, my god's do I wish I could go up where you've been.

  14. I'm surprised you never mentioned the Fourth Road Bridge in Scotland. That has the same issue, built in the same design, solved in the same way. They say you could put your ear to the suspensions and hear the occasional 'ping', as the wires snapped. They had to build a new bridge.

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