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.

60 Replies to “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. 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.

  3. 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.

  4. “The tops are a couple of centimeters apart because of the curvature of the earth.”
    The Flat Earth Society want to know your location

  5. 1:10 A giant steel core, A coating of carbon/hydrogen rich lindseed oil, Lead, and an outer coating of more steel…. add in salt water…. AND (The power puff girls were born!) No but you do have a hideously inefficient though highly corrosive Lead Salt/ iron carbon battery using the hydrogen produced by the lindseed oil and salt water buring through the steel like it were cotton candy!

  6. It takes a special type of person to work up on those wires. Thank God for them, there's no way I could ever go up there, and keep consciousness at least!

  7. Question for you Brits (I'm American). I've never heard that bridge engineer's accent before. Is that what a Hull accent sounds like?

  8. As much as I admire modern engineering, I am at awe with roman engineering that have structures still standing after two thousand years

  9. Makes me really worry about the i 74 bridge connecting iowa and Illinois. The bridge hasnt been maintained at all and were currently building another. No cable dehumidifcation at that one. Completely rusted red I can't imagine the state of the cables

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