It’s the world’s most recognisable bridge and an icon of America.
The Golden Gate of San Francisco.
One of the most difficult underwater construction feats ever attempted.
Defying incredible odds during its construction, the Golden Gate has stood for over 80 years,
and remains a critical piece of infrastructure — not just a pretty sight.
Today, it’s almost impossible to imagine San Francisco without
this engineering marvel on its skyline.
Unless you look to Hollywood. They love to imagine it.
But these frightening visions are now a very real possibility thanks
to a threat that has loomed over California for decades.
Seismologist Lucy Jones says the recent earthquakes are sending a
message — that an even bigger one is lurking.
The term ‘The Big One’ — it’s such a big event you change the nature of society.
The iconic Golden Gate Bridge may not survive this
massive earthquake unless it’s given some serious upgrades.
Fortunately though, that’s now what it’s getting in the form of this huge seismic
retrofit project that should see it stand for many more years to come.
It's vitally important that we protect this icon, not just so people can come and take photos,
but so our region can continue to function after a major seismic event.
For decades this remarkable bridge has stood as one of the most compelling and
awe-inspiring monuments to the power and potential of human ambition.
A formidable and bold source of wonder for people of all ages and tomorrow’s young engineers.
The structure simply has to keep standing if only to remind us of
what’s truly possible when we believe that we can.
This is the story of one of the world’s greatest feats of engineering,
of how the Golden Gate Bridge came to be, and how it’s now preparing for The Big One.
There aren’t many things more symbolic of America
than this long stretch of steel that sits just north of San Francisco.
Many factors have contributed to its iconic status — from its size,
looks and location to its countless movie appearances — but what’s often
forgotten is the incredible tale of its construction.
Long before the bridge, the mile-long Golden Gate Strait divided these two pieces of land.
It’s incredibly wide and deep — at over 100-metres — and has fast-flowing waters. So back in the
1920s most people discounted building any kind of structure as a way to cross it.
The only way to get from one side to the other — unless
you fancied a very long drive — was by ferry.
But as car ownership took off in America, to the point where millions of vehicles
were piling onto these boats every year, the service became far too congested.
Another way over the water was sorely needed and in the eyes of city officials,
a bridge would do nicely. But turning such a bold and daring idea into reality
wasn’t going to be easy as the strait’s geography presented extreme challenges.
To take on the task, the city appointed engineer Joseph Strauss. He had a great
track record in bridges, but his ideas weren’t always to everyone’s taste.
The Golden Gate was no exception and his first design tabled in 1921 was widely criticised.
Reluctantly, Strauss agreed to work with three other engineers and architects on
a new iteration. This one was approved by both the government and the public
and went on to eventually become the bridge we all know and love today.
By 1929 the vision was complete but for the Golden Gate Bridge, Highway and Transportation District —
a company set up to build and operate the bridge — the challenges had only just begun.
The team was met with thousands of legal challenges from the firm that
ran the ferries who wanted to stop the project.
On top of that, what was then called the US Department of War
was concerned the structure would become a sitting duck for enemy bombers
and that the bridge wouldn’t be visible enough in foggy conditions.
They even called for it to be painted yellow and black
so you couldn’t possibly miss it — a decision we’re kind of glad got overruled.
Then came a huge financial crisis which triggered
The Great Depression and wiped out all of the planned government funding.
To keep the project alive and in a remarkable demonstration
of public support for the bridge, the people of
San Francisco voted for a $35 million bond issue using their homes as collateral.
At long last, construction could begin.
It’s hard to imagine how the first teams must have felt in January 1933,
arriving at the site on day one and looking at the huge expanse of water that lay in front of them.
Their belief in their own abilities to build such a structure is awe-inspiring.
Things all started with the two main towers. Standing over 220-metres tall,
these immense structures each required 40,000 metric tonnes of steel.
Both were built in prefabricated sections shipped
all the way from the East Coast via the Panama Canal.
The North Tower came first and was by far the easier of the
two to build — mostly because it sits on the land.
But the one on the south side of the strait was a lot trickier.
Building over 300-metres out in the sea surrounded by water is not easy.
First, a large oval barrier was constructed
at the end of a temporary pier, which would also act as the base.
Nicknamed the Bathtub, for obvious reasons,
it was done by pouring concrete into a wooden formwork through underwater tubes.
When it was set, the water inside was pumped out, allowing more concrete and
steel reinforcement to be added inside before the tower itself could start to rise above.
At around the same time, the huge anchorages for the suspension cables that would lie on either
side of the strait were built too. Altogether that took around three years to complete.
With the massive towers in place, the task of connecting them with cables began.
With shipping lanes closed, a boat was used to pull the first wires across the strait.
They were then lifted up into cradles at the top of each tower by crane.
Next, a platform was set up so the rest of the wire strands could be
sent across the Strait and secured into those anchorages, before being passed back again.
It’s a very long and drawn out process known as spinning.
Just over six months later, more than
27,000 individual wires had been spun with a combined length of around 80,000 miles.
Hydraulic presses had compacted them into single large cables and for the
first time there was a physical, manmade link across the Strait.
Then came the bridge deck. To build this,
vertical cables were hung down from the main ones to support steel trusses.
This was done right across the bridge until the two sides connected.
Concrete was then poured onto this base, creating the roadway — the last major piece of the puzzle.
Now as you’ve probably noticed, health and safety was a little more laid back than it is today.
Those at the top of the towers worked for months in 45 mph winds, over 200 metres
above the water — and there were sadly many instances of workers falling from the bridge.
Despite multiple fatalities, the addition of a safety net did save many lives too,
with survivors becoming members of what was dubbed the “half-way to hell club”.
Tragedy struck on one occasion when a machine fell into the net taking many workers with it.
The net collapsed under the weight of the machinery and 10 people were killed.
Finally, in 1937, the bridge that no one thought could ever be built
was completed on budget and ahead of time, opening to much fanfare.
May 27, 1937. Opening day number one was just for people.
200,000 people showed up and paid a nickel each to walk across.
50 years later, the city held a similar pedestrian walk over to celebrate the bridge’s anniversary.
But in half a century, the Golden Gate had gained a lot more admirers.
There were 800,000 people that made it onto the bridge, quite a lot.
Serious overcrowding saw the typically arched bridge flatten under the immense weight of the
crowd – an extremely dangerous incident that has led officials
to commemorate anniversaries in different ways ever since.
Fast forward to today and tales of financial hardship
and the Great Depression feel all too familiar.
Thankfully this time around the federal government
is providing around half the funds for the bridge’s upgrade works.
That means less money has to come from state budgets and taxpayers' pockets,
something especially crucial, given current economic conditions.
One survey even found that half of wealthy Americans making over
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Now, let’s get back to that bridge.
Today, the Golden Gate is as important as when it was first opened — just ask
US Secretary of Transportation Pete Buttigieg.
This bridge plays an indispensable role in the
safe movement of countless people and goods across this region.
37 million vehicles cross it every year, including half a million freight trucks,
and it’s used by huge numbers of pedestrians and cyclists too.
Clearly, it would leave a huge hole —
both literally and figuratively — if anything bad were to happen to it.
And we already know what that would look like because we’ve
seen it multiple times in the movies.
It’s been nuked, destroyed by a tsunami and even bitten in half by a giant shark.
Thankfully in the real world, it remains very much intact,
but that doesn’t mean there’s nothing to worry about.
You see, the bridge — although seismically engineered when it
was first built — was constructed right in between two fault lines,
meaning it sits in the middle of an earthquake zone.
To make matters worse, experts have been saying for years that this part of
California is overdue for a particularly large quake, known as ‘The Big One’.
We are due for The Big One.
A reminder than in the Bay Area we're still at risk of That Big One coming.
It is the big fear for the people of California and they know that some day,
some time, it will happen.
This could be devastating to buildings and
infrastructure in the area, including the Golden Gate.
Other bridges and roads around the bay have fallen victim to seismic
activity in the past — like the Cypress Freeway in nearby Oakland.
Oh my god, look at that. The freeway has just completely collapsed.
Back in 1989, the 7.1-magnitude Loma Prieta earthquake hit the region,
causing 68 deaths, thousands of injuries and billions of dollars worth of damage.
Afterwards, the Golden Gate Bridge, Highway and Transportation District
conducted a vulnerability study of the structure.
It found that an earthquake of magnitude 7 with
an epicentre close to the bridge could cause severe damage to it.
And if an even bigger one hit — with a magnitude of at least 8 —
the viaducts leading up to the bridge could be at risk of collapse.
Now, while the bridge is deemed safe today,
the decision was taken to undertake a full seismic retrofit in four phases.
The first one, which took place from 1997 to 2001, focused on the North Approach Viaduct,
where the anchorage for the cables on the Marin side of the bridge is kept.
That work included strengthening the foundations of the area, replacing four supporting steel
towers and strengthening them, installing seismic expansion joints, installing isolator bearings
that minimise the effects of ground motions on the structure and the trusses specifically.
These isolator bearings sit between the horizontal supports underneath the roadbed and the four
vertical towers, reducing the amount of seismic energy transferred from the ground to the trusses.
They’re made up of thin layers of rubber and steel with a lead core in the centre.
This enables them to move laterally in the event of an earthquake while
retaining high vertical stiffness, with the core deforming and acting as a damper.
Phase 2, from 2001 to 2008, saw a lot of the same work from Phase 1
repeated on the South side, but with a few notable exceptions.
The Southern end has the distinctive Fort Point Arch, which was upgraded into a giant energy
damping element with new bearings, energy dissipation devices and isolation joints.
Surrounding the arch are two massive concrete pylons,
which were modified so they too dampen seismic energy.
It was achieved by expanding their foundations both above and below the surface,
drilling holes deep into the bedrock and inserting pre-stressed steel tendons.
All of this means the pylons can now rock in the event of an earthquake,
with the tendons pulling them back into place.
The bridge is safe today after the second phase of the seismic retrofit
was complete for an earthquake up to a low eight in magnitude.
And so, once that phase was completed, we breathed a large sigh of relief.
Our work is not fully done, as we embark on the last phase.
So, if a high-magnitude earthquake were to hit near the bridge today, there’s still a
chance this critical transport link would need to close afterwards — even after all that work.
But now, following the completion of Phase 3A in 2014, which focused on
strengthening the anchorage on the north side, Phase 3B is almost ready to begin.
In December 2022, the bridge secured a $400 million federal grant as part
of the $1.2TN Bipartisan Infrastructure Law.
That’s around half of the total needed for the final
phase, with the rest coming from state funds and tolls.
It’s a lot of money, but this last phase is the
biggest of all — retrofitting the main suspension element.
It involves strengthening the span by replacing the top lateral bracing system
with over 250 floor beams, and installing more seismic energy dissipation devices.
In an earthquake, special plates made from stainless steel and bronze will slide together,
using a process called abrasive friction to limit seismic forces on the structural components.
The towers themselves are also being upgraded.
The bases are being strengthened and equipped with steel plates,
new structural steel is going in and they’re getting a lick of paint too.
It's all a lot of work and it's going to take three decades and billions of dollars in total.
But it simply has to happen, not just so we can all admire this beautiful, fantastic bridge;
but so this part of America keeps moving.
In fact, right across the US there are similar cases of bridges that were built a long time ago
now in urgent need of improvement, albeit for many different reasons.
Some 46,000 bridges around the country are considered structurally deficient.
They might not be in earthquake zones or have the same iconic status,
but if nothing is done to these crumbling structures that so many of us depend on,
the results could be equally catastrophic.
As it steadily closes in on a century of service, the Golden Gate Bridge remains as
vital to the people and economy of California and the wider US today as it did when it first opened.
Its construction proves what humanity is capable of when presented with a challenge,
and the ongoing project to bolster its defences
against the scariest of dangers truly keeps that spirit alive.
This remarkable structure remains one of the single most important pieces
of road infrastructure in the US more than 80 years after its completion –
a powerful reminder of how construction shapes and enables so much of our world
and a truly compelling tool to inspire the next generation of engineers.
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There’s also the chance to dive deeper on the Golden Gate Bridge and the other
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