Ep 70 SPECIAL Golden Gate Bridge
Engineering News – Microplastic Magnets in Water (1:10)
This week's engineering marvel is the Golden Gate Bridge (3:20). After decades of design considerations (6:10) the Golden Gate Bridge opened in 1937 (16:40). 86 years later, San Francisco is working hard to maintain (21:00) the iconic bridge.
Golden Gate Bridge
Hi and welcome to Failurology; a podcast about engineering failures. I’m your host, Nicole
And I’m Brian. And we’re both from Calgary, AB.
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This week in engineering news, Microplastic Magnets in Water.
● Researchers at RMIT (Royal Melbourne Institute of Technology) University in Australia have developed magnets to attract and remove micro plastics in water in a fraction of the time compared to traditional methods.
● Using absorbents, in the form of powder, they can remove microplastics that are 1,000 times smaller than what can be removed by wastewater treatment plants. Microplastics smaller than 5mm are not detectable and take 450 years to degrade.
● The absorbents, made from a nano-pillar structure, are made from recycled waste and can be reused.
● The nano materials contain iron, which can then be picked up by magnets. So the absorbents attract the microplastics and the magnets attract the absorbents.
● It is said the process takes about an hour, but I’m assuming that is based on the size and how well the absorbents mix with the water. Either way this is a huge step forward for cleaning up our waters.
● If you want to read more about the study, check out the link on the web page for this episode at failurology.ca
Now on to this week’s episode. Every 10th episode, we talk about an engineering marvel instead of a failure. The marvel we’re going to talk about today is the Golden Gate Bridge.
We’ve been working our way through the American Society of Civil Engineers 7 wonders of the engineering world. We’ve already talked about the Channel Tunnel, Panama Canal, and the CN Tower from that list. Golden Gate Bridge is also on the list as are a few others that we hope to cover in future episodes.
If you’re thinking, oh it's just a bridge, how can it be on this list? I wondered that myself a bit at first. But it’s the size of the bridge, or more importantly it’s length, and the era it was built that make it so impressive. It’s also very photogenic and one of, if not the most, photographed bridge in the world. In fact, I myself took photos of it when I went to San Francisco in 2012.
● The Golden Gate Bridge is a suspension bridge that spans the Golden Gate.
○ Which I didn’t realize was a thing until I started researching. The Golden Gate is a 1.6km (1mi) strait that connects the San Francisco Bay with the Pacific Ocean.
○ I’ve always thought the geography of San Francisco was interesting. It's like a wye, you have San Jose at the bottom, then the west part of the wye is San Francisco and the east part is Oakland and Fremont. So San Francisco is a peninsula. The Golden Gate Bridge takes you north into wine country, but there isn’t really a metro area directly on the north side. There are three other bridges that take you east across to Oakland and Fremont; and while they are impressive in their own way, they are not the Golden Gate Bridge.
● When the bridge opened in 1937, it was the longest and tallest bridge in the world, with a main span, the part of the bridge over the water, of 1,280m (4,200ft) and a height of 227m (746ft), making it equivalent to a 75 story building. The clearance height on the bridge deck is 4.3m (14ft) which is not quite tall enough for trucks, which have to take a different route. The clearance below is 67.1m (220ft) at high tide. For reference, several cargo ships and some cruise ships can pass under the bridge. Even the Titanic would have fit.
○ Today the Golden Gate bridge is the 19th longest bridge and 40th tallest bridge in the world.
● Despite appearing to be red, the bridge is actually an orange vermillion called International Orange. The colour was chosen because it blends in well with the natural surroundings but is easily visible in fog.
● The bridge deck carries 6 lanes of traffic and an eastern and western walkway for pedestrian and bike traffic. I think the 6 lanes in itself were pretty impressive for 1937. A Lot of older bridges were two lanes each way or maybe three and they've had to be expanded over time. On average, 118,000 vehicles cross the bridge each day.
● The weight of the bridge deck is supported by 250 pairs of vertical suspended ropes attached to two main cables, passing over two main towers. Each cable is 27,572 strands of wire. Each tower has approximately 600,000 rivets.
● The bridge was built to provide a permanent link with the communities around the bay and improve the city’s growth rate. There was a ferry service, but it took about 20 minutes per trip. The issue was the long span, deep water and strong swirling tides and currents that the bridge design had to contend with.
● Early estimates for the bridge had an estimated cost of $100 million USD (equivalent to $2.5 billion USD today). But Joseph Strauss, an ambitious engineer, promised he his design could be built for $17 million USD ($423 million USD today).
● It took about 10 years to convince everyone the bridge was a good idea. There were concerns about shipping traffic, about blocking the entrance to a main navy harbor, guarantees for local workers to be used for construction, competition to the ferry fleet, and increased traffic on either side. One ally was the automobile industry, who saw the development of roads and bridges as an increase in demand for cars.
● While Strauss was the chief engineer for the bridge project and oversaw the design and construction, he had a limited understanding of cable-suspension designs and referred to many experts for this work. Which is great that he recognized his weakness and called for help, otherwise this could be a completely different episode where we talk about a failure and not a marvel.
● Architect Irving Marrow designed the shape of the bridge towers, the lighting scheme, art deco elements, and the International Orange colour we mentioned earlier.
● The final suspension design was conceived by Leon Moisseiff, who designed the Manhattan Bridge in New York City. Now that it’s been pointed out, it makes sense, the two bridges have a similar aesthetic.
○ It’s interesting to start to recognize similar designs around the world and look them up to see if they were designed by the same people. One example is Foster + Partners, who often uses a diagrid pattern of diagonally intersecting members on the outside of the building. The Bow in Calgary, the Gherkin in London, and the Hearst Tower in New York City all have a similar pattern.
○ Moisseiff created the basic structural design, which included his “deflection theory” that a thin, flexible roadway would flex in the wind and reduce the stress placed on the cables and towers.
○ Moisseiff also designed the Tacoma Narrows Bridge later on, which collapsed in a windstorm due to unexpected aeroelastic flutter.
● Charles Alton Ellis worked with Moisseiff as the principal engineer of the project, completing alot of the technical and theoretical work that built the bridge. Ellis also designed the “bridge with a bridge” on the south end to avoid demolishing Fort Point. He was fired in 1931 by Strauss for sending too many telegrams back and forth with Moisseiff. Ellis went on to turn in 10 volumes of hand calculations and became a structural expert writing the standard text of time, as well as being a professor of engineering. He was replaced by Clifford Paine.
● With the hopes of self promotion and posterity, Strauss downplayed his collaborators work, even though they are mostly responsible for the final form of the bridge and did so for little pay. Strauss died a year after the bridge was completed.
● In 2007, the Golden Gate Bridge District gave major credit for the bridge to Ellis.
● Construction began on Jan 5, 1933. The project ended up costing $35 million USD ($530 million USD today) and was completed ahead of schedule and under budget by $1.3 million USD, which is rare for a construction project.
● The steel company contracted to build the bridge, Bethlehem Steel, also manufactured steel for the George Washington Bridge between NYC and New Jersey, the Peace Bridge between Buffalo and Fort Erie, The Verrazano-Narrows bridge in NYC, the Hoover Dam, Madison Square Garden, Empire State Building, Merchandise Mart in Chicago, and Alcatraz Island among many others before filing for bankruptcy in 2003.
● Strauss innovated the use of a moveable safety net to catch workers who fell off the bridge, saving the lives of 19 men over the course of the bridge construction. On Feb 17, 1937, a scaffold with 12 men on it and undersized bolts, fell and broke through the netting, two of the 12 survived the fall.
● There were 5,000 men working directly on the bridge at a time. The bridge took 31 million work hours, in 134 cities, and 20 states, which with its timing relating to the Great Depression was enough of a boost to float the economy of the whole country.
● The bridge required so much concrete that they re-opened several cement factories that had closed during the Great Depression. And whole forests were cut down in Oregon to build the wood forms.
● The bridge opened on May 27, 1937.
● The bridge has undergone maintenance over the years.
● In 1953 and 1954 lateral and diagonal bracing was installed to connect the lower chords and the two side truss to stiffen the bridge deck in torsion. A December 1, 1951 windstorm revealed instabilities similar to the Tacoma Narrows Bridge.
● The original concrete bridge deck was replaced over 401 nights between 1982 and 1986 without closing the roadway completely. The concrete had been exposed to salt carried by fog or mist and was corroding the rebar and spalling the concrete. During this project, the roadway was widened 2ft, which gave a wider outside curb lane. The deck replacement cost $68 million USD, which if you deflate that value back to 1937 dollars, represented about one third of the total bridge cost.
● In the early 60s, the Bay Area Rapid Transit (BART) looked at the feasibility of running train tracks over the bridge or building a new lower deck. The conclusion was that this was not advisable.
● This is sad, but the bridge is the most used suicide site in the world. If you manage to survive the 4 second fall and hit the water at 120kph, of which 5% do, you will likely die of hypothermia in the cold water. A suicide barrier netting is under construction and scheduled to be completed in 2023. If you are struggling with mental health, please don’t jump off this or any other bridge, please get help.
● The bridge is designed to withstand 109 kph winds and has been closed on three occasions where wind exceeded this speed. As part of the suicide barrier project, the walkway railing is being replaced with thinner, more flexible slats to improve the aerodynamic tolerance to 161 kph. The new slats created an Aeolian tone (the sound produced by air flowing past a sharp edge) that can be heard on both sides of the bridge.
● The bridge is close to the San Andreas Fault and the area is prone to earthquakes. Seismic design is something we are hoping to talk about in a future episode, it’s been on the list for years. The bridge is in the process of a seismic upgrade to withstand a significant earthquake with only minimal damage. The southern approach to the bridge was also replaced with a more earthquake resistant design.
● The Golden Gate Bridge was designated a California Historical Landmark in 1987 and a San Francisco Designated Landmark in 1999.
So there you have it, the Golden Gate Bridge. Ahead of its time, it was the longest and tallest bridge when it was built, bringing much needed growth to San Fancisco and economic relief to the US during the Great Depression.
For photos, sources and an episode summary from this week’s episode head to Failurology.ca. If you’re enjoying what you’re hearing, please rate, review and subscribe to Failurology, so more people can find us. If you want to chat with us, our Twitter handle is @failurology, you can email us firstname.lastname@example.org, you can connect with us on Linked In or you can message us on our Patreon page. Check out the show notes for links to all of these. Thanks, everyone for listening. And tune in to the next episode where we will talk about the Tacoma Narrows Bridge. We don’t normally like to do two similar episodes back to back, but researching the Golden Gate Bridge had me wondering about the Tacoma Narrows so we’re gonna do it anyway.
Bye everyone, talk soon!