Golden Gate Bridge | The CRAZY Engineering behind it

Summary

This video explores the engineering marvel behind the Golden Gate Bridge, focusing on its design and construction. The suspension bridge was chosen for its efficiency in spanning the 2.7 km distance without obstructing ship traffic, unlike beam or arch bridges. The video discusses key challenges, such as balancing cable tension, constructing stable foundations in the Pacific Ocean, and addressing thermal expansion. It highlights innovations by chief engineer Joseph Strauss, including cable systems, tower designs, and safety measures, emphasizing the bridge's resilience even under extreme conditions.

Takeaways

• 🌉 The Golden Gate Bridge is a suspension bridge that spans 2.7 km over the Pacific Ocean, using a parabolic cable system for support.
• ⚠️ Without the suspension cable system, the bridge would fail due to the lack of structural support.
• 🏗️ Joseph Strauss, the chief engineer, chose a suspension design because beam and arch bridge designs were either impractical or costly for this location.
• 🔗 Suspension bridges rely on tall towers and cables anchored to the ground to balance tensile forces, preventing the towers from bending inward.
• 🔧 Strauss solved the issue of concrete cracking by connecting the suspension cables to a steel structure, which provided a strong and flexible connection.
• 🛠️ The bridge deck was divided into seven sections with finger expansion joints to allow for thermal expansion, preventing damage from temperature changes.
• 🏔️ Constructing the south tower foundation was challenging due to its location in the deep and turbulent waters of the Pacific Ocean.
• 📏 Taller towers in suspension bridges reduce tension on cables and increase bridge strength, which was key in the design of the Golden Gate Bridge.
• 🔩 The main cables were created by spinning 27,000 smaller wires, resulting in a total steel wire length of 129,000 km.
• 🎉 On the bridge's 50th anniversary, it successfully supported a massive crowd of 300,000 people, sagging by 2 meters but remaining structurally sound.

Q & A

What would happen to the Golden Gate Bridge if its suspension cable system was not present?

Without the suspension cable system, the bridge would collapse, as the cables provide crucial support to the road deck, distributing the weight and ensuring the bridge’s stability.

Why was the suspension bridge design chosen for the Golden Gate Bridge?

The suspension bridge design was chosen because it allows ships to pass underneath and avoids the need for costly underwater piers in deep water, making it an efficient solution for the 2.7 km distance between the coastlines.

How did the engineers resolve the issue of inward bending of the towers caused by the tension in the main cables?

The engineers resolved the issue by extending the main cable and anchoring it to the ground via an anchorage system. This balanced the horizontal forces acting on the towers.

Why did Mr. Joseph Strauss move the towers closer together, and how did this impact the cable design?

By moving the towers closer together, the length of the unsupported bridge deck was reduced, lowering the tension in the cables. This allowed for a reduction in the cable's cross-section area, optimizing costs.

How did Mr. Strauss address the issue of the suspension cables causing cracks in the concrete deck?

Mr. Strauss addressed this by connecting the steel suspenders to a steel structure beneath the road deck, as steel-to-steel connections are stronger and prevent the formation of cracks in the brittle concrete.

What solution did the engineers use to handle thermal expansion in the Golden Gate Bridge?

The engineers used finger expansion joints between the road deck sections to allow movement during temperature changes. These joints prevent stress on the towers and road deck caused by expansion and contraction.

Why is the height of the towers crucial in a suspension bridge design?

The height of the towers is crucial because taller towers reduce the tension in the cables by increasing the angle of the cables. This reduces the overall stress on the structure, making the bridge stronger.

How was the south tower foundation constructed, and what challenges did the engineers face?

The south tower foundation was built on bedrock 50 feet below the seabed. Engineers faced challenges from the violent Pacific Ocean currents. To overcome this, they built protective fender walls and an RCC slab to safely carry out the construction beneath the water.

How was the main cable of the Golden Gate Bridge constructed?

The main cable was constructed by spinning 27,000 smaller steel wires over the towers and clamping them together. The wires were pressed using a hydraulic press and then bound into a single large cable.

What happened to the Golden Gate Bridge during its 50th anniversary celebration when it was overloaded with people?

During the 50th anniversary, the Golden Gate Bridge sagged by almost 2 meters due to the weight of over 300,000 people, but the suspension system held strong and prevented any structural failure.

Outlines

00:00

🌉 Introduction to the Golden Gate Bridge's Engineering

This paragraph introduces the Golden Gate Bridge and its key structural component: the suspension cable system. It outlines how the bridge's construction involved overcoming the powerful currents of the Pacific Ocean with the help of Chief Engineer Joseph Strauss. The paragraph explains why a suspension bridge design was chosen over other designs, such as beam and arch bridges. It highlights the suspension bridge's basic design, consisting of two towers with a main cable suspended between them. Additionally, it touches on some of the challenges engineers faced, including how the tension in the main cable affects the towers and how the bridge deck is supported. The choice of suspension design was critical due to the large span and deep waters, making alternative designs costly and impractical.

05:00

🚧 Construction and Safety Measures of the Golden Gate Bridge

This section details the construction process of the bridge, emphasizing the importance of safety measures taken to protect workers. It describes how prefabricated components were brought to the site and assembled using derricks and rivets. A net was installed beneath the bridge deck to catch any falling workers. Suspension cables were then connected to the main cable to evenly distribute the load. The construction process involved painting the bridge with a special International Orange color for protection. The paragraph also describes the concrete road deck's construction, where wooden formwork and steel bars were used before pouring concrete. Finally, the section addresses the thermal expansion challenge and how Mr. Strauss used finger expansion joints to prevent damage from temperature changes, dividing the deck into separate sections to account for differential expansion between steel and concrete.

10:01

🌊 Overcoming Challenges in Building the South Tower

This part focuses on the challenges faced while constructing the South Tower, which was built in the turbulent waters of the Pacific Ocean. The foundation required digging down to the bedrock, 50 feet below the seabed, with divers performing underwater blasts to clear debris. The structure's cross-section reveals the construction of fender walls, which had to withstand inward oceanic forces. The workers built a thick reinforced concrete slab to support these walls, allowing them to dig safely underneath it. Once the foundation was complete, the assembly of the towers began using hollow steel cells, carefully planned to give the tower its final shape. The paragraph also explains how the main cables were constructed from 27,000 smaller wires. A catwalk bridge was created for workers to lay down the wires, which were wound together using galvanized steel wire, giving the cable its large pipe-like appearance. The construction of the deck and road was completed afterward.

15:01

🎉 The Golden Gate Bridge: Strength, Resilience, and Legacy

This concluding section recounts the Golden Gate Bridge's strength and resilience, particularly on its 50th anniversary when it supported an immense crowd, causing the road deck to sag by 2 meters. Despite the extreme load, the bridge held strong, showcasing the robust design engineered by Mr. Strauss 89 years ago. The paragraph acknowledges the technological marvel of the bridge and its significance in civil engineering history. It also invites viewers to join the team behind the video, thanking them for their time and highlighting the incredible feats achieved during the bridge's construction.

Keywords

💡Suspension Bridge

A suspension bridge is a type of bridge that relies on cables to support the deck. In the video, the Golden Gate Bridge is highlighted as a prime example of this engineering marvel. The main cables are anchored to towers and then to anchorages in the ground, creating a system that distributes the weight of the bridge and its traffic evenly. The script explains that without the suspension system, the bridge would not be able to span the vast distance over the Pacific Ocean, making it a critical component of the bridge's design.

💡Cable System

The cable system of a suspension bridge is integral to its structure, providing the necessary support and tension to keep the bridge stable. The video script mentions that the main cable of the Golden Gate Bridge is designed to approximate a parabolic shape, which is essential for distributing the load of the bridge. The absence of this system, as hypothesized in the script, would lead to a catastrophic failure of the bridge.

💡Towers

Towers in a suspension bridge are the vertical structures that support the main cables. The video script describes how the towers of the Golden Gate Bridge were constructed to withstand the forces exerted by the main cables. The towers are crucial in preventing the bridge from collapsing under its own weight and the weight of traffic.

💡Anchorage System

The anchorage system is a critical part of a suspension bridge's design, as it secures the main cables to the ground, preventing them from pulling out under tension. The script explains how extending the main cable and anchoring it to the ground via an anchorage system can counteract the horizontal forces that would otherwise cause the towers to bend inward.

💡Thermal Expansion

Thermal expansion refers to the tendency of materials to expand or contract with changes in temperature. In the context of the video, thermal expansion is a significant engineering challenge for the Golden Gate Bridge. The script describes how Mr. Strauss addressed this issue by incorporating finger expansion joints into the bridge's design, allowing for movement due to temperature changes without causing damage.

💡Concrete Road Deck

The concrete road deck is the surface of the bridge that vehicles travel on. The video script details the construction process of the Golden Gate Bridge's road deck, which involved laying wooden formwork, attaching steel bars, and pouring concrete. This deck is essential for providing a stable and durable surface for traffic.

💡Suspension Cables

Suspension cables, also known as hangers, connect the road deck to the main cable in a suspension bridge. The script explains that these cables are responsible for transferring the weight of the bridge and its traffic to the main cables and towers. The Golden Gate Bridge uses 250 pairs of these vertical cables to support its deck.

💡International Orange

International Orange is the distinctive color of the Golden Gate Bridge. The video script mentions that after the construction of the steel structures, workers painted the bridge this color. It was chosen for its visibility in the often foggy conditions of the San Francisco Bay and has since become iconic, symbolizing the bridge itself.

💡Finger Expansion Joints

Finger expansion joints are a type of expansion joint designed to accommodate the movement of bridge decks due to thermal expansion. The video script describes how Mr. Strauss incorporated these joints into the Golden Gate Bridge's design, allowing the bridge to expand and contract without damaging the structure. These joints are a key feature that ensures the bridge's longevity and stability.

💡Tensile Load

A tensile load is a force that tends to stretch or elongate a material. In the context of the video, the main cable of the Golden Gate Bridge is under a significant tensile load due to its weight and the weight of the bridge. The script explains how this load affects the bridge's structure, particularly the towers, and how the anchorage system helps to counteract the forces and maintain the bridge's integrity.

💡Optimal Tower Height

Optimal tower height refers to the most effective height for the towers of a suspension bridge, balancing the need for strength and stability with construction costs. The video script discusses how Mr. Strauss calculated the optimal tower height for the Golden Gate Bridge at 746 ft, which is a compromise between the need for a tall tower to reduce cable tension and the cost of constructing a taller tower.

Highlights

The Golden Gate Bridge's suspension cable system is crucial for its stability, without it, the bridge would fail.

A simplified suspension bridge is constructed by erecting two towers and suspending a cable in a parabolic shape between them.

The Golden Gate Bridge is a suspension bridge designed to allow for ship passage and to overcome the challenges of the site's geography.

Conventional beam bridges would block ship movement and are costly to construct at such depths, making them unsuitable for the site.

Arch bridges would require an extremely high structure to maintain their shape, leading to complexity and high construction costs.

Suspension bridges offer an efficient solution to the site's challenges, balancing cost and functionality.

The main issue with the initial suspension bridge design is the inward bending of towers due to the horizontal force from the main cable.

Extending the main cable and anchoring it to the ground via an anchorage system can resolve the horizontal force issue on the towers.

Optimizing the bridge's design by moving the towers closer together reduces the unsupported bridge deck length and the cable's tension.

The width of the main cables on the Golden Gate Bridge is more than half the height of an average human.

Directly connecting steel suspenders to a concrete deck can lead to cracks due to the brittle nature of concrete.

Mr. Strauss solved the connection issue by using a steel structure to connect the suspenders, ensuring a strong steel-to-steel connection.

The road deck's width was kept at 27 meters to accommodate current and future traffic demands.

Construction of the bridge was challenging due to foggy and windy conditions, requiring prefabrication of members and assembly on-site.

A net was installed under the bridge deck to ensure the safety of laborers during construction.

To maintain equal loading on the cable, the assembly system had to be assembled simultaneously and equally in two directions for each tower.

The bridge was painted International Orange, a special color chosen for its visibility and aesthetic appeal.

Thermal expansion is a significant engineering challenge addressed by dividing the deck into separate pieces with finger expansion joints.

Mr. Strauss designed the optimal tower height of 746 ft to balance strength and construction cost.

The construction of the south tower was particularly challenging due to the violent Pacific Ocean currents.

Divers were hired to blast the seabed and clear debris for the construction of the south tower's foundation.

A thick reinforced concrete slab was constructed to protect workers from ocean currents while digging for the hard strata.

The main cables of the bridge are composed of 27,000 smaller wires, totaling 129,000 km of steel wire.

The bridge's construction was a testament to the engineering advancements of the time, showcasing innovative solutions to complex problems.

On its 50th anniversary, the Golden Gate Bridge withstood an extreme load of over 300,000 people without collapsing, demonstrating its resilience.

Transcripts

when observing the Golden Gate Bridge

floating over the Pacific Ocean your

eyes may be drawn to its beautiful

suspension cable system what would

happen to the bridge if this cable

system was not

present in short it would be a

catastrophe let's Brave the deadly

currents of the Pacific Ocean and

construct the Golden Gate Bridge with

its Chief design engineer Mr Joseph

Strauss we'll also explore the

mesmerizing engineering Feats the Golden

Gate Bridge has achieved come

along the Golden Gate Bridge is a

suspension bridge a highly simplified

suspension bridge can be constructed the

following

way erect Two Towers at both ends of the

ocean and suspend a long cable between

the towers this cable can be

approximated as a parabola now let's

attach a concrete road Deck with

pillars this C clearly provides support

to the end of the road

deck when we connect the suspension

cables between the main cable and the

road deck the bridge is also supported

along its length so the road deck won't

fail as we saw

earlier this is the basic design behind

the suspension bridge before exploring

more about the Golden Gate Bridge let's

first understand why the engineers chose

a suspension design for this

site the distance between the two

coastlines of the Golden Gate is a

whopping 2.7 km let's construct a

conventional beam bridge

here you can see that the road deck is

supported by various

peers the presence of these peers blocks

the movement of ships

underneath as you can imagine

constructing them 300 ft deep in the

water would be extremely costly thus the

beam design does not make sense

here now let's consider an arch bridge

this would definitely provide

passageways for

ships however to maintain the arch shape

the bridge would need to be extremely

high such a structure would be quite

complex to

construct that's why Mr Joseph Strauss

opted for a suspension design a bridge

that could overcome all the drawbacks we

discussed in a very efficient way now

let's get into the design details of the

suspension

bridge this design has one glaring issue

if you construct the bridge like this

the towers will bend inward as

shown the main cable is under a huge

tensile load this applies force on the

tower when you resolve this Force you

can see that there is an imbalanced

horizontal force acting inward on the

tower which explains why the towers

Bend can you find a solution for this

issue to cancel this horizontal Force we

need the same force acting in the

opposite direction the straightforward

solution is to extend the main cable and

anchor it down to the ground via an

Anchorage

system however we can optimize the

financial resources needed to construct

this bridge with a simple

idea all we need to do is move the

towers closer to one

another now the length of the

unsupported bridge deck is reduced

due to this tension in the cable will be

reduced this will obviously lead to a

cable with less cross-section area the

width of the main cables are more than

half the height of the average human as

a tourist attraction a piece of this

impressive main cable is demonstrated

near the Golden Gate

Bridge however if you construct the

bridge with this exact design it will

experience a premature death can you

guess why this would be the

case connections are the weakest part in

any structural system the direct

connection of the steel suspenders with

the concrete deck will lead to the

formation of cracks on the deck since

concrete is brittle in

nature let's see how Mr Strauss solved

this

problem Mr Strauss decided to connect

the suspenders to a steel structure

steel to Steel connection is always

strong the details of the connection

between the suspenders and steel

structure are Illustrated

here the road deck is placed on this

structure Mr Strauss kept the width of

the road to 27 M to account for current

and future traffic

demands assembling the structure like

this was far from an easy task due to

foggy and windy conditions at the site

to facilitate the process workers

prefabricated each member of the trust

and brought them to the site VI

ships assembly of the individual members

was accomplished using a Derek and their

connections were secured via

rivets to ensure the safety of the

laborers a net was installed underneath

the bridge deck as the construction of

the bridge progressed they

simultaneously connected the structure

with the main cable using suspension

cables moreover to maintain equal

loading on the cable workers had to

assemble this system simultaneously and

equally in two directions for each Tower

thus the Golden Gate was

bridged 250 pairs of vertical cable were

used and they hung the whole bridge deck

to the main cable after the construction

of the steel structures the workers

painted the bridge a special

International Orange

color next let's examine some details of

concrete road construction on top of

this solid

structure workers first laid down wooden

form

workor they attached steel bars welded

them to the steel sections below

them and later poured and compacted the

concrete using a needle

vibrator our Bridge looks perfect now

but is it ready to support vehicle

movement not yet we must first tackle

another major engineering challenge

thermal

expansion the concrete and Associated

Steel structure will expand or contract

based on environmental temperature

variations if we had constructed this

bridge as a single piece during a hot

sunny day the bridge would expand and

cause tremendous stress on the tower as

well as on the

road eventually the bridge would

experience

damage if you have ever visited the

Golden Gate Bridge you may have noticed

peculiar connections on the

road these connection

called finger Expansion Joints were Mr

strauss's solution to solve the thermal

expansion

problem Mr Strauss divided the deck into

seven separate pieces you can see this

bridge has three cradles the finger

Expansion Joints are installed between

the gaps during an extreme temperature

increase the length of the road deck

increases and these joints move by

almost

4T what an elegant solution for a

serious issue however there is still a

small problem to solve the thermal

expansion of the steel is slightly

higher than that of the

concrete this differential expansion can

cause trouble for the concrete deck

which is composed of a mixture of

concrete and steel bars but this

expansion issue is negligible when the

length is small this is why the Golden

Gate contains tiny Expansion Joints

every 50

ft another great design challenge Mr

Strauss dealt with was the height of the

tower Let's do an experiment to gain a

better

understanding I had two Bridge designs

with me a toll Tower design it is having

a high sack and the next one a short

over design obviously a small

sag the question is that which design

gives more strength to a suspens kind of

bridge Let's test the first design using

a road dech that to a really heavy Road

deck

when I attach the road deck this design

is standing strong this design is

safe now let's attach the same weight to

the next design to the short to

design this bridge went for a sudden

failure I couldn't react to that so in

short we proved experimentally the toll

to design is the best for a suspens kind

of bridge is more strong the question is

why to get answer for this let's invite

the chief engineer of this whole project

Mr Joseph St to the video the major

difference between these two designs is

the angle of the cable in both the load

to be carried is the same the vertical

component of the cable tension balances

this weight since the small Tower design

has a low angle to balance the weight

the cable has to induce more

tension this is why the short Tower

fails during the experiment the tall

tower will obviously reduce the tension

in the cable but it will cost much more

to construct it that's precisely why Mr

Strauss calculated the optimal tower

height of 746 ft a happy average between

these two

scenarios now let's get into the most

exciting part of this video construction

of the Golden Gate Bridge in a hostile

environment first we start with the

tower const construction did you know

the construction of the Southside Tower

was tougher than the North Tower this is

because the south tower construction had

to overcome the violent Pacific Ocean a

tower Foundation must be constructed on

strong Bedrock called hard strata for

the South Side the hard strata was 50 ft

below the seabed level and had a steep

floor we need to dig this deep and build

an RCC foundation for the South

Tower to do so first professional divers

were hired to blast bombs underwater the

divers cleared the debris of the

explosion and made a better

surface now it's time to construct a

steel and wooden framework on this

surface the divers obviously did an

amazing job

here now let's see the cross-section of

the structure they built then the

concrete was poured to create something

called Fender walls afterwards all the

inside water was pumped out

now that the fender wall is ready can

the workers go inside and start digging

for the hard

strata here is the issue the ocean

currents are so nasty that the fender

wall will have to bear a huge inward

force and can collapse this kind of

construction is highly

unsafe Mr Strauss had a clever idea

initially they placed the blasting tubes

the workers shaft and the material shaft

inside the fender walls the trick was to

construct a thick reinforced concrete

slab so that workers can work beneath it

the way workers reached the workers

chamber was quite interesting it was via

the workers shaft they continuously

drilled The Boulders and dug underneath

the RCC

slab this RCC slab supported the fender

walls and protected the workers

underneath against deadly

currents during this process the entire

fender wall structure was allowed to

sink

slowly you can see its knife-like

shape eventually they reached the rocky

hard

strata after leveling the hard strata

they made a steel structure there and

built an RCC

Foundation the construction of the

complete Foundation is quite easy now

you can see how the fender walls protect

the main Foundation from the deadly

waves now it's to see the construction

of the gigantic

Towers once the foundation was ready

they assembled the steel base plate on

it now comes the magic of these hollow

steel cells they assembled and riveted

these cells as if they were constructing

a tower using Legos you can see how

cleverly they had to plan the shapes and

sizes of these cells so that the tower

would finally achieve the shape which it

was intended to

achieve Mr Strauss designed this unique

cellular structure to be economical as

well as

strong the tower construction was then

complete next it was time to lay down

the main cables for this they first

installed cable Saddles at top the

towers you may think that the main cable

is a single solid cable the main cable

is in fact made up of

27,000 smaller wires and a total length

of

129,000 KM length of Steel wire was

consumed for fabrication of it to start

laying these cables workers first

constructed a catwalk bridge for

themselves at first workers laid a

support

wire the main cables made their Journey

via these spinning

wheels furthermore these small wires

were passed over the tower through the

cable saddle one by one and were then

clamped by

laborers then the work pressed the wires

tightly using a hydraulic

press they simultaneously wound the

wires together using galvanized steel

wire which is why the main cable looks

like a single large

pipe these cables are anchored to the

Bedrock with strand shoe steel

plates after laying the main cables the

suspension cables were attached to it

all that was left to do was construct

the deck structure and lay down con for

the road you already know how they did

that a strange incident happened on the

Golden Gate Bridge on its 50th

Anniversary when more than 300,000

people gathered on the bridge all at

once you can probably predict what will

happen if a suspension bridge is

overloaded overloading a suspension

bridge can cause it to

Sag this can even cause the main Towers

to bend inward this is exactly what

happened on that day the road deck

sagged by almost two 2 m even with this

extreme load Mr strauss's Incredible

suspension bridge stood strong one can

only admire the Technologies they

developed 89 years ago in the design and

construction of the Golden Gate Bridge

this successful project signified a leap

in civil

engineering before you leave don't

forget to become a lesic team member we

hope you enjoyed the video thank you for

watching