Golden gate bridge

On January 5, 1933: Construction started officially. A suspension bridge has two types of parts. The tower is analysed using loads and deflection, which are determined from the global structure analysis previously described. In a suspension bridge, the traffic-carrying deck is supported by a series of wire ropes that hang from massive cables draped between tall towers. During construction of the anchorages, a large wrought iron eye-bars (steel bars with a circular hole at one end) linked together to form a chain which are embedded in the concrete. Work began in dry-docks with the assembly of doughnut-shaped cylinders of steel. At the same time the two towers, the highest ever built for a suspension bridge, were started. The cables were constructed high in the air using a process called cable spinning. To spin the cables, workers pulled a wire, about as thick as a pencil, from the concrete anchorage at one shore, up and over both towers, and on to the other anchorage. The main cables serve as the “hanger” for the vertical suspender ropes which, in turn, hold the Bridge’s roadway.

The entire bridge was painted orange-vermilion, called “international orange,” to blend with the natural setting. The caisson would enclose a football-field-sized area from which water would be pumped out. The cables had to be flexible enough to bend up to 8.2296 meters laterally, in the Gate’s threating winds, and strong enough to support the structure of the bridge. In an era, where thousands of deaths happens due to construction, chief engineer of the Golden Gate Bridge Joseph Strauss decided to make a change. In 1936, when delays decelerated construction, Strauss spent over $130,000 in a unique safety feature: a vast net alike to a circus net extended underneath the bridge. The first death was Kermit Moore On October 21, 1936. The dimensions and materials of the bridge defied all imagination here in a table to clarify things.

Table of Contents

List of Figures & Tables & Equations

1 Introduction

The Golden Gate Bridge is a well-recognized landmark in the United States. It spans the Golden Gate Strait – a mile-wide stretch of water that connects the San Francisco Bay to the Pacific Ocean. The Golden Gate Bridge itself connects the city of San Francisco with Marin County on the other side of the Strait. The Golden Gate Bridge is one of the most beautiful bridges in the world. It is also one of the tallest. The idea for a bridge across the strait had been around for many years, because San Francisco suffered from its isolated location. The only practical way to get across the San Francisco Bay was to take a ferry. Planning for the Golden Gate Bridge began in 1916, but the design underwent many changes before construction finally started in 1933.

Purpose of the report

This report provides you numerous information about one of the most astonishing suspension bridges in the world, it as well enlighten you with the history, design and the way that they have managed how to maintain the safety while construction was going on. Background to the reason to build the bridge

The idea of a bridge linking the city with its neighbouring counties was appealing, but the mile-wide gap between San Francisco and Marin presented huge challenges. At the mouth of the Gate, the oncoming force of the Pacific Ocean creates turbulent waves and ripping currents. The location is plagued by gale-force winds and dense fogs. Scope

There will be many specialist engineers reading this report, they are: 1. Site managers
2. Senior engineers
3. Construction manager
4. Project manager

Terms of reference
This report was required by Mr Jonathon Stegen, lecture ACK, Kuwait. It was submitted on the 11th December 2013.

Objections

It was not easy to get the project started. Financing had to be found, and there was much opposition to the very idea of a bridge. The U.S. Navy, for example, feared that a bridge would obstruct ship traffic. The Southern Pacific Railroad, which ran the ferry fleets, feared competition from the bridge. Many experts did not believe that it would be possible to build such a long bridge under such difficult circumstances. A suspension bridge of that length had never before been built. There are strong currents and heavy winds on the bridge site, which made construction dangerous.

2 History
In the paragraphs below it shows you the beauty of the history and background of the golden gate bridge. History & Background

For many years before the Golden Gate Bridge was built, the only way to get across San Francisco Bay was by ferry, and by the early twentieth century the Bay was clogged with them. In the 1920s, engineer and bridge-builder
Joseph Strauss became convinced that a bridge should be constructed across the Golden Gate. In 1916, Michael M., a San Francisco engineer was promoted for a bridge proposal by James H. Wilkins, a structure engineer and newspaper editor to consult with engineers around the nation to test the idea. Engineer Charles A. Ellis with Strauss, a Chicago bridge engineer designed the bridge Architect lrving F. Morrow.

Figure An old picture of the golden gate bridge
However on its way to construction many groups opposed him, each for their own selfish reasons: the military, loggers, the railroads. The engineering challenge was also enormous – the Golden Gate Bridge area often has winds of up to 60 miles per hour and, at the height of the Great Depression. Strauss and his workers overcame many difficulties: strong tides, frequent storms and fogs, and the problem of blasting rock 65 feet below the water to plant earthquake-proof foundations. Eleven men died during construction. If all that weren’t enough, it was the middle of the Great Depression, funds were scarce, and the San Francisco Bay Bridge was already under construction. In spite of everything, Strauss persisted, and Golden Gate Bridge history began when San Francisco voters overwhelmingly approved $35 million in bonds to construct the Golden Gate Bridge. Construction began on January 5, 1933 and on May 27, 1937; the Golden Gate Bridge was opened to great acclaim, a symbol of progress in the Bay Area during a time of economic crisis. Today, the Golden Gate Bridge remains one of the world’s most recognizable architectural structures. [1] Timeline

1. Spring 1924: a joint application made by San Francisco and Marin counties for a permit to build the bridge. 2. December 4, 1928: The association of counties forms the Golden Gate Bridge and Highway District to finance, design, and construct the bridge. 3. February 1930: a formal report submitted by Strauss to the bridge’s directors. 4. Late summer, 1929: all-suspension bridge plan was taken by Strauss and his initial plan to build a cantilever-suspension bridge. 5. Summer 1930: local architect were hired a Irving Morrow, to design an architectural treatment for the bridge accounting for changes including the conversion to an all-suspension bridge. 6. January 5, 1933: Construction started officially.

7. February 1933: Work began on the east approach road to the south end of the bridge. 8. October 24, 1934: San Francisco fender wall completed.
9. January 3, 1935: San Francisco pier reached its final height of 44 feet above the water. 10. January 1935 to June 28, 1935: San Francisco tower construction. 11. February 17, 1936: Eleven workers lose their lives when a platform holding 13 men falls off the bridge and through the safety net. 12. June 1936: The most dramatic safety feature in bridge-building history is introduced at the Golden Gate Bridge work site. A large net is slung under the entire bridge. 13. May 27, 1937: The Bridge was opened. [2]

3 Bridge Design
Here is a little introduction about the parts in the greatest bridge of all the “golden gate bridge” Structural Design

A suspension bridge has two types of parts. The superstructure above includes the deck, towers and main suspension cables. The substructure below includes piers and anchorages. Deck
The deck is the roadway or walkway of a suspension bridge and can be made of one or more pieces. The deck is also called the girder. Anchors

Anchorages of rock or concrete hold the cables at both ends of a suspension bridge. Cables entering the anchors are separated into strands within the rock to distribute the tension load. Piers/Towers

Piers are the lower foundations of a suspension bridge, supporting the towers over which the cables travel. The weight of the cables is transferred into the towers and piers. Cables
Main cables stretch from one anchorage, then over the towers, then into the anchor at the other side of the bridge. Suspension cables connect the deck to the main cables. Hangers
The hangers play an important role for the bridge geometry and are very sensitive to length error. It as well provides balance to design, fabrication, and erection.

Foundation
It is the basis of the bridge that holds the towers which one part of it is built in sea and the other part of it build on land. The sea section build by removing the water to reach to the bedrock so that it can be fixed and not be trembling which might lead the bride to fall.

Structural Analysis

1. Select Initial Configuration: Span length and cable sag are determined, and dead load and stiffness are assumed. 2. Analysis of the Structural Model: In the case of in-plane analysis, the forces on and deformations of members under live load are obtained by using finite deformation theory or linear finite deformation theory with a two-dimensional model. In the case of out-of-plane analysis, wind forces on and deformations of members are calculated by using linear finite deformation theory with a three-dimensional model.

3. Dynamic Response Analysis: The responses of earthquakes are calculated by using response spectrum analysis or time-history analysis. 4. Member Design: The cables and girders are designed using forces obtained from previous analyses. 5. Tower Analysis: The tower is analyzed using loads and deflection, which are determined from the global structure analysis previously described. 6. Verification of Assumed Values and Aerodynamic Stability: The initial values assumed for dead load and stiffness are verified to be sufficiently close to those obtained from the detailed analysis. Aerodynamic stability is to be investigated through analyses and/or wind tunnel tests using dimensions obtained from the dynamic analysis. [3]

4 Construction Methods

In a suspension bridge, the traffic-carrying deck is supported by a series of wire ropes that hang from massive cables draped between tall towers. The main forces in a suspension bridge of any type are tension in the cables and compression in the pillars. Since almost all the force on the pillars is vertically downwards and they are also stabilized by the main cables, the pillars can be made quite slender. First step in any bridge project is to measure the approximate span for the bridge – both ends of which should be at approximately the same elevation – and then decide what exactly you want to be able to cross the bridge. Those two facts set all the other dimensions. And then there is the math in a suspension bridge. This is actually a fairly easy part once you use a spread sheet and this formula:

y = (lbm/ft)/2T * x^2

Which gives the sag (“y”) in the catenary cable (which is not a catenary but rather a parabola) at any point along the deck (“x”) as a function of the suspended weight and the tension (“t”) at mid span. For my purposes, t is an input, along with the weight per linear foot of bridge (actually, half the linear weight as there are 2 cables) and the sag is what I aim for. Given the limitations of the equipment and dimensional lumber

4..1 The process of construction

In the below points, it clarifies the stages n steps taken to build the golden gate bridge.

1. Anchorage

During construction of the anchorages, a large wrought iron eye-bars (steel bars with a circular hole at one end) linked together to form a chain which are embedded in the concrete. These chains are imbedded in a brick vault by which in the end of the chain emerges in the anchorage vaults. The ends of each of the original twelve cables are fastened to the end of the eye-bar chain by clevises. It is mounted in front of the anchorage is a spray saddle, which will support the cable at the point where its individual wire bundles each wire bundle will be secured to one of the anchorage’s eyebars.

2. Foundation

A lengthy span was the only way to straddle the powerful tidal current and deep waters, a caisson construction method was adopted to place the structures on-site, from the water. It was a radical departure from the common approach of assembling most of the structure on land. Work began in dry-docks with the assembly of doughnut-shaped cylinders of steel. These caissons were then towed to their respective sites and sunk to the seabed. After the caissons were placed, removing the water from the caisson’s interior allows workers to excavate a foundation without actually working in water.They were plugged with a new type of marine concrete, called “anti washout underwater concrete,” specially developed to resist dissolution in seawater. The placing work involved displacing seawater from inside the caisson with concrete to build up a thick pillar.

3. Towers/piers

At the same time the two towers, the highest ever built for a suspension bridge, were started. The north one was located on shore which made construction easier, but the south tower was in the water over a thousand feet from the southern bank. To create an artificial island to put the tower on construction crews lowered concrete “fenders” 30 feet long down to the sea bed. The fenders enclosed an area about the size of a football field which was then pumped out and filled with concrete. The steel tower was then constructed on top of that. The Backspan piers are built to provide support for the main cables and the back spans. Typical construction techniques would employ conventional reinforced concrete foundation and substructure construction.

4. Main cables

The cables were constructed high in the air using a process called cable spinning. To spin the cables, workers pulled a wire, about as thick as a pencil, from the concrete anchorage at one shore, up and over both towers, and on to the other anchorage. The wire was then secured and sent back. It took many back-and-forth trips to place the 27,572 wires that are in each cable. Individual wires were grouped into heavier strands and compacted
together to form the finished cable. The spinning of the cables took just six months and nine days, setting records for speed and efficiency. During the spinning, workers standing on the catwalk make sure the wire unwinds smoothly, freeing any kinks. As spools are exhausted, the end of the wire is spliced to the wire from a new spool, forming a continuous strand. When the bundle is thick enough, tape or wire straps are applied at intervals.

5. Hangers

The main cables serve as the “hanger” for the vertical suspender ropes which, in turn, hold the Bridge’s roadway. They are uniformly distributed (equal intervals) and is connected to main cable by means of a cable clamp to allow attachment of the hangers.

6. Deck

It is understood that the Golden Gate Bridge is constructed under suspended construction, Therefore the deck structure must be built in both directions from the support towers at the correct rate in order to keep the forces on the towers balanced at all times. A moving crane lifts deck sections into place, where workers attach them to previously placed sections and to the vertical cables that hang from the main suspension cables to keep the wires together. The wire coming off the spool is cut and secured to the anchorage. Then the process begins again for the next bundle. In one technique, a moving crane that rolls atop the main suspension cable lifts deck sections into place, where workers attach them to previously placed sections and to the vertical cables that hang from the main suspension cables, extending the completed length. Alternatively, the crane may rest directly on the deck and move forward as each section is placed.

7. Paintings

The entire bridge was painted orange-vermilion, called “international orange,” to blend with the natural setting. This was obviously a much better selection than the black with yellow stripes the Navy wanted in order to
assure greater visibility for passing ships. High-pressure sodium vapour lamps to improve the amount of light, while preserving the warm glow by means of a plastic amber lens. [4]

5 Construction Challenges
During the construction of the bridge that you all see today in San Francisco, the workers have faced various types of challenges in which the most two well-known challenges where the caisson and cables. Caisson

Construction of the Golden Gate Bridge was the first time anyone had built a suspension bridge that one of its towers was suspended in the ocean. Were the conditions were harsh in the open atmosphere as well as in the ocean. Divers were employed to set explosives and blast away rock for seating the south tower’s supports Chief engineer Joseph Strauss came up with a plan for workers to first build a giant caisson to protect the pier from stray. The caisson would enclose a football-field-sized area from which water would be pumped out. The concrete tower foundation would be laid inside. Once this was completed, water was to be pumped back into the 40-foot-thick concrete walls of the fender, in order to strengthen the fender against the current. During constructing it the divers has faced powerful currents as they helped anchor the massive concrete bridge support onto the ocean floor. The savage currents rushing in and out of the bay from high to low tides as seen in the figure below.

Figure tides rushing hard through the caisson
Not to mention, divers worked blindly, forced to feel their way due to murky water, fast-changing currents and bulky diving suits. With the construction team’s tight schedule, divers were often forced to surface before having sufficient time to decompress, increasing the likelihood that they would develop caisson disease, a nitrogen deficiency also known as “the bends”, decompression chambers were kept nearby just in case. In which each dive had to take place in a narrow window of time as little as an hour and 15 minutes due to treacherous tidal currents. Whereas the major concern was that the diver’s life depended on the continuous pumping of air through a long hose to the surface because at that time portable air tanks for diving had not
yet been invented.

Cables
The bridge’s designers carefully calculated the graceful dip of the suspension cables between the two towers to carry the needed weight. The cables had to be flexible enough to bend up to 8.2296 meters laterally, in the Gate’s threating winds, and strong enough to support the structure of the bridge. The planned cables would be so long and strong that they would need to be constructed in place. The firm had devised the most efficient strength-to-rigidity ratio for cables. It had also developed a technique of spinning cables on-site. The innovative technique enabled a cable of any length and thickness to be formed by binding together thin wires. It promised to give engineers the freedom to build a bridge of infinite length.

Figure hydraulic press compacted thin wire strands into one large cable Hundreds of wires, each roughly the diameter of a pencil, were bound together into strands. Hydraulic jacks then bundled and compressed 61 strands to make a cable. The spinning was a main problem as it not only did it take time for the spinning wheel to travel the mile between the two shores, but the work had to be performed in a precise sequence, in order to create the balance needed for the cables to absorb the proper amount of wind pressure. The Golden Gate uses the largest bridge cables ever made long enough to encircle the world more than three times at the equator.

They were far too heavy to carry across the Golden Gate Strait on barges and lift up to the tops of the towers. Therefore, engineers had to balance the tower height and cable size in the final design of the Golden Gate Bridge, making them considerably taller to reduce the tension force in the cables would have been a more difficult and expensive design alternative. In addition to all these issues the construction budget was a burden to the workers as it was too tight to make their deadline, a second spinning wheel was constructed which met the first wheel in the middle of the bridge was designed to accelerate construction.

6 Health & Safety
Due to several injuries Mr Joseph Strauss decided to try preventing them from happening therefore he came up with these ideas. Measures

In an era, where thousands of deaths happens due to construction, chief engineer of the Golden Gate Bridge Joseph Strauss decided to make a change, he refused to accept the typical ignorance that the workers death were a cost of doing business therefore he had to come up with ideas to prevent accidents from happening on site during their construction and to that end they turn up to wearing the military helmets and constructing a safety net under the bridge [5]

Preventive Safety Hats

Safety hats were specially modified by local safety equipment Edward W. Bullard, manufacturer who wanted to improve the safety for the workers and began to create a helmet to protect them from falling objects as seen in Fig14 below. The hard hats of that age were called “hard-boiled hats,” and were made of leather and canvas. It was introduced due to “doughboy” hat that he had to wear in WW1. Russell Cone, a local engineer that supervised the safety procedures for all workers. He was a tough enforcer of the safety rules, since most workmen were injured by errant flying objects. He made sure hard hats were worn at all times. But the most innovative safety feature at the Golden Gate site was yet to come. Safety helmets have now become an important factor of matter of course on every building site.

Figure One of the workers wearing the safety hat

Safety Net

In 1936, when delays decelerated construction, Strauss spent over $130,000 in a unique safety feature: a vast net alike to a circus net extended underneath the bridge. Throughout the construction of the roadway structure, net made of manila rope was hanged below the floor of the Bridge. Not only, it was extended along the whole length of the span from pylon to pylon, but also it was extended ten feet wider than the bridge’s width and fifteen feet
further than the roadway’s length to give workers an abiding sense of security as they moved more freely and quickly across the slippery, half-constructed steel. While there was one deadly accident when a scaffold platform fell and broke through the net resulting in 10 deaths, there is no doubt the net saved many other lives. Nineteen survivors whose falls were stopped by the net became the members of “The Halfway to Hell Club.”

Accidents

Although the net did save 19 men. The first death was Kermit Moore On October 21, 1936. And the second was on February 17, 1937, a crew of twelve men were working on a stripping platform close to the north tower, while two men in the net below scraped away debris. In a flash, the west side of the platform gave way. The five-ton structure hung crazily from the bridge, tilting its panicked load of workers toward the water hundreds of feet below. One worker, Tom Casey, lunged and grabbed onto a bridge beam, where he dangled until he was rescued. Of the twelve men O.A. Anderson, Chris Anderson, William Bass, Orrill Desper, Fred Dümmatzen, Terence Hallinan, Eldridge Hillen, Charles Lindros, Jack Norman, and Louis Russell lost their lives. From who fell to the water, two survived. One of them was the foreman of the stripping crew, Slim Lambert. “As I was falling, a piece of lumber fell on my head. I was almost unconscious. Then the icy water of the channel brought me to,” said Lambert. He was twenty-six at the time. He struggled to free himself from the tangles of the net underwater. Lambert suffered a broken shoulder, several ribs, and neck several vertebrae, but he lived to tell the tale. In a single catastrophe, the project’s near-perfect safety record was obliterated. [6]

7 Specifications
The two tables below show the exact dimension and material used in the golden gate bridge. Dimensions

The dimensions of the bridge defied all imagination here is a table to clarify things:

Table dimensions
Specification
Dimension
Length of
Bridge
2,737 meter

Main cable
2,332 meter

Main span
1,280 meter

Side spans
343 meter
Height of
Tower above water
227 meter

Tower above roadway
152 meter

Width of
Deck
27 meter

Roadway
19 meter

Sidewalk
3 meter
Weight of
Bridge
811,476,750 kilogram

Both towers
40,200,000 kilogram

Steel used
75,296,333 kilogram

Load on each tower
39 916 129 kilogram

Anchorage
54,400,00 kilogram
Diameter of
Main cable
0.92 meter
Materials

Table materials used
Specification
Material used
Quantity
Cable
Galvanised steel wires
21,772,000 kilogram
Main tower
Steel
40,280,000 kilogram
Anchorage
Steel and Concrete
40,280,000 kilogram (steel)
139,160 cubic meter (concrete)
Deck
Concrete and Rebar
21,800 cubic meter (concrete)
9,250,000 kilogram (steel)

8 Conclusion
This part of summarises all the important facts of our report in case you were in a hurry, you can look in here and you’ll find all your answers.

Summary of main facts

This paper Is based on a report done by lujain salem and kawthar shehab, it provides you information about the history, design and the way that they have managed how to maintain the safety while construction was going on. The Golden Gate Bridge is a well-recognized landmark in the United States and the most astonishing suspension bridges in the world. Site managers, senior engineers, construction manager and project manager will read this report .The idea of a bridge linking the city with its neighbouring counties was appealing, but the mile-wide gap between San Francisco and Marin presented huge challenges. It was not easy to get the project started. Financing had to be found, and there was much opposition to the very idea of a bridge. . Charles A. Ellis with Strauss, a Chicago bridge engineer designed the bridge Architect lrving F. Morrow. On January 5, 1933: Construction started officially.

The tower is analysed using loads and deflection, which are determined from the global structure analysis previously described. . A suspension bridge has two types of parts. In a suspension bridge, the traffic-carrying deck is supported by a series of wire ropes that hang from massive cables draped between tall towers. Work began in dry-docks with the assembly of doughnut-shaped cylinders of steel. The two towers were built for a suspension bridge. The cables were constructed high in the air. The main cables serve to hold the Bridge’s roadway. The caisson would enclose a football-field-sized area. It has flexible cables to support the structure of the bridge. It faced a lot of death and objectives. Lastly, the entire bridge was painted orange-vermilion to blend with the natural setting. The Bridge was submitted on the 11th December 2013. 13 and was opened in May 27, 1937.

New technology or briefly about modern day suspension bridges

The modern suspension bridge originated in the 18th century when the
development of the bridge structure and the production of iron started on a full-scale basis. The recent developments in design technology in bridge engineering enable the construction of lighter, longer, and more slender bridges at the cost of losing stiffness and damping properties. Modern suspension bridges use a box section roadway supported by high tensile strength cables. Steel, which is very strong under tension, is an ideal material for cables; a single steel wire, only 0.1 inch thick, can support over half a ton without breaking. In the cable stay version of the suspension bridge, the deck is hung from diagonal cables that exert a force towards the towers as well as vertically. This makes the tension in the steel cables extremely high, and hence they are very stiff. In addition, the cables effectively stabilise the towers from both sides. Another major development in the modern suspension bridge was the pneumatic caisson, which permitted pier foundation at great depths. List of References

[1]

[2]

[3] http://freeit.free.fr/Bridge%20Engineering%20HandBook/ch18.pdf

[4] http://goldengatebridge.org/research/factsGGBIntOrngColor.php

[5] http://goldengatebridge.org/research/CheatingDeath.php

[6]

Bibliography

http://www.laboiteverte.fr/la-construction-du-golden-gate-bridge/

http://ohp.parks.ca.gov/ListedResources/Detail.aspx?num=974

http://edition.cnn.com/2013/11/01/us/golden-gate-bridge-fast-facts/

https://www.google.com.kw/search?q=golden+gate+bridge+construction&sa=X&tbm=isch&tbo=u&source=univ&ei=8NWdUoHqN-nG7Aapx4HAAw&ved=0CDsQsAQ&biw=1280&bih=843

Appendix A – photos