The iconic bridge spans over the East River and thousands of people cross the bridge every day to get between Manhattan and Brooklyn. It opened to the public on May 24, 1883 and was designed and constructed over two generations of the Roebling family by John, Washington, and Emily Roebling.
The design is a hybrid between a cable-stayed and suspension bridge and was the world’s first suspension bridge to incorporate steel wire. It’s a total of 1834 m long with the main span between the two suspension towers being 486.3 m long
The bridge evolved over time and has transported everything from horse-drawn vehicles, trolleys, and cars. However, the bridge has been renovated a couple of times in the 1950s, 1980s, and 2010s to maintain its safety and accommodate different transportation flows.
Unsurprisingly, it has been designated as a National Historic Landmark, a New York City Landmark, and a National Historic Civil Engineering Landmark.
The bridge was built to provide for vehicular and pedestrian traffic between Manhattan and Brooklyn. Prior to its construction, people had to take a ferry from Brooklyn to Manhattan which was incredibly time consuming.
To make matters worse, the site’s location was certainly not ideal – the East River is known to have very turbulent and harsh tidal conditions which would create additional challenges in the bridge’s design and construction. On top of this, because of the high volume of watercrafts of all sizes sailing on the East River at any time, the bridge’s design would practically have to be a very high suspension bridge.
As a result, the Brooklyn Bridge would have to be the longest and tallest suspension bridge ever built at the time. Many skeptics compounded these challenges and predicted that the entire structure was going to collapse into the East River. This would be devastating as the total bridge cost was about US $400 million in today’s currency and took 27 lives during its construction.
Unfortunately, the original designer and chief engineer of the bridge, John Roebling died during a preliminary survey of the project after injuring his foot and developing a tetanus infection. This left the construction team with a huge role to fill and uncertainty grew as to whether or not the bridge could really be built.
Design and construction
Although his death was rather unfortunate, Roebling was determined to prove the skeptics wrong and design a bridge that would stand as an icon in the New York City skyline. Roebling truly innovated as his design was the first suspension bridge to incorporate steel cables which would increase the strength relative to other cable materials used at the time
The bridge is able to hold a load of 18,700 short tons which is about 17,000,000 (16,964,355) kg, if we take an elephant weight of 6350 kg, the bridge could theoretically support about 2,700 (2,672) elephants simultaneously. Coincidently, shortly after the bridge opened, 21 elephants were led across it in a promotional event to prove the bridge’s stability.
Suspension and cable-stayed design
As we mentioned a bit earlier, the Brooklyn Bridge is a hybrid of a suspension and cable-stayed bridge, both designs of which contribute to its strength and stability.
The suspension portion involved large steel cables supported by the two central suspension towers which give the bridge its iconic look. These cables were then anchored on each side of the bank on both the Brooklyn and Manhattan sides. The deck of the bridge was then suspended from these steel cables from secondary steel wires.
Although the suspension design would likely have been sufficient from a design perspective, Roebling incorporated a cable-stayed portion as well. The cable-stayed portion involved diagonal cables that ran directly to the support towers which increases stability and adds redundancy.
Constructing the caissons
The month following John’s death, his son Washington Roebling took over his father’s role as the chief engineer.
The foundation of the bridge’s two suspension towers started off with caissons made of wood. Caissons are large boxes used in the foundations of bridge piers and are built such that materials inside like water and soil can be removed. This leaves the interior of the caisson dry and allows workers to move around freely.
The caissons used for the Brooklyn Bridge were large wooden bottomless boxes that were sunk to the bottom of the East River. The working chambers were filled with compressed air to prevent surrounding ground water from seeping in. Airlocks were located at the top of the caissons to allow workers to enter and exit while maintaining the air pressure inside the caissons.
Workers nick named “sandhogs” dug the Brooklyn side caisson 13.6 m to bedrock and the Manhattan side caisson much deeper to a sandy subsoil layer 23.9 m deep. You might be wondering why they didn’t just dig the Manhattan caisson to bedrock as they did with the Brooklyn caisson. This was because the bedrock layer was much deeper than anticipated and due to the higher air pressure in the deeper Manhattan caisson, many workers became sick with decompression sickness despite the use of airlocks. Essentially, the deeper you are in a body of water, the higher the pressure you’ll experience because more water is on top of you – this is called hydrostatic pressure. Washington decided to halt the Manhattan caisson construction at a 23.9m depth due to the increased risk of decompression sickness and deemed the sandy subsoil where they stopped digging to be sufficiently firm.
When the caissons were adequately sunk, they were subsequently filled with concrete in March 1871 and July 1872 respectively. Thus, the caissons were completed and formed the foundation for the two suspension towers
As Washington frequently entered the caissons to oversee the work, he developed a paralyzing injury from decompression sickness which left him unable to supervise the construction in person. He continued to design the caissons and other equipment from his apartment and thankfully his wife Emily Roebling stepped in to help. She spent the next 11 years facilitating the supervision of the bridge’s construction and took on many of the chief engineer’s responsibilities.
Towers, cables, and deck
After the caissons were completed, the two iconic suspension towers started their construction. The towers were constructed on top of each of the caissons by placing masonry blocks piece by piece through a pulley system to develop the tower’s shape. Both towers were completed by July 1876 and subsequently the cables began their installation in August 1876
The main cables were installed first, followed by the secondary suspender wires which would hang from the main cables and support the deck. The main cables were constructed by winding together smaller steel wires. Through an investigation during the main cables construction, eight wires were tested and it was discovered that only five of the eight met the design standards.
J. Lloyd Haigh, the steel contractor earned $300,000 (about US $8,000,000 in today’s currency) from this deception however he wasn’t fired to avoid public controversy.
However at this point, it was too late to replace them and Washington calculated that the lower quality wire would yield a bridge strength of 4 times what was necessary rather than the 6 to 8 times that would be achieved using the proper wires. The lower quality wire was accepted and an additional 150 wires were added to each cable at Haigh’s expense to compensate for the reduced strength.
Once the suspender wires were placed, the roadway and superstructure began their construction.
Finally, on May 24, 1883, the Brooklyn Bridge was open for use with thousands attending the opening ceremony. Emily Roebling was the first person to cross the bridge and although Washington could not attend the ceremony, he hosted a party on the day of the bridge opening consisting of a band, gunfire from ships, and a fireworks display. With the bridge complete it became the go-to way to get between Brooklyn and Manhattan and ferry crews reported a steep drop in passengers.
All in all, it should come as no surprise that the Brooklyn Bridge embodies what New York City is known for: resilience, amazing structures, and expansion. It truly symbolizes the incredible feats of engineering accomplished by the Roeblings and construction teams.
Today it continues to stand unmistakably in New York’s skyline for millions to cross and awe in wonder each year
Thanks for getting to the end of this article! The Brooklyn Bridge is one of my personal favourite structures and I had a lot of fun writing about it – I hope you learned something new.
Let me know in the comments what you learned and if you were to design the bridge with the tools we have now, what would you do differently?
This article was originally written for Structures Simplified,