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Brooklyn Bridge

Bridge in New York City

  • 56 min read
  • 6 chapters
The Brooklyn Bridge and the Lower Manhattan skyline seen from Pebble Beach; the glass pavilion of Jane's Carousel sits below the bridge, with One World Trade Center at right. Brooklyn, New York City.
Christian David · CC BY-SA 4.0

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Proposals for a bridge connecting Manhattan and Brooklyn were first made in the early 19th century; these plans evolved into what is now the Brooklyn Bridge, designed by John A. Roebling. The project's chief engineer, his son Washington Roebling, contributed further design work, assisted by the latter's wife, the engineer Emily Warren Roebling. Construction started in 1870 and was overseen by the New York Bridge Company, which in turn was controlled by the Tammany Hall political machine. Numerous controversies and the novelty of the design prolonged the project over thirteen years. After opening, the Brooklyn Bridge underwent several reconfigurations, having carried horse-drawn vehicles and elevated railway lines until 1950. To alleviate increasing traffic flows, additional bridges and tunnels were built across the East River. Due to gradual deterioration, the Brooklyn Bridge was renovated several times, including in the 1950s, 1980s, and 2010s.

The Brooklyn Bridge is the southernmost of five vehicular bridges connecting Manhattan Island and Long Island, with the Manhattan Bridge, the Williamsburg Bridge, the Queensboro Bridge, and the Robert F. Kennedy Bridge (formerly known as the Triborough Bridge) to the north. Only passenger vehicles and pedestrian and bicycle traffic are permitted. A major tourist attraction since it opened, the Brooklyn Bridge has become an icon of New York City. Over the years, the bridge has been used for stunts and performances, as well as several crimes, attacks and vandalism. The Brooklyn Bridge is designated a National Historic Landmark, a New York City landmark, and a National Historic Civil Engineering Landmark.

Description

The Brooklyn Bridge, an early example of a steel-wire suspension bridge, uses a hybrid design combining elements of cable-stayed and suspension bridges, with both vertical and diagonal suspender cables. Its stone towers are neo-Gothic, with characteristic pointed arches. The New York City Department of Transportation (NYCDOT), which maintains the bridge, says that its original paint scheme was "Brooklyn Bridge Tan" and "Silver", but other accounts state that it was originally entirely "Rawlins Red".

Deck

To provide sufficient clearance for shipping in the East River, the Brooklyn Bridge incorporates long approach viaducts on either end to raise it from low ground on both shores. Including approaches, the Brooklyn Bridge is a total of 6,016 feet (1,834 m) long when measured between the curbs at Park Row in Manhattan and Sands Street in Brooklyn. A separate measurement of 5,989 feet (1,825 m) is sometimes given; this is the distance from the curb at Centre Street in Manhattan.

Suspension span

The main span between the two suspension towers is 1,595.5 feet (486.3 m) long and 85 feet (26 m) wide. The bridge "elongates and contracts between the extremes of temperature from 14 to 16 inches". Navigational clearance is 127 ft (38.7 m) above mean high water (MHW). A 1909 Engineering Magazine article said that, at the center of the span, the height above MHW could fluctuate by more than 9 feet (2.7 m) due to temperature and traffic loads, while more rigid spans had a lower maximum deflection.

The side spans, between each suspension tower and each side's suspension anchorages, are 930 feet (280 m) long. At the time of construction, engineers had not yet discovered the aerodynamics of bridge construction, and bridge designs were not tested in wind tunnels. John Roebling designed the Brooklyn Bridge's truss system to be six to eight times as strong as he thought it needed to be. As such, the open truss structure supporting the deck is, by its nature, subject to fewer aerodynamic problems. However, due to a supplier's fraudulent substitution of inferior-quality wire in the initial construction, the bridge was reappraised at the time as being only four times as strong as necessary.

The main span and side spans are supported by a structure containing trusses that run parallel to the roadway, each of which is 33 feet (10 m) deep. Originally there were six trusses, but two were removed during a late-1940s renovation. The trusses allow the Brooklyn Bridge to hold a total load of 18,700 short tons (17,000 metric tons), a design consideration from when it originally carried heavier elevated trains. These trusses are held up by suspender ropes, which hang downward from each of the four main cables. Crossbeams run between the trusses at the top, and diagonal and vertical stiffening beams run on the outside and inside of each roadway.

An elevated pedestrian-only promenade runs in between the two roadways and 18 feet (5.5 m) above them. It typically runs 4 feet (1.2 m) below the level of the crossbeams, except at the areas surrounding each tower. Here, the promenade rises to just above the level of the crossbeams, connecting to a balcony that slightly overhangs the two roadways. The path is generally 10 to 17 feet (3.0 to 5.2 m) wide. The iron railings were produced by Janes & Kirtland, a Bronx iron foundry that also made the United States Capitol dome and the Bow Bridge in Central Park.

Approaches

Each of the side spans is reached by an approach ramp. The 971-foot (296 m) approach ramp from the Brooklyn side is shorter than the 1,567-foot (478 m) approach ramp from the Manhattan side. The approaches are supported by Renaissance-style arches made of masonry; the arch openings themselves were filled with brick walls, with small windows within. The approach ramp contains nine arch or iron-girder bridges across side streets in Manhattan and Brooklyn.

Underneath the Manhattan approach, a series of brick slopes or "banks" was developed into a skate park, the Brooklyn Banks, in the late 1980s. The park uses the approach's support pillars as obstacles. In the mid-2010s, the Brooklyn Banks were closed to the public because the area was being used as a storage site during the bridge's renovation. The skateboarding community has attempted to save the banks on multiple occasions; after the city destroyed the smaller banks in the 2000s, the city government agreed to keep the larger banks for skateboarding. When the NYCDOT removed the bricks from the banks in 2020, skateboarders started an online petition. In the 2020s, local resident Rosa Chang advocated for the 9-acre (3.6 ha) space under the Manhattan approach to be converted into a recreational area known as Gotham Park. Some of the space under the Manhattan approach reopened in May 2023 as a park called the Arches; this was followed in November 2024 by another 15,000-square-foot (1,400 m2) section of parkland.

Cables

The Brooklyn Bridge contains four main cables, which descend from the tops of the suspension towers and support the deck. Two are located to the outside of the bridge's roadways, while two are in the median of the roadways. Each main cable measures 15.75 inches (40.0 cm) in diameter and contains 5,282 parallel, galvanized steel wires wrapped closely together in a cylindrical shape. These wires are bundled in 19 individual strands, with 278 wires to a strand. This was the first use of bundling in a suspension bridge and took several months for workers to tie together. Since the 2000s, the main cables have also supported a series of 24-watt LED lighting fixtures, referred to as "necklace lights" due to their shape.

In addition, either 1,088, 1,096, or 1,520 galvanized steel wire suspender cables hang downward from the main cables. Another 400 cable stays extend diagonally from the towers. The vertical suspender cables and diagonal cable stays hold up the truss structure around the bridge deck. The bridge's suspenders originally used wire rope, which was replaced in the 1980s with galvanized steel made by Bethlehem Steel. The vertical suspender cables measure 8 to 130 feet (2.4 to 39.6 m) long, and the diagonal stays measure 138 to 449 feet (42 to 137 m) long.

Anchorages

Each side of the bridge contains an anchorage for the main cables. The anchorages are trapezoidal limestone structures located slightly inland of the shore, measuring 129 by 119 feet (39 by 36 m) at the base and 117 by 104 feet (36 by 32 m) at the top. Each anchorage weighs 60,000 short tons (54,000 long tons; 54,000 t). The Manhattan anchorage rests on a foundation of bedrock while the Brooklyn anchorage rests on clay.

The anchorages both have four anchor plates, one for each of the main cables, which are located near ground level and parallel to the ground. The anchor plates measure 16 by 17.5 feet (4.9 by 5.3 m), with a thickness of 2.5 feet (0.76 m) and weigh 46,000 pounds (21,000 kg) each. Each anchor plate is connected to the respective main cable by two sets of nine eyebars, each of which is about 12.5 feet (3.8 m) long and up to 9 by 3 inches (229 by 76 mm) thick. The chains of eyebars curve downward from the cables toward the anchor plates, and the eyebars vary in size depending on their position.

The anchorages also contain numerous passageways and compartments. Starting in 1876, in order to fund the bridge's maintenance, the New York City government made the large vaults under the bridge's Manhattan anchorage available for rent, and they were in constant use during the early 20th century. The vaults were used to store wine, as they were kept at a consistent 60 °F (16 °C) temperature due to a lack of air circulation. The Manhattan vault was called the "Blue Grotto" because of a shrine to the Virgin Mary next to an opening at the entrance. The vaults were closed for public use in the late 1910s and 1920s during World War I and Prohibition but were reopened thereafter. When New York magazine visited one of the cellars in 1978, it discovered a "fading inscription" on a wall reading: "Who loveth not wine, women and song, he remaineth a fool his whole life long." Leaks found within the vault's spaces necessitated repairs during the late 1980s and early 1990s. By the late 1990s, the chambers were being used to store maintenance equipment.

Towers

The bridge's two suspension towers are 278 feet (85 m) tall with a footprint of 140 by 59 feet (43 by 18 m) at the high water line. They are built of limestone, granite, and Rosendale cement. The limestone was quarried at the Clark Quarry in Essex County, New York. The granite blocks were quarried and shaped on Vinalhaven Island, Maine, under a contract with the Bodwell Granite Company, and delivered from Maine to New York by schooner. The Manhattan tower contains 46,945 cubic yards (35,892 m3) of masonry, while the Brooklyn tower has 38,214 cubic yards (29,217 m3) of masonry. There are 56 LED lamps mounted onto the towers.

Each tower contains a pair of Gothic Revival pointed arches, through which the roadways run. The arch openings are 117 feet (36 m) tall and 33.75 feet (10.29 m) wide. The tops of the towers are located 159 feet (48 m) above the floor of each arch opening, while the floors of the openings are 119.25 feet (36.35 m) above mean water level, giving the towers a total height of 278.25 feet (84.81 m) above mean high water.

Caissons

The towers rest on underwater caissons made of southern yellow pine and filled with cement. Inside both caissons were spaces for construction workers. The Manhattan side's caisson is slightly larger, measuring 172 by 102 feet (52 by 31 m) and located 78.5 feet (23.9 m) below high water, while the Brooklyn side's caisson measures 168 by 102 feet (51 by 31 m) and is located 44.5 feet (13.6 m) below high water. The caissons were designed to hold at least the weight of the towers which would exert a pressure of 5 short tons per square foot (49 t/m2) when fully built, but the caissons were over-engineered for safety. During an accident on the Brooklyn side, when air pressure was lost and the partially-built towers dropped full-force down, the caisson sustained an estimated pressure of 23 short tons per square foot (220 t/m2) with only minor damage. Most of the timber used in the bridge's construction, including in the caissons, came from mills at Gascoigne Bluff on St. Simons Island, Georgia.

The Brooklyn side's caisson, which was built first, originally had a height of 9.5 feet (2.9 m) and a ceiling composed of five layers of timber, each layer 1 foot (0.30 m) tall. Ten more layers of timber were later added atop the ceiling, and the entire caisson was wrapped in tin and wood for further protection against flooding. The thickness of the caisson's sides was 8 feet (2.4 m) at both the bottom and the top. The caisson had six chambers: two each for dredging, supply shafts, and airlocks.

The caisson on the Manhattan side was slightly different because it had to be installed at a greater depth. To protect against the increased air pressure at that depth, the Manhattan caisson had 22 layers of timber on its roof, seven more than its Brooklyn counterpart had. The Manhattan caisson also had fifty 4-inch-diameter (10 cm) pipes for sand removal, a fireproof iron-boilerplate interior, and different airlocks and communication systems.

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