Akashi Kaikyo Bridge

Brief information

Location: Kobe and Awaji-shima, Japan

Completion Date: 1998

Cost: $4.3 billion

Length: 12,828 feet

Type: Suspension

Purpose: Roadway

Materials: Steel

Longest Single Span: 6,527 feet

Engineer(s): Honshu-Shikoku Bridge Authority

In 1998, Japanese engineers stretched the limits of bridge engineering with the completion of the Akashi Kaikyo Bridge. Currently the longest spanning suspension bridge in the world, the Akashi Kaiko Bridge stretches 12,828 feet across the Akashi Strait to link the city of Kobe with Awaji-shima Island. It would take four Brooklyn Bridges to span the same distance! The Akashi Kaikyo Bridge isn't just long -- it's also extremely tall. Its two towers, at 928 feet, soar higher than any other bridge towers in the world. The Akashi Strait is a busy shipping port, so engineers had to design a bridge that would not block shipping traffic. They also had to consider the weather. Japan experiences some of the worst weather on the planet. Gale winds whip through the Strait. Rain pours down at a rate of 57 inches per year. Hurricanes, tsunamis, and earthquakes rattle and thrash the island almost annually. How did the Japanese engineers get around these problems? They supported their bridge with a truss, or complex network of triangular braces, beneath the roadway. The open network of triangles makes the bridge very rigid, but it also allows the wind to blow right through the structure. In addition, engineers placed 20 tuned mass dampers (TMDs) in each tower. The TMDs swing in the opposite direction of the wind sway. So when the wind blows the bridge in one direction, the TMDs sway in the opposite direction, effectively "balancing" the bridge and canceling out the sway. With this design, the Akashi Kaikyo can handle 180-mile-per-hour winds, and it can withstand an earthquake with a magnitude of up to 8.5 on the Richter scale!

Brooklyn Bridge

Brief information

Location: Manhattan and Brooklyn, New York, USA

Completion Date: 1883

Cost: $18 million

Length: 3,460 feet

Type: Suspension

Purpose: Roadway

Materials: Steel, granite

Longest Single Span: 1,595 feet

Engineer(s): John A. Roebling, Washington A. Roebling

Considered a brilliant feat of 19th-century engineering, the Brooklyn Bridge was a bridge of many firsts. It was the first suspension bridge to use steel for its cable wire. It was the first bridge to use explosives in a dangerous underwater device called a caisson. At the time it was built, the 3,460-foot Brooklyn Bridge was also crowned the longest suspension bridge in the world. But the Brooklyn Bridge was plagued with its share of problems. Before construction even began, the bridge's chief engineer, John A. Roebling, died from tetanus. The project was taken over and seen to its completion by his son, Washington Roebling. Three years later, Roebling developed a crippling illness called caisson's disease, known today as "the bends." Bedridden but determined to stay in charge, Roebling used a telescope to keep watch over the bridge's progress. He dictated instructions to his wife, Emily, who passed on his orders to the workers. During this time, an unexpected blast wrecked one caisson, a fire damaged another, and a cable snapped from its anchorage and crashed into the river.

Despite these problems, construction continued at a feverish pace. By 1883, 14 years after it began, Roebling successfully guided the completion of one of the most famous bridges in the world -- without ever leaving his apartment.

Fast Facts:

1. Although he was physically able to leave his apartment, Washington Roebling refused to attend the opening celebration honoring his remarkable achievement.

2. The bridge opened to the public on May 24, 1883, at 2:00 p.m. A total of 150,300 people crossed the bridge on opening day. Each person was charged one cent to cross.

3. The bridge opened to vehicles on May 24, 1883, at 5:00 p.m. A total of 1,800 vehicles crossed on the first day. Vehicles were charged five cents to cross. Today, the Brooklyn Bridge is the second busiest bridge in New York City. One hundred forty-four thousand vehicles cross the bridge every day.

Tower Bridge

Tower Bridge is a bridge in London, England, over the River Thames. It is close to the Tower of London, which gives it its name. It is occasionally incorrectly referred to as London Bridge, which is in fact the next bridge upstream.

In the second half of the 19^th century increased commercial development in the East End of London led to a requirement of a new river crossing downstream of London Bridge. However, a traditional bridge could not be built because it would cut off access to the port facilities situated at that time in the Pool of London, between London Bridge and the Tower of London. A tunnel beneath the Thames, the Tower Subway was opened in 1870, but it could only accommodate pedestrian traffic.

A Special Bridge or Subway Committee was formed in 1876 to find a solution to the river crossing problem. It opened the design of the new crossing to public competition. Over 50 designs were submitted including one from civil engineer Sir Joseph Bazalgette. However, the evaluation of the designs was surrounded by controversy, and it was not until 1844 that a design submitted by Horace Jones, the City Architect, was finally approved. Jones’ design was for a bascule bridge 800 feet (244 m) in length with two towers each 213 feet (65 m) high, built on piers.

The central span of 200 feet (61m) between the towers is split into two equal bascules, or leaves, which can be raised to an angle of 86 degrees to allow river traffic to pass through. Although each bascule weighs over 1, 000 tons, they are counterbalanced to minimize the force and time required to raise them, and they can be raised in under one minute. The original hydraulic raising mechanism was powered by pressurized water stored in six accumulators. Water was pumped into the accumulators by steam engines. Although the bridge is raised today electrically, the original steam engines are preserved as a visitor attraction.

Construction of the bridge started in 1886 and took 8 years, employing 5 major contractors and 432 construction workers. Two massive piers containing over 70, 000 tons of concrete were sunk into the river bed to support the construction. Over 11, 000 tons of steel provided the framework for the towers and walkways. This was then clad in Cornish granite and Portland Stone, both to protect the underlying steelwork and to give the bridge a more pleasant appearance. Jones died in 1887, and his chief engineer, Sir John Wolfe-Barry, took over the project.

Wolfe-Barry replaced Jones’ original medieval style of façade with more ornate Victorian gothic style that makes the bridge such a distinctive landmark. The bridge was opened in 1894. The official opening ceremony was conducted by the Prince of Wales, the future King Edward VII of the United Kingdom and his wife Alexandra of Denmark.

The high-level walkways between the towers were never much used and were closed in 1910, but have now been reopened. The towers and walkways contain an exhibition about the Bridge’s history, including the original steam engines that once powered the Bridge bascules. A “Behind the Scene” tour can be booked in advance where it is possible to see the bridge’s command center (where the raising of the bridge is controlled when a vessel passes underneath). The bascules of the bridge are raised round five hundred times a year. The bridge sits almost directly above the Tower Subway, the world’s first underground tube railway (1870), which, until the Bridge was opened, was the shortest way to cross the river from Tower Hill to Tooley Sreet.