FORTH BRIDGE MAP

FORTH BRIDGE MAP

LONGEST STEEL CANTILEVER IN THE WORLD 1890-1917

Crossing Firth of Forth, Queensferry, Scotland Designers/Engineers Benjamin Baker, John Fowler Completed 1890 Span 1,710 feet (521 meters)

Material Steel Type Cantilever truss

Bold and unadorned, the Forth trailblazed a new understanding of structural beauty.

A monument of the Victorian age, the Forth Bridge over the Forth River in eastern Scotland was the first large-span bridge to be built entirely of steel. Once completed, it shattered all records for length, height, and the sheer volume of materials used. The earliest multi-span cantilever bridge, it is also one of the longest, with a total length of 1.6 miles (2.5 kilometers).

It was co-designed by engineers Sir Benjamin Baker (1840-1907) and Sir John Fowler (1817-1898). Like James B. Eads, Baker would build many types of structures but only one bridge, and it would be his magnum opus. Highlights of his varied career include the design, with Fowler, of London’s first underground railways; construction of a ship to transport Cleopatra’s Needle, an obelisk, from Egypt to London; and the damming of the Nile at Aswan.

FORTH BRIDGE MAP Photo Gallery




Baker was not the first to attempt bridging the Firth of Forth, which lay critically in the path of the rail route from Edinburgh to Dundee. Thomas Bouch had been commissioned to build the Forth bridge and another across the Firth of Tay. The first built was the Tay in 1878; a year later, the bridge collapsed in a gale while a train was crossing, leaving at least sixty dead (see here). Bouch’s career was ruined and, not surprisingly, his design for the Forth crossing was dropped.

The [Forth Bridge] has often been criticized as being overbuilt; but this is not so. It is simply the very essence of strength.

DAVID PLOWDEN, BRIDGE MAPS: THE SPANS OF NORTH AMERICA, 1974

Determined not to repeat the engineering mistakes that led to the Tay catastrophe, Baker and Fowler designed the bridge to withstand wind pressure of 56 pounds per foot, nearly five times the resistance of the Tay. They decided to use steel (newly legal in Britain as a building material) for its superior strength, in a cantilever design. Earlier, in a series of articles on long-span rail bridges published in the British journal Engineering, Baker had concluded that cantilevers were the most efficient structures for long spans.

In a cantilevered bridge, a rigid beam projects from a base, much like a branch from a tree trunk, to support the span. The Forth consists of three doublecantilever towers that rise 361 feet (110 meters) above round granite piers, with cantilever arms to each side. Each arm projects 679 feet (207 meters) from the towers, and they are linked together by two suspended girder spans, each 351 feet (107 meters) long, resulting in three spans, each 1,710 feet (521 meters). One of the massive towers was built on Inchgarvie, a small midstream island; two more were built on the Fife and Queensferry sides.

Baker arranged a living model of a cantilever bridge to assuage safety concerns.

In homage to the cantilever’s ancient Asian origins, Baker placed Kaichi Watanabe, his Japanese assistant, in the center.

Much ado was made of the design among the general public: its safety, its cost (at that time an astronomical $15 million), and above all, its distinctive industrial aesthetic, painted a bold red. Although Victorian tastemaker William Morris deemed the Forth the “supreme specimen of all ugliness,” both Baker and Fowler were knighted upon its completion. A century later, UNESCO affirmed the Forth’s structural and aesthetic value, inscribing it on the 2015 World Heritage List as a “Category A” property, which affords it the highest level of protection.

Standing at Baker’s side as the Prince of Wales declared the bridge open in 1890 was Gustave Eiffel, who had completed his landmark Parisian tower the year before. Like the Eiffel Tower, the Forth Bridge is pure structurehaving no unnecessary partsand endures as both a work of art and an icon of man’s mastery over the power of the wind.

In this 1888 construction photo, an elaborate, visually dense configuration of ties and struts braces the giant tubes, 12 feet (3.7 meters) in diameter, that rise above the waterline. Below, a contemporary view.

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