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Forth Rail Bridge

Introduction

Completed in 1880, the Forth Bridge connects Edinburgh, Scotland’s capital city, with Fife. After Thomas Bouch’s Tay Bridge collapsed in 1879, his design for the Forth Bridge was rejected, and Benjamin Baker and Sir John Fowler were chosen to create a new design for the structure. The result was an iconic steel cantilever bridge. This engineering feat successfully accomplished the goal of constructing a safe means of connecting railways across a long span. Overall, the Forth Bridge represents an efficient design through its use of materials; an economical design through its ability to connect both commerce and tourism; and an elegant design, accentuated by its pure form and smooth lines.

Forth Rail Bridge

Structural Description	Forth Rail Bridge
Date Completed	1890
Location	South Queensferry and North Queensferry, Scotland
Carries	Rail traffic
Design Type	Cantilever bridge
Architects	Benjamin Baker and Sir John Fowler
Total Length	8,276 ft
Material	Steel
Cantilever Length	680 ft
Longest Single Span	350 ft

Cantilever Bridge Human Model

Structural Description

After the collapse of the Tay Bridge, Baker and Fowler set out to design a bridge that would be able to withstand the elements. This inspired the engineers to base their design on the notoriously safe form of a cantilever bridge, a more complex version of the truss bridge.

The Forth Rail Bridge adopts the form of a cantilever railway bridge with three massive double-cantilevers. At the time of its construction in 1890, the Forth Rail Bridge had the longest cantilever span in the world. Its longest single span is reported at 350 ft. The design of the Forth Rail Bridge consists of a pair of cantilevers protruding from the two main towers. The diagonal steel tubes that support the beams also support the central span. The two outside cantilever ends carry around 1000 tons and “counter-balance” the weight of the live load and suspended span.

The Forth Rail Bridge also serves as one of the first structures comprised primarily of steel. The construction of this bridge required 54,000 tons of steel. Thus, not only did the Forth Rail Bridge utilize one of the most advanced structural techniques of its time, but it also relied on one of the most modern materials of the time. Since the design required a simple design with large sub-elements holding large load amounts, a strong material, such as steel, was necessary.

Qualifications as Structural Art

The engineers of the Forth Bridge succeeded in creating an efficient design for the bridge. Since the public lost confidence in engineering with the collapse of the Tay Bridge, engineers Baker and Fowler sought to create the safest bridge they could fathom. Consequently, they adopted the form of a balanced, cantilever bridge constructed out of steel. Some of the scientific advances in efficiency exist in the use of the continuous girder principle, which ensured a more effective distribution of self-weight, decreasing the amount of structural materials required in construction; and the full triangulation of the internal geometry of the structure. The Forth Bridge’s design also attests to the strength and efficiency of steel, especially due to the small amount of sub-elements carrying large loads and the large span across the Firth of Forth. The Forth Bridge required 54,000 tonnes of steel for its construction. It must also be noted that the Forth Bridge was the first bridge to be constructed primarily of steel, further attesting to the scientific advancements and pioneering of new materials by Baker and Fowler.

While the Forth Bridge was hugely expensive to build, its initial cost of $15 million can be offset by its extensive use by society for both commerce and tourism. Thus, the Forth Bridge’s economical significance is evident in the extensive use it receives by society. The Forth Bridge was initially constructed to simplify the rail route from Edinburgh to Dundee. Today, the Forth Bridge connects several major train routes and receives an estimated daily traffic of 180-200 trains per day. Furthermore, the Forth Bridge’s strong, balanced construction helped to restore public confidence in structural engineering after the Tay Bridge disaster.

While many have debated the aesthetic appeal of the Forth Bridge, its true elegance lies in its pure, simplistic form. Baker and Fowler succeeded in designing a typical cantilever truss bridge in a more, unique way. While the bridge profile emphasizes the smoothness of line, the denser, complex interior resembles other structures of the 1880s, such as the Eiffel Tower. The Forth Bridge serves as a representation of engineering as an art form, since it emphasizes the pure geometric forms and linear qualities of structures without the distraction of unnecessary decoration. In addition to the symbolic design of the Forth Bridge, it is also a landmark for Scotland. The Collins Encyclopaedia of Scotland describes the Forth Bridge as “the one immediately and internationally recognized Scottish landmark.”

I experienced the Forth Bridge while studying abroad at the University of St. Andrews. I took the East Coast train line across the Firth of Forth numerous times and was always struck by the unique appearance of the Forth Bridge. While not conventionally beautiful, the Forth Bridge, in its bare form, showcases the ingenuity of the Baker and Fowler’s design and emphasizes the elegance of dynamic field of civil engineering.