Britannia Bridge - Pushing the Limits: New Adventures in Engineering - page 39

Britannia Bridge
A group portrait painted by the artist John Lucas shows an assembly of engineers and contractors
gathered around the nineteenth-century English engineer Robert Stephenson, whose hand rests on
a set of plans spread before him. In the background is an imposing structure, a partially completed
bridge constructed of huge iron tubes. It is unlike any that any other engineer would design then
or now. Yet this bridge across the Menai Strait between northwest Wales and the Isle of Angle-
sey was by far the most talked-about construction project of the late 1840s. It showed the achieve-
ment that was possible even though there was little theory about and virtually no experience with
such a structure. The immensity of the task of fabricating nearlyfive-hundred-foot-long, 1,500-ton
wrought-iron tubes and assembling them into a bridge drew considerable attention from technical
and nontechnical onlookers alike.
The site of the Britannia Bridge project was frequently the scene of gatherings of engineers and
others interested in design and construction, and Lucas's painting records only one such occasion.
Joseph Pax-ton was attending a railway-board meeting there when he made his famous sketches for
the Crystal Palace, and Isambard Kingdom Brunel no doubt gained from his visits to the Menai site
much confidence for raising the spans of his own Saltash Bridge a few years later. Stephenson's
bridge was the subject of some of the earliest photographs recording a construction project in pro-
gress, and topics by Edwin Clark, the resident engineer, and William Fairbairn, whose model tests
defined the geometry of the tubular girders, make the bridge one of the most documented engineer-
ing projects of the nineteenth century.
To today's eye, the configuration of the bridge looks utterly anomalous, without obvious structur-
al antecedents or descendants, and the apparently functionless height of its towers above the tubes
raises questions about Stephenson's engineering knowledge and intent. Still, although the structur-
ally innovative qualities of the bridge are not immediately apparent and were overshadowed within
five years of its completion, the conception and execution of the Britannia Bridge across the Menai
Strait remains one of the most significant achievements not only of the mid-nineteenth century but
also of all time. The story of the design and erection of this bridge remains relevant and instructive
for understanding and practicing engineering today.
But why Robert Stephenson failed to apply a seemingly more logical arch or suspension principle
at the site and chose instead to build his bridge out of longer, heavier, and more complex beams
than had ever been used before, and why he thus brought upon himself engineering problems of
an unprecedented magnitude, are questions with answers that lie in social and political as well as
technical considerations. The questions and answers are understandable only in a historical context.