BRIDGES AND BRIDGE BUILDERS

Press, Volume CX, Issue 32406, 19 September 1970, Page 10

BRIDGES AND BRIDGE BUILDERS

A Span Of Bridges. By H. J. Hopkins. David and Charles. 288 pp. Apart from its immense value to the student of civil engineering, Professor Hopkins’s illustrated history of bridge building opens up new vista? for the lay reader. A bridge can no longer be thought of as a functional route across a chasm but must be considered as the product of great mathematical and engineering ingenuity and the sheer skill of craftsmen, not forgetting a marked aesthetic challenge. Very fine features of this book are the illustrations, diagrams to illustrate mathematical theories and sketches to show constructional variations. A great many excellent photographs are carefully placed near the appropriate reference in the text.

Introducing his book, Professor Hopkins comments that in the past there has often been needless delay between scientific discovery and engineering exploitation and this has often impeded progress. The cause has been the failure of both the scientist and the engineer to acknowledge the limitations of his own and the validity of each other’s viewpoint. Bridges can only be built in large numbers if they are economically viable and this depends upon the engineer’s mastery of his craft. But, he notes, basically bridges are not built because scientists have elegant methods of analysis, or because engineers have economic methods of design; they are built by men for men.

The first chapter discusses the uncertain origin of the arch and the magnitude of the Roman achievement in constructing arches that are still in existence today. The author goes on to examine early theories of the arch from the philosophical and theological to the rigorously mathematical and logical. It was Robert Hooke (bom 1635)—"the greatest of all philopsophical mechanics”—who discovered the catenarian arch with his theory: “As hangs a flexible cable, so, inverted, stand the touching pieces of an arch.” He cites Jean-Rodolphe Perronet (1708-94) as the father of modem bridge-building, for his excellent judgment and tenacity of purpose were founded on a belief in scientific method backed by wide experience and observation. John Smeaton (bom 1708), a notable bridge builder, was the founder of civil engineering in Britain. He coined the phrase "consultant engineer” and with five colleagues formed the Smeatonian Society of Civil Engineers. Tribute is also paid to the work of men like James Brindley, John Rennie and Thomas Telford. By the early nineteenth century, engineering was about to become "truly wedded to science.” With the development of other engineering materials, however, the stone arch for spanning large distances was nearing the end of its useful life. In a chapter on the problem of tension, Professor Hopkins describes the vita! role of timber bridges before going on to the development of cast iron, wrought iron, and then steel. He gives a short history of steel as the ironmaster, the blacksmith and the metallurgist developed it and then exaihines the uses to which the .Special mention is made of the St Louis, Forth rail, and Sydney Harbour engineer put iron and steel in bridges, bridges; and there are explanations for several notable failures. There is an interesting section on the development of suspension bridges. Although they existed about the turn of time, they did not develop fully until the mid-nineteenth century. Discussing some spectacular failures, the author notes that nowadays no major suspen-

sion bridge is built until its aerodynamic properties have been analysed by wind tunnel tests. In a section on concrete bridges, the historical outline begins with the binding agents used in mortar by the ancient civilisations. Improvements through the ages have led to modem, pre-stressed concrete. Progress has been steady but unspectacular, says Professor Hopkins. The possibilities are infinite, but there must be another breakthrough before they become realities. Research into properties of materials must continue, he urges, but warns against repetitive or unnecessary experiments. “So many exciting vistas confront us, so many exacting tasks await us, that we cannot afford *a great expense of intellectual energy’

reconquering ‘positions .. . already occupied’.”An epilogue features the economy and charm of funicular. Today, says Professor Hopkins, the funicular cable, seen and unseen, free and pre-stressed, has restored to the engineer the chance to effect economy and bring ingenuity and grace to modem bridges. Interpreted with sense and sensitivity, it gives satisfaction to the structural engineer, the scientist, the aesthete, and the “man in the street.” Professor Hopkins has been head of the department of civil engineering at the University of Canterbury since 1951 and he acknowledges the help and interest of friends and colleagues there and the benefit of study leave. There is an index and the bibliography is cited for each chapter.