By P.C.Helwig
Telegram Special for Engineering Week: March 3/2001
Have you ever traveled on Route 91 between Colinet and Placentia? Did you stop for a visit to Cataracts Provincial Park? If you didn’t, you should have – because you would have discovered the beautiful Cataracts Bridge (see Photo 1), which is the centrepiece of the Park. This elegant structure was built exactly 75 years ago. The contractor was H. Simmons, from the Colinet area, and design engineer Rudolph Cochius, apparently from Montreal.
The arch is a structure of strength and beauty and of ancient lineage. Builders of ancient times had few choices of building materials. Their preferred building materials for durable construction were stone or fired bricks rather than wood; since wooden structures were vulnerable to fire, rot and termites. Simple structures in stone could only span a few metres, the extent of a single slab, since stone is weak is tension. Ancient builders discovered that this shortcoming of stone, or masonry construction, could be overcome if the structure was formed in a curved or “arched” shape, with each stone supported by its neighbor. With the proper shape, external loads would be supported entirely in compression by the stones forming an arch ring of wedge-shaped (voussoir) stones, thereby benefiting from the great strength of stone in compression. This type of design permitted very much larger spans between supporting pillars and abutments than was possible for simple stone structures.
Historians differ in their opinions about the discoverers of the principle of the arch; some suggest the Sumerians of Mesopotamia (ca. 14th century B.C.) but most credit the Etruscans (ca. 5th century B.C.). However, it was the Roman engineers, who capitalized on the advantages of arch structures to build some of the most useful and enduring structures of all time. Consider the Puente Romano at Alcántara, Spain, (see Photo 2) built by Caius Julius Lacer, in 104 A.D. for Emperor Trajan and still in use after almost 1900 years. Another spectacular structure is the Pont du Gard Aqueduct (see Photo 3) in France, built in 18 B.C. to supply water to Nemansus (now Nîmes). It operated reliably for about 300 years, eventually ceasing to function through lack of maintenance.
The Romans also perfected construction of the dome, a three dimensional form of the arch. Their greatest dome is the dome of the Pantheon (Temple for all the Roman Gods) in Rome that was built in A.D. 102 for Emperor Hadrian. In 609 it was rededicated as a church to Madonna and All the Martyrs and is still in service today. With a diameter of 43.3 m (142 ft) it is slightly larger than the dome of St. Peters, in Rome and still one of the largest, if not the largest, masonry dome ever built.
For all their accomplishments, it appears that the Romans never developed a scientific understanding of the structural behaviour of arches, and that their understanding and rules of practice were entirely derived from practical experience.
The first concerted attempts to develop the science of arch behaviour were not taken up until the 1700’s, when this question was explored, both theoretically and experimentally, by the greatest engineers of that era, notably – Hooke, Coulomb and Castigliano. The challenge was to apply the new rules of Newtonian mechanics and elasticity to describe the behaviour of the masonry arch. However, it wasn’t until a century later – the mid 1800’s that a complete rational design method was available in the standard engineering text books. Co-incidentally, about the time that the masonry arch construction was losing favour to construction in other materials, cast iron, steel and concrete!
Interestingly, the study of masonry arch bridges was revived in the 1940’s when military planners and highway engineers in Britain became concerned about the strength of aging masonry arch bridges, built in the horse and buggy era, to support modern traffic loads. Prof. Jacques Heymann of Cambridge University extended this work in the 1980s, using modern plastic analysis and was able to show that 90% of Britain’s 70,000 masonry arch bridges are safe for modern traffic. To replace them all would have cost about $14 Billion (CDN).
Arch dams form another interesting category of arch structures where the applied load is transferred by arch action into the valley walls. While the earliest arch dams date back to the 1600’s in Spain, technology of arch dam design and construction was largely developed in the twentieth century.
The modern arch dam, built in concrete, is a structure of complex geometry and subject to a variety of loading conditions, from water, ice and temperature. Now-a-days, arch dam design is always carried out with the aid of computers. The arch dam is the preferred design where a river is confined in a gorge or steep sided valley. Arch dams figure among the highest dams ever built, such as Inguri (Republic of Georgia) 272 m, Vajont (Italy) 262 m and Ertan (China) 245 m. Paradise River Arch Dam, completed in 1988, near Monkstown, (see Photo 4) is small compared to these giants, but at 43 m in height, it is 78 % as tall as Confederation Building. The volume of concrete required in its construction was 3,240 m³ compared to about 15,000 m³ that would have been required if constructed as a conventional concrete gravity dam. Except for the parapet walls and spillway overhang, no reinforcing steel was used in its construction.
Therefore, in addition to strength and beauty a further attribute of arch construction is efficiency!
Article contributed by Phil Helwig, P.Eng. AMEC E&C Services Limited. Phil was the designer of record for the Paradise River Arch Dam. (Phil can be contacted at hydrophil2003@yahoo.ca)
More information about arches can be found from the following sources.
a) Book/Magazines:
“Testing Times for Arches”
by Bill Harvey
New Scientist – May 15, 1986 issue.
“Bridging: Discovering the Beauty of Bridges”
by R.S. Cortright
available from
American Society of Civil Engineers
(www.asce.org)
“The Masonry Arch”
by Jacques Heyman
Wiley and Sons
Rexdale, Ontario
A basic knowledge of calculus and statics is required to understand this book.
b) Video Tape:
“Building Big”
5-part video series
$69.95 U.S.
Available from
American Society for Civil Engineers
(or wait for a re-run on PBS Television, one episode features domes, another bridges).
c) On the internet:
www.britanica.com/arches about arch structures in general
www.myron.sjsu.edu/ROMEWEB/ENGINEER about Roman engineering
www.usbr.gov/cdams about U.S. arch dams
www.ot.nimes.fr about Pont du Gard Aqueduct
d) Government of Newfoundland
Ms. Lynn Evans
Director of Public Relations
Dept. of Works, Services and Transportation
Confederation Building
St. John’s, NF Tel: (709) 729-3015 about Cataracts Bridge
e) Newfoundland and Labrador Hydro
Mr. Trevor Arbuckle, P.Eng.
Manager – Hydro Generation
Bay d’Espoir, NF (709) 882-2551 about Paradise River Arch Dam
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