Grand Coulee Dam - Washington State

Commenced during the Great Depression, Washington State’s Grand Coulee Dam, on the Columbia River about 88 miles (142 kilometers) west of Spokane, is a monument to engineering prowess and to the resolve of those people who for 23 years fought for its creation. The key to the Columbia Basin Irrigation Project, it provides the region with electric power, irrigation, and flood control and contributes to wildlife conservation. The Grand Coulee Dam is the largest concrete structure ever built in the United States and the nation’s largest hydroelectric facility. Its 550-foot-high (168-meter) gravity-type concrete wall, 500 feet (152 meters) thick at the base, spans a little under 1 mile (1,592 meters) and raises the water surface 350 feet above the former riverbed. Nearly 12 million cubic yards (over 9 million cubic meters) of concrete were needed to build it. Franklin Delano Roosevelt Lake (often simply called Roosevelt Lake), created by the dam, has a 600-mile (960-kilometer) shoreline and extends 150 miles (240 kilometers) to the Canadian border.

After several ruinous years of drought in the Northwest early in the twentieth century, the U.S. Reclamation Service Bureau (now the Bureau of Reclamation) considered pumping water from the Columbia River to irrigate agricultural land in eastern Washington, a region then served by artesian wells. In 1917 an Ephrata attorney named William Clapp proposed an alternative: build a high-level dam on the Columbia and raise water to the Grand Coulee, the 50-mile-long (80-kilometer) natural channel of the old riverbed, thereby opening up more than 1 million acres (403,230 hectares) of irrigated farmland. Rufus Woods, editor of the Wenatchee Daily World, publicized the notion a few months later. In 1919 the Michigan lawyer James O’Sullivan became interested enough to put it before the Reclamation Service, which directed Washington State’s Columbia Basin Survey Commission to include it in a current feasibility study focused on irrigating the basin by gravity canals from the Pend Oreille River. In the teeth of opposition from vested interests connected with the latter scheme, the dam’s protagonists managed to enthuse, among others, A. P. Davis, director of the Reclamation Service. At O’Sullivan’s prompting, Davis suggested that the state commission an objective report from Seattle engineer Willis Batchelor, who in 1921 recommended a dam on the Columbia, 220 feet (67 meters) above river level.

Several years of argument followed. In 1923 George Goethals of Panama Canal fame—apparently a paid prophet—endorsed the canal system, and two years later the federal Columbia Basin Survey Board of Engineers supported his view. But O’Sullivan, Woods, Clapp, and others unflaggingly kept the dam project alive, and in 1927 the U.S. Senate authorized the Army Corps of Engineers, under Major John Butler, to look for possible sites during a 1929 survey of the upper Columbia River. In June the Columbia River Development League was formed with Woods as president and O’Sullivan as secretary. The Wenatchee Daily World became its mouthpiece. Late in 1931 Butler told Congress that a dam was more economical than a gravity canal: besides providing irrigation and flood control, it would raise revenue from electrical energy. O’Sullivan lobbied for authorization, and the Bureau of Reclamation soon recommended development of the project, almost in the form in which it was eventually realized. In 1933 the Columbia Basin Commission was established, and the state of Washington committed $377,000 to the Grand Coulee Dam. Recently elected President Franklin D. Roosevelt allocated $63 million under the Public Works Administration—a New Deal program. Through the Great Depression men and women from all over the United States would find work at the dam site: averaging 3,000, the labor force peaked at 6,000.

Excavation began in December 1933, and seven months later a $29.34 million contract for the foundation work was awarded to MWAK, a consortium formed by Silas Mason Company of New York City; Walsh Construction Company of Davenport, Iowa; and the Atkinson-Kier Company of San Francisco. Such a large undertaking called for a complex infrastructure: high-tension power lines were set up, the Columbia River was bridged, and over 30 miles (nearly 50 kilometers) of railroad and 60 miles of sealed roads were constructed. A contractor’s town, Mason City, and Coulee Dam, a government town, were built at the site. Four years later, a consortium formed by linking MWAK and the Six Companies—Kaiser Construction of Seattle; Morrison Knudsen of Boise, Idaho; Utah Construction; J. F. Shea Pacific Bridge; and McDonald and Kahn (all of San Francisco) and General Construction Company of Seattle—won the $34.4 million contract for the completion of the dam. Their bid was 80 percent of the only other tender.

The proposed height of the dam had been determined by the rather parochial notion that the impounded water should not back up beyond the Canadian border. Then the project’s main reason for being was irrigation—there were more droughts in the early 1930s—and flood control, rather than power generation. The Pacific Northwest had plenty of electricity and there was little prospect of industrial expansion. Therefore the original designs included a 350-foot (107-meter) “low” dam about 3,500 feet (1,070 meters) long, which would bring the water surface to only 150 feet (46 meters) above the river level. Should the demand for power increase, it was intended to later raise the wall. That was flawed thinking. Achieving a tight joint between the two parts of the wall would have been difficult, even dangerous; later changes to the turbines would be costly; and it was more expedient to construct the concrete foundation of a high dam at the start of the project. So, with the approval of Congress, the contracts were redrawn in June 1935 to build the high dam to plans by John Lucian, chief designer of BuRec engineers.

The main dam was completed by 1941 and work commenced on the pumping plant and powerhouses. The entry of the United States into World War II meant dramatic changes in priorities for the dam. Power generation was given first place because the region’s aluminum industry, a large consumer of electricity, was critical to the defense effort. Six generators were commissioned at the Grand Coulee, and two more were borrowed from the incomplete Shasta Dam project in northern California. Soon after the war, construction resumed on the pumping plant and in 1951 the irrigation system was inaugurated. Six huge pumps lifted water through 280 feet (85.6 meters) from Roosevelt Lake to Banks Lake equalizing reservoir in the Grand Coulee. In 1973 two more reversible pump-generator units were installed, followed by another four late in 1983. Feeding more than 300 miles (480 kilometers) of associated canals, and nearly 5,500 miles (8,800 kilometers) of laterals, siphons, and drains, the pumps can fully supply almost 1.1 million acres (about 440,000 hectares) of formerly dry land. They are not yet being used at their full capacity.

The reversible pump-generators installed could of course be used for power generation, augmenting the already remarkable output of the Grand Coulee Dam, whose power production facilities are by far the largest in North America. Two plants, with a total of eighteen generators, were operational by 1951. A third, coming on line in 1975, increased capacity to about 7,200 megawatts. By 1978 the three were producing over 6,000 megawatts, and subsequently additional generators—the total number is now 33—have achieved an output of over 6,800 megawatts.

In the 1950s the American Society of Civil Engineers included the Grand Coulee Dam and the Columbia Basin Project among the seven civil-engineering wonders of the United States. The project has also been popularly and superlatively dubbed “the Eighth Wonder of the World,” “the Greatest Structure in the World,” “the World’s Greatest Engineering Wonder,” and “the Biggest Thing on Earth.”

Golden Gate Bridge - San Francisco, California

When it opened to traffic in May 1937, San Francisco’s Golden Gate Bridge boasted the longest single clear span in the world, a claim held true for twenty-seven years. The center span, at 4,200 feet (1,285 meters), was three times longer than the Brooklyn Bridge and 700 feet (214 meters) longer than the recently completed George Washington Bridge in New York. Including the two side spans of 1,125 feet (344 meters) and the 90-foot-wide (27.5-meter) road approaches, its total length was 8,981 feet (2,746 meters). Its towers were the tallest, its main cables the thickest and longest, its submarine foundations the largest ever built. Moreover, the foundation piers of the Golden Gate Bridge were built in

the surging currents of the sea and its superstructure was erected across a canyon through which the wind howled at speeds up to 60 mph (96 kph). And all this was achieved without government funding in the midst of a deep economic depression. Against all the odds, the Golden Gate Bridge was a brilliant answer to a whole cluster of “insoluble” problems.

On 5 August 1775 Lieutenant Don Juan Manuel Ayala of the Spanish navy sailed the San Carlos from the Pacific Ocean into San Francisco Bay through the 3-mile-long by 1-mile-wide (4.8-by-1.6-kilometer) strait now known as the Golden Gate (one Captain John Fremont of the U.S. Army Topographical Engineers named it some 60 years later after Turkey’s Golden Horn).

There is a compelling myth that the San Francisco eccentric Joshua Norton, self-styled “Norton the First, Emperor of the United States and Protector of Mexico,” decreed in 1869 that a bridge be built across the Golden Gate. The story may have become confused with his pronouncement of March 1872 ordering a bridge across the Bay between Oakland Point and Goat Island, an idea he probably gleaned from well-publicized current transportation debates. In fact, the possibility of spanning the Golden Gate was first raised in 1872 by the railroad owner Charles Crocker, who naturally wanted to build a railroad bridge. But little more was heard of the matter until July 1916.

James Wilkins, editor of the San Francisco Call Bulletin, began a campaign that provoked City Engineer Michael O’Shaughnessy to seek, nationwide, the opinion of engineers on the project. Most said a bridge could not be built; the objections raised included the width of the strait, persistent foggy conditions, high winds and ocean currents, and not least, the high cost: some forecast $100 million. However, the experienced Chicago bridge builder Joseph Baermann Strauss (1870–1938) believed that a bridge was feasible and that it could be built for under $30 million. In June 1921 he proffered a preliminary design for a railroad trestle with a cost estimated at $27 million. Then he energetically tried to convince local politicians that he was right. Although urban growth and traffic congestion led to an urgent need to cross the Golden Gate, all available state and federal finance had then been diverted to other projects.

In 1922 O’Shaughnessy, Strauss, and Edward Rainey, secretary to San Francisco’s mayor James Rolph Jr., proposed the formation of a special bridge district comprising the twenty-one affected counties to oversee financing, design, and construction of the bridge. The California State legislature passed the Golden Gate Bridge and Highway District Act in May 1923. In December 1924 the War Department authorized San Francisco and Marin Counties to construct a bridge. Despite opposition from vested interests, the Golden Gate Bridge and Highway District was immediately formed to realize the project.

Eleven engineering firms submitted proposals, and Strauss, assisted by Clifford Paine, was selected as chief engineer in August 1929. Consulting engineers Othmar Amman and Leon Moisseiff, both of New York, and Professor Charles Derleth Jr. of the University of California were appointed. The consulting architects were the husband-wife team of Irving and Gertrude Morrow. Strauss, who had never designed a suspension bridge, first proposed an inelegant cantilever-cum-suspension structure, but Moisseiff, convinced that a simple suspension bridge was possible (although such a span had never been attempted), helped refine the design that was eventually built. The architects did their part, too, designing handrails and light poles, tapering the tower portals, and designing lighting, all to emphasize the bridge’s simple beauty. And, setting aside the conventional paint colors used on bridges, they selected the distinctive “international airways orange” for which the Golden Gate Bridge is famous. That, Irving Morrow believed, would look better in the spectacular landscape and would be more visible in the sea mists for which the Bay Area is noted.

In August 1930 the War Department approved a 4,200-foot (1,285-meter) main span, 220 feet (67 meters) above the sea. Although the United States was sunk in the Great Depression, a $35 million bond issue to finance the bridge received overwhelming popular support. Contracts worth $23.8 million were let in November 1932, and construction started the following January. Over the next four years it proceeded in the face of many natural problems—rapid

sea currents, frequent fogs, and high winds—and technical ones, especially the construction of earthquake-resistant piers in 100 feet of open water. The latter was solved by building elliptical concrete fenders, 300 feet long and 155 wide (92 by 48 meters), within which the 148,000-ton (134,500-tonne) concrete piers could be poured; rising 15 feet (4.6 meters) above high-water mark, the fenders also protect the piers from the onslaught of the sea. The piers and the approach trestles were completed by December 1934 and the 121-foot-wide (37-meter), 750-foot-high (230-meter) towers were standing a little over six months later. The steel sections for the towers, fabricated in Bethlehem, Pennsylvania, were sent via East Coast seaports through the Panama Canal to McClintic-Marshall’s yards in Alameda. Then they were carried by lighters to the site, lifted by cranes, and erected by teams of riggers.

Catwalks spanned the Golden Gate by July 1935, and John A. Roebling and Sons of New Jersey began spinning the two main cables from the San Francisco and Marin anchorages four months later. Each galvanized steel cable is 36.375 inches (920 millimeters) in diameter, comprising 61 strands of 452 wires. They were completed by March 1936, and the roadway steel was placed from June through November, allowing construction of the flexible in situ concrete road deck, finished by April 1937. The bridge was opened to pedestrian traffic on 27 May 1937 and to vehicles at noon the following day. It had been achieved ahead of schedule and under budget. An estimated 200,000 people walked over it on the first day, and a weeklong Golden Gate Bridge Fiesta celebrated the event with fireworks, parades, and other entertainment.

German Pavilion - Barcelona, Spain

The German Pavilion at the Barcelona Universal Exhibition of 1929, designed by Ludwig Mies van der Rohe, is the first built expression of what he called “the architecture of almost nothing.” About a decade earlier he had designed projects for multistory tower blocks, crystal prisms whose uninterrupted glass skins enveloped slender steel frames. They were just ideas, but the Barcelona Pavilion, as it is popularly known, set a standard—some would say, generated a fashion—for the austere minimalist architecture that would be dubbed the International

Style at an exhibition in New York’s Museum of Modern Art just three years later. Esthetically, it was a major development in modern architecture.

The temporary single-story building, constructed in 1928–1929 and opened in May 1929, exhibited nothing but itself, a pristine, new kind of architectural space. The only purpose it had to serve was brief: to house a reception for the king and queen of Spain when they attended the official opening. For them, Mies designed the now-famous Barcelona chair, handcrafted from stainless steel and covered in white pigskin. The commanding location of the pavilion took advantage of the flow of visitors between the other display halls and the rest of the exhibition. It stood on a low travertine platform that gave a good view of the grounds and beyond to the city. The northern half of the podium was covered by a flat roof, carried on two rows of equally spaced, cruciform steel columns and an asymmetrical series of discontinuous walls of marble, glass, and onyx, parallel or perpendicular to each other. None of the rectilinear spaces thus formed was fully defined—that is, they formed an open plan—and the interior and the exterior of the pavilion were treated in the same way. This was the kind of spatial organization that Mies had observed in the work of Frank Lloyd Wright twenty years earlier. The attention to reductive detail and fine finish was the German’s own. His most often quoted axioms were “Less is more” and “God is in the details.”

A minimalist approach probably was justifiable for the Barcelona Pavilion because the building had no set functional program. It was in essence architecture as sculpture, an end in itself. But Mies also applied the philosophy to more functionally complex buildings. An almost contemporary example was the Tugendhat House in Brno, Czechoslovakia; commissioned in 1927, it was completed in 1930. Then in 1945 he designed a small weekend house in 9 acres (3.6 hectares) of woodland and fields on the bank of the Fox River south of Plano, Illinois, for his mistress, the Chicago physician Edith Farnsworth—a single room partitioned by a core that includes a kitchen, a fireplace, bathrooms, and a service area. The house is a mechanically perfect cuboid carried on a skeleton frame of sandblasted steel channels and defined by 9-foot (2.7-meter) glass walls and concrete floor and roof slabs. Interior finishes include a travertine floor, natural timber fittings, and a stainless-steel counter in the kitchen. Such obsession with refinement, causing Mies to take his architecture of almost nothing almost to the limit, did little to create a comfortable living space. It may have been admirable architecture; it was hardly congenial. It is emphasized that the issue was unimportant in the case of the German Pavilion at Barcelona, which was built simply to be seen and admired—as someone called it, “a place for contemplative lingering.”

When the Barcelona Universal Exhibition closed, the German government tried to sell the pavilion to the municipality, without success. It was taken down in January 1930. It was not until 1983 that the Mies van der Rohe Foundation was established to reconstruct the building in Montjuïc Park, Barcelona, under the superintendence of the architects Cristian Cirici, Fernando Ramos, and Ignasi de Solà-Morales.

Geodesic domes

A geodesic dome is a fractional part of a geodesic sphere, composed of a complex network of triangles. The archetypal geodesic sphere is made up of twenty curved triangles, each corresponding to one facet of the icosahedron, a twenty-faceted solid geometrical figure. The more complex the network (that is, the smaller the triangles), the more closely the form approximates a true sphere. Using triangles of varying size, a sphere can be symmetrically divided by thirty-one great circles (the largest that can be traced on the surface of a sphere). The triangles form a self-bracing framework that develops structural strength with a minimum amount of material. Thus, the geodesic dome combines the sphere (the most efficient container of volume per unit of surface area) with the polyhedron, which has the greatest strength per unit of mass. Developed in the first half of the twentieth century, it provided a completely new way of building light, transportable structures with efficient thermal and wind-resisting properties. For example, the aluminum-and-Teflon geodesic “Pillow Dome” designed by Jay Baldwin is a permanent insulated structure that can resist 135-mph (216-kph) winds and carry tons of snow; it weighs only 0.5 pound per square foot (2.43 kilograms per square meter).

The world’s first geodesic dome was assembled on the roof of the Carl Zeiss Optical Works in Jena, Germany, in 1922. The 52-foot-diameter (16-meter) structure, designed by Zeiss’s chief designer, Dr. Walter Bauersfeld, was necessary to test what he no doubt regarded as his more important invention, the planetarium projector. He built a complex skeleton of 3,480 light iron rods, accurate in length to 0.002 inch (0.05 millimeter) to form a highly subdivided icosahedron. Twenty-five years later, the American genius Richard Buckminster Fuller (1895–1983) independently derived his geodesic dome (patented 29 June 1954) from general principles, and he is generally credited with the invention of the form.

Fuller was deeply interested in the issues of shelter and housing, and by the end of World War II he had developed industrialized prototypes of the now-famous Dymaxion Houses, which he built for the Beech Aircraft Company in Wichita, Kansas. He then moved his attention to the construction of domes, because he believed that they reflected “nature’s coordinate system” and therefore provided the optimally efficient way to enclose space. Through much of the 1940s he worked on small models of spheres or part-spheres made up of intersecting great circles, just as Bauersfeld had done. Fuller coined the name “geodesic dome” because the arcs of great circles are known as geodesics (Greek, “earth dividing”). In 1948 he seized the chance to take part in the summer school of Black Mountain College in North Carolina, taking with him the material needed to build a large-scale geodesic dome. Applying engineering strategy that he dubbed “tensegrity” (a contraction of “tensional integrity”)—Fuller loved to invent words, too—he devised a system that depended on a continuous tension element rather than “discontinuous local compression members.” He soon built a number of geodesic domes.

In 1953, Fuller built his first commercial dome, for the Ford Motor Company, and it was followed in 1954 by a 42-foot-diameter (12.8-meter) cardboard shelter in his exhibit at the Milan Triennale in Italy; it was awarded the Grand Prize. A few large-scale applications included the Union Tank Car dome (1958). In I960 Fuller proposed a 2-mile-wide (3.2-kilometer), 200-foot-high (60-meter), temperature-controlled geodesic dome to enclose part of New York’s Manhattan Island, claiming that the savings of snow-removal costs would amortize the cost within 10 years. On a more practical level, his domes covered military projects including sensitive radar installations (“radomes”), emergency shelters, and mobile housing. They were and are also used for weather stations, industrial workshops, and greenhouses. One was even proposed for a cinema, in collaboration with the architect Frank Lloyd Wright.

Fuller’s magnum opus is the former United States Pavilion at Expo 67 in Montreal, Canada, designed with Shoji Sadao. The huge, lacy dome, framed with steel pipes enclosing 1,900 molded acrylic panels, has a diameter of 250 feet (76.5 meters) and stands 200 feet (60 meters) high, “weightless against the sky.” It has been adapted by Environment Canada and the city of Montreal and is now known as the Biosphere, an environmental water-monitoring center on the St. Lawrence River.

Gateway Arch

The 630-foot-high (192-meter) stainless-steel Gateway Arch rises from a wooded park within what became the Jefferson National Expansion Memorial Park on the bank of the Mississippi in St. Louis, Missouri. Taller than the Washington Monument in the national capital and twice as high as the Statue of Liberty, the sleek and seamless Gateway Arch (now known as the St. Louis Arch) is a major achievement of twentieth-century architecture and structural engineering.

A decision was taken in 1935 to establish a national monument in St. Louis, Missouri, to commemorate the nineteenth-century westward expansion that pursued Thomas Jefferson’s dream of a continental United States. A large tract of riverfront land in the older part of the city was acquired and cleared, but the project was interrupted by the country’s involvement in World War II. With the return to peace, in 1947–1948 the Jefferson National Expansion Memorial Association sponsored a design competition for an appropriate monument. The Finnish-American architect Eero Saarinen was awarded first prize.

Work on design development began in 1961, the year of the architect’s death, the project being managed by his firm, Eero Saarinen Associates. Fred Severud of the structural engineering practice Severud, Elstad, Krueger and Associates undertook a feasibility study about the buildability of the daring concept, and Dr. Hannskarl Bandel generated exacting calculations for the weighted catenary (an inverted version of the curve of a suspended chain) that forms the basis of the structure. Bruce Detmers and other architects converted the mathematics into working drawings.

The main contractor was MacDonald Construction, and the steel was fabricated and erected by Pittsburgh-Des Moines Steel. The first concrete pour for the massive 60-foot-deep (18-meter) foundations took place late in June 1962 and construction of the arch itself began eight months later. The span of the arch is the same as its height, and the composite structure consists of 142 welded, stainless-steel-faced sections of equilateral triangular cross sections. The length of their side at the base is 54 feet (16.5 meters), and the sections are 12 feet (3.6 meters) high; at the top, they have a side length of 17 feet (5.4 meters) and are 8 feet (2.4 meters) high. The legs have double walls with an inner skin of 0.375-inch-thick (about 10-millimeter) carbon steel and an outer skin of stainless steel, set 3 feet (90 centimeters) apart; at the 400-foot (120-meter) level, the gap between the skins reduces to less than 8 inches (20 centimeters). For the first 300 feet the space between the walls is filled with concrete; above that, to the crown of the arch, the structure is braced with steel stiffeners. It is clear that the engineering design is highly complicated, but all that can be seen from the outside is the sheer skin of polished stainless steel.

The wall components were fabricated and bolted together in Pennsylvania and transported to St. Louis by rail. On-site, the triangular sections were welded by highly skilled tradesmen. In July 1998 their specialized work was recognized by the American Welding Society’s Historical Welded Structure Award. The completed 50-ton (45.5-tonne) double-walled sections were transported to the site on a specially designed railroad car and lifted into place. For the first 72 feet (21.6 meters), conventional cranes on the ground were used; above that, purpose-made creeper cranes handled the sections. In effect, each leg of the arch was a vertical cantilever and therefore had no need of scaffolding. But when the 530-foot (162-meter) level was reached, a steel stabilizing truss was lifted into place and fixed to brace the two legs while the remaining twenty-one sections and the central “keystone” were located. The arch was completed on 28 October 1965. As the creeper cranes moved back to the ground, their tracks were dismantled and bolt holes in the stainless-steel surface were made good.

In 1967–1968 passenger trams were constructed in the hollow core of the arch, to carry visitors—there were 4 million in 1999—to a 140-person observation platform at the top, where tiny plate-glass windows

give access to views up to 30 miles (50 kilometers) eastward and westward. The total cost of the arch, including $2 million for the internal transportation system, was $13 million. The building received the American Institute of Architects 25 Year Award in 1990.

Galerie des Machines (Gallery of Machines)

The Galerie des Machines was designed for the 1889 Paris International Exhibition—L’Exposition Tricolorée—by architect Ferdinand Dutert (1845–1906) in collaboration with engineer Victor Contamin (1840–1893). It was remarkable for its vast exhibition hall, made possible by exploiting a new structural innovation, the three-pin hinged or portal arch. Although used previously in bridge construction, this was the first application of the arch on such a large scale.

The concept of exhibiting to the world a nation’s resources and achievements in art, science, and industry has its origins in ancient times. According to the Bible, the fifth-century-b.c. Persian king Xerxes I showed the riches of his kingdom for five months. More recently, fine art exhibitions were mounted, but such shows gradually added inventions. Following the Industrial Revolution and the consequent rise of mechanization, expositions demonstrating industrial progress were held regularly. Before 1900, no fewer than thirteen were organized in the manufacturing centers and capitals of Europe. They were popular events and buildings were purpose-built for them; perhaps the most renowned was Joseph Paxton’s revolutionary Crystal Palace, built in London for the Great Exhibition of 1851. In turn, many of those structures became showpieces of structural and technological advances.

Following the celebrated success of the Great Exhibition and Britain’s abandonment of such shows after 1862, the French seized the opportunity to take center stage, so to speak. Between 1855 and 1900 five international exhibitions were presented in Paris, boasting of the progress of French industry and the country’s rapid transition from a predominantly agrarian to an industrial economy. By 1889 when L’Exposition Tricolorée commemorated the centenary of the French Revolution, the size and variety of machines and other items offered for display were so great that a range of special exhibition spaces was needed. A formal entrance structure was built—the famed Eiffel Tower—and two long galleries were dedicated to the fine and liberal arts and a third to clothing and furniture exhibits. Beyond them and behind the Dome Central that terminated the long axis of the showground rose the vast and impressive Galerie des Machines.

Built principally of iron and glass, the structure employed a three-hinged or portal arch spanning a phenomenal 375 feet (114 meters); the widest previously achieved was 242 feet (74 meters) in the train shed of St. Pancras Station, London, about 25 years earlier. The display hall was 1,270 feet (380 meters)

long, and its colossal proportions provided the largest unobstructed floor area of any building in history—an ideal setting in which to show the world the massive engines, transformers, dynamos, and other wonders of the age. The 20 prefabricated wrought-iron trusses of the main span comprised two half-arches, hinged at their meeting point 143 feet (45 meters) above the floor. They curved and tapered to a slender wedgelike base, where their loads were distributed to the ground through a hinged joint. The apparent lightness with which they touched the ground defied the conventional, rational notion that the base was the principal load-bearing component of any structure; here that role was seemingly reversed. The hinges allowed small movements between the foot of the frames and the foundation but made the arches statically determinate. Thus, stresses and reactions at the supports could be calculated beforehand and were only slightly influenced by movements of the supports or thermally induced dimensional variations.

The iron frame of the galerie was exposed at each end in a frank display of its construction system. The walls were generally glazed, in part with colored glass. Paintings, mosaic, and ceramic bricks also formed part of the cladding. Elevated tracks on each side of the long axis carried mobile walkways above the exhibition space, allowing visitors to travel in carriages and to look down on the machines. The interior was lit by electric lights, invented only some seven years earlier. The galerie was more than just a place for displaying machinery; it was in itself, as one historian has observed, an “exhibiting machine.” It was enlarged for the 1900 Paris Exposition but demolished in 1910, because (so the reason was given) it spoiled the view of the church of Les Invalides. By then, the three-hinged arch was in wide use.

Firth of Forth Railway Bridge

Firth of Forth Railway Bridge

Scotland

Nine miles west of Edinburgh, Scotland, the mouth of the River Forth is spanned by Europe’s first all-steel, long-span bridge. Completed in 1890 it was then the longest bridge in the world. Until 1917 it was also the largest metal cantilever, and at the beginning of the twenty-first century it remains the second largest ever built. It was a major accomplishment of Victorian engineering.

The extension of the railroad along Scotland’s east coast, to complete the direct route between Edinburgh and Aberdeen, was hampered for most of the nineteenth century by two broad inlets of the North Sea: the Firth (mouth) of Tay and the Firth of Forth. The River Forth rises near Aberfoyle and widens into its firth about 50 miles (80 kilometers) from the ocean.

Vessels up to about 300 tons (270 tonnes) could navigate as far as Alloa, about 16 miles (26 kilometers) inland; those up to about 100 tons (91 tonnes) could reach Stirling, a little further on.

After earlier aborted proposals—a tunnel in 1806 and a bridge in 1818—for crossing the firth, little more was attempted for fifty years. In 1865 an act of Parliament sanctioned a bridge across the Queens-ferry Narrows, where the river passes between steep banks at the neck of the firth. Four railroad companies—North British, North Eastern, Midland, and Great Northern—formed a consortium in 1873 and commissioned Thomas Bouch, engineer for North British, to design the bridge. He proposed a suspension structure with twin spans of 1,600 feet (480 meters). The project was delayed for five years because of lack of funds; by spring 1879 only one pier had been started.

When the much-vaunted Tay Railway Bridge, also designed by Bouch and less than two years old, collapsed in a gale on 28 December 1879 with the loss of seventy-five lives, work on the Forth bridge was immediately suspended by another act of Parliament. In January 1881 a British Board of Trade inquiry found that the Tay disaster was caused by inadequate design and poor supervision. Bouch’s Firth of Forth scheme was abandoned. Within months the engineer died, a broken man. The engineers of the Forth consortium’s member railways, Thomas Harrison, William Barlow, John Fowler, and Benjamin Baker, had to develop a new design. In May 1881 Fowler and Baker submitted a plan for a continuous girder, or balanced cantilever, structure. In July 1882 yet another act authorized construction. The Tay bridge affair had so undermined public confidence in railroads that the legislation insisted that the Forth bridge should “enjoy a reputation of being not only the biggest and strongest, but also the stiffest bridge in the world.” There was to be no vibration, even as trains passed over it. Consequently, it was greatly over-engineered.

Before 1877 steel bridges had been banned by the Board of Trade because the Bessemer conversion process produced steel of unpredictable strength. The Siemens-Martin open-hearth process, developed by 1875, bad changed that, yielding material of consistent quality. That kind of steel was used in the Forth bridge, heralding the transition from cast and wrought iron in such structures. A smaller steel cantilever bridge had been built in Germany, but the Scottish project was on a larger scale than had been seen before. There is little doubt that its designers owed much to a U.S. model of several years earlier. Between 1869 and 1874 James B. Eads had designed and built the world’s first steel bridge, over the Mississippi at St. Louis, Missouri. Its three-arch superstructure, with a center span of 520 feet (156 meters) and side spans of 502 feet (150 meters), supported by four massive limestone piers, carried a railroad and a road for other traffic on two levels. Other pioneering features of Eads’s bridge were adopted by the British: the use of pneumatic caissons (large diving bells fed with compressed air) to excavate the foundation, tubular steel structural members, and a balanced cantilever design that allowed construction to proceed without temporary supports that would have obstructed the waterway.

In December 1882 the contract for the Forth bridge was awarded to a consortium led by Tancred Arrol, an experienced and respected company headed by William Arrol, which already had contracts for the Caledonian Railway Bridge over the Clyde and the replacement Tay bridge. At the height of building activity, there would be 4,600 Britons, Italians, Germans, and Austrians working shifts around the clock. The construction of the foundations and piers took until the end of 1885. Each of the bridge’s three cantilever towers stands on four 70-foot-diameter (21-meter) granite piers, founded on the bedrock. Eight of the piers are in water, and their foundations were excavated by men working in wrought-iron pneumatic caissons, sunk up to 90 feet (27 meters) below the river surface. The massive cylinders were prefabricated in Glasgow, then dismantled and taken to Queensferry, where they were reassembled. Once excavation was complete, the air shafts and the working spaces were filled with concrete, and the granite piers rose above them.

Work on the superstructure began in 1886 using 64,800 tons (54,860 tonnes) of steel from two steelworks in Scotland and another in Wales, fixed with rivets from a Glasgow foundry. All the structural

members were fabricated in on-site workshops, pre-drilled, test-assembled—exact dimensions were needed in a riveted structure—and then dismantled to be painted and carried to the site for erection. Each of the 331-foot-high (99.3-meter) cantilevers consists of two inward-sloping trusses fabricated from huge, internally stiffened tubular members up to 12 feet (3.6 meters) in diameter. They support 680-foot-long (204-meter) cantilever arms that are linked midspan by suspended girders of about half that length, making the distances between the towers about 1,700 feet (540 meters). The length of the bridge between the end piers is about 5,300 feet (1,600 meters). Together with the approach viaducts and arches at each end, the bridge carries the double-track railroad for 2,765 yards (2,490 meters), 150 feet (45 meters) above the surface of the Firth of Forth. The central gap was closed on 14 November 1889, and the Prince of Wales ceremonially opened the bridge on 4 March 1890.