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To the engineers and builders of the amazing, elegant, and powerful structures commonly known as Great Bridges. Outside ankind has been building bridges conquests. Examples include the Pont du Gard since the time of early civilizations. aqueduct (40–60 AD), a three tiered stone bridge, Today, bridges are all around us Caesar’s bridges over the Rhine river during his the Box – they provide easier, faster, and conquest of Gaul (50s BC), and Trajan’s Bridge Msafer connections between two points. Bridges (104 AD) and Constantine’s Bridge (328 AD), have evolved from merely utilitarian structures to both over the Danube river. highlighting the out-of-the- become symbols of cities, countries, and human Medieval and Renaissance bridges were often stone ordinary within the realm of progress. Iconic bridge structures embody engi- bridges serving as crossings within cities, and structural engineering neers’ eternal aspiration to greater achievement including buildings and shops on top of the bridge – longer and taller, stronger and faster. We all structure. Examples include the Ponte Vecchio admire bridges that span gracefully over a deep in Florence (1564), the Rialto Bridge in Venice ravine, canyon, large river or bay, and rightfully (1591) and the “Old” London Bridge (1209). consider them high technical achievements. The bridges of the Industrial Revolution were However, very few of these bridges have acquired some of the first long® span bridges. These heroic the prestigious title of “Great Bridges.” It may be era bridges include: the Menai Strait Suspension interesting to find out what makes a Great Bridge. Bridge (1826, 577-foot span); the Britannia Bridge A Great Bridge is one that can be distinguished (1850, two 459-foot spans, a wrought continuous from others by something unique or exceptional – box girder bridge), also over the Menai Strait; the longer span, singular beauty, appeal to the general Clifton Suspension Bridge (1864, 702-foot span) public. ThroughoutCopyright history, people have over the Avon Gorge; the Garabit Viaduct (1884, admired and prized remarkable buildings 541-foot span) by Gustave Eiffel; and the Firth and structures. As early as about 150 BC, of Forth Bridge (1890, two 1,709-foot spans). Great Bridges the Seven Wonders of the World defined a grouping of the most renowned con- High-Level Achievements structions of the time. While there were Remarkable, Signature some bridges built as early as 850 BC (like the in Bridges or Great Bridges? Caravan Bridge at Smyrna in Turkey, still in use), Several bridges are notable for their high level of no bridge was included in the Seven Wonders. achievement, but still don’t qualify individually With the development of civilization and cor- as a great bridge. These include the Verrazano By Roumen V. Mladjov, S.E., P.E. respondingly higher standards of construction, Narrows Bridge, for its span, and the Bosphorus many other buildingsmagazine and structures were in their Bridge I, built between two continents. Several S Tturn namedR as an “EighthU WonderC of theT World” Ucable-stayed R bridges E should be noted for their in recognition of their high achievement. Among long spans, including the Normandy, Sutong, others, these have included the Brooklyn Bridge Stonecutters, Maracaibo Bay, Rion Antirion, in 1883 and the Golden Gate Bridge in 1937. Millau Viaduct, Sunniberg, and Russky Island We also often see the term “great” applied to a Bridges. This structural system, in just 50 years, new architectural or structural project. However, reached free-spans exceeding 3,280 feet. It is still Roumen V. Mladjov has more than mere months later, few of these achievements are too soon to tell if any of these bridges will be 52 years in structural and bridge still identified as exceptionally great. added to the group of Great Bridges. engineering and construction One way to estimate the development of a society is management. He lives in San by considering the level of its structural achievement. “Signature” Bridges Francisco, and his main interests The great architectural and structural achievements are structural performance, at different periods of human history are a product Many cities have commissioned eminent engineers efficiency, and economy. He can be of the building knowledge and available construc- to design new “signature” bridges, intended to reached at [email protected]. tion technology at the time of their creation. There become symbols of the adjacent city or area. The are enormous differences between the construction most prominent bridges identified as “signature” possibilities in Roman times and those in the last bridges include: Erasmus Bridge, Rotterdam, six to seven decades. Therefore, when we review the 1996, a cable-stayed bridge, main span 932 feet; development of bridges, it would be fair to consider Millennium Bridge, London, 2002, a cable-stayed their achievements in relation to the technical level pedestrian bridge, main span 472 feet; and the at the period of their creation. Sundial Bridge, CA, 2004, a pedestrian cable- stayed bridge, main span 492 feet. Calatrava’s Historical Great Bridges Alamillo Bridge (Seville, Spain, 1992, 656-foot [200 meters] main span) is a beautiful, yet contro- Based on the historical development of construc- versial bridge design due to its deviation from basic tion, remarkable bridges can be subdivided into cable-stayed systems, resulting in high inefficiency. ancient, medieval, industrial revolution, and The notable omission of back span cable-stays modern Great Bridges. Ancient greats include those creates a dramatic view and contributes to the bridges serving as aqueducts or bridges for military attractiveness of the bridge, but such a concept

10 October 2017 (a) (b)

Figure 1. a) Golden Gate Bridge; b) Golden Gate Bridge, south tower. Figure 2. Brooklyn® Bridge. has been discouraged for any bridge not built Bridge and have been able to preserve the Ocean to San Francisco Bay. The bridge’s as a monument. title. Therefore, merely breaking the record central span is 4,200 feet (1,280 meters) The self-anchored suspension part of the East for the longest span is not sufficient in and and was the longest span in the world until span of the SF-Oakland Bay Bridge (2016, of itself; entering into this prestigious club 1964 (Figures 1a and b). The bridge created 1,263 feet) became an example for an inef- depends on Copyrightthe long-lasting perception of a much-needed link between San Francisco ficient design concept. The cost, construction the public at large. and the Northern Bay Area. The Golden material quantities, and building schedule Gate Bridge was designed by chief engi- were 7 to 8 times greater than for bridges with Modern Great Bridges neer Joseph Strauss, who assembled a team similar span but with other structural systems. of experienced bridge engineers. Architect All these bridges resulted in very costly The fast development of structural analysis Irving Morrow worked closely with the projects and proved inefficient in materials and construction technologies in the 20th engineers, making the decisive aesthetical and construction time. These “signature” century provided a significant development improvements, providing the Art Deco style bridges are closer to structural extravagance and improvement in bridge construction, of the bridge towers and the “International than to Great Bridges. While these “signa- resulting in the creation of the modern Great Orange” color, thus contributing to it rec- ture” bridges have interesting, even attractive Bridges. Some of their forerunners among ognizable image and fame. The combination looking structures and often became symbolic late-19magazineth-century bridges are also included of a dramatic site and the elegant, powerful of their locations, none of theseS exceptional T Rin this group.U C T Ustructure R is essentialE for considering it one of pre-planned structures has gained recognition Golden Gate Bridge, San Francisco, the greatest bridges ever built. The changing as a Great Bridge. California, USA, 1937, spans the Golden day and night visual conditions, from bright Gate Strait, the entrance from the Pacific sunlight and shade to an almost opaque layer Record Long-Spans? Every new bridge that establishes a record for longest span may be considered a Connect Steel to Steel without Great Bridge in some way. Breaking the Welding or Drilling

long-span record is a move into new visit www.STRUCTUREmag.orgADVERTISEMENT–For Information, Advertiser territory; it requires an extremely tal- • Full line of high-strength, corrosion-resistant fasteners ented, well-prepared team of designers • Ideal for secondary steel connections and in-plant equipment and builders. Such achievement is only • Easy to install or adjust on site possible by using the highest available • Will not weaken existing steel or harm protective coatings level of bridge engineering, some recent • Guaranteed Safe Working Loads innovations and experience gained from previous complicated structures, and challenges and competitions between engineers, architects, companies, and nations. Several sources list the longest BoxBolt® for HSS blind FastFit universal kits bridge spans (absolute or per structural connections. ICC-ES for faster, easier steel system like suspension, arch, continuous certified. connections. girders). This provides for simple differ- entiation, as the span length is the only value to be considered. However, just a few of these bridges, holders of record- For a catalog and pricing, call toll-free 1-888-724-2323 span at the time of their completion, have A KEE SAFETY COMPANY gained the prestigious title of a Great or visit www.LNAsolutions.com/BC-2

STRUCTURE magazine11 October 2017 ® Figure 3. Akashi-Kaikyo Bridge. Figure 4. Great Belt East Bridge. of fog, provide countless view variations for route between the residential North Shore and significantly; previously taking about an hour the bridge and its elements. the central business district of the city. It was by ferry, the Great Belt can now be crossed in Brooklyn Bridge, New York, USA, 1883, designed and built by the British firm Dorman about ten minutes. The construction of the spans the East River, connecting Manhattan Long and Co.Copyright The beautiful view of the bridge link and the previously completed Øresund with Brooklyn. The Brooklyn Bridge is with the harbor and the Sydney Opera House Bridge enabled driving from mainland Europe a hybrid of a suspension and cable-stayed completes the familiar, breathtaking skyline of to Scandinavia. structure, the first bridge using steel wire the city. It is a symbol of Sydney and Australia. George Washington Bridge, NYC, New cables. It was envisioned and designed by John The arch was constructed first and served as a York, USA, 1931. The chief engineer of the Roebling. The construction was complicated, support for the superstructure. bridge was Othmar Ammann, with Cass with a much longer central span, 1,594 feet Akashi-Kaikyō Bridge, Japan, 1998, Gilbert as architect. With a span of 3,500 feet (486 meters), than any other bridge at that was designed by Honshu-Shikoku Bridge (1,067 meters), this bridge held the longest time. From its opening day, the bridge became Authority with a span 6,532 feet (1,991 span record until 1937, at nearly double the one of the landmarks of New York; it is still meters). The bridge is a suspension steel struc- span of the previous record holder. one of the city’s major attractions (Figure 2, ture crossing the Akashi Strait and connecting The George Washington Bridge is a dou- page 11). The link between Manhattan and the magazinecity of Kobe on the Japanese island of ble-decked suspension bridge spanning the Brooklyn was essential for theS development T RHonshu toU Iwaya on CAwaji Island.T Since U its Hudson R River E between the Washington of Brooklyn. The beautiful bridge, with the completion, the bridge holds the world record Heights neighborhood in the borough of Manhattan skyline behind it, is a favorite for longest bridge span (Figure 3). According Manhattan in New York City and New choice for photography due to the pedestrian to some experts, this bridge is the top achieve- Jersey. As of 2015, the George Washington access to the bridge deck, from the ground ment in the classic suspension bridge system Bridge carries over 106 million vehicles per on both sides near the structure, and from with stiffening trusses largely used and devel- year, making it the world’s busiest motor vessels on the river. oped in Northern America. The bridge was vehicle bridge. Originally, the steel towers Tower Bridge, London, UK, was built from designed with a two-hinged stiffening girder of the bridge were designed to be encased in 1886 until 1894. The bridge is a combination system, allowing the structure to withstand concrete and granite. However, the towers of a suspension and a bascule system over the winds of 178 mph (286 km per hour), earth- were left as exposed steel to reduce costs. River Thames, with the largest span at 270 quakes measuring up to magnitude 8.5, and These steel towers, with their distinctive feet (82 meters). It is located near the Tower of strong sea currents. The bridge also contains crisscrossed bracing, have become one of the London, which gave the bridge its name, today tuned mass dampers that are designed to oper- bridge’s most identifiable characteristics. The an equally recognizable symbol of London. The ate at the resonance frequency of the bridge world renowned architect Le Corbusier said structure was designed by Sir Horace Jones to reduce seismic and wind forces. Visitors of the exposed steel structure: “The George and supervised by Sir John Wolfe-Barry. It can walk under the bridge deck at the level of Washington Bridge over the Hudson is the was a great relief for most Londoners, provid- lower truss bracing and can go up an elevator most beautiful bridge in the world. Made of ing a connection between the two sides of the to the top of one of the bridge towers. cables and steel beams, it gleams in the sky Thames, as the then-existing London Bridge Great Belt East Bridge, Denmark, 1998, like a reversed arch.” was far insufficient for the demand. The bridge has a main span of 5,328 feet (1,624 meters). San Francisco-Oakland 1936 Bay Bridge, contains two bascules which can be raised for The structure was designed by COWI, Klaus San Francisco, USA. The San Francisco- river traffic and pedestrian walkways at 141 Ostenfeld et. al. The central suspension span is Oakland Bay Bridge connects San Francisco feet above the river, a smart design approach the longest span in Europe and currently the and Oakland. The bridge is actually a com- that permits pedestrians to use the bridge even third-longest bridge span in the world (Figure bination of several structures with different when the bascules are raised. 4). The bridge is part of the Great Belt Fixed systems. Its main part is 10,302 feet (3,140 Sydney Harbor Bridge, Sydney, Australia, Link that runs between the islands of Zealand meters) in length. The West crossing from 1932, is a steel through-arch bridge crossing and Funen, and replaced the ferry service that San Francisco to Yerba Buena Island (YBI) is Sydney Harbor with a main span of 1,650 had been the primary transportation means a twin suspension bridge with central spans of feet (503 meters). The bridge carries a primary in the past. The link has reduced travel times 2,310 feet (704 meters) (Figure 5). The bridge STRUCTURE magazine12 October 2017 DO IT ONCE ® Figure 5. San Francisco – Oakland Bay Bridge, West span. WITH Copyright GRIDFORM was designed by Ralph Modjeski, Charles these bridges are more efficient than the ear- ™

Purcell, et al. and built by the American lier American suspension bridges with steel visit www.STRUCTUREmag.orgADVERTISEMENT–For Information, Advertiser Bridge Company. stiffener trusses, they needed strengthening to At the time of completion, the bridge was the accommodate increased traffic loads. longest bridge in the world – 8.5 miles includ- ing approaches. It featured the second longest Conclusions suspension span at 2,310 feet (704 meters), the third longest cantilever truss span at 1,401 What makes a Great Bridge? A bridge that: feet, the deepest pier foundation (243 feet • Is an exceptionally designed and built below the water surface at low tide), and the structure; largest bored tunnel. The West crossing was • Is magazinebuilt in locations where the bridge was the only major bridge withS two consecutive T Ra longtime U dream; C T U R E suspension spans. The bridge, with its three • Has to surpass previous records or excels principal segments, is listed as “One of the over other structures; largest and most important historic bridges in • Is attractive, elegant, simple, slender, with the country.” President Herbert Hoover called a feel of robustness; this project “The greatest bridge yet erected.” • Fits harmoniously within and comple- It is not by chance that the designers of the ments its environment; Akashi-Kaikyo Bridge used the same type of • Is easily accessible; GRIDFORM™ main towers as the Bay Bridge. • Is accepted as an engineering and archi- Stay-in-place FRP Humber Estuary Bridge, East Yorkshire, tectural achievement; Bridge Deck System UK, 1981, was developed by Freeman Fox • Is highly recognized and celebrated by the solves many of the headaches & Partners. With its central span of 4,626 community; and associated with steel-reinforced feet (1,410 meters), this bridge is a suspen- • Withstands the test of time. bridge decks. The lightweight, sion steel bridge with towers consisting of Even when all the requirements are met, the high-strength FRP system elim- a pair of hollow vertical concrete columns, result can be just one more perfectly designed inates labor-intensive and time- each 510 feet (155 meters) tall. The bridge is and built structure, but still not recognized as consuming steps such as setting designed to accommodate constant motion a Great Bridge. It should be understood that forms and tying rebar. In addition, due to winds of 80 mph (129 km/h). The there is no recipe for designing and building GRIDFORM™ does not corrode bridge held the record for the world’s longest a Great Bridge; the identification as a Great when exposed to deicing salts and single-span suspension bridge for 16 years, Bridge is a public recognition. They come other corrosive road chemicals, from its completion in July 1981 until the into being by a fortunate combination of reducing maintenance and extend- opening of the Akashi-Kaikyo Bridge. With outstanding qualities of structural design in ing the life of bridge decks. the Humber Bridge, Freeman Fox & Partners relation to their natural settings and superior developed their previous design for the Severn construction achievements.▪ Bridge and Bosphorus I; these structures rep- resent the “new modern type of suspension The online version of this article bridges” with shallower aerodynamic (aero- contains references. Please visit foil) deck and inclined suspenders. While www.STRUCTUREmag.org.

STRUCTURE magazine13 October 2017 References Billington, D. The Tower and the Bridge. Basic Books, Inc, New York, 1983

Leonhardt, F. The Significance of Aesthetics in Structures, SEI, 2/1996

Virlogeux, M. Structural and Architectural Design of Bridges, SEI 2/1996

McCullough, D. The Great Bridge. The Epic Story of the Building of the Brooklyn Bridge. Simon & Schuster, New York, 1972

Menn, C. The Place of Aesthetics in Bridge Design, SEI 2/ 1996

Mladjov, R. Long Span Bridges and the Art of American Bridge Engineering, SEAOC Convention, 2009

Starr, K. Golden Gate, the Life and Time of America’s Greatest Bridge, Bloomsbury Press, New York, 2010 ® Copyright

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STRUCTURE magazine14 October 2017