The golden age of bridges is now. Never before in the history of the world has man had such a wealth of means in money, materials and technology to fulfill his inborn desire to get to the other side. By using strong new steels and ingeniously strengthened concrete, he has made it possible to move himself and his goods over barriers his forebears thought uncrossable.
Not only is man building his bridges longer and stronger than ever before, he is also erecting more of them than at any other time in history. In the past six years, the U.S.'s interstate-highway program has spent $5.6 billion building almost 20,000 new bridges, will spend another $8 billion to $9 billion in the next eight years on bridge construction.
In Europe, bridge building is becoming almost as commonplace as house building. Britain has built 120 new bridges in the past five years as parts of its new highways, and figures that by the 1970s it will have built 280 more. Germany now completes 1,000 new bridges every year, at this moment has under construction nine spans more than 3,000 ft. long.
The result is not only new efficiency and new speed in getting from place to place; almost inevitably, when a great new bridge goes up, the result is also breath-taking beauty. The very nature of the barriers that man seeks to cross makes them some of the loveliest spots on the globe—gorges, bays, broad rivers, mountain valleys, the approaches to towering cities. By necessity, bridges are the purest sort of expression of the architectural concept of form following function. A steel-arch bridge over a deep canyon cannot help completing the frame of a picture of classic beauty: rushing waters below, soaring steel above, and all framing the natural art of rock shaped by wind and water.
What has allowed man to create these great structures is a new mastery over matter and mind.
> Steel has played the dominant role in modern bridges. A bridge built with today's steels is lighter, yet nearly twice as strong as a span of equal length built just 25 years ago. Today's bridge builders use as many as 18 different types of steel in the same bridge.
> Concrete mixers of today are producing wonders. Reinforced with steel wire and prestressed for still more strength, whole slabs of concrete now form single spans up to almost 700 ft.
in length.
> Technology has taken dramatic strides over the past two decades. Bridge designers are well-grounded in modern physics and aerodynamics before formulating their designs, then run them through computers that have already been fed data on snow and rain conditions, wind velocities, low and high temperatures, traffic loads and substrata strength.
The results, say today's bridge builders, are awesome. Using their new tools and talents, builders think suspension bridges can be built twice as long as they are now. "I don't think a suspension bridge of 10,000 ft. is impossible," says Raymond Boynton of the Manhattan engineering firm of Steinman, Boynton, Gronquist & London. Bridge strength will also increase. "I tell people we put up bridges that will last 1,000 years," says American Bridge Engineer William K. McGrath. "But I'm not sure they couldn't last forever."