BROBDINGNAGIAN BRIDGES 



By Othmar H. Ammann 



[With 7 plates] 



A hundred years ago it was predicted that the famous bridge across 

 the Menai Straits in England, with a span of 570 feet, would forever 

 constitute a world wonder. Only 50 years later that maximum 

 length of span was more than doubled and the suspended mass in- 

 creased tenfold in the Brooklyn Bridge across the East River in 

 New York. And if we compare Brooklyn Bridge, which 50 years 

 ago was by far the most outstanding engineering work of its kind, 

 with the George Washington Bridge in New York now nearing com- 

 pletion, we find that the span length in the last 50 years has been 

 again more than doubled, the traffic capacity multiplied at least four 

 times, and the total mass suspended over the river more than eight 

 times. 



It is also of interest to note that in spite of this enormous increase in 

 the mass and quantity of material in the George Washington Bridge, 

 the time of construction will be less than one-half that consumed by 

 the Brooklj^n Bridge, and that the total cost, in proper consideration 

 of the depreciation of the purchase value of money, will be less than 

 twice that consumed by the much smaller Brooklyn Bridge. These 

 results have, of course, been made possible only by the far-reaching 

 developments in other technical lines, such as mechanical and electri- 

 cal engineering, and metallurgy, as well as in the field of theory and 

 experiment. 



From the engineering or technical point of view, progress in bridge 

 construction manifests itself in improved types and forms of con- 

 struction and details, in better and stronger materials, in more accu- 

 rate and cheaper shopwork, and in more expeditious and safer erec- 

 tion, all of which are essential for the construction of larger bridges. 

 It is principally along these lines that I desire to illustrate progress 

 made in recent years. 



TYPES OF BRIDGES 



The selection of the type or form of bridge to be used for an;j^ 

 particular crossing is, from the engineering point of view, one of the 



^ Reprinted by permission from the Teclinology Review, vol. 33, No. 9, July, 1931. 



571 



