In 1502 Leonardo da Vinci, known among other tings for his daring bridge designs, completed a drawing for an arched bridge. This bridge would link the two cities of Pera and Constantinople in a single span over the Bosporus. The sultan of the Ozmanian Empire wished to replace the temporary pontoon bridge over the Golden Horn with a permanent structure. At that time, da Vinci's plan was virtually invonceivable. The bridge he proposed would be 350 meters long, 234 of them over water. The narrowest section measured 23 meters wide.
In 1943 the Sandö Bridge spanning the Ångerman river opened, several centuries after da Vinci completed his design. It was the longest concrete bridge in the world to be built in one arch, measuring 264 meters long and rising 40 meters above the river. The middle section of the bridge collapsed during the casting process, killing several construction workers. Despite the tragedy, Sandö Bridge was masterpiece of structural engineering. However, public attention was understandably focused on the events of World War II and the bridge never received the recognition it deserved.
Half a century later, in 1997, the Sandö Bridge has been replaced by yet another masterpiece. The new structure is an enormous suspension bridge only 70 meters shorter than San Francisco's famed Golden Gate Bridge. At the Veda ferry slip the bridge spans a distance of over 1,400 meters. It took eleven years to complete the project, from drafting board to finished product. The 1,800 meter long section of roadbed is supported by two pairs of 180 meter high pylons. The pylons hold two thick cables. The 6.5 decimeter thick cables are made of 11,300 steel wires, each wire nearly six millimeters thick. The design and construction of the bridge allows for a one meter lateral swing in a strong wind; it also enables the structure to bear the thousands of tons of extra weight accumulated during snowstorms. The Sandö Bridge, the gateway to the High Coast area, is rightly one of the most impressive attractions along European Highway 4.
Could da Vinci's bridge - a structure designed to be "carried on its own shoulders" - have been built with 16th century technology? This question has occupied many designers since the 1950s when his plans were discovered. Numerous engineers believe that the bridge could have been successfully erected.
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