Jgads

Eldridge came up with a plan to span the Tacoma Narrows with a 5000 foot two-lane suspension bridge, which when completed would be the third longest suspension bridge in the world. Between 1938 and 1939, numerous bridge experts reviewed and modified Eldridge's design. At that time, the appearance of being streamlined was considered important, and the increasing popularity of automobile transportation and the decline of the railroads lessened the load requirements for the bridge. One of the engineers, Leon Moisseiff, made the significant substitution of a open stiffening truss with a shallow plate girder, resulting in a much lighter and streamlined looking bridge.

The Tacoma Narrow Bridge which is a mile long (1600 meters) suspension bridge and with main span of (850 m). It was opened to the traffic on July 1st, 1940 after its two year construction. This bridge was built on Washington State Route 16 across the Tacoma Narrow of Puget Sound from Tacoma to Gig Harbor, Washington. When it was originally built it was given the nickname of Galloping Gertie, because of its rolling and undulating behavior. The Tacoma Bridge was designed by Clark Eldridge and altered by Leon Moisseiff. Right after it was built, it became famous for its wind -induced structural collapse, which has been caught on motion picture.

When the designers were set out to build the bridge they forgot about the wind induced motion to the bridge. The bridge was solidly built, with girders of carbon steel anchored in huge blocks of concrete. Preceding designs typically had open lattice beam trusses underneath the roadbed. This bridge was the first of its type to employ plate girders (pairs of deep I beams) to support the roadbed. With the earlier designs any wind would simply pass through the truss, but in the new design the wind would be diverted above and below the structure. Shortly after its construction in July 1940 (opened to traffic on July 1), it was discovered that the bridge would sway and buckle dangerously in windy conditions. This resonance was longitudinal, meaning the bridge buckled along its length, with the roadbed alternately raised and depressed in certain locations -- one half of the central span would rise while the other lowered. Drivers would see cars approaching from the other direction disappear into valleys which were dynamically appearing and disappearing. From this behavior the bridge gained the nickname "Galloping Gertie." However,

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