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Tacoma Narrows BridgeThe efforts that went into the design of the second Narrows Bridge were unique and had an important effect on the design of suspension bridges and other similar structures that followed. Approximately four years were spent in original research to study aerodynamics and design features to achieve stability in the new structure. The Consulting Board recognized that the question of aerodynamic stability of suspension bridges would have to be resolved. Although the development of aerodynamics in the 1940s was not unique as applied to aircraft, there had been no previous scientific effort devoted to the dynamic effect of winds passing over a bridge structure. A special wind tunnel was constructed at the University of Washington for testing three-dimensional bridge models; the first time such models had ever been built. A 1:50 scale three-dimensional model of the original bridge was built. The tests would prove that wind velocities acting on models scaled to match the bridge's form and elastic properties would create the same motions as those actually measured and recorded in the field.

The first test proved the theory of similitude between model and prototype with almost perfect accuracy establishing confidence in tests on other designs. Many modifications were necessary and the tests were spread over nearly four years during the shortages of World War II, with its attendant handicaps, before the desired degree of stability was found. Methods and devices necessary to obtain the required stability were also determined. Tests were performed under the general direction of Charles E. Andrew with the approval of the Board of Consulting Engineers. Professor F.B. Farquharson of the University of Washington directed the construction of the wind tunnel and bridge models. Dr. Theodore von Karman supervised testing of the models. Test results formed the basis for a continuing study by a national committee comprised of many engineers in the country interested in suspension bridges.

Because of the extreme shortage of steel and wire during World War II, attempts were made to salvage all remaining material from the first bridge. Ironically, it would have been more economical for the state to drop the remaining portions of the structure into the deep waters of the Puget Sound.

Designs for the new bridge were completed in 1947 and checked aerodynamically with the use of models. Contracts were let for construction on March 31 and April 1, 1948. The primary contractors for construction of the bridge were the Bethlehem Pacific Coast Steel Corporation and John A. Roeblings Sons Company. Both of these firms were notable for their innovative construction skills in the fabrication and erection of steel bridges.

The Tacoma Narrows Bridge opened to traffic on October 14, 1950; all components of the structure were finally in place by November 1951. Construction was financed through a $14,000,000 bond issue. The bridge operated as a toll facility until the bonds were retired, at which time the tolls were removed along with the toll plaza and booths (although the toll houses remain off the south end of the bridge). The toll for an automobile and driver was 50 cents. Each additional passenger paid 10 cents.

At the time of completion, the Tacoma Narrows Bridge included the third longest suspension span in the world. As of 1991 it ranked as the fifth longest span in North America. This bridge is of major significance because of its numerous unique design features. It was the first time a research program was implemented to investigate the aerodynamic effects of wind acting upon a bridge. In designing this structure, bridge engineers first used wind tunnel tests to determine the behavior and stability of a physical model of a proposed bridge. The research and design provided significant information to suspension bridge engineers nationwide and had an important effect on all suspension bridge designs that followed. The design incorporated unique features into the structure, such as the open steel grid slots, the greater ratio of the depth of stiffening truss to span length, the double lateral system, the hydraulic energy absorbing and damping devices, and the record depth below water at which pier construction occurred with the aid of submerged caissons. Few bridges have received as much engineering significance in technical publications or as much nation-wide attention and publicity, due largely to the failure of the first Tacoma Narrows Bridge. The present structure represents an extraordinary achievement in bridge design and construction engineering. This effort produced a structure of unprecedented function, stability, and virtually unequaled esthetic attraction spanning one of the country's most challenging crossings. In addition, the bridge established one of the most significant transportation corridors in Washington State by connecting the mainland with the Kitsap and Olympic peninsulas.

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