Conclusion

---

.....The original Tacoma Narrows Bridge, a 5,939-foot-long structure popularly known as “Galloping Gertie,” opened on July 1, 1940, linking the Washington mainland to the Olympic Peninsula over the Puget Sound. The engineers attempted to make a new and unique bridge with a sleeker architectural design that made the bridge aesthetically pleasing. This new look also saved money, initially. However, the bridge collapsed just four months later on November 7, 1940, ending a trend of bridge engineering towards a maximum of lightness, grace, and flexibility. Since the turn of the century, suspension bridge construction valued structural appearance, and the bridge over the Narrows was the embodiment of artistic quality in bridge construction. However, the Tacoma Narrows Bridge focused too much on looks and abandoned the more important issues of safety and reliability.
.....The bridge earned its nickname “Galloping Gertie” due to its tendency to sway from side to side during heavy windstorms. It was a suspended plate girder type bridge that caught wind rather than allowing wind to pass by. As the wind intensity increased, the rolling and swaying of the bridge increased as well. With a shape similar to that of an aircraft wing, the bridge would generate a great deal of lift and become very unstable under windy conditions. It is because of this structural flaw, and the intensity of the winds, that the Tacoma Narrows Bridge finally tore apart and collapsed into the Puget Sound.
.....Heavy winds have been known to induce large responses out of objects such as bridges, creating vibrations in a step or phase that can build up in proportions large enough to be destructive. This phenomenon is known as resonance and is one of the major theories behind the collapse of the Narrows Bridge. The theory is that the wind, which reached speeds of up to 42 miles per hour, produced a fluctuating extensive force in resonance. This, along with the natural frequency of the structure, caused a steady increase in the amplitude until the bridge was finally destroyed. Due to this phenomena, and its disastrous results, new wind tunnel testing is being implemented before bridges are constructed. Further, the structural formation of the new Tacoma Narrows Bridge included numerous unique design features that are still being used today. Features such as open steel grid slots, the greater ratio of the depth of stiffening truss to span length, the double lateral system, and new hydraulic energy absorbing and damping devices that had an important effect on all suspension bridge designs for the future.



Click picture to return to home page!