Slender, elegant and graceful, the Tacoma Narrows Bridge stretched like a steel ribbon across Puget Sound in 1940. The third longest suspension span in the world opened on July 1st. Only four months later, the great span's short life ended in disaster. "Galloping Gertie," collapsed in a windstorm on November 7,1940.
The City of Tacoma and Pierce County Board of Commissioners asked the State to construct a bridge across the Tacoma Narrows in 1935. The legislature appropriated $25,000 to study the request and, satisfied with the results, the State of Washington submitted an application to the Public Works Administration (PWA) requesting funds for construction of a new suspension bridge on May 23, 1938.
The 1940 Narrows Bridge was built "primarily as a military necessity" to link McChord Air Field south of Tacoma and the Puget Sound Navy Shipyard in Bremerton. This important fact is often is often overlooked today. But, it was well known to area residents and local newspapers in 1940.
Between the time the state legislature authorized the money to study the proposal and the completion of that study, Lacey Murrow, Director of the Washington State Department of Highways, had given Clark Eldridge, a bridge engineer with the department, the green light to design a bridge to span the Narrows. Eldridge’s plan called for a 5,000 foot, two-lane suspension bridge. When completed, the structure would be the third longest suspension bridge in the world.
After examination of Eldridge's plans in May of 1938, the Public Works Administration agreed to finance 45 percent of the construction, provided that the State of Washington retain a board of independent engineering consultants to reexamine Eldridge's design. The State complied and employed the firm of Moran and Proctor to study the plans for the substructure. Furthermore, the State retained Leon S. Moisseiff, the world-renowned suspension bridge builder to examine the plans concerning the superstructure. Both Moran and Proctor and Moisseiff made significant alterations to Eldridge's original design. Specifically, Moran and Proctor wanted an entirely different substructure. As to Moisseiff, he substituted the 25 foot deep open stiffening truss with an eight foot, shallow plate girder, resulting in a much lighter bridge.
Prior to the opening of the construction bids, a group of contractors
notified the engineers they could not meet the specifications for the
substructure. As a result, Moran and Proctor's plans for the substructure
were scrapped, and Eldridge's original plans for the substructure were
reintroduced. After consultation with Moisseiff, it was agreed that
Eldridge's design for the substructure would be used in conjunction
with Moisseiff's plans for the superstructure. This modified plan was
approved by the Public Works Administration and bids for construction
were opened on September 27, 1938. The Pacific Bridge Company's low
bid of $5,594,730.40 was accepted. The Bethlehem Steel Company was
an associate contractor that supplied and erected the steel and wire.
Work on the bridge began in early 1939 and on July 1, 1940, the $6.4
million bridge opened and the link between the Washington mainland
and the Olympic Peninsula was complete.
Vertical oscillations of the roadbed occurred even during the construction phase and raised questions about the structure's stability. Some breezes as low as four miles per hour caused oscillations, while stronger breezes often had no effect. Prior to the bridge's opening, hydraulic buffers were installed at the towers to control the stresses. The undulations continued, however, and further studies were undertaken at the University of Washington. Their recommendation of the installation of tie-down cables in the side spans were implemented, but to little effect.
Local folks lost no time in nicknaming the bridge "Galloping Gertie." Fascinated by Gertie, thousands of people drove hundreds of miles to experience the sensation of crossing the rolling center span. The disappearance and then reappearance of cars often highlighted the experience. For four months, the Washington Toll Bridge Authority thrived as traffic had trebled from what had been expected. Although concerns about the bridge's stability had been voiced, bridge officials were so confident of the structure, they considered canceling the insurance policies in order to obtain reduced rates on a new one.
Throughout the early morning hours of Thursday, November 7, 1940, the center span had been undulating three to five feet in winds of 35 to 46 miles per hour. Alarmed by this constant motion, highway officials and state police closed the bridge at 10:00 A.M. Shortly thereafter the character of the motion dramatically changed from a rhythmic rising and falling to a two-wave twisting motion. The twisting motion grew stronger with each twist; span movement had gone from 5 foot to 28 foot undulations. This twisting motion caused the roadbed to tilt 45 degrees from horizontal one way and then 45 degrees from horizontal the other way.
For about 30 minutes, the center span endured the twisting. At about 10:30 A.M., a center span floor panel dropped into the water 195 feet below. The roadbed was breaking up, and chunks of concrete were raining into the Sound. At 11:02 A.M., 600 feet of the western end of the span twisted free, flipped over, and plunged down into the water. Engineers on the scene hoped that once this had happened, the remainder of the span would settle down. The twisting continued, and at 11:09 A.M., the remaining bridge sections ripped free and thundered down into the Sound. When this happened, the 1,100 foot side spans dropped 60 feet, only to bounce up and then settle into a sag of 30 feet. As for the center span, it rested on the dark and tide-swept bottom of the Narrows.
Scandal: Who Was to Blame?
| Community | Commute | Ferry Cams | History