The 1940 Tacoma Narrows Bridge is a unique chapter in bridge engineering that has become a classic lesson used to show the need for diligence and caution in the engineering process. The 1950 Tacoma Narrows Bridge, built upon the foundations of the 1940 bridge, is a demonstration of the ability of civil engineers to find solutions to difficult problems and to put them into practice. In combination, the two bridges provide a unique bridge engineering story that has influenced not only the succeeding efforts in suspension bridge design world-wide, but as a serious engineering lesson that has application to all fields of engineering and human endeavor.

The bridge failure was spectacular, and although no human lives were lost, it was a major event that brought crisis to suspension bridge engineering practice. Investigations and panels were convened to determine the cause and to make recommendations for the design of future bridges. The 1950 replacement bridge, built on top of the 1940 bridge foundations, used a more conservative stiffening element and other measures to ensure aerodynamic stability. The result was that these two bridges, in combination, became a pivotal chapter in suspension bridge design and also a lesson for all engineers.

ASCE Historic Civil Engineering Landmark Dedication CeremonyWhenSaturday, August 11th, 2012 - 1:30 pm

WhereWar Memorial ParkSixth Avenue and South MacArthur StreetTacoma, Washington

Directions to park entrance from SR-16Take the Jackson Avenue Exit 4 from SR-16Turn South onto Jackson AvenueTurn East onto 6th AvenueEntrance to parking area is on north side of road!

Special Thanks to Our Sponsors

Tacoma Olympia Section PresentsHistoric Civil Engineering Landmark Dedication of the 1940 and 1950 Tacoma Narrows Bridges

Image from Google Maps, 2012

Entrance to parking area off of 6th Ave

Opening of “Galloping Gertie”July 1, 1940

Construction of the first Tacoma Narrows Bridge began on November 23, 1938 and was completed and opened to traffic on July 4, 1940. It carried two lanes of highway traffic between Tacoma and Kitsap County and the Olympic Peninsula in Washington State. Prior to this facility, travelers between these areas used a ferry from Point Defiance in Tacoma to Gig Harbor on the Kitsap side. This was a slow and limited transportation link, and did not meet the growing demand for land development and commerce. A highway bridge across the Narrows had been first proposed in 1923 by civic groups, and was authorized by the state legislature in 1929, but not funded. Due to uncertainty of sufficient toll revenue to pay for construction bonds, nothing developed until the depression era Public Works Agency provided funding in 1938.

Collapse of “Galloping Gertie”November 7, 1940

The first Tacoma Narrows Bridge was a long span suspension bridge of unprecedented slenderness. The trend in suspension bridges during the 1930's was to make them with a more slender stiffening deck structure to save cost and improve aesthetics. The increased slenderness allowed the spans to be more sensitive to wind forces. In spite of some problems with deflections from wind on other bridges, Moiseiff chose to make the Tacoma bridge the most slender yet, by a large margin. Its slenderness proved to be a fatal flaw, the 1940 Tacoma Narrows Bridge was destroyed by uncontrollable deflections of the light roadway plate girder stiffening system. The catastrophic failure occurred during a relatively moderate (42 mph) windstorm on November 7, 1940, only four months after it opened to traffic.

bridge engineers in an exhaustive 12-year effort (from 1942 to 1954) to understand and incorporate design measure to counter the aerodynamic effects of wind.

Design and Constructionof “Sturdy Gertie”

Due to the need to carefully investigate the cause of failure, and the shortage of materials during World War II, the bridge was not immediately replaced. Design work began July 15, 1941 and continued until April 1946. 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, and much of this material was used in the war effort. The 1940 bridge had a two lane roadway, and the traffic volume during its short existence substantially exceeded forecasts, validating the need and financial viability for the second bridge to have a four lane roadway. Even though the 1950 Tacoma Narrows Bridge has a wider superstructure to accommodate four lanes, it utilizes the underwater foundations remaining in place from the first bridge.

1940 TacomaNarrows

Bridge

1940 1950Tower Elevations

Deck SectionsComparative Bridge

1950 Tacoma Narrows

Bridge

Opening of “Sturdy Gertie”October 14, 1950

The foundation caissons had fortunately been conservatively proportioned and were not damaged during the 1940 failure. The main cable gravity anchorages were also undamaged, and portions of these massive concrete structures were incorporated into the cable anchorages for the second bridge. Therefore the 1950 structure truly is a combination of the 1940 bridge foundations and new bridge superstructure construction to create the complete bridge. In addition to these major elements, some materials from the original 1940 approach spans were salvaged and re-used in the second bridge. Construction of the second Tacoma Narrows Bridge began on April 9, 1948 and was completed for traffic opening on October 14, 1950.

Lessons Learned from aCatastrophic Failure

Fortunately, no human lives were lost in the failure because the bridge had been closed to traffic as the magnitude of oscillation began to increase. Major portions of the superstructure broke up and fell into the water below, and the main towers were damaged. The substructure, cable anchorages, and approach spans were undamaged. The event triggered a world-wide response among bridge engineers to evaluate other existing suspension bridges and take measures to minimize potentially dangerous oscillations. Although a number of shorter span suspension bridges were built during the 1940s, plans for several large suspension spans were put in abeyance. An Advisory Board on the Investigation of Suspension Bridges assembled the nation’s leading suspension