Tacoma Narrows Bridge (1940)

Tacoma Narrows Bridge (1940)
University of Washington Libraries Digital Collections · Public domain · source
Name	Tacoma Narrows Bridge (1940)
Caption	The original span during construction, 1940
Cross	Puget Sound
Locale	Tacoma, Washington to Gig Harbor, Washington
Owner	Washington State Department of Transportation
Designer	Leon Moisseiff; Coeur d'Alene?
Length	5127 ft
Mainspan	2800 ft
Open	July 1, 1940
Collapse	November 7, 1940

Tacoma Narrows Bridge (1940) The Tacoma Narrows Bridge (1940)was a suspension bridge across the Tacoma Narrows in Puget Sound connecting Tacoma, Washington and Gig Harbor, Washington. Opened in 1940, it became internationally notorious for its dramatic aerodynamic failure and collapse on November 7, 1940, during a period of sustained high winds. The failure profoundly affected civil engineering practice, influencing aerodynamic testing, structural dynamics, and later projects such as Golden Gate Bridge, Brooklyn Bridge, and Severn Bridge.

Background and Planning

Planning for a crossing of the Tacoma Narrows involved local civic groups, state agencies, and private financiers. The proposal emerged amid regional growth centered on Tacoma, Washington and the Puget Sound Naval Shipyard, with competition among ferry operators, the Washington State Highway Commission, and municipal leaders. Early studies referenced precedents including George Washington Bridge, Mackinac Bridge, and designs by firms associated with McClintic-Marshall, invoking techniques used on the Humber Bridge and proposals from Joseph Strauss. Funding and authorization involved state legislation, local bonds, and consultation with engineers experienced in long-span suspension bridges such as those who had worked on Golden Gate Bridge and George Washington Bridge.

Design and Construction

Design responsibilities were assigned to engineers influenced by contemporaries like Leon Moisseiff and construction firms with ties to companies that worked on Brooklyn Bridge and San Francisco–Oakland Bay Bridge. The final design featured a 2800-foot main span, slender plate girders, and relatively shallow stiffening trusses to economize materials during the late 1930s, a period when supply chains and priorities echoed those of projects like Bonneville Dam and Hoover Dam. Construction contracts were awarded to firms connected to the broader American bridge-building industry, whose workers had experience on Tacoma Narrows-era projects and whose techniques paralleled those used on Mackinac Bridge projects. The roadway was a narrow, 39-foot deck with open grillwork, and the towers and cables reflected suspension practices also seen on George Washington Bridge and earlier Menai Suspension Bridge innovations.

Collapse of November 7, 1940

On November 7, 1940, with sustained winds gusting from a Pacific storm system reminiscent of those that affect Puget Sound, the bridge entered large-amplitude oscillations described by eyewitnesses from Tacoma, Washington and journalists from outlets that covered events like the Great Depression recovery. The deck exhibited torsional motion, rotating about its longitudinal axis, while the cables and towers remained largely intact. The central span experienced failure of the deck connections and eventual collapse into the waters of the Tacoma Narrows, drawing comparisons in contemporary reports to failures investigated after incidents like the Silver Bridge collapse. The dramatic footage captured by local photographers and newsreel crews later circulated in engineering schools alongside case studies such as Sultana (steamboat) footage and industrial disaster reels.

Causes and Engineering Analysis

Immediate analyses invoked aerodynamic excitation, resonance phenomena familiar from studies of Charles F. Kettering-era vibration research and from earlier observations of wind-induced motion on structures like Menai Suspension Bridge and Saltash Bridge precedents. Researchers from institutions including University of Washington, Massachusetts Institute of Technology, and Princeton University studied the collapse, examining concepts advanced by Lord Rayleigh, Theodore von Kármán, and Ludwig Prandtl. The failure was attributed to aeroelastic flutter, vortex shedding, and torsional divergence rather than classical harmonic resonance alone, a distinction developed further by later scholars at Imperial College London and California Institute of Technology. Wind-structure interaction experiments in wind tunnels and theoretical models referencing work by Gustave Eiffel and Hugh G. Merewether led to reformulation of design criteria, emphasizing aerodynamic stability, coupled modes, and stiffness-to-mass ratios.

Aftermath and Legal/Policy Impact

After the collapse, litigation and insurance disputes involved contractors, state agencies, and bondholders, echoing legal complexities seen in other infrastructure failures like the Sultana (steamboat) litigation and claims after the Great Molasses Flood. The event influenced procurement policies used by the Washington State Department of Transportation and prompted revisions in standards promulgated by professional bodies such as the American Society of Civil Engineers and the American Institute of Steel Construction. Federal and state transportation policy responded with increased requirements for wind tunnel testing and consideration of aerodynamic effects in approvals for projects like Severn Bridge replacements and Mackinac Bridge upgrades. The collapse also affected academic curricula at schools such as University of Washington, Cornell University, and Columbia University where structural dynamics and aeroelasticity became emphasized topics.

Legacy and Influence on Bridge Engineering

The Tacoma Narrows Bridge (1940) remains a canonical case in engineering education and practice, cited alongside studies of Brooklyn Bridge maintenance, Golden Gate Bridge retrofits, and investigations of suspension bridges worldwide. Its legacy spurred routine wind tunnel testing at facilities like Ames Research Center-affiliated labs and university aerodynamic centers, informed standards by American Society of Civil Engineers, and inspired research by figures such as Frederick W. Taylor-era methodologists and later scholars at Stanford University and Massachusetts Institute of Technology. The event accelerated development of stiffening trusses, aerodynamic deck sections, and tuned mass dampers used in structures including Severn Bridge, Great Belt Fixed Link, and modern cable-stayed bridges. The collapse also fostered richer interdisciplinary collaboration among practitioners from University of Washington, Imperial College London, and California Institute of Technology who advanced the modern understanding of aeroelasticity, ensuring that the bridge’s dramatic end contributed constructively to safer, more resilient infrastructure worldwide.

Category:Suspension bridges in the United States Category:Bridges in Washington (state)