Tacoma Narrows Bridge (Galloping Gertie)

This website covers the history of all three suspension bridges that are currently in or were in service over the Narrows that are (or were) a part of what is now known at Washington State Route 16 connecting Interstate 5 to Bremerton.

This website identifies them by the following names:

Galloping Gertie-Opened July 4, 1940. Collapsed November 7, 1940. It was built as a WPA project to provide transportation needs for military services between Bremerton and McCord (which opened the same time the bridge did).

Sturdy Gertie-Opened September 1950. Built in the existing location of where Galloping Gertie stood and uses the same anchors and caissons as well as towers 1-3 on the peninsula side of the bridge. This bridge handles traffic from Tacoma into Gig Harbor.

Greedy Gertie-Opened July 2007. Built south of Sturdy Gertie and provides service from Gig Harbor to Tacoma. This span provide pedestrian traffic as well. The nickname is given for the expensive tolls collected.

(source: James Bashford (creative commons licensing))

Living in the Puget Sound area for a majority of my life, exploring, photographing, and documenting many parts of the Puget Sound for several years has been a fun hobby, but most of the time, this section of Puget Sound was recorded the most.

To find a major suspension bridge being constructed in the 21st century in America is rare. A major suspension bridge hasn't been constructed since 1964 in the United States. While many major suspension bridges have been built in other parts of the world for the past several years, the lessons about the application and their design happened right here as American was getting involved in World War 2.

The first Tacoma Narrows Bridge was constructed in 1939 and went into service on July of 1940. When constructed, it was the third largest suspension bridge in the world. Only the Golden Gate and the George Washington Bridge were larger.

Unlike the suspension bridges built in San Francisco, this bridge was built on a very low budget using cheap beams and girders to create a two lane bridge that looked like ribbon and moved freely in the wind.

Engineers didn't see a reason to test bridges in a wind tunnel. After the bouncing of the roadbed was reported to the engineer (Leon Moiseiff) he did indicate that the Bronx Whitestone Bridge and the Deer Island Bridge were doing the same thing, it became the responsibility of the state to find out why it was happening and how to prevent it.

University of Washington Engineering Professor Farquarson made a scale model of the bridge to test the affects of wind using a wind tunnel. To solve the bouncing, it was decided to add additional cables below the bridge and secure them using concrete block or cables connected to the towers. While this helped in 50 mph winds, early November was a stormy time of the year and eventually the cables broke (many bridges today use additional cable supports above the roadbed rather than below).

It was during this time that Professor Farquarson would present his findings to the State of Washington. His suggestions were to either drill holes in the side beams or using fairings on the outer sides of the bridge to deflect the wind. The state was interested in the fairlings (they didn't want to drill holes in the bridge) and could have had the work completed within 40 days but it was too late.

The center span of the bridge fell on November 7th 1940 at wind speeds that had gusts from 38-42 mph after the bridge twisted from side to side for about 30 minutes.

The video produced by Barney Elliot shows the roadbed movement while a vehicle (left on the roadway) was left behind by Tacoma News Tribune reporter Leonard Coatsworth.  Farquarson and others tried to get the dog, Tubby from the vehicle but the dog didn't want to get out of the vehicle biting those that tried.

What caused the bridge to fail?

Because the bridge didn't have anywhere for the wind to travel through the bridge, the solid girders on the the sides of the bridge pushed it causing the twisting of the center span of the roadbed (in the same way you push a child on swing at the park).

The bouncing movement could have been prevented if venting were added to the roadbed.

When Sturdy Gertie was built, grated surfaces were added to the roadbed as well as railings that were opened for airflow.

The current bridges has steel girders added below the roadbed to stiffen the bridge as well. After Galloping Gertie broke, bridges that didn't have these girders below the roadbed were added above the roadbed instead.

While these girders did help save the bridges from twisting or moving, the additional weight to the roadbed added weight restrictions so that semi truck couldn't use them. Eventually these roadbeds were replaced with the fairlings added to the sides of the bridge.

The math behind what happened

In th 1970's IBM had an exhibit at the Pacific Science Center (known as Mathematica) that brought up the fact that no one was able to come up with a mathematical equation at to what happened.

Some of the reasons for this was due to the fact that that many concluded the bridge failure was due to resonance, which collapsed at the result of the harmonics (oscillation frequency) being greater than the bridge itself. The problem with this answer is the wind velocity varies (as demonstrated after the collapse when smoke testing was done).

Around the time of the 50th anniversary of the collapse, Princeton University engineers came up with better conclusion (and the math) that concluded that vortex shredding was responsible for the failure of the bridge.

The Wikipedia page goes into detail about this subject which is still up for debate in college classrooms even today.