Gertie the Dancing Bridge

She wasn’t meant to be a roller coaster yet she was a gigantic bouncing “baby” from day one.  She only lived for four months before plunging into Puget Sound.

She was the third longest suspension bridge in the world in terms of main span length.  She was built to connect Tacoma with the Kitsap Peninsula and would cut a trip of two and a half hours to a mere eleven minutes.

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Location of Tacoma Narrows Bridge

Construction commenced on 27 September 1938.

The original design by Clark Eldridge would need a budget of $11 million, but the illustrious New York bridge engineer Leon Moisseiff presented a design which would cost considerably less.  Instead of the 25 foot (7.6m) trusses originally proposed, the new design would utilize 8 foot (2.4m) deep plate girders under the roadway.   Moisseiff’s design was based on a new untried Austrian concept known as “deflection theory” which held that aerodynamic forces only move a structure from side to side and not up and down.  Moisseiff had an impeccable reputation as a bridge engineer, having designed as well as consulted on a number of other well known bridges, and his concept was readily accepted.

Some of the engineers at the Washington State Highway Department had reservations about the modern minimalist design.

A year after the great fall David Glenn, a field engineer with the Public Works Administration claimed that he had refused to sign off the bridge when it was completed.  He had advised against recommending the design.  However the PWA and the Washington State Toll Bridge Authority accepted it.

Mr Glenn was fired by the PWA two weeks after making his dramatic assertions.

The actual construction cost came to $6.4 million.  As the new road over the bridge would be a toll road, the Public Works Administration would be able to recoup some of their expenses.  The toll fee was 75c for motorists and a dime for pedestrians.  So many people wanted to see the new bridge that the takings on the opening day amounted to $11 541.

tollbooth
The toll booth was a safe place to head for when she began to fail

The bridge was constructed with just two lanes and was 12m (39 feet) wide.  It had an unusually large depth to width ratio of 1:72 which caused extreme flexibility.

During construction some of the bridge workers were alarmed by the bridge’s erratic movements and chewed lemons to ward off the motion sickness they encountered!  They didn’t expect to feel as if they were aboard a ship out at sea.  It was these workers who coined the nickname Galloping Gertie from a popular saloon song.

opening day tacoma narrows
Opening Day 1 July 1940

Mr F S Heffernan, whose company supplied sand and gravel to the Pacific Bridge Company, reckoned the bridge wouldn’t last a year.  He was quite right!  When the bridge did fall, he commented sadly that he couldn’t take the money due to him.

Transverse vibration was observed from the beginning.  Drivers would notice cars coming from the opposite direction seem to rise and fall as they crossed the centre span.

Methods used to control Gertie’s swinging

  • In October tie-down cables were attached to the plate girders, anchored to 50 ton concrete blocks on the shore. These cables snapped soon after installation, so proved of little use.
  • A pair of inclined cable stays was added to connect the main cables to the bridge deck at mid-span. These stayed in place  until the final collapse, but did nothing to prevent the oscillations.
  • Hydraulic buffers were installed between the towers and the floor system of the deck in order to lessen the longitudinal motion of the main deck. This also proved useless because the seals of these units were damaged when the bridge was sand-blasted prior to being painted.

As soon as the Washington Toll Bridge Authority realized none of their solutions were working effectively they brought in Professor Frederick Bert Farquharson from the University of Washington.  The eminent professor and his students built a 1:200 scale model of the bridge as well as a 1:20 model of a section of the deck.  Farquharson and his students tested these scale models in wind tunnels.  Their tests with the model bridge showed that it would twist violently during extreme wind conditions.

“We watched it, and we said that if that sort of motion ever occurred on the real bridge, that would be the end of the bridge.”

On the 2 November Professor Farquharson proposed two possible remedies:

  • Drill holes in the lateral girders and along the deck to enable air circulation, which would reduce lift;
  • Add fairings or deflector vanes to the deck, attached to the girder fascia to improve the aerodynamics of the transverse section.

The second choice was approved but there was no time to get it done because it was just five days before the countdown to calamity.

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Farquharson’s team’s recommendations: too late to save Gertie

On the evening of 6 November, Carol Peacock from the Fife High School sat down to write her journalism assignment.  The given topic was “Just suppose…”  Carol chose to write her essay on “Just suppose Tacoma Narrows Bridge collapses…

The wind was blowing at 40 mph (64 km/h) early on that fateful morning:  stronger than any Galloping Gertie had hitherto experienced in her brief life.  The gale force winds buffeted her from the southwest.

Thursday 7 November:  Countdown to Catastrophe

08:30 – Bridge engineer Clark Eldridge drives across the bridge to inspect it and then returns to his office a mile away.  Despite the wind the oscillation is no more than usual at this point.  When he gets to his office he begins to make sketches and get quotes for the materials to upgrade the bridge according to Farquharson’s recommendations.

09:30 – Professor Farquharson arrives from Seattle and begins taking motion pictures of the bridge for his continued investigation.  As one of the foremost engineers of his day he has resolved to find out as much as possible.

10:00 – A college student from the University of Puget Sound, Winfield Brown, is the last pedestrian allowed on.  A van from the Rapid Transfer Company drives onto the bridge. At 10:03 a violent lateral twisting motion rocks the road surface.  Occupants Ruby Jacox and Walter Hagen climb out just seconds before the van is thrown on its side.  They cling desperately to the curb. By 10:07 the roadway is rocking violently every 5 seconds like a thrashing snake.

looking west from easterly pier
Looking west from the bridge’s easterly pier

10:05 – Highway officials and State Police close the bridge to everyone except the press and Professor Farquharson.  Two frightened workmen at the East Tower scurry for the safety of the toll plaza.

Mr Leonard Coatsworth, a news editor for the Tacoma News Tribune, is the last driver to drive onto the bridge on his way to take his daughter’s black spaniel Tubby back to her at their summer house on the Peninsula.

He has just passed the East Tower when the road tilts sideways and throws his car against the curb.  Mr Coatsworth climbs out of an open window and lands face down on the road surface.  He staggers to the tower, some 150 metres away.  From there he somehow makes his way to the toll plaza at the Tacoma end of the bridge, roughly 500m further.  He tells the toll attendant about Tubby, left in the car on the twisted bridge.

Later Mr Coatsworth describes his ordeal thus:

Around me I could hear concrete cracking. I started back to the car to get the dog, but was thrown before I could reach it. The car itself began to slide from side to side on the roadway. I decided the bridge was breaking up and my only hope was to get back to shore.”

“On hands and knees most of the time, I crawled 500 yards or more to the towers . . . . My breath was coming in gasps; my knees were raw and bleeding, my hands bruised and swollen from gripping the concrete curb . . . . Toward the last, I risked rising to my feet and running a few yards at a time . . . . Safely back at the toll plaza, I saw the bridge in its final collapse and saw my car plunge into the Narrows.

He then phones his office which immediately dispatches a reporter and a photographer to record the drama.

On the way there, along Sixth Avenue they pass a large, bright billboard advertising Pacific National Bank as “secure as the Narrows Bridge”.  As they are in a hurry to get to the bridge before it collapses they make a note to photograph this billboard on their return.  But by that time they pass that way again it has hastily been painted over and removed. It is no longer the message the bank wishes to convey to its investors…

10:10 – Gertie’s movement changes from the usual rolling motion to a new, ominous twisting motion.  Barney Elliott and Harbine Monroe from a nearby film company arrive with their new Bell & Howell 16mm cameras and several rolls of Kodachrome colour film and begin shooting as much footage as they can.

monroe
Monroe footage

10:15 – Bridge engineer Clark Eldridge arrives and sees a number of people struggling on foot to escape the wildly swaying bridge.  He joins Professor Farquharson on the East end and they warn people not to venture onto the bridge.

10:30 – A big chunk of concrete breaks off the centre section and plunges off the bridge.  Meanwhile at the western end workmen use a truck to try and reach the trapped Ruby Jacox and Walter Hagen. Several cameramen are taking motion pictures and photographs of the unfolding drama. For a short while the wind subsides and photographer Howard Clifford tries to reach Tubby in the car, but has to turn back.  He carries on taking photos.

The photographer and reporter from the Tribune as well as a freelance photographer named James Bashford arrive and begin recording the climactic scenes before them.

10:45 – Farquharson, still hoping the bridge would settle down and recover, continues to take photos and shoot motion footage.

10:55 – Farquharson decides to make one final effort to rescue Tubby, but the terrified dog snaps at him and bites his finger.  The bridge has now become too dangerous for comfort.  Abandoning further efforts in order to preserve his life he stumbles to the East Tower, still wearing his tie and trenchcoat and carrying his pipe and stopwatch.

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Professor Farquharson trying to keep his footing

11:00 – Witnesses observe pieces of concrete ripping off “like popcorn” and cascading into the water far below.  Farquharson watches in disbelief as six light poles break off and steel suspender cables snap off and fly into the air “like fishing lines”.   The bridge ripples up and down in an immense wave which leaves him 30 feet lower than he had been seconds before.

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Roller coaster bridge not for the faint-hearted…

11:01 – Several hundred people are now watching Gertie’s finale as the shrill din of stressed metal and concrete combine with the banshee howling of the gale and the whistle of a workman trying to warn the coastguard cutter Atlanta not to sail under the bridge.

The Atlanta was the first vessel to pass under the spans of the new bridge when it opened on 1 July 1940 and would now also be the last one.  They cannot hear the workman’s whistle amid all the other deafening noises.  It cruises under the bridge just moments before the final collapse, and the deck is showered with pieces of concrete.  Commander Hogan radios news of the collapse to his Seattle headquarters.  This would be the first report to reach the outside world.

11:02 – A 600 foot long section of roadway on the eastern half of the centre span, wrenches loose and  plummets into the sound 195 feet (59m) below with a thunderous noise, causing a mighty splash of spray and foam to shoot upwards 100 feet (30m).  Huge flashes from shorting electric cables fly through the air.

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Collapse!

11:03 – A shocked Bert Farquharson, still on the bridge, runs the 1100 feet (335m) to the toll plaza as fast as his jellied legs can carry him.  Just in front of him Howard Clifford is also sprinting for the safety of solid ground.

11:05-11:10 – Most of Gertie’s remaining structure gradually gives way and plunges into Puget Sound, taking three vehicles with it including Leonard Coatsworth’s one with Tubby inside.

Hundreds of cars were making their curious way westward along Sixth Avenue to see the calamity for themselves.

No human lives were lost.  The only casualty was the unfortunate Tubby.  Neither his body nor Mr Coatsworth‘s car were ever recovered from the swirling depths.  After a long delay Mr Coatsworth received some compensation for the loss of his car and its contents, though nothing would bring poor Tubby back.

Four days later the low pressure system which caused the unusually strong winds around Tacoma, created a massive storm in the Great Lakes area, known as the Armistice Day Blizzard.  The Chicago Tribune described the winds as the heaviest of the century. 145 people in the Midwest were killed in this blizzard.

Looking at why Gertie collapsed

Initially, the majority of engineers and scientists blamed the collapse on resonance, but in recent years a new theory of “aeroelastic flutter” has been proposed.  Perhaps resonance did play a role and these two forces acted together to bring Gertie down.  This isn’t an engineering or science blog, so I’ll try to keep it simple.  For those who want more info, here’s a link:

http://motherboard.vice.com/read/the-myth-of-galloping-gertie

When wind hits certain non-aerodynamic bodies at a certain speed, they shed little eddies of wind on each side and in the wake of each eddy, a small vortex of low pressure builds up on the opposite side.  These forces caused the whole structure to begin moving up and down as well as sideways due to a phenomenon called the Karman Vortex Street resonance effect.

Vortex-street-animation
Vortex Street animation

The bridge had been moving much the same as usual, but on this day the high winds caused a cable to snap, causing the bridge to be thrown off balance and begin a self-destructing twisting motion as “aeroelastic flutter” began.  The rolling motion became a twisting one which would stress the bridge beyond endurance.

Due to the weakening caused by the snapped cable it began to twist along its central axis in a motion which would prove irreversible.  Interacting with the wind, this twisting got worse until the breakup an hour later.  Inertial, elastic and aerodynamic forces were all at play on the doomed bridge.

1940 to present

Due to delays caused by the US’s entry into World War II, it would be a whole ten years before the brand new, much stronger Tacoma Narrows Bridge was opened in the same spot on 14 October 1950.  The cable anchorages, tower pedestals and most of the remaining substructure from the old bridge were comparatively undamaged and were used for the new one.   The new bridge has more traffic lanes and is 40 feet (12m) longer than the original.

The new bridge uses 33-foot open stiffening trusses (as opposed to the 8-foot ones on the earlier bridge) as one as wind grates and hydraulic shock absorbers.  Her nickname is Sturdy Gertie.

Due to the inevitable increase in traffic with the passing of time, a new parallel bridge was constructed and completed in 2007 and the 1950 bridge now carries only westbound traffic.

What remains of Galloping Gertie is now an artificial reef some 180 feet (55m) under the surface of the chilly swirling waters of Puget Sound.

Tacoma_Narrows_Bridge_2009
The side-by-side Tacooma Narrows Bridges as they are today
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Published by: envirozentinel63

Diagnosed with asperger syndrome. Keen runner and writer who wants to share the ups and downs of all my many experiences and maybe reach out to someone who needs encouragement.

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