The Tumultuous Tacoma Narrows
The Tacoma Narrows bridge, spanning across the ‘Puget Sound,’ in Washington, America. It was the third longest suspension bridge in the world, falling in just behind the George Washington bridge and the eponymous Golden Gate.
Construction started in late 1938 and proceeded at breakneck speed; something however, was amiss. Once the deck had been built the construction workers saw that it would move up and down whenever there was a strong wind. Henceforth the construction workers and eventually the wider public, came to know the bridge as Galloping Gertie.
19 months and $6.4 million later the bridge was complete. An impressive spectacle crossing a span of exactly 853.4 metres. It’s lithe form was gracefully thin against the sky; the decision to make it out of thinner girders was a combination of aesthetic and cost-conscious decisions and did result in a beautiful bridge. July 1940, the bridge was opened to the public.
Still the vertical movements persisted. Whenever a strong wind blew along the bridge it would twist and warp and wobble, much to the chagrin of the bridge designers and the local government. To stop this squirming suspension bridge several measures were put in place.
Firstly the girders running across the underside of the bridge were attached via cables to 50 ton concrete blocks on the shore below. This effort was to no avail as the cables snapped during a particularly windy day. Furthermore extra cables were spun from the larger cables down to the centre of the bridge, these though didn’t snap, or work, their effect on the oscillations was zero. The final anti-oscillatory measure was a set hydraulic buffers between the big towers and the floor system. These should have stopped and longitudinal movement of the bridge, instead they were broken before the bridge even opened, during a sand-blasting process getting the bridge ready for a fresh coat of paint.
So Galloping Gertie went on her way, bucking and jerking during any windy spell. It became a spectacle and tourist attraction, bringing people in from miles around to observe the solid bridge become almost as malleable as rubber. This effect was caused by the wind vibrating the concrete at exactly the speed concrete responds too, leading to the concrete adding more to the vibration which in turn causes the wind to vibrate the bridge more and so on. This amazing phenomenon is known as Aeroelastic flutter.
Nine months after construction, thanks to some overenthusiastic cost cutting during construction, the bridge belatedly broke.
The wind-induced collapse happened during the 7th November, 1940. The time was 11:00 am.
The wind was blowing at an impressive 64 km per hour the bridge was twisting and turning with great fervour. The lampposts lining the bridge swayed side to side like the legs of an upset millipede. A single car was on the bridge at the time, containing a Leonard Coatsworth and his dog. Mr Coatsworth and his dog forged across the bridge at a standard pace, but eventually the oscillations of the bridge were too much, causing the car to skid across the roadway. After violently losing control once more he held on the brakes and opened the door.
A well-timed wobble from Gertie sent him hurling out of the car and face first into the curb. The stationary car then began to slide from side to side on the bridge. He was only just halfway across the bridge. In his own words:
“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…”
The dog however, a terrified cocker spaniel named Tubby, remained in the car. So a pair of rescuers emerged, dashing and stumbling over the audibly cracking concrete in a bid to save its life. The first rescuer to reach the car, a Professor Farquharson, wrenched open the door and tried to coax the dog out. So terrified was the dog that it steadfastly refused and promptly bit him. The second rescuer was an unnamed news reporter. Although similar in his efforts he managed to avoid getting but, unfortunately the dog would no budge.
Eventually the cracking of concrete was of such note that the two promptly fled the scene. And lucky they were too for not long after their departure did the bridge collapse, taking Coatsworth’s car and Tubby the dog down with it. The car was never recovered and Tubby was the sole fatality.
There was a grand aftermath. Galloping Gertie’s collapse spurned hundreds of engineers to put in much more research into the effect of aerodynamics on bridges as well as many other fields, preventing many a further catastrophe.
Mr Coatsworth was also reimbursed by the government. A sum of $540 for the loss of his car and $364.40 for its contents, including Tubby.
Below is the footage of the collapse itself. Observe: