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Kane's Bridge

This article was first published in the White Hat Melbourne Newsletter No.306 on 2nd April 2009.

Kane's Bridge in Studley Park

It had been a strenuous run through Studley Park. I sat underneath the shade of the suspension bridge to recover for a while and enjoy the solitude. My reverie was interrupted by a loud banging. On looking up I could just make out the shape of a red haired boy of about 10 or 11 years of age. He was jumping on the bridge presumably with the intention of making it wobble. “Ouch!” I said loudly. “Who said that?” said the urchin on the bridge. At least he had stopped jumping. “Me.“ I said, feeling that was full and sufficient information. The obnoxious minor jumped once more. I was reminded of W. C. Fields’ observation that “anyone who hates dogs and small children can't be all bad”. “How would you like it if people kept jumping on you?” I said. “Who are you?” demanded the trainee juvenile delinquent. “You deserve red hair” I thought. “I am” I said putting on my best bridge voice, “Kane’s Bridge, and I would take it most kindly if you would desist from your percussive animations.” “What? “Stop jumping!” I said firmly.

“But you’re such a funny old bridge and wobble each time I jump.” “We suspension bridges are not ‘funny’ as you so quaintly put it and I’m not that old – I was built in the late 1920s. In ancient civilisations people would sling a rope across a ravine and clamber monkey-like underneath it to get across. Later they would have three ropes with the middle one lower so that you could walk on the lower one and hold onto the outer ones. Look above your head. Those two cables are just the same and they form a catenary curve. People got the idea of suspending a platform underneath the cables and you ended up with a suspension bridge like me. We have a long and proud history.”

“You still wobble.” said the brat. “All suspension bridges wobble.” I explained. “Recently an Australian engineering company built a suspension pedestrian bridge across the Thames in London called the Millennium Bridge. The cables are so tight it’s hard to see it’s a suspension bridge. On opening day with thousands of people walking across, it started to wobble badly from side to side and they had to close it. The engineers found that as we walk we press outwards slightly with each step much like a skater or skier. Once a few people are walking in step causing a slight sway then others subconsciously adjust their walking to brace against the sway and their push creates an even bigger swing. The engineers closed the bridge, figured out the problem and installed dampers to stop the resonance. And if you keep jumping on me you might start a resonance.” The child jumped once more. Obviously he had no respect for physics, engineering, history or my solitude.

“Then there’s the Tacoma Narrows Bridge Disaster all caused by a small boy jumping on the bridge.” I said in my most serious bridge voice. “What was that?” “A small boy started jumping on a suspension bridge in America and started it wobbling. The wind picked up the wobble and set it vibrating at its natural frequency and the giant bridge collapsed. Go home and look up ‘Tacoma Narrows Bridge Collapse Newsreel’ on a search engine.” “Cool!” said the wide-eyed youth. Clearly, knowing how things work held no fascination for him but watching them collapse or blow-up was ‘cool’. I must admit I made up the bit about the collapse being initiated by a small boy’s jumping, but it did collapse, and where would Western Civilisation be without some myths and legends to frighten the young into submission. I relaxed in the shade of the bridge pleased with my morning’s work.

I was still quite pleased with my little deception and was ready to move on. “Parabola!” said a deep voice. “What was that?” I said. “Parabola.” repeated the voice. “If you’re going to impersonate me, at least get it right. A cable suspended from two points forms a catenary but once you hang a platform below it transforms into a parabola.” “Well I . . “ “And as for Galloping Gertie . . “ “”Galloping Gertie?” “That’s the nickname we other suspension bridges gave to the Tacoma Narrows Bridge, well Galloping Gertie didn’t collapse through being excited into her natural frequency by the wind despite what you’ll read in text books, it was due to aeroelastic flutter. Do try to get these things right. Besides, even though I was originally built in the late 1920s the great flood of 1934 my moorings were swept away and I ended up all swept to one side of the river so I had become a swing bridge. So then I was rebuilt up here, way above the flood level, by susso labour in 1935.” “You mean like Work for the Dole?” “No, the dole pays money, susso only payed food rations. If you’re going into the bridge impersonating business you’re going to have to do better than that.”

I remembered I had been accompanied for part of my run by someone who said he was an engineer. Maybe it was his voice on the other side of the knoll. I was about to investigate when I was interrupted. “Hey Mister! How do you spell Tacoma?”

 

BL

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Other articles in the series Seven Monuments of Melbourne:

Seven Bridges of Melbourne - overview

No. 1 – Princes Bridge
No. 2 – MacRobertson Bridge
No. 3 - Sandridge Rail Bridge
No. 4 – Lines composed upon Spencer Street Bridge
No. 5 - Kane's Bridge
No. 6 - West Gate Bridge
No. 7 - Chandler Highway Bridge


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