We bridge engineers have had our share of brickbats over the years, and are usually fair game for the press reporters, but I was more than a little surprised when one morning I opened the office copy of Truth, to find a new banner headline:
Another Example of the Incompetence of the Ministry of Works NOW THEY'VE GOT A BRIDGE THAT SINGS!
This was too much for me. I talked to the chief civil engineer, who was perfectly relaxed about it. 'Bob, you know for years how we have been trying to get government approval to publish a house journal. Well, now we've got one: it's called Truth!'
The singing bridge was quite a story. As part of the Dunedin motorway system, we had designed a neat bridge at Dall Street, which sailed right over the motorway lanes in a circular curve. The bridge railing was of the typical 'graveyard' type, with light hollow steel balusters welded between the horizontal railing pieces. The problem occurred when the wind blew at a certain speed, and caused the balusters to vibrate and resonate. This created a banshee-type wail that kept people awake at night and, because the bridge was built on a curve in plan, there was always one section of the railing at the right angle to the wind direction to produce the sound.
So the best of brains were put to work to sort this one out. One suggestion, for example, was to fill all the hollow balusters with cement grout- a very expensive operation. Finally, as so often is the case, the solution was extremely simple, and was devised by one of the overseers. He just went along with a big wrench and gave every baluster a slight twist. This meant that any two adjacent balusters were no longer opposite each other, and could not entrap the pocket of air that was causing the resonance. The singing bridge was silenced immediately."