Box girder bridges

Box girder bridges don't have a great track record, and the news of a crack in the West Gate Bridge - which is such a bridge - caused me to pause for thought.

Sure, the crack a few days ago seems only to relate to the surface, and not to the structure.  In fact, I'm told that the fact that there was yellow at the bottom of the crack is somewhat reassuring, as that means the membrane under the asphalt that protects the structural steel is intact.  Had the steel itself (which is under the membrane and is red) been visible, then the integrity of the membrane would have been breached and the issues would have been somewhat more serious.

More generally, however, what would be the implications for Melbourne if a structural problem with this bridge did emerge?   Perhaps life would go on with lower load limits and lower speed limits - but in a "worst-case" scenario, if the bridge had to be closed for safety reasons, there would be enormous disruption.



Bridges - like other structures - do fail from time to time, but it's interesting that the West Gate Bridge is a box girder bridge.    Some of these bridges failed during construction including,  as well as the West Gate Bridge itself,  the Milford Haven Bridge in West Wales (also known as the Cleddau Bridge) and South River Bridge in Koblenz, Germany. Since then the Cline Avenue bridge in Indiana has been closed.

Failures can occur in any sort of structure, of course, but apparently box girder bridges can be more susceptible to rusting and corrosion than some other types because water can begin to pool within the cell of the beam.   Hence, the authorities presumably keep a close watch on the West Gate Bridge and  seem to think that (and in relation to the latest incident, here) all is OK with it.