Sooooooo there is this bridge in New Orleans called the Twins Spans (actually its on interstate 10 and it more near New Orleans than actually in it). There was this little storm called Katrina and it messed the bridge up. It was discovered that as the water rose up and got to the level of the girders air was trapped between the rising water and the bridge deck. This caused the spans to become buoyant and the push of the current was able to push them off their supports and some times all the way into the water (same thing happened in Florida in 05 during Ivan iirc) as shown below:
So in the spirt of the better mouse trap the new bridge was constructed with ‘highchairs’ built around the riser pad to prevent the girders from being pushed off. as seen here and here:
sooo if your ever stranded on an island at least you know this much…….
~Le Singe (evil commodites speculator M.D.)